Internet Draft R. Braden, Ed.
Expiration: September 1996 ISI
File: draft-ietf-rsvp-spec-11.txt L. Zhang
PARC
S. Berson
ISI
S. Herzog
ISI
S. Jamin
USC
Resource ReSerVation Protocol (RSVP) --
Version 1 Functional Specification
March 18, 1996
Status of Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet- Drafts Shadow
Directories on ds.internic.net (US East Coast), nic.nordu.net
(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
Rim).
Abstract
This memo describes version 1 of RSVP, a resource reservation setup
protocol designed for an integrated services Internet. RSVP provides
receiver-initiated setup of resource reservations for multicast or
unicast data flows, with good scaling and robustness properties.
Braden, Zhang, et al. Expiration: September 1996 [Page 1]
Internet Draft RSVP Specification February 1996
Table of Contents
1. Introduction ........................................................4
1.1 Data Flows ......................................................7
1.2 Reservation Model ...............................................8
1.3 Reservation Styles ..............................................11
1.4 Examples of Styles ..............................................13
2. RSVP Protocol Mechanisms ............................................18
2.1 RSVP Messages ...................................................18
2.2 Port Usage ......................................................20
2.3 Merging Flowspecs ...............................................21
2.4 Soft State ......................................................22
2.5 Teardown ........................................................24
2.6 Errors ..........................................................25
2.7 Confirmation ....................................................27
2.8 Policy and Security .............................................27
2.9 Non-RSVP Clouds .................................................28
2.10 Host Model .....................................................29
3. RSVP Functional Specification .......................................31
3.1 RSVP Message Formats ............................................31
3.2 Sending RSVP Messages ...........................................44
3.3 Avoiding RSVP Message Loops .....................................45
3.4 Blockade State ..................................................49
3.5 Local Repair ....................................................51
3.6 Time Parameters .................................................52
3.7 Traffic Policing and Non-Integrated Service Hops ................53
3.8 Multihomed Hosts ................................................54
3.9 Future Compatibility ............................................56
3.10 RSVP Interfaces ................................................58
4. Message Processing Rules ............................................70
5. Acknowledgments .....................................................90
APPENDIX A. Object Definitions .........................................91
APPENDIX B. Error Codes and Values .....................................107
APPENDIX C. UDP Encapsulation ..........................................112
Braden, Zhang, et al. Expiration: September 1996 [Page 2]
Internet Draft RSVP Specification February 1996
What's Changed
The most important changes in this document from the rsvp-spec-10
draft are:
o RSVP-layer fragmentation machinery was removed.
However, the common header was rearranged to allow message
length to be expanded beyond 16 bits in the future, should
that be necessary.
o A little more discussion of IPv6 in Introduction.
o Service preemption now triggers a ResvTear message.
o Traffic Control can return updated FLOWSPEC. (This forced a
significant change in the UPDATE TRAFFIC CONTROL processing
in section 4).
o The discussion at the end of Section 2.3 was rewritten.
o The Message Processing Rules were updated.
The most important changes in this document from the rsvp-spec-09
draft are:
o Multiple POLICY_DATA objects in any order are now allowed.
o The length field in the common header is now the total
message length [Section 3.1.1].
o The meaning of Message Id is refined and more completely
specified [Section 3.1.1].
o RSVP fragmentation is specifically called for, and IP
fragmentation disallowed [Section 3.1.1].
o The granularity of state timeouts is now specified [Section
3.6].
Braden, Zhang, et al. Expiration: September 1996 [Page 3]
Internet Draft RSVP Specification February 1996
1. Introduction
This document defines RSVP, a resource reservation setup protocol
designed for an integrated services Internet [RSVP93,ISInt93].
The RSVP protocol is used by a host, on behalf of an application data
stream, to request a specific quality of service (QoS) from the
network. The RSVP protocol is also used by routers to deliver QoS
requests to all nodes along the path(s) of the data stream and to
establish and maintain state to provide the requested service. RSVP
requests will generally, although not necessarily, result in
resources being reserved along the data path.
RSVP requests resources for simplex data streams, i.e., it requests
resources in only one direction. Therefore, RSVP treats a sender as
logically distinct from a receiver, although the same application
process may act as both a sender and a receiver at the same time.
RSVP operates on top of IP (either IPv4 or IPv6), occupying the place
of a transport protocol in the protocol stack. However, RSVP does
not transport application data but is rather an Internet control
protocol, like ICMP, IGMP, or routing protocols. Like the
implementations of routing and management protocols, an
implementation of RSVP will typically execute in the background, not
in the data forwarding path, as shown in Figure 1.
RSVP is not itself a routing protocol; RSVP is designed to operate
with current and future unicast and multicast routing protocols. An
RSVP daemon consults the local routing database(s) to obtain routes.
In the multicast case, for example, a host sends IGMP messages to
join a multicast group and then sends RSVP messages to reserve
resources along the delivery path(s) of that group. Routing
protocols determine where packets get forwarded; RSVP is only
concerned with the QoS of those packets that are forwarded in
accordance with routing.
Braden, Zhang, et al. Expiration: September 1996 [Page 4]
Internet Draft RSVP Specification February 1996
HOST ROUTER
_________________________ RSVP _____________________________
| | .--------------. |
| _______ ______ | / | ________ . ______ |
| | | | | | / || | . | | | RSVP
| |Applic-| | RSVP <----/ ||Routing | -> RSVP <---------->
| | App <----->daemon| | ||Protocol| |daemon| _____ |
| | | | | | || daemon <----> >|Polcy||
| |_______| |___.__| | ||_ ._____| |__.__.||Cntrl||
| | | | | | | .|_____||
|===|===============|=====| |===|=============|====.======|
| data .........| | | | ...........| .____ |
| | ____V_ ____V____ | | _V__V_ _____V___ |Admis||
| | |Class-| | || data | |Class-| | ||Cntrl||
| |=> ifier|=> Packet ============> ifier|==> Packet ||_____|| data
| |______| |Scheduler|| | |______| |Scheduler|===========>
| |_________|| | |_________| |
|_________________________| |_____________________________|
Figure 1: RSVP in Hosts and Routers
Each node that is capable of resource reservation passes incoming
data packets through a "packet classifier", which determines the
route and the QoS class for each packet. On outgoing interface, a
"packet scheduler" then makes forwarding decisions for every packet,
to achieve the promised QoS on the particular link-layer medium used
by that interface.
If the link-layer medium is QoS-active, i.e., if it has its own QoS
management capability, then the packet scheduler is responsible for
negotiation with the link layer to obtain the QoS requested by RSVP.
This mapping to the link layer QoS may be accomplished in a number of
possible ways; the details will be medium-dependent. On a QoS-
passive medium such as a leased line, the scheduler itself allocates
packet transmission capacity. The scheduler may also allocate other
system resources such as CPU time or buffers.
In order to efficiently accommodate large groups, dynamic group
membership, and heterogeneous receiver requirements, RSVP makes
receivers responsible for requesting QoS [RSVP93]. A QoS request,
which typically originates from a receiver host application, is
passed to the local RSVP implementation, shown as a daemon process in
Figure 1. The RSVP protocol then carries the request to all the
nodes (routers and hosts) along the reverse data path(s) to the data
source(s).
Braden, Zhang, et al. Expiration: September 1996 [Page 5]
Internet Draft RSVP Specification February 1996
At each node, the RSVP daemon communicates with two local decision
modules, "admission control" and "policy control". Admission control
determines whether the node has sufficient available resources to
supply the requested QoS. Policy control determines whether the user
has administrative permission to make the reservation. If both
checks succeed, the RSVP daemon sets parameters in the packet
classifier and scheduler to obtain the desired QoS. If either check
fails, the RSVP program returns an error notification to the
application process that originated the request. We refer to the
packet classifier, packet scheduler, and admission control components
as "traffic control".
RSVP is designed to scale well for very large multicast groups.
Since both the membership of a large group and the topology of large
multicast trees are likely to change with time, the RSVP design
assumes that router state for traffic control will be built and
destroyed incrementally. For this purpose, RSVP uses "soft state" in
the routers. That is, RSVP sends periodic refresh messages to
maintain the state along the reserved path(s); in absence of
refreshes, the state will automatically time out and be deleted.
RSVP protocol mechanisms provide a general facility for creating and
maintaining distributed reservation state across a mesh of multicast
or unicast delivery paths. Except for certain well-defined
operations on the parameters, RSVP transfers QoS and policy
parameters as opaque data, passing them to the appropriate traffic
control and policy control modules for interpretation.
In summary, RSVP has the following attributes:
o RSVP makes resource reservations for both unicast and many-to-
many multicast applications, adapting dynamically to changing
group membership as well as to changing routes.
o RSVP is simplex, i.e., it makes reservations for unidirectional
data flows.
o RSVP is receiver-oriented, i.e., the receiver of a data flow
initiates and maintains the resource reservation used for that
flow.
o RSVP maintains "soft state" in the routers, providing graceful
support for dynamic membership changes and automatic adaptation
to routing changes.
o RSVP is not a routing protocol but depends upon present and
future routing protocols.
Braden, Zhang, et al. Expiration: September 1996 [Page 6]
Internet Draft RSVP Specification February 1996
o RSVP transports and maintains opaque state for traffic control,
and policy control.
o RSVP provides several reservation models or "styles" (defined
below) to fit a variety of applications.
o RSVP provides transparent operation through routers that do not
support it.
o RSVP supports both IPv4 and IPv6.
Further discussion on the objectives and general justification for
RSVP design are presented in [RSVP93,ISInt93].
The remainder of this section describes the RSVP reservation
services. Section 2 presents an overview of the RSVP protocol
mechanisms. Section 3 contains the functional specification of RSVP,
while Section 4 presents explicit message processing rules. Appendix
A defines the variable-length typed data objects used in the RSVP
protocol. Appendix B defines error codes and values. Appendix C
defines an extension for UDP encapsulation of RSVP messages.
1.1 Data Flows
RSVP defines a "session" to be a data flow with a particular
destination and transport-layer protocol. The destination of a
session is defined by DestAddress, the IP destination address of
the data packets, and perhaps by DstPort, a "generalized
destination port", i.e., some further demultiplexing point in the
transport or application protocol layer. RSVP treats each session
independently, and this document often omits the implied
qualification "for the same session".
DestAddress is a group address for multicast delivery or the
unicast address of a single receiver. DstPort could be defined by
a UDP/TCP destination port field, by an equivalent field in
another transport protocol, or by some application-specific
information. Although the RSVP protocol is designed to be easily
extensible for greater generality, the basic protocol documented
here supports only UDP/TCP ports as generalized ports. Note that
it is not strictly necessary to include DstPort in the session
definition when DestAddress is multicast, since different sessions
can always have different multicast addresses. However, DstPort
is necessary to allow more than one unicast session addressed to
the same receiver host.
Figure 2 illustrates the flow of data packets in a single RSVP
session, assuming multicast data distribution. The arrows
Braden, Zhang, et al. Expiration: September 1996 [Page 7]
Internet Draft RSVP Specification February 1996
indicate data flowing from senders S1 and S2 to receivers R1, R2,
and R3, and the cloud represents the distribution mesh created by
multicast routing. Multicast distribution forwards a copy of each
data packet from a sender Si to every receiver Rj; a unicast
distribution session has a single receiver R. Each sender Si may
be running in a unique Internet host, or a single host may contain
multiple senders distinguished by "generalized source ports".
Senders Receivers
_____________________
( ) ===> R1
S1 ===> ( Multicast )
( ) ===> R2
( distribution )
S2 ===> ( )
( by Internet ) ===> R3
(_____________________)
Figure 2: Multicast Distribution Session
For unicast transmission, there will be a single destination host
but there may be multiple senders; RSVP can set up reservations
for multipoint-to-single-point transmission.
1.2 Reservation Model
An elementary RSVP reservation request consists of a "flowspec"
together with a "filter spec"; this pair is called a "flow
descriptor". The flowspec specifies a desired QoS. The filter
spec, together with a session specification, defines the set of
data packets -- the "flow" -- to receive the QoS defined by the
flowspec. The flowspec is used to set parameters in the node's
packet scheduler (assuming that admission control succeeds), while
the filter spec is used to set parameters in the packet
classifier. Data packets that are addressed to a particular
session but do not match any of the filter specs for that session
are handled as best-effort traffic.
Note that the action to control QoS occurs at the place where the
data enters the medium, i.e., at the upstream end of the logical
or physical link, although an RSVP reservation request originates
from receiver(s) downstream. In this document, we define the
directional terms "upstream" vs. "downstream", "previous hop" vs.
"next hop", and "incoming interface" vs "outgoing interface" with
respect to the direction of data flow.
Braden, Zhang, et al. Expiration: September 1996 [Page 8]
Internet Draft RSVP Specification February 1996
The flowspec in a reservation request will generally include a
service class and two sets of numeric parameters: (1) an "Rspec"
(R for `reserve') that defines the desired QoS, and (2) a "Tspec"
(T for `traffic') that describes the data flow. The formats and
contents of Tspecs and Rspecs are determined by the integrated
service model [ServTempl95, ISdata95], and are generally opaque to
RSVP. The exact format of a filter spec depends upon whether IPv4
or IPv6 is in use; see Appendix A.
In the most general approach [RSVP93], filter specs may select
arbitrary subsets of the packets in a given session. Such subsets
might be defined in terms of senders (i.e., sender IP address and
generalized source port), in terms of a higher-level protocol, or
generally in terms of any fields in any protocol headers in the
packet. For example, filter specs might be used to select
different subflows in a hierarchically-encoded signal by selecting
on fields in an application-layer header. In the interest of
simplicity (and to minimize layer violation), the present RSVP
version uses a much more restricted form of filter spec,
consisting of sender IP address and optionally the UDP/TCP port
number SrcPort.
Because the UDP/TCP port numbers are used for packet
classification, each router must be able to examine these fields.
As a result, it is generally necessary to avoid IP fragmentation
of a data stream for which a resource reservation is desired.
There are two cases where the use of transport-layer ports for
selecting an RSVP flow may cause problems.
1. IPv6 inserts a variable number of variable-length Internet-
layer headers before the transport header, increasing the
difficulty and cost of packet classification for QoS.
Efficient classification of IPv6 data packets could be
obtained using the Flow Label field of the IPv6 header. The
details will be provided in the future.
2. IP-level Security, under either IPv4 or IPv6, may encrypt the
entire transport header, rendering the port numbers invisible
to intermediate routers.
A small extension to RSVP for IP Security under IPv4 is
described separately in [IPSEC96]. A corresponding solution
for IPv6 will be provided in the future.
RSVP messages carrying reservation requests originate at receivers
and are passed upstream towards the sender(s). At each
Braden, Zhang, et al. Expiration: September 1996 [Page 9]
Internet Draft RSVP Specification February 1996
intermediate node, two general actions are taken on a request.
1. Make a reservation
The request is passed to admission control and policy
control. If either test fails, the reservation is rejected
and RSVP returns an error message to the appropriate
receiver(s). If both succeed, the node uses the flowspec to
set up the packet scheduler for the desired QoS and the
filter spec to set the packet classifier to select the
appropriate data packets.
2. Forward the request upstream
The reservation request is propagated upstream towards the
appropriate senders. The set of sender hosts to which a
given reservation request is propagated is called the "scope"
of that request.
The reservation request that a node forwards upstream may differ
from the request that it received from downstream, for two
reasons. First, the traffic control mechanism may modify the
flowspec hop-by-hop. Second, reservations for the same sender, or
the same set of senders, from different downstream branches of the
multicast tree(s) are "merged" as reservations travel upstream; as
a result, a node forwards upstream only the reservation request
with the "maximum" flowspec.
When a receiver originates a reservation request, it can also
request a confirmation message to indicate that its request was
(probably) installed in the network. A successful reservation
request propagates upstream along the multicast tree until it
reaches a point where an existing reservation is equal or greater
than that being requested. At that point, the arriving request is
merged with the reservation in place and need not be forwarded
further; the node may then send a reservation confirmation message
back to the receiver. Note that the receipt of a confirmation is
only a high-probability indication, not a guarantee, that the
requested service is in place all the way to the sender(s), as
explained in Section 2.7.
The basic RSVP reservation model is "one pass": a receiver sends a
reservation request upstream, and each node in the path either
accepts or rejects the request. This scheme provides no easy way
for a receiver to find out the resulting end-to-end service.
Therefore, RSVP supports an enhancement to one-pass service known
as "One Pass With Advertising" (OPWA) [OPWA95]. With OPWA, RSVP
control packets are sent downstream, following the data paths, to
Braden, Zhang, et al. Expiration: September 1996 [Page 10]
Internet Draft RSVP Specification February 1996
gather information that may be used to predict the end-to-end QoS.
The results ("advertisements") are delivered by RSVP to the
receiver hosts and perhaps to the receiver applications. The
advertisements may then be used by the receiver to construct, or
to dynamically adjust, an appropriate reservation request.
1.3 Reservation Styles
A reservation request includes a set of options that are
collectively called the reservation "style".
One reservation option concerns the treatment of reservations for
different senders within the same session: establish a "distinct"
reservation for each upstream sender, or else make a single
reservation that is "shared" among all packets of selected
senders.
Another reservation option controls the selection of senders; it
may be an "explicit" list of all selected senders, or a "wildcard"
that implicitly selects all the senders to the session. In an
explicit sender-selection reservation, each filter spec must match
exactly one sender, while in a wildcard sender-selection no filter
spec is needed.
Sender || Reservations:
Selection || Distinct | Shared
_________||__________________|____________________
|| | |
Explicit || Fixed-Filter | Shared-Explicit |
|| (FF) style | (SE) Style |
__________||__________________|____________________|
|| | |
Wildcard || (None defined) | Wildcard-Filter |
|| | (WF) Style |
__________||__________________|____________________|
Figure 3: Reservation Attributes and Styles
The following styles currently defined (see Figure 3):
o Wildcard-Filter (WF) Style
The WF style implies the options: "shared" reservation and
"wildcard" sender selection. Thus, a WF-style reservation
creates a single reservation shared by flows from all
Braden, Zhang, et al. Expiration: September 1996 [Page 11]
Internet Draft RSVP Specification February 1996
upstream senders. This reservation may be thought of as a
shared "pipe", whose "size" is the largest of the resource
requests from all receivers, independent of the number of
senders using it. A WF-style reservation is propagated
upstream towards all sender hosts, and it automatically
extends to new senders as they appear.
Symbolically, we can represent a WF-style reservation request
by:
WF( * {Q})
where the asterisk represents wildcard sender selection and Q
represents the flowspec.
o Fixed-Filter (FF) Style
The FF style implies the options: "distinct" reservations and
"explicit" sender selection. Thus, an elementary FF-style
reservation request creates a distinct reservation for data
packets from a particular sender, not sharing them with other
senders' packets for the same session.
Symbolically, we can represent an elementary FF reservation
request by:
FF( S{Q})
where S is the selected sender and Q is the corresponding
flowspec; the pair forms a flow descriptor. RSVP allows
multiple elementary FF-style reservations to be requested at
the same time, using a list of flow descriptors:
FF( S1{Q1}, S2{Q2}, ...)
The total reservation on a link for a given session is the
`sum' of Q1, Q2, ... for all requested senders.
o Shared Explicit (SE) Style
The SE style implies the options: "shared" reservation and "
explicit" sender selection. Thus, an SE-style reservation
creates a single reservation shared by selected upstream
senders. Unlike the WF style, the SE style allows a receiver
to explicitly specify the set of senders to be included.
Braden, Zhang, et al. Expiration: September 1996 [Page 12]
Internet Draft RSVP Specification February 1996
We can represent an SE reservation request containing a
flowspec Q and a list of senders S1, S2, ... by:
SE( (S1,S2,...){Q} )
Shared reservations, created by WF and SE styles, are appropriate
for those multicast applications in which multiple data sources
are unlikely to transmit simultaneously. Packetized audio is an
example of an application suitable for shared reservations; since
a limited number of people talk at once, each receiver might issue
a WF or SE reservation request for twice the bandwidth required
for one sender (to allow some over-speaking). On the other hand,
the FF style, which creates distinct reservations for the flows
from different senders, is appropriate for video signals.
The RSVP rules disallow merging of shared reservations with
distinct reservations, since these modes are fundamentally
incompatible. They also disallow merging explicit sender
selection with wildcard sender selection, since this might produce
an unexpected service for a receiver that specified explicit
selection. As a result of these prohibitions, WF, SE, and FF
styles are all mutually incompatible.
It would seem possible to simulate the effect of a WF reservation
using the SE style. When an application asked for WF, the RSVP
daemon on the receiver host could use local state to create an
equivalent SE reservation that explicitly listed all senders.
However, an SE reservation forces the packet classifier in each
node to explicitly select each sender in the list, while a WF
allows the packet classifier to simply "wild card" the sender
address and port. When there is a large list of senders, a WF
style reservation can therefore result in considerably less
overhead than an equivalent SE style reservation. For this
reason, both SE and WF are included in the protocol.
Other reservation options and styles may be defined in the future.
1.4 Examples of Styles
This section presents examples of each of the reservation styles
and shows the effects of merging.
Figure 4 illustrates a router with two incoming interfaces,
labeled (a) and (b), through which data streams will arrive, and
two outgoing interfaces, labeled (c) and (d), through which data
will be forwarded. This topology will be assumed in the examples
that follow. There are three upstream senders; packets from
Braden, Zhang, et al. Expiration: September 1996 [Page 13]
Internet Draft RSVP Specification February 1996
sender S1 (S2 and S3) arrive through previous hop (a) ((b),
respectively). There are also three downstream receivers; packets
bound for R1 (R2 and R3) are routed via outgoing interface (c)
((d), respectively). We furthermore assume that outgoing
interface (d) is connected to a broadcast LAN, and that R2 and R3
are reached via different next hop routers (not shown).
We must also specify the multicast routes within the nod of Figure
4. Assume first that data packets from each Si shown in Figure 4
is routed to both outgoing interfaces. Under this assumption,
Figures 5, 6, and 7 illustrate Wildcard-Filter, Fixed-Filter, and
Shared-Explicit reservations, respectively.
________________
(a)| | (c)
( S1 ) ---------->| |----------> ( R1 )
| Router | |
(b)| | (d) |---> ( R2 )
( S2,S3 ) ------->| |------|
|________________| |---> ( R3 )
|
Figure 4: Router Configuration
For simplicity, these examples show flowspecs as one-dimensional
multiples of some base resource quantity B. The "Receive" column
shows the RSVP reservation requests received over outgoing
interfaces (c) and (d), and the "Reserve" column shows the
resulting reservation state for each interface. The "Send"
column shows the reservation requests that are sent upstream to
previous hops (a) and (b). In the "Reserve" column, each box
represents one reserved "pipe" on the outgoing link, with the
corresponding flow descriptor.
Figure 5, showing the WF style, illustrates two distinct
situations in which merging is required. (1) Each of the two next
hops on interface (d) results in a separate RSVP reservation
request, as shown; these two requests must be merged into the
effective flowspec, 3B, that is used to make the reservation on
interface (d). (2) The reservations on the interfaces (c) and (d)
must be merged in order to forward the reservation requests
upstream; as a result, the larger flowspec 4B is forwarded
upstream to each previous hop.
Braden, Zhang, et al. Expiration: September 1996 [Page 14]
Internet Draft RSVP Specification February 1996
|
Send | Reserve Receive
|
| _______
WF( *{4B} ) <- (a) | (c) | * {4B}| (c) <- WF( *{4B} )
| |_______|
|
-----------------------|----------------------------------------
| _______
WF( *{4B} ) <- (b) | (d) | * {3B}| (d) <- WF( *{3B} )
| |_______| <- WF( *{2B} )
Figure 5: Wildcard-Filter (WF) Reservation Example
Figure 6 shows Fixed-Filter (FF) style reservations. The flow
descriptors for senders S2 and S3, received from outgoing
interfaces (c) and (d), are packed (not merged) into the request
forwarded to previous hop (b). On the other hand, the three
different flow descriptors specifying sender S1 are merged into
the single request FF( S1{4B} ) that is sent to previous hop (a).
For each outgoing interface, there is a separate reservation for
each source that has been requested, but this reservation will be
shared among all the receivers that made the request.
|
Send | Reserve Receive
|
| ________
FF( S1{4B} ) <- (a) | (c) | S1{4B} | (c) <- FF( S1{4B}, S2{5B} )
| |________|
| | S2{5B} |
| |________|
---------------------|---------------------------------------------
| ________
<- (b) | (d) | S1{3B} | (d) <- FF( S1{3B}, S3{B} )
FF( S2{5B}, S3{B} ) | |________| <- FF( S1{B} )
| | S3{B} |
| |________|
Figure 6: Fixed-Filter (FF) Reservation Example
Figure 7 shows an example of Shared-Explicit (SE) style
Braden, Zhang, et al. Expiration: September 1996 [Page 15]
Internet Draft RSVP Specification February 1996
reservations. When SE-style reservations are merged, the
resulting filter spec is the union of the original filter specs,
and the resulting flowspec is the largest flowspec.
|
Send | Reserve Receive
|
| ________
SE( S1{3B} ) <- (a) | (c) |(S1,S2) | (c) <- SE( (S1,S2){B} )
| | {B} |
| |________|
---------------------|---------------------------------------------
| __________
<- (b) | (d) |(S1,S2,S3)| (d) <- SE( (S1,S3){3B} )
SE( (S2,S3){3B} ) | | {3B} | <- SE( S2{2B} )
| |__________|
Figure 7: Shared-Explicit (SE) Reservation Example
The three examples just shown assume that data packets from S1,
S2, and S3 are routed to both outgoing interfaces. The top part
of Figure 8 shows another routing assumption: data packets from S2
and S3 are not forwarded to interface (c), e.g., because the
network topology provides a shorter path for these senders towards
R1, not traversing this node. The bottom part of Figure 8 shows
WF style reservations under this assumption. Since there is no
route from (b) to (c), the reservation forwarded out interface (b)
considers only the reservation on interface (d).
Braden, Zhang, et al. Expiration: September 1996 [Page 16]
Internet Draft RSVP Specification February 1996
_______________
(a)| | (c)
( S1 ) ---------->| >-----------> |----------> ( R1 )
| - |
| - |
(b)| - | (d)
( S2,S3 ) ------->| >-------->--> |----------> ( R2, R3 )
|_______________|
Router Configuration
|
Send | Reserve Receive
|
| _______
WF( *{4B} ) <- (a) | (c) | * {4B}| (c) <- WF( *{4B} )
| |_______|
|
-----------------------|----------------------------------------
| _______
WF( *{3B} ) <- (b) | (d) | * {3B}| (d) <- WF( * {3B} )
| |_______| <- WF( * {2B}
Figure 8: WF Reservation Example -- Partial Routing
Braden, Zhang, et al. Expiration: September 1996 [Page 17]
Internet Draft RSVP Specification February 1996
2. RSVP Protocol Mechanisms
2.1 RSVP Messages
Previous Incoming Outgoing Next
Hops Interfaces Interfaces Hops
_____ _____________________ _____
| | data --> | | data --> | |
| A |-----------| a c |--------------| C |
|_____| Path --> | | Path --> |_____|
<-- Resv | | <-- Resv _____
_____ | ROUTER | | | |
| | | | | |--| D |
| B |--| data-->| | data --> | |_____|
|_____| |--------| b d |-----------|
| Path-->| | Path --> | _____
_____ | <--Resv|_____________________| <-- Resv | | |
| | | |--| D' |
| B' |--| | |_____|
|_____| | |
Figure 9: Router Using RSVP
Figure 9 illustrates RSVP's model of a router node. Each data
stream arrives from a "previous hop" through a corresponding
"incoming interface" and departs through one or more "outgoing
interface"(s). The same physical interface may act in both the
incoming and outgoing roles for different data flows in the same
session. Multiple previous hops and/or next hops may be reached
through a given physical interface, as a result of the connected
network being a shared medium, or the existence of non-RSVP
routers in the path to the next RSVP hop (see Section 2.9).
There are two fundamental RSVP message types: Resv and Path.
Each receiver host sends RSVP reservation request (Resv) messages
upstream towards the senders. These messages must follow exactly
the reverse of the path(s) the data packets will use, upstream to
all the sender hosts included in the sender selection. They
create and maintain "reservation state" in each node along the
path(s). Resv messages must finally be delivered to the sender
hosts themselves, so that the hosts can set up appropriate traffic
control parameters for the first hop. The processing of Resv
messages was discussed previously in Section 1.2.
Braden, Zhang, et al. Expiration: September 1996 [Page 18]
Internet Draft RSVP Specification February 1996
Each RSVP sender host transmits RSVP "Path" messages downstream
along the uni-/multicast routes provided by the routing
protocol(s), following the paths of the data. These Path messages
store "path state" in each node along the way. This path state
includes at least the unicast IP address of the previous hop node,
which is used to route the Resv messages hop-by-hop in the reverse
direction. (In the future, some routing protocols may supply
reverse path forwarding information directly, replacing the
reverse-routing function of path state).
A Path message may carry the following information in addition to
the previous hop address:
o Sender Template
A Path message is required to carry a Sender Template, which
describes the format of data packets that the sender will
originate. This template is in the form of a filter spec
that could be used to select this sender's packets from
others in the same session on the same link.
Sender Templates have exactly the same expressive power and
format as filter specs that appear in Resv messages.
Therefore a Sender Template may specify only the sender IP
address and optionally the UDP/TCP sender port, and it
assumes the protocol Id specified for the session.
o Sender Tspec
A Path message is required to carry a Sender Tspec, which
defines the traffic characteristics of the data stream that
the sender will generate. This Tspec is used by traffic
control to prevent over-reservation, and perhaps unnecessary
Admission Control failures.
o Adspec
A Path message may optionally carry a package of OPWA
advertising information, known as an "Adspec". An Adspec
received in a Path message is passed to the local traffic
control, which returns an updated Adspec; the updated version
is then forwarded in Path messages sent downstream.
Path messages are sent with the same source and destination
addresses as the data, so that they will be routed correctly
through non-RSVP clouds (see Section 2.9). On the other hand,
Resv messages are sent hop-by-hop; each RSVP-speaking node
forwards a Resv message to the unicast address of a previous RSVP
Braden, Zhang, et al. Expiration: September 1996 [Page 19]
Internet Draft RSVP Specification February 1996
hop.
2.2 Port Usage
An RSVP session is normally defined by the triple: (DestAddress,
ProtocolId, DstPort). Here DstPort is a UDP/TCP destination port
field (i.e., a 16-bit quantity carried at octet offset +2 in the
transport header). DstPort may be omitted (set to zero) if the
ProtocolId specifies a protocol that does not have a destination
port field in the format used by UDP and TCP.
RSVP allows any value for ProtocolId. However, end-system
implementations of RSVP may know about certain values for this
field, and in particular the values for UDP and TCP (17 and 6,
respectively). An end system may give an error to an application
that either:
o specifies a non-zero DstPort for a protocol that does not
have UDP/TCP-like ports, or
o specifies a zero DstPort for a protocol that does have
UDP/TCP-like ports.
Filter specs and sender templates specify the pair: (SrcAddress,
SrcPort), where SrcPort is a UDP/TCP source port field (i.e., a
16-bit quantity carried at octet offset +0 in the transport
header). SrcPort may be omitted (set to zero) in certain cases.
The following rules hold for the use of zero DstPort and/or
SrcPort fields in RSVP.
1. Destination ports must be consistent.
Path state and reservation state for the same DestAddress and
ProtocolId must each have DstPort values that are all zero or
all non-zero. Violation of this condition in a node is a
"Conflicting Dest Port" error.
2. Destination ports rule.
If DstPort in a session definition is zero, all SrcPort
fields used for that session must also be zero. The
assumption here is that the protocol does not have UDP/TCP-
like ports. Violation of this condition in a node is a
"Conflicting Src Port" error.
3. Source Ports must be consistent.
Braden, Zhang, et al. Expiration: September 1996 [Page 20]
Internet Draft RSVP Specification February 1996
A sender host must not send path state both with and without
a zero SrcPort. Violation of this condition is an "Ambiguous
Path" error.
2.3 Merging Flowspecs
As noted earlier, a single physical interface may receive multiple
reservation requests from different next hops for the same session
and with the same filter spec, but RSVP should install only one
reservation on that interface. The installed reservation should
have an effective flowspec that is the "largest" of the flowspecs
requested by the different next hops. Similarly, a Resv message
forwarded to a previous hop should carry a flowspec that is the
"largest" of the flowspecs requested by the different next hops
(however, in certain cases the "smallest" is taken rather than the
largest, see Section 3.4). These cases both represent flowspec
merging.
Flowspec merging requires calculation of the "largest" of a set of
flowspecs. However, since flowspecs are generally multi-
dimensional vectors (they may contain both Tspec and Rspec
components, each of which may itself be multi-dimensional), it may
not be possible to strictly order two flowspecs. For example, if
one request calls for a higher bandwidth and another calls for a
tighter delay bound, one is not "larger" than the other. In such
a case, instead of taking the larger, RSVP must compute and use a
third flowspec that is at least as large as each. Mathematically,
RSVP merges flowspecs using the "least upper bound" (LUB) instead
of the maximum. Typically, the LUB is calculated by creating a
new flowspec whose components are individually either the max or
the min of corresponding components of the flowspecs being merged.
For example, the LUB of Tspecs defined by token bucket parameters
is computed by taking the maximums of the bucket size and the rate
parameters. In some cases, the GLB (Greatest Lower Bound) is
required instead of the LUB; this simply interchanges max and min
operations.
The following steps are used to calculate the effective flowspec
(Te, Re) to be installed on an interface. Here Te is the
effective Tspec and Re is the effective Rspec. As an example,
consider interface (d) in Figure 9.
1. RSVP calculates the LUB of the flowspecs that arrived in Resv
messages from different next hops (e.g., D and D') but the
same outgoing interface (d).
This calculation yields a flowspec that is opaque to RSVP but
actually consists of the pair (Re, Resv_Te), where Re is the
Braden, Zhang, et al. Expiration: September 1996 [Page 21]
Internet Draft RSVP Specification February 1996
LUB of the Rspecs and Resv_Te is the LUB of the Tspecs from
the Resv messages.
2. RSVP calculates Path_Te, the sum of all Tspecs that were
supplied in Path messages from different previous hops (e.g.,
some or all of A, B, and B' in Figure 9).
3. RSVP passes these two results, (Re, Resv_Te) and Path_Te, to
traffic control. Traffic control will compute the "minimum"
of Path_Te and Resv_Te in an appropriate, perhaps service-
dependent, manner.
The definition and implementation of the rules for comparing
flowspecs, calculating LUBs and GLBs, and summing Tspecs are
outside the definition of RSVP. Section 3.10.4 shows generic
calls that an RSVP daemon could use for these functions.
2.4 Soft State
RSVP takes a "soft state" approach to managing the reservation
state in routers and hosts. RSVP soft state is created and
periodically refreshed by Path and Resv messages. The state is
deleted if no matching refresh messages arrive before the
expiration of a "cleanup timeout" interval. State may also be
deleted by an explicit "teardown" message, described in the next
section. At the expiration of each "refresh timeout" period and
after a state change, RSVP scans its state to build and forward
Path and Resv refresh messages to succeeding hops.
Path and Resv messages are idempotent. When a route changes, the
next Path message will initialize the path state on the new route,
and future Resv messages will establish reservation state there;
the state on the now-unused segment of the route will time out.
Thus, whether a message is "new" or a "refresh" is determined
separately at each node, depending upon the existence of state at
that node.
RSVP sends its messages as IP datagrams with no reliability
enhancement. Periodic transmission of refresh messages by hosts
and routers is expected to handle the occasional loss of an RSVP
message. If the effective cleanup timeout is set to K times the
refresh timeout period, then RSVP can tolerate K-1 successive RSVP
packet losses without falsely deleting state. the network traffic
control mechanism should be statically configured to grant some
minimal bandwidth for RSVP messages to protect them from
congestion losses.
The state maintained by RSVP is dynamic; to change the set of
Braden, Zhang, et al. Expiration: September 1996 [Page 22]
Internet Draft RSVP Specification February 1996
senders Si or to change any QoS request, a host simply starts
sending revised Path and/or Resv messages. The result will be an
appropriate adjustment in the RSVP state in all nodes along the
path; unused state will time out if it is not explicitly torn
down.
In steady state, refreshing is performed hop-by-hop, to allow
merging. When the received state differs from the stored state,
the stored state is updated. If this update results in
modification of state to be forwarded in refresh messages, these
refresh messages must be generated and forwarded immediately, so
that state changes can be propagated end-to-end without delay.
However, propagation of a change stops when and if it reaches a
point where merging causes no resulting state change. This
minimizes RSVP control traffic due to changes and is essential for
scaling to large multicast groups.
State that is received through a particular interface I* should
never be forwarded out the same interface. Conversely, state that
is forwarded out interface I* must be computed using only state
that arrived on interfaces different from I*. A trivial example
of this rule is illustrated in Figure 10, which shows a transit
router with one sender and one receiver on each interface (and
assumes one next/previous hop per interface). Interfaces (a) and
(c) serve as both outgoing and incoming interfaces for this
session. Both receivers are making wildcard-style reservations,
in which the Resv messages are forwarded to all previous hops for
senders in the group, with the exception of the next hop from
which they came. The result is independent reservations in the
two directions.
There is an additional rule governing the forwarding of Resv
messages: state from RESV messages received from outgoing
interface Io should be forwarded to incoming interface Ii only if
Path messages from Ii are forwarded to Io.
Braden, Zhang, et al. Expiration: September 1996 [Page 23]
Internet Draft RSVP Specification February 1996
________________
a | | c
( R1, S1 ) <----->| Router |<-----> ( R2, S2 )
|________________|
Send | Receive
|
WF( *{3B}) <-- (a) | (c) <-- WF( *{3B})
|
Receive | Send
|
WF( *{4B}) --> (a) | (c) --> WF( *{4B})
|
Reserve on (a) | Reserve on (c)
__________ | __________
| * {4B} | | | * {3B} |
|__________| | |__________|
|
Figure 10: Independent Reservations
2.5 Teardown
Upon arrival, RSVP "teardown" messages remove path and reservation
state immediately. Although it is not necessary to explicitly
tear down an old reservation, we recommend that all end hosts send
a teardown request as soon as an application finishes.
There are two types of RSVP teardown message, PathTear and
ResvTear. A PathTear message travels towards all receivers
downstream from its point of initiation and deletes path state, as
well as all dependent reservation state, along the way. An
ResvTear message deletes reservation state and travels towards all
senders upstream from its point of initiation. A PathTear
(ResvTear) message may be conceptualized as a reversed-sense Path
message (Resv message, respectively).
A teardown request may be initiated either by an application in an
end system (sender or receiver), or by a router as the result of
state timeout or service preemption. Once initiated, a teardown
request must be forwarded hop-by-hop without delay. A teardown
message deletes the specified state in the node where it is
received. As always, this state change will be propagated
immediately to the next node, but only if there will be a net
change after merging. As a result, an ResvTear message will prune
the reservation state back (only) as far as possible.
Braden, Zhang, et al. Expiration: September 1996 [Page 24]
Internet Draft RSVP Specification February 1996
Like all other RSVP messages, teardown requests are not delivered
reliably. The loss of a teardown request message will not cause a
protocol failure because the unused state will eventually time out
even though it is not explicitly deleted. If a teardown message
is lost, the router that failed to receive that message will time
out its state and initiate a new teardown message beyond the loss
point. Assuming that RSVP message loss probability is small, the
longest time to delete state will seldom exceed one refresh
timeout period.
It should be possible to tear down any subset of the established
state. For path state, the granularity for teardown is a single
sender. For reservation state, the granularity is an individual
filter spec. For example, refer to Figure 7. Receiver R1 could
send a ResvTear message for sender S2 only (or for any subset of
the filter spec list), leaving S1 in place.
A ResvTear message specifies the style and filters; any flowspec
is ignored. Whatever flowspec is in place will be removed if all
its filter specs are torn down.
2.6 Errors
There are two RSVP error messages, ResvErr and PathErr. PERR
messages are very simple; they are simply sent upstream to the
sender that created the error, and they do not change path state
in the nodes though which they pass. There are only a few
possible causes of path errors.
However, there are a number of ways for a syntactically valid
reservation request to fail at some node along the path. A node
may also decide to preempt an established reservation. The
handling of ResvErr messages is somewhat complex (Section 3.4).
Since a request that fails may be the result of merging a number
of requests, a reservation error must be reported to all of the
responsible receivers. In addition, merging heterogeneous
requests creates a potential difficulty known as the "killer
reservation" problem, in which one request could deny service to
another. There are actually two killer-reservation problems.
1. The first killer reservation problem (KR-I) arises when there
is already a reservation Q0 in place. If another receiver
now makes a larger reservation Q1 > Q0, the result of merging
Q0 and Q1 may be rejected by admission control in some
upstream node. This must not deny service to Q0.
The solution to this problem is simple: when admission
control fails for a reservation request, any existing
Braden, Zhang, et al. Expiration: September 1996 [Page 25]
Internet Draft RSVP Specification February 1996
reservation is left in place.
2. The second killer reservation problem (KR-II) is the
converse: the receiver making a reservation Q1 is persistent
even though Admission Control is failing for Q1 in some node.
This must not prevent a different receiver from now
establishing a smaller reservation Q0 that would succeed if
not merged with Q1.
To solve this problem, a ResvErr message establishes
additional state, called "blockade state", in each node
through which it passes. Blockade state in a node modifies
the merging procedure to omit the offending flowspec (Q1 in
the example) from the merge, allowing a smaller request to be
forwarded and established. The Q1 reservation state is said
to be "blockaded". Detailed rules are presented in Section
3.4.
A reservation request that fails Admission Control creates
blockade state but is left in place in nodes downstream of the
failure point. It has been suggested that these reservations
downstream from the failure represent "wasted" reservations and
should be timed out if not actively deleted. However, the
downstream reservations are left in place, for the following
reasons:
o There are two possible reasons for a receiver persisting in a
failed reservation: (1) it is polling for resource
availability along the entire path, or (2) it wants to obtain
the desired QoS along as much of the path as possible.
Certainly in the second case, and perhaps in the first case,
the receiver will want to hold onto the reservations it has
made downstream from the failure.
o If these downstream reservations were not retained, the
responsiveness of RSVP to certain transient failures would be
impaired. For example, suppose a route "flaps" to an
alternate route that is congested, so an existing reservation
suddenly fails, then quickly recovers to the original route.
The blockade state in each downstream router must not remove
the state or prevent its immediate refresh.
o If we did not refresh the downstream reservations, they might
time out, to be restored every Tb seconds (where Tb is the
blockade state timeout interval). Such intermittent behavior
might be very distressing for users.
Braden, Zhang, et al. Expiration: September 1996 [Page 26]
Internet Draft RSVP Specification February 1996
2.7 Confirmation
To request a confirmation for its reservation request, a receiver
Rj includes in the Resv message a confirmation-request object
containing Rj's IP address. At each merge point, only the largest
flowspec and any accompanying confirmation-request object is
forwarded upstream. If the reservation request from Rj is equal
to or smaller than the reservation in place on a node, its Resv
are not forwarded further, and if the Resv included a
confirmation-request object, a ResvConf message is sent back to
Rj. If the confirmation request is forwarded, it is forwarded
immediately, and no more than once for each request.
This confirmation mechanism has the following consequences:
o A new reservation request with a flowspec larger than any in
place for a session will normally result in either a ResvErr
or a ResvConf message back to the receiver from each sender.
In this case, the ResvConf message will be an end-to-end
confirmation.
o The receipt of a ResvConf gives no guarantees. Assume the
first two reservation requests from receivers R1 and R2
arrive at the node where they are merged. R2, whose
reservation was the second to arrive at that node, may
receive a ResvConf from that node while R1's request has not
yet propagated all the way to a matching sender and may still
fail. Thus, R2 may receive a ResvConf although there is no
end-to-end reservation in place; furthermore, R2 may receive
a ResvConf followed by a ResvErr.
2.8 Policy and Security
RSVP-mediated QoS requests will result in particular user(s)
getting preferential access to network resources. To prevent
abuse, some form of back pressure on users is likely to be
required. This back pressure might take the form of
administrative rules, or of some form of real or virtual billing
for the "cost" of a reservation. The form and contents of such
back pressure is a matter of administrative policy that may be
determined independently by each administrative domain in the
Internet.
Therefore, there is likely to be policy control as well as
admission control over the establishment of reservations. As
input to policy control, RSVP messages may carry "policy data".
Policy data may include credentials identifying users or user
Braden, Zhang, et al. Expiration: September 1996 [Page 27]
Internet Draft RSVP Specification February 1996
classes, account numbers, limits, quotas, etc. Like flowspecs,
policy data will be opaque to RSVP, which will simply pass it to a
"Local Policy Module" (LPM) for a decision.
To protect the integrity of the policy control mechanisms, it may
be necessary to ensure the integrity of RSVP messages against
corruption or spoofing, hop by hop. For this purpose, RSVP
messages may carry integrity objects that can be created and
verified by neighbor RSVP-capable nodes. These objects use a
keyed cryptographic digest technique and assume that RSVP
neighbors share a secret [Baker96].
User policy data in reservation request messages presents a
scaling problem. When a multicast group has a large number of
receivers, it will be impossible or undesirable to carry all
receivers' policy data upstream to the sender(s). The policy data
will have to be administratively merged at places near the
receivers, to avoid excessive policy data. Administrative merging
implies checking the user credentials and accounting data and then
substituting a token indicating the check has succeeded. A chain
of trust established using integrity fields will allow upstream
nodes to accept these tokens.
In summary, different administrative domains in the Internet may
have different policies regarding their resource usage and
reservation. The role of RSVP is to carry policy data associated
with each reservation to the network as needed. Note that the
merge points for policy data are likely to be at the boundaries of
administrative domains. It may be necessary to carry accumulated
and unmerged policy data upstream through multiple nodes before
reaching one of these merge points.
This document does not specify the contents of policy data, the
structure of an LPM, or any generic policy models. These will be
defined in the future.
2.9 Non-RSVP Clouds
It is impossible to deploy RSVP (or any new protocol) at the same
moment throughout the entire Internet. Furthermore, RSVP may
never be deployed everywhere. RSVP must therefore provide correct
protocol operation even when two RSVP-capable routers are joined
by an arbitrary "cloud" of non-RSVP routers. Of course, an
intermediate cloud that does not support RSVP is unable to perform
resource reservation. However, if such a cloud has sufficient
capacity, it may still provide useful realtime service.
RSVP is designed to operate correctly through such a non-RSVP
Braden, Zhang, et al. Expiration: September 1996 [Page 28]
Internet Draft RSVP Specification February 1996
cloud. Both RSVP and non-RSVP routers forward Path messages
towards the destination address using their local uni-/multicast
routing table. Therefore, the routing of Path messages will be
unaffected by non-RSVP routers in the path. When a Path message
traverses a non-RSVP cloud, it carries to the next RSVP-capable
node the IP address of the last RSVP-capable router before
entering the cloud. An Resv message is then forwarded directly to
the next RSVP-capable router on the path(s) back towards the
source.
Even though RSVP operates correctly through a non-RSVP cloud, the
non-RSVP-capable nodes will in general perturb the QoS provided to
a receiver. Therefore, RSVP tries to inform the receiver when
there are non-RSVP-capable hops in the path to a given sender, by
means of two flag bits in the SESSION object of a Path message;
see Section 3.7 and Appendix A.
Some topologies of RSVP routers and non-RSVP routers can cause
Resv messages to arrive at the wrong RSVP-capable node, or to
arrive at the wrong interface of the correct node. An RSVP daemon
must be prepared to handle either situation. If the destination
address does not match any local interface and the message is not
a Path or PathTear, the message must be forwarded without further
processing by this node. When a Resv message does arrive at the
addressed node, the IP destination address (or the LIH, defined
later) must be used to determine the interface to receive the
reservation.
2.10 Host Model
Before a session can be created, the session identification,
comprised of DestAddress, ProtocolId, and perhaps the generalized
destination port, must be assigned and communicated to all the
senders and receivers by some out-of-band mechanism. When an RSVP
session is being set up, the following events happen at the end
systems.
H1 A receiver joins the multicast group specified by
DestAddress, using IGMP.
H2 A potential sender starts sending RSVP Path messages to the
DestAddress.
H3 A receiver application receives a Path message.
H4 A receiver starts sending appropriate Resv messages,
specifying the desired flow descriptors.
Braden, Zhang, et al. Expiration: September 1996 [Page 29]
Internet Draft RSVP Specification February 1996
H5 A sender application receives a Resv message.
H6 A sender starts sending data packets.
There are several synchronization considerations.
o H1 and H2 may happen in either order.
o Suppose that a new sender starts sending data (H6) but there
are no multicast routes because no receivers have joined the
group (H1). Then the data will be dropped at some router
node (which node depends upon the routing protocol) until
receivers(s) appear.
o Suppose that a new sender starts sending Path messages (H2)
and data (H6) simultaneously, and there are receivers but no
Resv messages have reached the sender yet (e.g., because its
Path messages have not yet propagated to the receiver(s)).
Then the initial data may arrive at receivers without the
desired QoS. The sender could mitigate this problem by
awaiting arrival of the first Resv message (H5); however,
receivers that are farther away may not have reservations in
place yet.
o If a receiver starts sending Resv messages (H4) before
receiving any Path messages (H3), RSVP will return error
messages to the receiver.
The receiver may simply choose to ignore such error messages,
or it may avoid them by waiting for Path messages before
sending Resv messages.
A specific application program interface (API) for RSVP is not
defined in this protocol spec, as it may be host system dependent.
However, Section 3.10.1 discusses the general requirements and
outlines a generic interface.
Braden, Zhang, et al. Expiration: September 1996 [Page 30]
Internet Draft RSVP Specification February 1996
3. RSVP Functional Specification
3.1 RSVP Message Formats
An RSVP message consists of a common header, followed by a body
consisting of a variable number of variable-length, typed "
objects". The following subsections define the formats of the
common header, the standard object header, and each of the RSVP
message types.
For each RSVP message type, there is a set of rules for the
permissible choice of object types. These rules are specified
using Backus-Naur Form (BNF) augmented with square brackets
surrounding optional sub-sequences. The BNF implies an order for
the objects in a message. However, in many (but not all) cases,
object order makes no logical difference. An implementation
should create messages with the objects in the order shown here,
but accept the objects in any permissible order.
3.1.1 Common Header
0 1 2 3
+-------------+-------------+-------------+-------------+
| Vers | Flags| Msg Type | RSVP Checksum |
+-------------+-------------+-------------+-------------+
| Send_TTL | (Reserved) | RSVP Length |
+-------------+-------------+-------------+-------------+
The fields in the common header are as follows:
Vers: 4 bits
Protocol version number. This is version 1.
Flags: 4 bits
0x01-0x08: Reserved
No flag bits are defined yet.
Msg Type: 8 bits
1 = Path
2 = Resv
Braden, Zhang, et al. Expiration: September 1996 [Page 31]
Internet Draft RSVP Specification February 1996
3 = PathErr
4 = ResvErr
5 = PathTear
6 = ResvTear
7 = ResvConf
RSVP Checksum: 16 bits
The one's complement of the one's complement sum of the
message, with the checksum field replaced by zero for the
purpose of computing the checksum. An all-zero value
means that no checksum was transmitted.
Send_TTL: 8 bits
The IP TTL value with which the message was sent. See
Section 3.7.
RSVP Length: 16 bits
The total length of this RSVP message in bytes, including
the common header and the variable-length objects that
follow.
3.1.2 Object Formats
Every object consists of one or more 32-bit words with a one-
word header, in the following format:
0 1 2 3
+-------------+-------------+-------------+-------------+
| Length (bytes) | Class-Num | C-Type |
+-------------+-------------+-------------+-------------+
| |
// (Object contents) //
| |
+-------------+-------------+-------------+-------------+
An object header has the following fields:
Length
A 16-bit field containing the total object length in
Braden, Zhang, et al. Expiration: September 1996 [Page 32]
Internet Draft RSVP Specification February 1996
bytes. Must always be a multiple of 4, and at least 4.
Class-Num
Identifies the object class; values of this field are
defined in Appendix A. Each object class has a name,
which is always capitalized in this document. An RSVP
implementation must recognize the following classes:
NULL
A NULL object has a Class-Num of zero, and its C-Type
is ignored. Its length must be at least 4, but can
be any multiple of 4. A NULL object may appear
anywhere in a sequence of objects, and its contents
will be ignored by the receiver.
SESSION
Contains the IP destination address (DestAddress),
the IP protocol id, and some form of generalized
destination port, to define a specific session for
the other objects that follow. Required in every
RSVP message.
RSVP_HOP
Carries the IP address of the RSVP-capable node that
sent this message and a logical outgoing interface
handle (LIH; see Section 3.2). This document refers
to a RSVP_HOP object as a PHOP ("previous hop")
object for downstream messages or as a NHOP (" next
hop") object for upstream messages.
TIME_VALUES
Contains the value for the refresh period R used by
the creator of the message; see 3.6. Required in
every Path and Resv message.
STYLE
Defines the reservation style plus style-specific
information that is not in FLOWSPEC or FILTER_SPEC
objects. Required in every Resv message.
FLOWSPEC
Braden, Zhang, et al. Expiration: September 1996 [Page 33]
Internet Draft RSVP Specification February 1996
Defines a desired QoS, in a Resv message.
FILTER_SPEC
Defines a subset of session data packets that should
receive the desired QoS (specified by an FLOWSPEC
object), in a Resv message.
SENDER_TEMPLATE
Contains a sender IP address and perhaps some
additional demultiplexing information to identify a
sender. Required in a Path message.
SENDER_TSPEC
Defines the traffic characteristics of a sender's
data stream. Required in a Path message.
ADSPEC
Carries OPWA data, in a Path message.
ERROR_SPEC
Specifies an error in a PathErr, ResvErr, or a
confirmation in a ResvConf message.
POLICY_DATA
Carries information that will allow a local policy
module to decide whether an associated reservation is
administratively permitted. May appear in Path,
Resv, PathErr, or ResvErr message.
INTEGRITY
Carries cryptographic data to authenticate the
originating node and to verify the contents of this
RSVP message. The use of the INTEGRITY object is
described in [Baker96].
SCOPE
Carries an explicit list of sender hosts towards
which the information in the message is to be
forwarded. May appear in a Resv, ResvErr, or
ResvTear message. See Section 3.3.
Braden, Zhang, et al. Expiration: September 1996 [Page 34]
Internet Draft RSVP Specification February 1996
RESV_CONFIRM
Carries the IP address of a receiver that requested a
confirmation. May appear in a Resv or ResvConf
message.
C-Type
Object type, unique within Class-Num. Values are defined
in Appendix A.
The maximum object content length is 65528 bytes. The Class-
Num and C-Type fields may be used together as a 16-bit number
to define a unique type for each object.
The high-order two bits of the Class-Num is used to determine
what action a node should take if it does not recognize the
Class-Num of an object; see Section 3.9.
3.1.3 Path Messages
Each sender host periodically sends a Path message containing a
description of each data stream it originates. The Path
message travels from a sender to receiver(s) along the same
path(s) used by the data packets. The IP source address of a
Path message is an address of the sender it describes, while
the destination address is the DestAddress for the session.
These addresses assure that the message will be correctly
routed through a non-RSVP cloud.
The format of a Path message is as follows:
<Path Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <POLICY_DATA> ... ]
<sender descriptor>
<sender descriptor> ::= <SENDER_TEMPLATE> <SENDER_TSPEC>
[ <ADSPEC> ]
If the INTEGRITY object is present, it must immediately follow
Braden, Zhang, et al. Expiration: September 1996 [Page 35]
Internet Draft RSVP Specification February 1996
the common header. There are no other requirements on
transmission order, although the above order is recommended.
Any number of POLICY_DATA objects may appear.
The PHOP (i.e., the RSVP_HOP) object of each Path message
contains the previous hop address, i.e., the IP address of the
interface through which the Path message was most recently
sent. It also carries a logical interface handle (LIH).
The SENDER_TEMPLATE object defines the format of data packets
from this sender, while the SENDER_TSPEC object specifies the
traffic characteristics of the flow. Optionally, there may be
an ADSPEC object carrying advertising (OPWA) data.
Each RSVP-capable node along the path(s) captures a Path
message and processes it to create path state for the sender
defined by the SENDER_TEMPLATE and SESSION objects. Any
POLICY_DATA, SENDER_TSPEC, and ADSPEC objects are also saved in
the path state. If an error is encountered while processing a
Path message, a PathErr message is sent to the originating
sender of the Path message. PATH messages must satisfy the
rules on SrcPort and DstPort in Section 2.2.
Periodically, the RSVP daemon at a node scans the path state to
create new Path messages to forward towards the receiver(s).
Each message contains a sender descriptor defining one sender,
and carries the original sender's IP address as its IP source
address. Path messages eventually reach the applications on
all receivers; however, they are not looped back to a receiver
running in the same application process as the sender.
The RSVP daemon forwards Path messages, and replicates them as
required, using routing information it obtains from the
appropriate uni-/multicast routing daemon. The route depends
upon the session DestAddress, and for some routing protocols
also upon the source (sender's IP) address. The routing
information generally includes the list of none or more
outgoing interfaces to which the Path message to be forwarded.
Because each outgoing interface has a different IP address, the
Path messages sent out different interfaces contain different
PHOP addresses. In addition, ADSPEC objects carried in Path
messages will also generally differ for different outgoing
interfaces.
Some IP multicast routing protocols (e.g., DVMRP, PIM, and
MOSPF) also keep track of the expected incoming interface for
each source host to a multicast group. Whenever this
information is available, RSVP should check the incoming
Braden, Zhang, et al. Expiration: September 1996 [Page 36]
Internet Draft RSVP Specification February 1996
interface of each Path message and do special handling of those
messages Path messages that have arrived on the wrong
interface; see Section 3.8.
3.1.4 Resv Messages
Resv messages carry reservation requests hop-by-hop from
receivers to senders, along the reverse paths of data flows for
the session. The IP destination address of a Resv message is
the unicast address of a previous-hop node, obtained from the
path state. The IP source address is an address of the node
that sent the message.
The Resv message format is as follows:
<Resv Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <RESV_CONFIRM> ] [ <SCOPE> ]
[ <POLICY_DATA> ... ]
<STYLE> <flow descriptor list>
<flow descriptor list> ::= <flow descriptor> |
<flow descriptor list> <flow descriptor>
The STYLE object followed by the flow descriptor list must
occur at the end of the message, and objects within the flow
descriptor list must follow the BNF given below. There are no
other requirements on transmission order, although the above
order is recommended.
The NHOP (i.e., the RSVP_HOP) object contains the IP address of
the interface through which the Resv message was sent and the
LIH for the logical interface on which the reservation is
required.
The appearance of a RESV_CONFIRM object signals a request for a
reservation confirmation and carries the IP address of the
receiver to which the ResvConf should be sent. Any number of
POLICY_DATA objects may appear.
Braden, Zhang, et al. Expiration: September 1996 [Page 37]
Internet Draft RSVP Specification February 1996
The BNF above defines a flow descriptor list as simply a list
of flow descriptors. The following style-dependent rules
specify in more detail the composition of a valid flow
descriptor list for each of the reservation styles.
o WF Style:
<flow descriptor list> ::= <WF flow descriptor>
<WF flow descriptor> ::= <FLOWSPEC>
o FF style:
<flow descriptor list> ::=
<FLOWSPEC> <FILTER_SPEC> |
<flow descriptor list> <FF flow descriptor>
<FF flow descriptor> ::=
[ <FLOWSPEC> ] <FILTER_SPEC>
Each elementary FF style request is defined by a single
(FLOWSPEC, FILTER_SPEC) pair, and multiple such requests
may be packed into the flow descriptor list of a single
Resv message. A FLOWSPEC object can be omitted if it is
identical to the most recent such object that appeared in
the list; the first FF flow descriptor must contain a
FLOWSPEC.
o SE style:
<flow descriptor list> ::= <SE flow descriptor>
<SE flow descriptor> ::=
<FLOWSPEC> <filter spec list>
<filter spec list> ::= <FILTER_SPEC>
| <filter spec list> <FILTER_SPEC>
The reservation scope, i.e., the set of senders towards which a
Braden, Zhang, et al. Expiration: September 1996 [Page 38]
Internet Draft RSVP Specification February 1996
particular reservation is to be forwarded (after merging), is
determined as follows:
o Explicit sender selection
Select a particular sender by matching each FILTER_SPEC
object against the path state created from SENDER_TEMPLATE
objects. This match must follow the rules of Section 2.2.
o Wildcard sender selection
All senders that route to the given outgoing interface
match this request. A SCOPE object, if present, contains
an explicit list of sender IP addresses. If there is no
SCOPE object, the scope is determined by the relevant set
of senders in the path state.
Whenever a Resv message with wildcard sender selection is
forwarded to more than one previous hop, a SCOPE object
must be included in the message. See Section 3.3 below.
3.1.5 Teardown Messages
There are two types of RSVP teardown message, PathTear and
ResvTear.
o A PathTear message deletes path state (which in turn
deletes any reservation state for that sender), traveling
towards all receivers that are downstream from the
initiating node. A PathTear message must be routed
exactly like the corresponding Path message. Therefore,
its IP destination address must be the session
DestAddress, and its IP source address must be the address
of the sender being torn down.
o A ResvTear message deletes reservation state, travelling
towards all matching senders upstream from the initiating
node. A ResvTear message must be routed link the
corresponding Resv message, and its IP destination address
will be the unicast address of a previous hop. An
ResvTear message will be initiated by a receiver, by a
node in which reservation state has timed out, or by a
node in which a reservation has been preempted.
<PathTear Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
Braden, Zhang, et al. Expiration: September 1996 [Page 39]
Internet Draft RSVP Specification February 1996
<sender descriptor>
<sender descriptor> ::= (see earlier definition)
<ResvTear Message> ::= <Common Header> [<INTEGRITY>]
<SESSION> <RSVP_HOP>
[ <SCOPE> ] <STYLE>
<flow descriptor list>
<flow descriptor list> ::= (see earlier definition)
FLOWSPEC objects in the flow descriptor list of a ResvTear
message will be ignored and may be omitted. The order
requirements for sender descriptor, STYLE object, and flow
descriptor list are as given earlier for Path and Resv
messages. A ResvTear message may specify any subset of the
filter specs in FF- or SE-style reservation state.
Note that, unless it is accidentally dropped along the way, a
PTEAR message will reach all receivers downstream from the
originating node. On the other hand, a ResvTear message will
cease to be forwarded at the node where merging would have
suppressed forwarding of the corresponding Resv message. In
each node N along the way, if the ResvTear message causes the
removal of all state for this session, N will create a new
teardown message to be propagated further upstream; otherwise,
the ResvTear message may result in the immediate forwarding of
a modified Resv refresh message.
For example, consider the FF-style reservations in Figure 6.
If receiver R3 send a ResvTear message for its reservation
S1{B}, there is no change in the effective reservation S1{3B}
on (d), and no message will be forwarded. If receiver R2 sends
a ResvTear message for its reservation S3{B}, the corresponding
reservation will be removed from (d) and an ResvTear for S3{B}
will be forwarded out interface (b). Finally, if receiver R1
sends a ResvTear for its reservation S1{4B}, the result will be
to remove the reservation from interface (c), and to forward
immediately a Resv message FF( S1{3B} ) out interface (a).
Deletion of path state as the result of a PathTear message or a
timeout must cause any adjustments in related reservation state
required to maintain consistency in the local node. The
adjustment in reservation state depends upon the style. For
Braden, Zhang, et al. Expiration: September 1996 [Page 40]
Internet Draft RSVP Specification February 1996
example, suppose a PathTear deletes the path state for a sender
S. If the style specifies explicit sender selection (FF or
SE), any reservation with a filter spec matching S should be
deleted; if the style has wildcard sender selection (WF), the
reservation should be deleted if S is the last sender to the
session. These reservation changes should not trigger an
immediate Resv refresh message, since the PathTear message have
already made the required changes upstream. However, at the
node in which a ResvTear message stops, the change of
reservation state may trigger a Resv refresh starting at that
node.
3.1.6 Error Messages
There are two types of RSVP error messages.
o PathErr messages result from Path messages and travel
upstream towards senders. PathErr messages are routed
hop-by-hop using the path state; at each hop, the IP
destination address is the unicast address of a previous
hop. PathErr messages do not modify the state of any node
through which they pass; instead, they are only reported
to the sender application.
o ResvErr messages result from Resv messages and travel
downstream towards the appropriate receivers. They are
routed hop-by-hop using the reservation state; at each
hop, the IP destination address is the unicast address of
a next-hop node.
<PathErr message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <ERROR_SPEC>
[ <POLICY_DATA> ...]
<sender descriptor>
<sender descriptor> ::= (see earlier definition)
<ResvErr Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <ERROR_SPEC>
[ <SCOPE> ]
Braden, Zhang, et al. Expiration: September 1996 [Page 41]
Internet Draft RSVP Specification February 1996
[ <POLICY_DATA> ...]
<STYLE> <error flow descriptor>
The ERROR_SPEC object specifies the error and includes the IP
address of the node that detected the error (Error Node
Address). One or more POLICY_DATA objects may be included in
an error message to provide relevant information (i.e., when an
administrative failure is being reported). The STYLE object is
copied from the Resv message in error. The use of the SCOPE
object in a ResvErr message is defined below in Section 3.3.
The following style-dependent rules define the composition of a
valid error flow descriptor; the object order requirements are
as given earlier for a Resv message.
o WF Style:
<error flow descriptor> ::= <WF flow descriptor>
o FF style:
<error flow descriptor> ::= <FF flow descriptor>
Each flow descriptor in a FF-style Resv message must be
processed independently, and a separate ResvErr message
must be generated for each one that is in error.
o SE style:
<error flow descriptor> ::= <SE flow descriptor>
An SE-style ResvErr message may list the subset of the
filter specs in the corresponding Resv message to which
the error applies.
Note that a ResvErr message contains only one flow descriptor.
Therefore, a Resv message that contains N > 1 flow descriptors
(FF style) may create up to N separate ResvErr messages.
Generally speaking, a ResvErr message should be forwarded
towards all receivers that may have caused the error being
reported. More specifically:
o The node that detects an error in a reservation request
Braden, Zhang, et al. Expiration: September 1996 [Page 42]
Internet Draft RSVP Specification February 1996
sends a RERR message to the next hop from which the
erroneous reservation came.
This message must contain the information required to
define the error and to route the error message in later
hops. It therefore includes an ERROR_SPEC object, a copy
of the STYLE object, and the appropriate error flow
descriptor. If the error is an admission control failure,
any reservation already in place must be left in place,
and the InPlace flag bit must be on in the ERROR_SPEC of
the ResvErr message.
o Succeeding nodes forward the ResvErr message to next hops
that have local reservation state. For reservations with
wildcard scope, there is an additional limitation on
forwarding ResvErr messages, to avoid loops; see Section
3.3. There is also a rule restricting the forwarding of a
Resv message after an Admission Control failure; see
Section 3.4.
A ResvErr message that is forwarded should carry the
FILTER_SPEC from the corresponding reservation state.
o When a ResvErr message reaches a receiver, the STYLE
object, flow descriptor list, and ERROR_SPEC object
(including its flags) should be delivered to the receiver
application.
An error encountered while processing an error message must
cause the error message to be discarded without creating
further error messages; however, logging of such events may be
useful.
3.1.7 Confirmation Messages
ResvConf messages are sent to (probabilistically) acknowledge
reservation requests. A ResvConf message is sent as the result
of the appearance of a RESV_CONFIRM object in a Resv message.
A ResvConf message is sent to the unicast address of a receiver
host; the address is obtained from the RESV_CONFIRM object.
However, a ResvConf message is forwarded to the receiver hop-
by-hop, to accommodate the hop-by-hop integrity check
mechanism.
<ResvConf message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <ERROR_SPEC>
Braden, Zhang, et al. Expiration: September 1996 [Page 43]
Internet Draft RSVP Specification February 1996
<RESV_CONFIRM>
<STYLE> <flow descriptor list>
<flow descriptor list> ::= (see earlier definition)
The object order requirements are the same as those given
earlier for a Resv message.
The RESV_CONFIRM object is a copy of that object in the Resv
message that triggered the confirmation. The ERROR_SPEC is
used only to carry the IP address of the originating node, in
the Error Node Address; the Error Code and Value are zero to
indicate a confirmation. The flow descriptor list specifies
the particular reservations that are being confirmed; it may be
a subset of flow descriptor list of the Resv that requested the
confirmation.
3.2 Sending RSVP Messages
RSVP messages are sent hop-by-hop between RSVP-capable routers as
"raw" IP datagrams with protocol number 46. Raw IP datagrams are
also intended to be used between an end system and the first/last
hop router, although it is also possible to encapsulate RSVP
messages as UDP datagrams for end-system communication, as
described in Appendix C. UDP encapsulation is needed for systems
that cannot do raw network I/O.
Path, PathTear, and ResvConf messages must be sent with the Router
Alert IP option [Katz95] in their IP headers. This option may be
used in the fast forwarding path of a high-speed router to detect
datagrams that require special processing.
Upon the arrival of an RSVP message M that changes the state, a
node must forward the modified state immediately. However, this
must not trigger sending a message out the interface through which
M arrived (which could happen if the implementation simply
triggered an immediate refresh of all state for the session).
This rule is necessary to prevent packet storms on broadcast LANs.
In this version of the spec, each RSVP message must occupy exactly
one IP datagram. If it exceeds the MTU, such a datagram will be
fragmented by IP and reassembled at the recipient node. This has
several consequences:
o A single RSVP message may not exceed the maximum IP datagram
size, approximately 64K bytes.
Braden, Zhang, et al. Expiration: September 1996 [Page 44]
Internet Draft RSVP Specification February 1996
o A congested non-RSVP cloud could lose individual message
fragments, and any lost fragment will lose the entire
message.
Future versions of the protocol will provide solutions for these
problems if they prove burdensome. The most likely direction will
be to perform "semantic fragmentation", i.e., break the path or
reservation state being transmitted into multiple self-contained
messages, each of an acceptable size.
RSVP uses its periodic refresh mechanisms to recover from
occasional packet losses. Under network overload, however,
substantial losses of RSVP messages could cause a failure of
resource reservations. To control the queueing delay and dropping
of RSVP packets, routers should be configured to offer them a
preferred class of service. If RSVP packets experience noticeable
losses when crossing a congested non-RSVP cloud, a larger value
can be used for the timeout factor K (see section 3.6 below).
Some multicast routing protocols provide for "multicast tunnels",
which do IP encapsulation of multicast packets for transmission
through routers that do not have multicast capability. A
multicast tunnel looks like a logical outgoing interface that is
mapped into some physical interface. A multicast routing protocol
that supports tunnels will describe a route using a list of
logical rather than physical interfaces. RSVP can operate across
such multicast tunnels in the following manner:
1. When a node N forwards a Path message out a logical outgoing
interface L, it includes in the message some encoding of the
identity of L, called the "logical interface handle" or LIH.
The LIH value is carried in the RSVP_HOP object.
2. The next hop node N' stores the LIH value in its path state.
3. When N' sends a Resv message to N, it includes the LIH value
from the path state (again, in the RSVP_HOP object).
4. When the Resv message arrives at N, its LIH value provides
the information necessary to attach the reservation to the
appropriate logical interface. Note that N creates and
interprets the LIH; it is an opaque value to N'.
Note that this only solves the routing problem posed by tunnels.
The tunnel appears to RSVP as a non-RSVP cloud. To establish RSVP
reservations within the tunnel, additional machinery will be
required, to be defined in the future.
Braden, Zhang, et al. Expiration: September 1996 [Page 45]
Internet Draft RSVP Specification February 1996
3.3 Avoiding RSVP Message Loops
Forwarding of RSVP messages must avoid looping. In steady state,
Path and Resv messages are forwarded on each hop only once per
refresh period. This avoids looping packets, but there is still
the possibility of an "auto-refresh" loop, clocked by the refresh
period. Such auto-refresh loops keep state active "forever", even
if the end nodes have ceased refreshing it, until either the
receivers leave the multicast group and/or the senders stop
sending Path messages. On the other hand, error and teardown
messages are forwarded immediately and are therefore subject to
direct looping.
Consider each message type.
o Path Messages
Path messages are forwarded in exactly the same way as IP
data packets. Therefore there should be no loops of Path
messages, even in a topology with cycles.
o PathTear Messages
PathTear messages use the same routing as Path messages and
therefore cannot loop.
o PathErr Messages
Since Path messages do not loop, they create path state
defining a loop-free reverse path to each sender. PathErr
messages are always directed to particular senders and
therefore cannot loop.
o Resv Messages
Resv messages directed to particular senders (i.e., with
explicit sender selection) cannot loop. However, Resv
messages with wildcard sender selection (WF style) have a
potential for auto-refresh looping.
o ResvTear Messages
Although ResvTear messages are routed the same as Resv
messages, during the second pass around a loop there will be
no state so any ResvTear message will be dropped. Hence
there is no looping problem here.
o ResvErr Messages
Braden, Zhang, et al. Expiration: September 1996 [Page 46]
Internet Draft RSVP Specification February 1996
ResvErr messages for WF style reservations may loop for
essentially the same reasons that Resv messages loop.
o ResvConf Messages
ResvConf messages are forwarded towards a fixed unicast
receiver address and cannot loop.
If the topology has no loops, then looping of Resv and ResvErr
messages with wildcard sender selection can be avoided by simply
enforcing the rule given earlier: state that is received through a
particular interface must never be forwarded out the same
interface. However, when the topology does have cycles, further
effort is needed to prevent auto-refresh loops of wildcard Resv
messages and fast loops of wildcard ResvErr messages. The
solution to this problem adopted by this protocol specification is
for such messages to carry an explicit sender address list in a
SCOPE object.
When a Resv message with WF style is to be forwarded to a
particular previous hop, a new SCOPE object is computed from the
SCOPE objects that were received in matching Resv messages. If
the computed SCOPE object is empty, the message is not forwarded
to the previous hop; otherwise, the message is sent containing the
new SCOPE object. The rules for computing a new SCOPE object for
a Resv message are as follows:
1. The union is formed of the sets of sender IP addresses listed
in all SCOPE objects in the reservation state for the given
session.
If reservation state from some NHOP does not contain a SCOPE
object, a substitute sender list must be created and included
in the union. For a message that arrived on outgoing
interface OI, the substitute list is the set of senders that
route to OI.
2. Any local senders (i.e., any sender applications on this
node) are removed from this set.
3. If the SCOPE object is to be sent to PHOP, remove from the
set any senders that did not come from PHOP.
Figure 11 shows an example of wildcard-scoped (WF style) Resv
messages. The address lists within SCOPE objects are shown in
square brackets. Note that there may be additional connections
among the nodes, creating looping topology that is not shown.
Braden, Zhang, et al. Expiration: September 1996 [Page 47]
Internet Draft RSVP Specification February 1996
________________
a | | c
R4, S4<----->| Router |<-----> R2, S2, S3
| |
b | |
R1, S1<----->| |
|________________|
Send on (a): | Receive on (c):
|
<-- WF( [S4] ) | <-- WF( [S4, S1])
|
Send on (b): |
|
<-- WF( [S1] ) |
|
Receive on (a): | Send on (c):
|
WF( [S1,S2,S3]) --> | WF( [S2, S3]) -->
|
Receive on (b): |
|
WF( [S2,S3,S4]) --> |
|
Figure 11: SCOPE Objects in Wildcard-Scope Reservations
SCOPE objects are not necessary if the multicast routing uses
shared trees or if the reservation style has explicit sender
selection. Furthermore, attaching a SCOPE object to a reservation
should be deferred to a node which has more than one previous hop
for the reservation state.
The following rules are used for SCOPE objects in ResvErr messages
with WF style:
1. The node that detected the error initiates an ResvErr message
containing a copy of the SCOPE object associated with the
reservation state or message in error.
2. Suppose a wildcard-style ResvErr message arrives at a node
with a SCOPE object containing the sender host address list
L. The node forwards the ResvErr message using the rules of
Section 3.1.6. However, the ResvErr message forwarded out OI
must contain a SCOPE object derived from L by including only
those senders that route to OI. If this SCOPE object is
Braden, Zhang, et al. Expiration: September 1996 [Page 48]
Internet Draft RSVP Specification February 1996
empty, the ResvErr message should not be sent out OI.
3.4 Blockade State
The basic rule for creating a Resv refresh message is to merge the
flowspecs of the reservation requests in place in the node, by
computing their LUB. However, this rule is modified by the
existence of "blockade state" resulting from ResvErr messages, to
solve the KR-II problem (Section 2.6). The blockade state also
enters into the routing of ResvErr messages for Admission Control
failure.
When a ResvErr message for an Admission Control failure is
received, its flowspec Qe is used to create or refresh an element
of local blockade state. Each element of blockade state consists
of a blockade flowspec Qb taken from the flowspec of the ResvErr
message, and an associated blockade timer Tb. When a blockade
timer expires, the corresponding blockade state is deleted.
The granularity of blockade state depends upon the style of the
ResvErr message that created it. For an explicit style, there may
be a blockade state element (Qb(S),Tb(S)) for each sender S. For
a wildcard style, blockade state is per previous hop P.
An element of blockade state with flowspec Qb is said to
"blockade" a reservation with flowspec Qi if Qb is not (strictly)
greater than Qi. For example, suppose that the LUB of two
flowspecs is computed by taking the max of each of their
corresponding components. Then Qb blockades Qi if for some
component j, Qb[j] <= Qi[j].
Suppose that a node receives a ResvErr message from previous hop P
(or, if style is explicit, sender S) as the result of an Admission
Control failure upstream. Then:
1. An element of blockade state is created for P (or S) if it
did not exist.
2. Qb(P) (or Qb(S)) is set equal to the flowspec Qe from the
ResvErr message.
3. A corresponding blockade timer Tb(P) (or Tb(S)) is started or
restarted for a time Kb*R. Here Kb is a fixed multiplier and
R is the refresh interval for reservation state. Kb should
be configurable.
4. If there is some local reservation state that is not
blockaded (see below), an immediate reservation refresh for P
Braden, Zhang, et al. Expiration: September 1996 [Page 49]
Internet Draft RSVP Specification February 1996
(or S) is generated.
5. The ResvErr message is forwarded to next hops in the
following way. If the InPlace bit is off, the ResvErr
message is forwarded to all next hops for which there is
reservation state. If the InPlace bit is on, the ResvErr
message is forwarded only to the next hops whose Qi is
blockaded by Qb.
Finally, we present the modified rule for merging flowspecs to
create a reservation refresh message.
o If there are any local reservation requests Qi that are not
blockaded, these are merged by computing their LUB. The
blockaded reservations are ignored; this allows forwarding of
a smaller reservation that has not failed and may perhaps
succeed, after a larger reservation fails.
o Otherwise (all local requests Qi are blockaded), they are
merged by taking the GLB (Greatest Lower Bound) of the Qi's.
This refresh merging algorithm is applied separately to each flow
(each sender or PHOP) contributing to a shared reservation (WF or
SE style).
Figure 12 shows an example of the the application of blockade
state for a shared reservation (WF style). There are two previous
hops labelled (a) and (b), and two next hops labelled (c) and (d).
The larger reservation 4B arrived from (c) first, but it failed
somewhere upstream via PHOP (a), but not via PHOP (b). The
figures show the final "steady state" after the smaller
reservation 2B subsequently arrived from (d). This steady state
is perturbed roughly every Kb*R seconds, when the blockade state
times out. The next refresh then sends 4B to previous hop (a);
presumably this will fail, sending a ResvErr message that will
re-establish the blockade state, returning to the situation shown
in the figure. At the same time, the ResvErr message will be
forwarded to next hop (c) and to all receivers downstream
responsible for the 4B reservations.
Braden, Zhang, et al. Expiration: September 1996 [Page 50]
Internet Draft RSVP Specification February 1996
Send Blockade | Reserve Receive
State {Qb}|
| ________
(a) <- WF(*{2B}) {4B} | | * {4B} | WF(*{4B}) <- (c)
| |________|
|
---------------------------|-------------------------------
|
| ________
(b) <- WF(*{4B}) (none)| | * {2B} | WF(*{2B}) <- (d)
| |________|
Figure 12: Blockading with Shared Style
3.5 Local Repair
When a route changes, the next Path or Resv refresh message will
establish path or reservation state (respectively) along the new
route. To provide fast adaptation to routing changes without the
overhead of short refresh periods, the local routing protocol
module can notify the RSVP daemon of route changes for particular
destinations. The RSVP daemon should use this information to
trigger a quick refresh of state for these destinations, using the
new route.
The specific rules are as follows:
o When routing detects a change of the set of outgoing
interfaces for destination G, RSVP should wait for a short
period W, and then send Path refreshes for all sessions G/*
(i.e., for any session with destination G, regardless of
destination port).
The short wait period before sending Path refreshes is to
allow the routing protocol getting settled with the new
change(s), and the exact value for W should be chosen
accordingly. Currently W = 2 sec is suggested; however, this
value should be configurable per interface.
o When a Path message arrives with a Previous Hop address that
differs from the one stored in the path state, RSVP should
send immediate Resv refreshes for that session.
Braden, Zhang, et al. Expiration: September 1996 [Page 51]
Internet Draft RSVP Specification February 1996
3.6 Time Parameters
There are two time parameters relevant to each element of RSVP
path or reservation state in a node: the refresh period R between
generation of successive refreshes for the state by the neighbor
node, and the local state's lifetime L. Each RSVP Resv or Path
message may contain a TIME_VALUES object specifying the R value
that was used to generate this (refresh) message. This R value is
then used to determine the value for L when the state is received
and stored. The values for R and L may vary from hop to hop.
In more detail:
1. Floyd and Jacobson [FJ94] have shown that periodic messages
generated by independent network nodes can become
synchronized. This can lead to disruption in network
services as the periodic messages contend with other network
traffic for link and forwarding resources. Since RSVP sends
periodic refresh messages, it must avoid message
synchronization and ensure that any synchronization that may
occur is not stable.
For this reason, the refresh timer should be randomly set to
a value in the range [0.5R, 1.5R].
2. To avoid premature loss of state, L must satisfy L >= (K +
0.5)*1.5*R, where K is a small integer. Then in the worst
case, K-1 successive messages may be lost without state being
deleted. To compute a lifetime L for a collection of state
with different R values R0, R1, ..., replace R by max(Ri).
Currently K = 3 is suggested as the default. However, it may
be necessary to set a larger K value for hops with high loss
rate. K may be set either by manual configuration per
interface, or by some adaptive technique that has not yet
been specified.
3. Each Path or Resv message carries a TIME_VALUES object
containing the refresh time R used to generate refreshes.
The recipient node uses this R to determine the lifetime L of
the stored state created or refreshed by the message.
4. The refresh time R is chosen locally by each node. If the
node does not implement local repair of reservations
disrupted by route changes, a smaller R speeds up adaptation
to routing changes, while increasing the RSVP overhead. With
local repair, a router can be more relaxed about R since the
periodic refresh becomes only a backstop robustness
Braden, Zhang, et al. Expiration: September 1996 [Page 52]
Internet Draft RSVP Specification February 1996
mechanism. A node may therefore adjust the effective R
dynamically to control the amount of overhead due to refresh
messages.
The current suggested default for R is 30 seconds. However,
the default should be configurable per interface.
5. When R is changed dynamically, there is a limit on how fast
it may increase. Specifically, the ratio of two successive
values R2/R1 must not exceed 1 + Slew.Max.
Currently, Slew.Max is 0.30. With K = 3, one packet may be
lost without state timeout while R is increasing 30 percent
per refresh cycle.
6. To improve robustness, a node may temporarily send refreshes
more often than R after a state change (including initial
state establishment).
7. The values of Rdef, K, and Slew.Max used in an implementation
should be easily modifiable per interface, as experience may
lead to different values. The possibility of dynamically
adapting K and/or Slew.Max in response to measured loss rates
is for future study.
3.7 Traffic Policing and Non-Integrated Service Hops
Some QoS services may require traffic policing at some or all of
(1) the edge of the network, (2) a merging point for data from
multiple senders, and/or (3) a branch point where traffic flow
from upstream may be greater than the downstream reservation being
requested. RSVP knows where such points occur and must so
indicate to the traffic control mechanism. On the other hand,
RSVP does not interpret the service embodied in the flowspec and
therefore does not know whether policing will actually be applied
in any particular case.
The RSVP daemon passes to traffic control a separate policing flag
for each of these three situations.
o E_Police_Flag -- Entry Policing
This flag is set in the first-hop RSVP node that implements
traffic control (and is therefore capable of policing).
For example, sender hosts must implement RSVP but currently
many of them do not implement traffic control. In this case,
the E_Police_Flag should be off in the sender host, and it
Braden, Zhang, et al. Expiration: September 1996 [Page 53]
Internet Draft RSVP Specification February 1996
should only be set on when the first node capable of traffic
control is reached. This is controlled by the E_Police flag
in SESSION objects.
o M_Police_Flag -- Merge Policing
This flag should be set on for a reservation using a shared
style (WF or SE) when flows from more than one sender are
being merged.
o B_Police_Flag -- Branch Policing
This flag should be set on when the flowspec being installed
is smaller than, or incomparable to, a FLOWSPEC in place on
any other interface, for the same FILTER_SPEC and SESSION.
RSVP must also detect and report to receivers the presence of
non-RSVP (which implies non-integrated-service compliant) hops in
the path. For this purpose, an RSVP daemon sets the Non_RSVP flag
bit in SESSION object of Path messages. With normal IP
forwarding, RSVP can detect a non-RSVP hop by comparing the IP TTL
with which a Path message is sent to the TTL with which it is
received, and set the Non_RSVP bit on. For this purpose, the
transmission TTL is placed in the common header.
However, the TTL is not always a reliable indicator of non-RSVP
hops, and other means must be used. For example, if the routing
protocol uses IP encapsulating tunnels, then the routing protocol
must inform RSVP when non-RSVP hops are included. If no automatic
mechanism will work, manual configuration will be required.
Finally, there may still be cases where an RSVP cannot reliably
determine whether or not a non-RSVP hop was used. To report this
to the receiver, the SESSION object carries another flag bit,
Maybe_RSVP.
3.8 Multihomed Hosts
Accommodating multihomed hosts requires some special rules in
RSVP. We use the term `multihomed host' to cover both hosts (end
systems) with more than one network interface and routers that are
supporting local application programs.
An application executing on a multihomed host may explicitly
specify which interface any given flow will use for sending and/or
for receiving data packets, to override the system-specified
default interface. The RSVP daemon must be aware of the default,
and if an application sets a specific interface, it must also pass
that information to RSVP.
Braden, Zhang, et al. Expiration: September 1996 [Page 54]
Internet Draft RSVP Specification February 1996
o Sending Data
A sender application uses an API call (SENDER in Section
3.10.1) to declare to RSVP the characteristics of the data
flow it will originate. This call may optionally include the
local IP address of the sender. If it is set by the
application, this parameter must be the interface address for
sending the data packets; otherwise, the system default
interface is implied.
The RSVP daemon on the host then sends Path messages for this
application out the specified interface (only).
o Making Reservations
A receiver application uses an API call (RESERVE in Section
3.10.1) to request a reservation from RSVP. This call may
optionally include the local IP address of the receiver,
i.e., the interface address for receiving data packets. In
the case of multicast sessions, this is the interface on
which the group has been joined. If the parameter is
omitted, the system default interface is used.
In general, the RSVP daemon should send Resv messages for an
application out the specified interface. However, when the
application is executing on a router and the session is
multicast, a more complex situation arises. Suppose in this
case that a receiver application joins the group on an
interface Iapp that differs from Isp, the shortest-path
interface to the sender. Then there are two possible ways
for multicast routing to deliver data packets to the
application. The RSVP daemon must determine which case holds
by examining the path state, to decide which incoming
interface to use for sending Resv messages.
1. The multicast routing protocol may create a separate
branch of the multicast distribution `tree' to deliver
to Iapp. In this case, there will be path state for
both Isp and Iapp. The path state on Iapp should only
match a reservation from the local application; it must
be marked "Local_only" by the RSVP daemon. If
"Local_only" path state for Iapp exists, the Resv
message should be sent out Iapp.
Note that it is possible for the path state blocks for
Isp and Iapp to have the same next hop, if there is an
intervening non-RSVP cloud.
Braden, Zhang, et al. Expiration: September 1996 [Page 55]
Internet Draft RSVP Specification February 1996
2. The multicast routing protocol may forward data within
the router from Isp to Iapp. In this case, Iapp will
appear in the list of outgoing interfaces of the path
state for Isp, and the Resv message should be sent out
Isp.
3.9 Future Compatibility
We may expect that in the future new object C-Types will be
defined for existing object classes, and perhaps new object
classes will be defined. It will be desirable to employ such new
objects within the Internet using older implementations that do
not recognize them. Unfortunately, this is only possible to a
limited degree with reasonable complexity. The rules are as
follows (`b' represents a bit).
1. Unknown Class
There are three possible ways that an RSVP implementation can
treat an object with unknown class. This choice is
determined by the two high-order bits of the Class-Num octet,
as follows.
o Class-Num = 0bbbbbbb
The entire message should be rejected and an "Unknown
Object Class" error returned.
o Class-Num = 10bbbbbb
The node should ignore the object, neither forwarding it
nor sending an error message.
o Class-Num = 11bbbbbb
The node should ignore the object but forward it,
unexamined and unmodified, in all messages resulting
from the state contained in this message.
For example, suppose that a Resv message that is received
contains an object of unknown class number 11bbbbbb. Such an
object should be saved in the reservation state without
further examination; however, only the latest object with a
given (unknown class, C-Type) pair should be saved. When a
Resv message is forwarded, it should include copies of such
saved unknown-class objects from all reservations that are
merged to form the new Resv message.
Braden, Zhang, et al. Expiration: September 1996 [Page 56]
Internet Draft RSVP Specification February 1996
Note that objects with unknown class cannot be merged;
however, unmerged objects may be forwarded until they reach a
node that knows how to merge them. Forwarding objects with
unknown class enables incremental deployment of new objects;
however, the scaling limitations of doing so must be
carefully examined before a new object class is deployed with
both high bits on.
These rules should be considered when any new Class-Num is
defined.
2. Unknown C-Type for Known Class
One might expect the known Class-Num to provide information
that could allow intelligent handling of such an object.
However, in practice such class-dependent handling is
complex, and in many cases it is not useful.
Generally, the appearance of an object with unknown C-Type
should result in rejection of the entire message and
generation of an error message (ResvErr or PathErr as
appropriate). The error message will include the Class-Num
and C-Type that failed (see Appendix B); the end system that
originated the failed message may be able to use this
information to retry the request using a different C-Type
object, repeating this process until it runs out of
alternatives or succeeds.
Objects of certain classes (FLOWSPEC, ADSPEC, and
POLICY_DATA) are opaque to RSVP, which simply hands them to
traffic control or policy modules. Depending upon its
internal rules, either of the latter modules may reject a C-
Type and inform the RSVP daemon; RSVP should then reject the
message and send an error, as described in the previous
paragraph.
Braden, Zhang, et al. Expiration: September 1996 [Page 57]
Internet Draft RSVP Specification February 1996
3.10 RSVP Interfaces
RSVP on a router has interfaces to routing and to traffic control.
RSVP on a host has an interface to applications (i.e, an API) and
also an interface to traffic control (if it exists on the host).
3.10.1 Application/RSVP Interface
This section describes a generic interface between an
application and an RSVP control process. The details of a real
interface may be operating-system dependent; the following can
only suggest the basic functions to be performed. Some of
these calls cause information to be returned asynchronously.
o Register Session
Call: SESSION( DestAddress , ProtocolId, DstPort ,
[ , SESSION_object ]
[ , Upcall_Proc_addr ] ) -> Session-id
This call initiates RSVP processing for a session, defined
by DestAddress together with ProtocolId and possibly a
port number DstPort. If successful, the SESSION call
returns immediately with a local session identifier
Session-id, which may be used in subsequent calls.
The Upcall_Proc_addr parameter defines the address of an
upcall procedure to receive asynchronous error or event
notification; see below. The SESSION_object parameter is
included as an escape mechanism to support some more
general definition of the session ("generalized
destination port"), should that be necessary in the
future. Normally SESSION_object will be omitted.
o Define Sender
Call: SENDER( Session-id,
[ , Source_Address ] [ , Source_Port ]
[ , Sender_Template ]
[ , Sender_Tspec ] [ , Data_TTL ]
[ , Sender_Policy_Data ] )
Braden, Zhang, et al. Expiration: September 1996 [Page 58]
Internet Draft RSVP Specification February 1996
A sender uses this call to define, or to modify the
definition of, the attributes of the data stream. The
first SENDER call for the session registered as `Session-
id' will cause RSVP to begin sending Path messages for
this session; later calls will modify the path
information.
The SENDER parameters are interpreted as follows:
- Source_Address
This is the address of the interface from which the
data will be sent. If it is omitted, a default
interface will be used. This parameter is needed on
a multihomed sender host.
- Source_Port
This is the UDP/TCP port from which the data will be
sent. If it is omitted or zero, the port is "wild"
and can match any port in a FILTER_SPEC.
- Sender_Template
This parameter is included as an escape mechanism to
support a more general definition of the sender
("generalized source port"). Normally this parameter
may be omitted.
- Sender_Tspec
This optional parameter describes the traffic flow to
be sent. It may be included to prevent over-
reservation on the initial hops.
- Data_TTL
This is the (non-default) IP Time-To-Live parameter
that is being supplied on the data packets. It is
needed to ensure that Path messages do not have a
scope larger than multicast data packets.
- Sender_Policy_Data
This optional parameter passes policy data for the
sender. This data may be supplied by a system
service, with the application treating it as opaque.
Braden, Zhang, et al. Expiration: September 1996 [Page 59]
Internet Draft RSVP Specification February 1996
o Reserve
Call: RESERVE( session-id, [ receiver_address , ]
[ CONF_flag, ] style, style-dependent-parms )
A receiver uses this call to make or to modify a resource
reservation for the session registered as `session-id'.
The first RESERVE call will initiate the periodic
transmission of Resv messages. A later RESERVE call may
be given to modify the parameters of the earlier call (but
note that changing existing reservations may result in
admission control failures).
The optional `receiver_address' parameter may be used by a
receiver on a multihomed host (or router); it is the IP
address of one of the node's interfaces. The CONF_flag
should be set on if a reservation confirmation is desired,
off otherwise. The `style' parameter indicates the
reservation style. The rest of the parameters depend upon
the style; generally these will include appropriate
flowspecs, filter specs, and possibly receiver policy data
objects.
The RESERVE call returns immediately. Following a RESERVE
call, an asynchronous ERROR/EVENT upcall may occur at any
time.
o Release
Call: RELEASE( session-id )
This call removes RSVP state for the session specified by
session-id. The node then sends appropriate teardown
messages and ceases sending refreshes for this session-id.
o Error/Event Upcalls
The general form of a upcall is as follows:
Upcall: <Upcall_Proc>( ) -> session-id, Info_type,
information_parameters
Here "Upcall_Proc" represents the upcall procedure whose
address was supplied in the SESSION call. This upcall may
Braden, Zhang, et al. Expiration: September 1996 [Page 60]
Internet Draft RSVP Specification February 1996
occur asynchronously at any time after a SESSION call and
before a RELEASE call, to indicate an error or an event.
Currently there are five upcall types, distinguished by
the Info_type parameter. The selection of information
parameters depends upon the type.
1. Info_type = PATH_EVENT
A Path Event upcall results from receipt of the first
Path message for this session, indicating to a
receiver application that there is at least one
active sender.
Upcall: <Upcall_Proc>( ) -> session-id,
Info_type=PATH_EVENT,
flags,
Sender_Tspec, Sender_Template,
[ , Advert ] [ , Policy_data ]
This upcall presents the Sender_Tspec and the
Sender_Template from a Path message; it also passes
the advertisement and policy data if they are
present. The possible flags correspond to Non_RSVP
and Maybe_RSVP flags of the SESSION object.
2. Info_type = RESV_EVENT
A Resv Event upcall is triggered by the receipt of
the first RESV message, or by modification of a
previous reservation state, for this session.
Upcall: <Upcall_Proc>( ) -> session-id,
Info_type=RESV_EVENT,
Style, Flowspec, Filter_Spec_list,
[ , Policy_data ]
Here `Flowspec' will be the effective QoS that has
been received. Note that an FF-style Resv message
Braden, Zhang, et al. Expiration: September 1996 [Page 61]
Internet Draft RSVP Specification February 1996
may result in multiple RESV_EVENT upcalls, one for
each flow descriptor.
3. Info_type = PATH_ERROR
An Path Error event indicates an error in sender
information that was specified in a SENDER call.
Upcall: <Upcall_Proc>( ) -> session-id,
Info_type=PATH_ERROR,
Error_code , Error_value ,
Error_Node , Sender_Template,
[ Policy_data_list ]
The Error_code parameter will define the error, and
Error_value may supply some additional (perhaps
system-specific) data about the error. The
Error_Node parameter will specify the IP address of
the node that detected the error. The
Policy_data_list parameter, if present, will contain
any POLICY_DATA objects from the failed Path message.
4. Info_type = RESV_ERR
An Resv Error event indicates an error in a
reservation message to which this application
contributed.
Upcall: <Upcall_Proc>( ) -> session-id,
Info_type=RESV_ERROR,
Error_code , Error_value ,
Error_Node , Error_flags ,
Flowspec, Filter_spec_list,
[ Policy_data_list ]
The Error_code parameter will define the error and
Error_value may supply some additional (perhaps
Braden, Zhang, et al. Expiration: September 1996 [Page 62]
Internet Draft RSVP Specification February 1996
system-specific) data. The Error_Node parameter will
specify the IP address of the node that detected the
event being reported.
There are two Error_flags:
- InPlace
This flag may be on for an Admission Control
failure, to indicate that there was, and is, a
reservation in place at the failure node. This
flag is set at the failure point and forwarded
in ResvErr messages.
- NotGuilty
This flag may be on for an Admission Control
failure, to indicate that the flowspec requested
by this receiver was strictly less than the
flowspec that got the error. This flag is set
at the receiver API.
Filter_spec_list and Flowspec will contain the
corresponding objects from the error flow descriptor
(see Section 3.1.6). List_count will specify the
number of FILTER_SPECS in Filter_spec_list. The
Policy_data _list parameter will contain any
POLICY_DATA objects from the ResvErr message.
5. Info_type = RESV_CONFIRM
A Confirmation event indicates that a ResvConf
message was received.
Upcall: <Upcall_Proc>( ) -> session-id,
Info_type=RESV_CONFIRM,
Style, List_count,
Flowspec, Filter_spec_list,
[ Policy_data ]
The parameters are interpreted as in the Resv Error
upcall.
Braden, Zhang, et al. Expiration: September 1996 [Page 63]
Internet Draft RSVP Specification February 1996
Although RSVP messages indicating path or resv events may
be received periodically, the API should make the
corresponding asynchronous upcall to the application only
on the first occurrence or when the information to be
reported changes. All error and confirmation events
should be reported to the application.
3.10.2 RSVP/Traffic Control Interface
In an RSVP-capable node, enhanced QoS is achieved by a group of
inter-related traffic control functions: a packet classifier,
an admission control module, and a packet scheduler. This
section describes a generic RSVP interface to traffic control.
o Make a Reservation
Call: TC_AddFlowspec( Interface, TC_Flowspec,
TC_Tspec, Police_Flags )
-> RHandle [, Fwd_Flowspec]
The TC_Flowspec parameter defines the desired effective
QoS to admission control; its value is computed as the
maximum over the flowspecs of different next hops (see the
Compare_Flowspecs call below). The TC_Tspec parameter
defines the effective sender Tspec Path_Te (see Section
2.3). The Police_Flags parameter carries the three flags
E_Police_Flag, M_Police_Flag, and B_Police_Flag; see
Section 3.7.
The TC_AddFlowspec call returns an error code if Flowspec
is malformed or if the requested resources are
unavailable. Otherwise, it establishes a new reservation
channel corresponding to Rhandle. It returns the opaque
number Rhandle for subsequent references to this
reservation. If the service updates the flowspec, the
call will also return the updated object as Fwd_Flowspec.
o Modify Reservation
Call: TC_ModFlowspec( Interface, Rhandle, TC_Flowspec,
Sender_Tspec, Police_flags )
-> [ Fwd_Flowspec ]
Braden, Zhang, et al. Expiration: September 1996 [Page 64]
Internet Draft RSVP Specification February 1996
This call is used to modify an existing reservation.
TC_Flowspec is passed to Admission Control; if it is
rejected, the current flowspec is left in force. The
corresponding filter specs, if any, are not affected. The
other parameters are defined as in TC_AddFlowspec. If the
service updates the flowspec, the call will also return
the updated object as Fwd_Flowspec.
o Delete Flowspec
Call: TC_DelFlowspec( Interface, Rhandle )
This call will delete an existing reservation, including
the flowspec and all associated filter specs.
o Add Filter Spec
Call: TC_AddFilter( Interface, Rhandle,
Session , FilterSpec ) -> FHandle
This call is used to associate an additional filter spec
with the reservation specified by the given Rhandle,
following a successful TC_AddFlowspec call. This call
returns a filter handle FHandle.
o Delete Filter Spec
Call: TC_DelFilter( Interface, FHandle )
This call is used to remove a specific filter, specified
by FHandle.
o OPWA Update
Call: TC_Advertise( Interface, Adspec )
-> New_Adspec
This call is used for OPWA to compute the outgoing
advertisement New_Adspec for a specified interface.
o Preemption Upcall
Braden, Zhang, et al. Expiration: September 1996 [Page 65]
Internet Draft RSVP Specification February 1996
Upcall: TC_Preempt() -> RHandle, Reason_code
In order to grant a new reservation request, the admission
control and/or policy control modules may preempt one or
more existing reservations. This will trigger a
TC_Preempt() upcall to RSVP for each preempted
reservation, passing the RHandle of the reservation and a
sub-code indicating the reason.
3.10.3 RSVP/Routing Interface
An RSVP implementation needs the following support from the
packet forwarding and routing mechanisms of the node.
o Promiscuous Receive Mode for RSVP Messages
Packets received for IP protocol 46 but not addressed to
the node must be diverted to the RSVP program for
processing, without being forwarded. On a router, the
identity of the interface, real or virtual, on which it is
received as well as the IP source address and IP TTL with
which it arrived must also be available to the RSVP
daemon.
The RSVP messages to be diverted will carry the Router
Alert IP option, which can be used to pick them out of a
high-speed forwarding path. Alternatively, the node can
intercept all protocol 46 packets.
o Route Query
To forward Path and PathTear messages, an RSVP daemon must
be able to query the routing daemon(s) for routes.
Ucast_Route_Query( [ SrcAddress, ] DestAddress,
Notify_flag ) -> OutInterface
Mcast_Route_Query( [ SrcAddress, ] DestAddress,
Notify_flag )
-> [ IncInterface, ] OutInterface_list
Depending upon the routing protocol, the query may or may
not depend upon SrcAddress, i.e., upon the sender host IP
Braden, Zhang, et al. Expiration: September 1996 [Page 66]
Internet Draft RSVP Specification February 1996
address, which is also the IP source address of the
message. Here IncInterface is the interface through which
the packet is expected to arrive; some multicast routing
protocols may not provide it. If the Notify_flag is True,
routing will save state necessary to issue unsolicited
route change notification callbacks (see below) whenever
the specified route changes.
A multicast route query may return an empty
OutInterface_list if there are no receivers downstream of
a particular router. A route query may also return a `No
such route' error, probably as a result of a transient
inconsistency in the routing (since a Path or PathTear
message for the requested route did arrive at this node).
In either case, the local state should be updated as
requested by the message, which cannot be forwarded
further. Updating local state will make path state
available immediately for a new local receiver, or it will
tear down path state immediately.
o Route Change Notification
If requested by a route query with the Notify_flag True,
the routing daemon may provide an asynchronous callback to
the RSVP daemon that a specified route has changed.
Ucast_Route_Change( ) -> [ SrcAddress, ] DestAddress,
OutInterface
Mcast_Route_Change( ) -> [ SrcAddress, ] DestAddress,
[ IncInterface, ] OutInterface_list
o Outgoing Link Specification
RSVP must be able to force a (multicast) datagram to be
sent on a specific outgoing virtual link, bypassing the
normal routing mechanism. A virtual link may be a real
outgoing link or a multicast tunnel. Outgoing link
specification is necessary to send different versions of
an outgoing Path message on different interfaces. It is
also necessary in some cases to avoid routing loops.
o Source Address Specification
RSVP must be able to specify the IP source address to be
Braden, Zhang, et al. Expiration: September 1996 [Page 67]
Internet Draft RSVP Specification February 1996
used when sending Path messages.
o Interface List Discovery
RSVP must be able to learn what real and virtual
interfaces are active, with their IP addresses.
It should be possible to logically disable an interface
for RSVP. When an interface is disabled for RSVP, a Path
message should never be forwarded out that interface, and
if an RSVP message is received on that interface, the
message should be silently discarded (perhaps with local
logging).
3.10.4 Service-Dependent Manipulations
Flowspecs, Tspecs, and Adspecs are opaque objects to RSVP;
their contents are defined in service specification documents.
In order to manipulate these objects, RSVP daemon must have
available to it the following service-dependent routines.
o Compare Flowspecs
Compare_Flowspecs( Flowspec_1, Flowspec_2 ) ->
result_code
The possible result_codes indicate: flowspecs are equal,
Flowspec_1 is greater, Flowspec_2 is greater, flowspecs
are incomparable but LUB can be computed, or flowspecs are
incompatible.
Note that comparing two flowspecs implicitly compares the
Tspecs that are contained. Although the RSVP daemon
cannot itself parse a flowspec to extract the Tspec, it
can use the Compare_Flowspecs call to implicitly calculate
Resv_Te (see Section 2.3).
o Compute LUB of Flowspecs
LUB_of_Flowspecs( Flowspec_1, Flowspec_2 ) ->
Flowspec_LUB
Braden, Zhang, et al. Expiration: September 1996 [Page 68]
Internet Draft RSVP Specification February 1996
o Compute GLB of Flowspecs
GLB_of_Flowspecs( Flowspec_1, Flowspec_2 ) ->
Flowspec_GLB
o Compare Tspecs
Compare_Tspecs( Tspec_1, Tspec_2 ) -> result_code
The possible result_codes indicate: Tspecs are equal, or
Tspecs are unequal.
o Sum Tspecs
Sum_Tspecs( Tspec_1, Tspec_2 ) -> Tspec_sum
This call is used to compute Path_Te (see Section 2.3).
Braden, Zhang, et al. Expiration: September 1996 [Page 69]
Internet Draft RSVP Specification February 1996
4. Message Processing Rules
This section provides a generic description of the rules for RSVP
operation. It is intended to outline a set of algorithms that will
accomplish the needed function, omitting some details.
This section assumes the generic interface calls defined in Section
3.10 and the following data structures. An actual implementation may
use additional or different data structures and interfaces. The data
structure fields that a shown are required unless they are explicitly
labelled as optional.
o PSB -- Path State Block
Each PSB holds path state for a particular (session, sender)
pair, defined by SESSION and SENDER_TEMPLATE objects,
respectively, received in a Path message.
PSB contents include the following values from a Path message:
- Session
- Sender_Template
- Sender_Tspec
- The previous hop IP address and the Logical Interface
Handle (LIH) from a PHOP object
- The remaining IP TTL
- POLICY_DATA and/or ADSPEC objects (optional)
- Non_RSVP and Maybe_RSVP flags (Section 3.7).
- E_Police flag (Section 3.7)
- Local_Only flag (Section 3.8)
In addition, the PSB contains the following information provided
by routing: OutInterface_list, which is the list of outgoing
interfaces for this (sender, destination), and IncInterface,
which is the expected incoming interface. For a unicast
destination, OutInterface_list contains one entry and
IncInterface is undefined.
o RSB -- Reservation State Block
Braden, Zhang, et al. Expiration: September 1996 [Page 70]
Internet Draft RSVP Specification February 1996
Each RSB holds a reservation request that arrived in a
particular Resv message, corresponding to the triple: (session,
next hop, Filter_spec_list). Here "Filter_spec_list" may be a
list of FILTER_SPECs (for SE style), a single FILTER_SPEC (FF
style), or empty (WF style). We define the virtual object type
"FILTER_SPEC*" for such a data structure.
RSB contents include:
- Session specification
- Next hop IP address
- Filter_spec_list
- The outgoing (logical) interface OI on which the
reservation is to be made or has been made.
- Style
- Flowspec
- A SCOPE object (optional, depending upon style)
- RESV_CONFIRM object that was received (optional)
o TCSB -- Traffic Control State Block
Each TCSB holds the reservation specification that has been
handed to traffic control for a specific outgoing interface. In
general, TCSB information is derived from RSB's for the same
outgoing interface. Each TCSB defines a single reservation for
a particular triple: (session, OI, Filter_spec_list). TCSB
contents include:
- Session
- OI
- Filter_spec_list
- TC_Flowspec, the effective flowspec, i.e., the LUB over the
corresponding FLOWSPEC values from matching RSB's.
TC_Flowspec is passed to traffic control to make the actual
reservation.
- Fwd_Flowspec, the updated object to be forwarded after
merging.
Braden, Zhang, et al. Expiration: September 1996 [Page 71]
Internet Draft RSVP Specification February 1996
- TC_Tspec, equal to Path_Te, the effective sender Tspec.
- Police Flags
The flags E_Police_Flag, M_Police_Flag, and B_Police_Flag
are defined in Section 3.7.
- Rhandle, F_Handle_list
Handles returned by the traffic control interface,
corresponding to a flowspec and perhaps a list of filter
specs.
- A RESV_CONFIRM object to be forwarded.
o BSB -- Blockade State Block
Each BSB contains an element of blockade state. Depending upon
the reservation style in use, the BSB's may be per (session,
sender_template) pair or per (session, PHOP) pair. In practice,
an implementation might embed a BSB within a PSB; however, for
clarity we describe BSB's independently.
The contents of a BSB include:
- Session
- Sender_Template (which is also a filter spec)
- PHOP
- FLOWSPEC Qb
- Blockade timer Tb
The following Boolean Flag variables are used in this section:
Path_Refresh_Needed, Resv_Refresh_Needed, Tear_Needed, Need_Scope,
B_Merge, and NeworMod. Refresh_PHOP_list is a variable-length list
of PHOPs to be refreshed.
MESSAGE ARRIVES
Verify version number and RSVP checksum, and discard message if any
mismatch is found.
If the message type is ResvConf, forward the message to IP
destination address and return.
Braden, Zhang, et al. Expiration: September 1996 [Page 72]
Internet Draft RSVP Specification February 1996
If the message type is not Path or PathTear and if the IP destination
address does not match any of the addresses of the local interfaces,
then forward the message to IP destination address and return.
Parse the sequence of objects in the message. If any required
objects are missing or the length field of the common header does not
match, discard the message and return.
Verify the INTEGRITY object, if any. If the check fails, discard the
message and return.
Verify the consistent use of port fields. If the DstPort in the
SESSION object is zero but the SrcPort in a SENDER_TEMPLATE or
FILTER_SPEC object is non-zero, then the message has a "conflicting
source port" error; silently discard the message and return.
Processing of POLICY_DATA objects will be specified in the future.
Further processing depends upon message type.
Path MESSAGE ARRIVES
Process the sender descriptor object sequence in the message as
follows. The Path_Refresh_Needed and Resv_Refresh_Needed flags
are initially off.
o Search for a path state block (PSB) whose (session,
sender_template) pair matches the corresponding objects in
the message. During this search:
1. If a PSB is found whose session matches the
DestAddress and Protocol Id fields of the received
SESSION object, but the DstPorts differ and one is
zero, then build and send a "Conflicting Dst Port"
PathErr message, drop the Path message, and return.
2. If a PSB is found with a matching sender host but the
SrcPorts differ and one of the SrcPorts is zero, then
build and send an "Ambiguous Path" PathErr message,
drop the Path message, and return.
o If there was no matching PSB, then:
1. Create a new PSB.
2. Copy contents of the SESSION, SENDER_TEMPLATE,
SENDER_TSPEC, and PHOP (IP address and LIH) objects
into the PSB.
Braden, Zhang, et al. Expiration: September 1996 [Page 73]
Internet Draft RSVP Specification February 1996
3. Calculate initial routing information. If the sender
is from the local API, OutInterface_List is set to the
single interface whose address matches the sender
address, and IncInterface is undefined. Otherwise,
call the appropriate Route_Query routine, using
DestAddress from SESSION and (for multicast routing)
SrcAddress from SENDER_TEMPLATE. Store the values of
OutInterface_list and IncInterface from routing into
the PSB.
4. If IncInterface is defined and if a multicast message
arrived on an interface different from IncInterface,
turn on the Local_Only flag in the PSB and store the
actual incoming interface into IncInterface.
5. If this is the first PSB for the session, set a
refresh timer for the session.
6. Turn on the Path_Refresh_Needed flag.
o Otherwise (there is a matching PSB):
1. If there is no route change notification in place,
call the appropriate Route_Query routine using
DestAddress from SESSION and (for multicast routing)
SrcAddress from Sender_Template.
- If the OutInterface_list that is returned differs
from that in the PSB, then execute the Path LOCAL
REPAIR event sequence below.
- If a multicast message arrived on an interface
different from IncInterface, then execute the
Resv REFRESH event sequence below for the
previous hop.
2. If the PHOP IP address, the LIH, or Sender_Tspec
differs between the message and the PSB, copy the new
value into the PSB and turn on the Path_Refresh_Needed
flag. If the PHOP IP address or the LIH differ, also
turn on the Resv_Refresh_Needed flag.
o Update the PSB
1. If the message contains an ADSPEC object, copy it into
the PSB.
2. Start or Restart the cleanup timer for the PSB.
Braden, Zhang, et al. Expiration: September 1996 [Page 74]
Internet Draft RSVP Specification February 1996
3. Copy E_Police flag from SESSION object into PSB.
4. Store the received TTL into the PSB.
If the received TTL differs from Send_TTL in the RSVP
common header, set the Non_RSVP flag on in the PSB.
o If the Path_Refresh_Needed flag is now off, drop the Path
message and return.
Otherwise (the path state is new or modified) then do
refreshes, upcalls, and state updates.
1. If this Path message came from a network interface and
not from a local application, make a Path Event upcall
for each local application for this session:
Call: <Upcall_Proc>( session-id, PATH_EVENT,
flags, sender_tspec, sender_template,
[ADSPEC], [POLICY_DATA] )
2. Execute the Path REFRESH event sequence (below) for
the sender defined by the PSB.
3. Search for an RSB whose Filter_spec_list includes a
FILTER_SPEC matching the SENDER_TEMPLATE and whose OI
appears in the OutInterface_list. If none is found,
drop the Path message and return.
Otherwise, make this the `active RSB' and execute the
event sequence UPDATE TRAFFIC CONTROL to update the
local traffic control state if necessary. If this
modifies the traffic control state, it will make a
RESV_EVENT upcall to any matching local application
and turn on the Resv_Refresh_Needed flag.
4. If the Resv_Refresh_Needed flag is now on, execute the
Resv REFRESH sequence for the PHOP in the PSB.
o Drop the Path message and return.
PathTear MESSAGE ARRIVES
o Search for a PSB whose (Session, Sender_Template) pair
matches the corresponding objects in the message. If no
matching PSB is found, drop the PathTear message and
Braden, Zhang, et al. Expiration: September 1996 [Page 75]
Internet Draft RSVP Specification February 1996
return.
o Forward a copy of the PathTear message to each outgoing
interface listed in OutInterface_list of the PSB.
o Find each RSB that matches this PSB, i.e., that whose
Filter_spec_list matches Sender_Template in the PSB and
whose OI is included in OutInterface_list.
If this RSB matches no other PSB, then tear down the RSB,
as described below under ResvTear MESSAGE ARRIVES.
o Delete the PSB.
o Drop the PathTear message and return.
PathErr MESSAGE ARRIVES
o Search for a PSB whose (SESSION, SENDER_TEMPLATE) pair
matches the corresponding objects in the message. If no
matching PSB is found, drop the PathErr message and return.
o If the previous hop address in the PSB is the local API,
make an error upcall to the application:
Call: <Upcall_Proc>( session-id, PATH_ERROR,
Error_code, Error_value,
Node_Addr, Sender_Template,
[Policy_Data] )
Any SENDER_TSPEC or ADSPEC object in the message is
ignored.
Otherwise, send a copy of the PathErr message to the PHOP
IP address.
o Drop the PathErr message and return.
Resv MESSAGE ARRIVES
Initially, Refresh_PHOP_list is empty and the
Resv_Refresh_Needed and NeworMod flags are off. These variables
are used to control immediate reservation refreshes.
o Determine the Outgoing Interface OI
Braden, Zhang, et al. Expiration: September 1996 [Page 76]
Internet Draft RSVP Specification February 1996
The logical outgoing interface OI is taken from the LIH in
the NHOP object. (If the physical interface is not implied
by the LIH, it can be learned from the interface matching
the IP destination address).
o Check the path state
1. If there are no existing PSB's for SESSION then build
and send a ResvErr message (as described later)
specifying "No path information", drop the Resv
message, and return.
2. If a PSB is found with a matching sender host but the
SrcPorts differ and one of the SrcPorts is zero, then
build and send an "Ambiguous Path" PathErr message,
drop the Resv message, and return.
o Check for incompatible styles.
If any existing RSB for the session has a style that is
incompatible with the style of the message, build and send
a ResvErr message specifying "Conflicting Style", drop the
Resv message, and return.
Process the flow descriptor list to make reservations, as
follows, depending upon the style. The following uses a filter
spec list struct Filtss, of type FILTER_SPEC* (defined earlier).
For FF style: execute the following steps independently for each
flow descriptor in the message, i.e., for each (FLOWSPEC,
Filtss) pair. Here the structure Filtss consists of the
FILTER_SPEC from the flow descriptor.
For SE style, execute the following steps once for (FLOWSPEC,
Filtss), with Filtss consisting of the list of FILTER_SPEC
objects from the flow descriptor.
For WF style, execute the following steps once for (FLOWSPEC,
Filtss), with Filtss an empty list.
o Check the path state, as follows.
1. Locate the set of PSBs (senders) whose
SENDER_TEMPLATEs match Filtss and whose
OutInterface_list includes OI.
If this set is empty, build and send an error message
specifying "No sender information", and continue with
Braden, Zhang, et al. Expiration: September 1996 [Page 77]
Internet Draft RSVP Specification February 1996
the next flow descriptor in the Resv message.
2. If the style has explicit sender selection (e.g., FF
or SE) and if any FILTER_SPEC included in Filtss
matches more than one PSB, build and send a ResvErr
message specifying "Ambiguous filter spec" and
continue with the next flow descriptor in the Resv
message.
3. Add the PHOP from the PSB to Refresh_PHOP_list, if the
PHOP is not already on the list.
o Find or create a reservation state block (RSB) for the
triple: (session, NHOP, Filtss). Call this the "active
RSB".
o If the active RSB is new:
1. Set the session, NHOP, OI and style of the RSB from
the message.
2. Copy Filtss into the Filter_spec_list of the RSB.
3. Copy the FLOWSPEC and any SCOPE object from the
message into the RSB.
4. Set NeworMod flag on.
o Start or restart the cleanup timer on the active RSB.
o If the message contained a RESV_CONFIRM object, copy it
into the RSB and turn on Resv_Refresh_Needed flag.
o If the active RSB is not new, check whether STYLE, FLOWSPEC
or SCOPE objects have changed; if so, copy changed object
into RSB and turn on the NeworMod flag.
o If NeworMod flag is off, continue with the next flow
descriptor in the Resv message, if any.
o Otherwise (the NeworMod flag is on, i.e., the active RSB is
new or modified), execute the UPDATE TRAFFIC CONTROL event
sequence (below). If the result is to modify the traffic
control state, the Resv_Refresh_Needed flag will be turned
on and a RESV_EVENT upcall will be made to the application.
o Continue with the next flow descriptor.
Braden, Zhang, et al. Expiration: September 1996 [Page 78]
Internet Draft RSVP Specification February 1996
o When all flow descriptors have been processed, check the
Resv_Refresh_Needed flag. If it is now on, execute the
Resv REFRESH sequence (below) for each PHOP in
Refresh_PHOP_list.
o Drop the Resv message and return.
If processing a Resv message finds an error, a ResvErr message
is created containing flow descriptor and an ERRORS object. The
Error Node field of the ERRORS object is set to the IP address
of OI, and the message is sent unicast to NHOP.
ResvTear MESSAGE ARRIVES
A ResvTear message arrives with an IP destination address
matching outgoing interface OI. Flags Tear_Needed and
Resv_Refresh_Needed are initially off and Refresh_PHOP_list is
empty.
o Process the STYLE object and the flow descriptor list in
the ResvTear message to tear down local reservation state,
as follows. We assume a filter spec list struct Filtss, of
type FILTER_SPEC* (defined earlier).
For FF style: execute the following steps independently for
each flow descriptor in the message, i.e., for each
(FLOWSPEC, Filtss) pair. Here the structure Filtss
consists of the FILTER_SPEC from the flow descriptor.
For SE style, execute the following steps once for
(FLOWSPEC, Filtss), with Filtss consisting of the list of
FILTER_SPEC objects from the flow descriptor.
For WF style, execute the following steps once for
(FLOWSPEC, Filtss), with Filtss an empty list.
1. Find matching RSB for the triple: (SESSION, NHOP,
Filtss); call this the active RSB. If no active RSB
is found, continue with next flow descriptor.
2. Delete the active RSB.
3. Execute the event sequence UPDATE TRAFFIC CONTROL
(below) to update the traffic control state to be
consistent with the reservation state.
4. Search for a TCSB remaining for the (session, OI,
Filtss) triple; if not, set the Tear_Needed flag on.
Braden, Zhang, et al. Expiration: September 1996 [Page 79]
Internet Draft RSVP Specification February 1996
5. Continue with the next flow descriptor.
o If Tear_Needed and Resv_Refresh_Needed flags are both off,
then drop the ResvTear message and return.
o If Tear_Needed is off but Resv_Refresh_Needed is on, then
execute the Resv REFRESH sequence for each PHOP in
Refresh_PHOP_list, drop the ResvTear message, and return.
o Otherwise (Tear_Needed is on), need to forward ResvTear
and/or Resv refresh messages.
Do the following for each PSB whose OutInterface_list
includes the outgoing interface OI:
1. Pick each flow descriptor Fj in the ResvTear message
whose FILTER_SPEC matches the PSB, and do the
following.
- If there is no RSB whose FILTER_SPEC matches the
PSB, then add Fj to the new ResvTear message
being built.
- Otherwise (there is a matching RSB), note the PSB
as needing a Resv refresh message and set the
Resv_Refresh_Needed flag True.
2. If the new ResvTear message contains any flow
descriptors, send it to PHOP in the PSB.
o If the Resv_Refresh_Needed flag is now on, execute the RESV
REFRESH sequence (below) for each PHOP in
Refresh_PHOP_list.
o Drop the ResvTear message and return.
ResvErr MESSAGE ARRIVES
A ResvErr message arrives through the (real) incoming interface
In_If.
o If there is no path state for SESSION, drop the ResvErr
message and return.
o If the Error Code = 01 (Admission Control failure), do
special processing as follows:
Braden, Zhang, et al. Expiration: September 1996 [Page 80]
Internet Draft RSVP Specification February 1996
1. Find or create a Blockade State Block (BSB), in the
following style-dependent manner.
For WF (wildcard) style, there will be one BSB per
(session, PHOP) pair.
For FF style, there will be one BSB per (session,
filter_spec) pair. Note that an FF style ResvErr
message carries only one flow descriptor.
For SE style, there will be one BSB per (session,
filter_spec), for each filter_spec contained in the
filter spec list of the flow descriptor.
2. For each BSB in the preceding step, set (or replace)
its FLOWSPEC Qb with FLOWSPEC from the message, and
set (or reset) its timer Tb to Kb*R seconds [Section
3.4]. If the BSB is new, set its PHOP value, and set
its Sender_Template equal to the appropriate
filter_spec from the message.
3. Partially execute the Resv REFRESH event sequence
shown below, for the previous hop PHOP.
In particular, execute the refresh sequence with the
B_Merge flag off. If this results in no refresh
messages being generated, because all matching
reservations are blockaded, do not turn B_Merge on but
instead exit the refresh sequence and return here.
o For all ResvErr messages, execute the following for each
RSB for this session whose OI differs from In_If and whose
Filter_spec_list has at least one filter spec in common
with the FILTER_SPEC* in the ResvErr message. For WF
style, empty FILTER_SPEC* structures are assumed to match.
1. If Error_Code = 01 and the InPlace flag is 1 and one
or more of the BSB's found/created above has a Qb that
is strictly greater than Flowspec in the RSB, then
continue with the next matching RSB, if any.
2. If NHOP in the RSB is the local API, then:
- If the FLOWSPEC in the ResvErr message is
strictly greater than the RSB Flowspec, then turn
on the NotGuilty flag in the ERROR_SPEC.
- Deliver an error upcall to application:
Braden, Zhang, et al. Expiration: September 1996 [Page 81]
Internet Draft RSVP Specification February 1996
Call: <Upcall_Proc>( session-id, RESV_ERROR,
Error_code, Error_value,
Node_Addr, Error_flags,
Flowspec, Filter_Spec_List,
[Policy_data] )
and continue with the next RSB.
3. If the style has wildcard sender selection, use the
SCOPE object SC.In from the ResvErr message to
construct a SCOPE object SC.Out to be forwarded.
SC.Out should contain those sender addresses that
appeared in SC.In and that route to OI [LIH?], as
determined by scanning the PSB's. If SC.Out is empty,
continue with the next RSB.
4. Create a new ResvErr message containing the error flow
descriptor and send to the NHOP address specified by
the RSB. Include SC.Out if the style has wildcard
sender selection.
5. Continue with the next RSB.
o Drop the ResvErr message and return.
Resv CONFIRM ARRIVES
o If the (unicast) IP address found in the RESV_CONFIRM
object in the ResvConf message matches an interface of the
node, a confirmation upcall is made to the matching
application:
Call: <Upcall_Proc>( session-id, RESV_CONFIRM,
Error_code, Error_value, Node_Addr,
LUB-Used, nlist, Flowspec,
Filter_Spec_List, NULL, NULL )
o Otherwise, the ResvConf message is forwarded immediately to
the address in the IP address in its RESV_CONFIRM object.
o Drop the ResvConf message and return.
UPDATE TRAFFIC CONTROL
Braden, Zhang, et al. Expiration: September 1996 [Page 82]
Internet Draft RSVP Specification February 1996
The sequence is invoked by the Path MESSAGE ARRIVES or the Resv
MESSAGE ARRIVES sequence, to (re-)calculate and adjust the local
traffic control state in accordance with the current reservation
and path state. An implicit parameter of this sequence is the
`active' RSB.
If the result is to modify the traffic control state, this
sequence turns on the Resv_Refresh_Needed flag and notifies any
matching local applications with a RESV_EVENT upcall.
o Compute the traffic control parameters using the following
steps.
1. Consider the set of RSB's matching SESSION,
Filter_spec_list, and OI from the active RSB.
Initially the local flag Is_Biggest is off.
- Compute the effective kernel flowspec,
TC_Flowspec, as the LUB of the FLOWSPEC values in
these RSB's.
- Compute the effective traffic control filter spec
(list) TC_Filter_Spec* as the union of the
Filter_spec_lists from these RSB's.
- If the active RSB has a FLOWSPEC larger than all
the others, turn on the Is_Biggest flag.
2. Scan all RSB's matching session and Filtss, for all
OI. Set TC_B_Police_flag on if TC_Flowspec is smaller
than, or incomparable to, any FLOWSPEC in those RSB's.
3. Locate the set of PSBs (senders) whose
SENDER_TEMPLATEs match Filter_spec_list in the active
RSB and whose OutInterface_list includes OI.
4. Set TC_E_Police_flag on if any of these PSBs have
their E_Police flag on. Set TC_M_Police_flag on if it
is a shared style and there is more than one PSB in
the set.
5. Compute Path_Te as the sum of the SENDER_TSPEC objects
in this set of PSBs.
o Search for a TCSB matching SESSION and OI; for distinct
style (FF), it must also match Filter_spec_list.
If none is found, create a new TCSB.
Braden, Zhang, et al. Expiration: September 1996 [Page 83]
Internet Draft RSVP Specification February 1996
o If TCSB is new:
1. Store TC_Flowspec, TC_Filter_Spec*, Path_Te, and the
police flags into TCSB.
2. Turn the Resv_Refresh_Needed flag on and make the
traffic control call:
TC_AddFlowspec( OI, TC_Flowspec,
Path_Te, police_flags)
-> Rhandle, Fwd_Flowspec
3. If this call fails, build and send a ResvErr message
specifying "Admission control failed" and with the
InPlace flag off. Delete any RESV_CONFIRM object from
the active RSB and return.
4. Otherwise (call succeeds), record Rhandle and
Fwd_Flowspec in the TCSB. For each filter_spec F in
TC_Filter_Spec*, call:
TC_AddFilter( OI, Rhandle, Session, F)
-> Fhandle
and record the returned Fhandle in the TCSB.
o Otherwise, if TCSB is not new but the TC_Flowspec, Path_Te,
and/or police flags just computed differ from corresponding
values in the TCSB, then:
1. Turn the Resv_Refresh_Needed flag on and make the
traffic control call:
TC_ModFlowspec( OI, Rhandle, TC_Flowspec,
Path_Te, police_flags )
-> Fwd_Flowspec
2. If this call fails, build and send a ResvErr message
specifying "Admission control failed" and with the
InPlace bit on. Delete any RESV_CONFIRM object from
the active RSB and return.
3. Otherwise (the call succeeds), update the TCSB with
Braden, Zhang, et al. Expiration: September 1996 [Page 84]
Internet Draft RSVP Specification February 1996
the new values and save Fwd_Flowspec in the TCSB.
o Otherwise, if the TCSB is not new but the TC_Filter_Spec*
just computed differs from the FILTER_SPEC* in the TCSB,
then:
1. Turn on the Resv_Refresh_Needed flag.
2. Make an appropriate set of TC_DelFilter and
TC_AddFilter calls to transform the Filter_spec_list
in the TCSB into the new TC_Filter_Spec*.
o If the active RSB contains a RESV_CONFIRM object, then:
1. If the Is_Biggest flag is on, move the RESV_CONFIRM
object into the TCSB and turn on the
Resv_Refresh_Needed flag. (This will invoke the Resv
REFRESH sequence, which will either forward or return
the RESV_CONFIRM object, deleting it from the TCSB
again).
2. Otherwise, create and send a ResvConf message to the
address in the RESV_CONFIRM object. Include the
RESV_CONFIRM object in the ResvConf message. The RACK
message should also include an ERROR_SPEC object whose
Error_Node parameter is IP address of OI from the TCSB
and that specifies "No Error".
o If the Resv_Refresh_Needed flag is on, make a RESV_EVENT
upcall to the application:
Call: <Upcall_Proc>( session-id, RESV_EVENT,
style, Flowspec, Filter_spec_list,
[POLICY_DATA] )
where Flowspec and Filter_spec_list come from the TCSB and
the style comes from the active RSB.
o Return to the event sequence that invoked this one.
Path REFRESH
This sequence sends a path refresh for a particular sender,
i.e., a PSB. This sequence may be entered by either the
expiration of the path refresh timer or directly as the result
of the Path_Refresh_Needed flag being turned on during the
Braden, Zhang, et al. Expiration: September 1996 [Page 85]
Internet Draft RSVP Specification February 1996
processing of a received Path message.
o Insert TIME_VALUES object into the Path message being
built. Compute the IP TTL for the Path message as one less
than the TTL value received in the message. However, if
the result is zero, return without sending the Path
message.
o Create a sender descriptor containing the SENDER_TEMPLATE,
SENDER_TSPEC, and POLICY_DATA objects, if present in the
PSB, and pack it into the Path message being built.
o Send a copy of the Path message to each interface OI in
OutInterfact_list. Before sending each copy:
1. If the PSB has the E_Police flag on and if interface
OI is not capable of policing, turn the E_Police flag
on in the Path message being built.
2. Pass any ADSPEC and SENDER_TSPEC objects present in
the PSB to the traffic control call TC_Advertise.
Insert the modified ADSPEC object that is returned
into the Path message being built.
3. Insert into its PHOP object the interface address and
the LIH for the interface.
Resv REFRESH
This sequence sends a reservation refresh towards a particular
previous hop with IP address PH. This sequence may be entered
by the expiration of a reservation refresh timer, or invoked
from the Path MESSAGE ARRIVES, Resv MESSAGE ARRIVES, or ResvErr
MESSAGE ARRIVES sequence.
In general, this sequence considers each of the PSB's with PHOP
address PH. For a given PSB, it scans the TCSBs for matching
reservations and merges the styles, FLOWSPECs and
Filter_spec_list's appropriately. It then builds a Resv message
and sends it to PH. The details depend upon the attributes of
the style(s) included in the reservations.
Initially the Need_Scope flag is off and the new_SCOPE object is
empty.
o Create an output message containing INTEGRITY (if
configured), SESSION, RSVP_HOP, and TIME_VALUES objects.
Braden, Zhang, et al. Expiration: September 1996 [Page 86]
Internet Draft RSVP Specification February 1996
o Determine the style for these reservations from the first
RSB for the session, and move the STYLE object into the
proto-message. (Note that the present set of styles are
never themselves merged; if future styles can be merged,
these rules will become more complex).
o If style is wildcard and if there are PSB's from more than
one PHOP and if the multicast routing protocol does not use
shared trees, set the Need_Scope flag on.
o Select each sender PSB whose PHOP has address PH. Set the
local flag B_Merge off and execute the following steps.
1. Select all TCSB's whose Filter_spec_list's match the
SENDER_TEMPLATE object in the PSB and whose OI appears
in the OutInterface_list of the PSB.
2. If B_Merge flag is off then ignore a blockaded TCSB,
as follows.
- Select BSB's that match this TCSB. If any of
these BSB's has a Qb that is not strictly larger
than TC_Flowspec, then continue processing with
the next TCSB.
However, if steps 1 and 2 result in finding that all
TCSB's matching this PSB are blockaded, then:
- If this Resv REFRESH sequence was invoked from
RESV ERROR RECEIVED, then return to the latter.
- Otherwise, turn on the B_Merge flag and restart
at step 1, immediately above.
3. Merge the flowspecs from this set of TCSB's, as
follows:
- If B_Merge flag is off, compute the LUB over the
flowspec objects. From each TCSB, use the
Fwd_Flowspec object if present, else use the
normal Flowspec object.
While computing the LUB, check for a RESV_CONFIRM
object in each TCSB. If a RESV_CONFIRM object is
found:
- If the flowspec (Fwd_Flowspec or Flowspec)
in that TCSB is larger than all other (non-
Braden, Zhang, et al. Expiration: September 1996 [Page 87]
Internet Draft RSVP Specification February 1996
blockaded) flowspecs being compared, then
save this RESV_CONFIRM object for forwarding
and delete from the TCSB.
- Otherwise (the corresponding flowspec is not
the largest), create and send a ResvConf
message to the address in the RESV_CONFIRM
object. Include the RESV_CONFIRM object in
the ResvConf message. The ResvConf message
should also include an ERROR_SPEC object
whose Error_Node parameter is IP address of
OI from the TCSB and specifying "No Error".
- Delete the RESV_CONFIRM object from the
TCSB.
- Otherwise (B_Merge flag is on), compute the GLB
over the Flowspec objects of this set of TCSB's.
While computing the GLB, check for a RESV_CONFIRM
object in each TCSB. If one is found, delete it.
4. (All matching TCSB's have been processed). The next
step depends upon the style attributes.
Distinct reservation (FF) style
Use the Sender_Template as the merged
FILTER_SPEC. Pack the merged (FLOWSPEC,
FILTER_SPEC, F_POLICY_DATA) triplet into the
message as a flow descriptor.
Shared wildcard reservation (WF) style
There is no merged FILTER_SPEC. Merge (compute
the LUB of) the merged FLOWSPECS from the TCSB's,
across all PSB's for PH.
Shared distinct reservation (SE) style
Using the Sender_Template as the merged
FILTER_SPEC, form the union of the FILTER_SPECS
obtained from the TCSB's. Merge (compute the LUB
of) the merged FLOWSPECS from the TCSB's, across
all PSB's for PH.
Braden, Zhang, et al. Expiration: September 1996 [Page 88]
Internet Draft RSVP Specification February 1996
5. If the Need_Scope flag is on and the sender specified
by the PSB is not the local API:
- Find each RSB that matches this PSB, i.e., whose
Filter_spec_list matches Sender_Template in the
PSB and whose OI is included in
OutInterface_list.
- If the RSB either has no SCOPE list or its SCOPE
list includes the sender IP address from the PSB,
insert the sender IP address into new_SCOPE.
o (All PSB's for PH have been processed). Finish the Resv
message.
1. If Need_Scope flag is on but new_SCOPE is empty, no
RESV message should be sent; return. Otherwise, if
Need_Scope is on, move new_SCOPE into the message.
2. If a shared reservation style is being built, move the
final merged FLOWSPEC object and filter spec list into
the message.
3. If a RESV_CONFIRM object was saved earlier, copy it
into the new Resv message.
4. Set the RSVP_HOP object in the message to contain the
IncInterface address through which it will be sent and
the LIH from (one of) the PSB's.
o Send the message to the address PH.
ROUTE CHANGE NOTIFICATION
This sequence is triggered when routing sends a route change
notification to RSVP.
o Each PSB is located whose SESSION matches the destination
address and whose SENDER_TEMPLATE matches the source
address (for multicast).
1. If the OutInterface_list from the notification differs
from that in the PSB, execute the Path LOCAL REPAIR
sequence.
2. If the IncInterface from the notification differs from
that in the PSB, update the PSB.
Braden, Zhang, et al. Expiration: September 1996 [Page 89]
Internet Draft RSVP Specification February 1996
Path LOCAL REPAIR
The sequence is entered to effect local repair after a route
change for a given PSB.
o Wait for a delay time of W seconds [Section 3.5].
o Execute the Path REFRESH event sequence (above) for the
PSB.
5. Acknowledgments
The design of RSVP is based upon research performed in 1992-1993 by a
collaboration including Lixia Zhang (Xerox PARC), Deborah Estrin
(USC/ISI), Scott Shenker (Xerox PARC), Sugih Jamin (USC/Xerox PARC),
and Daniel Zappala (USC). Sugih Jamin developed the first prototype
implementation of RSVP and successfully demonstrated it in May 1993.
Shai Herzog, and later Steve Berson, continued development of RSVP
prototypes.
Since 1993, many members of the Internet research community have
contributed to the design and development of RSVP; these include (in
alphabetical order) Steve Berson, Bob Braden, Lee Breslau, Dave
Clark, Deborah Estrin, Shai Herzog, Craig Partridge, Scott Shenker,
John Wroclawski, and Daniel Zappala. In addition, a number of host
and router vendors have made valuable contributions, particularly
Fred Baker (Cisco), Mark Baugher (Intel), Don Hoffman (Sun), Steve
Jakowski (NetManage), John Krawczyk (Bay Networks), and Bill Nowicki
(SGI). Ron Frederick, Bobby Minnear, Eve Schooler, and Garrett
Wollman did early interfacing of multicast applications to RSVP.
Steve Deering, Bill Fenner, and Ajit Thyagarajan helped with the
interface between RSVP and multicast routing.
Braden, Zhang, et al. Expiration: September 1996 [Page 90]
Internet Draft RSVP Specification February 1996
APPENDIX A. Object Definitions
C-Types are defined for the two Internet address families IPv4 and
IPv6. To accommodate other address families, additional C-Types
could easily be defined. These definitions are contained as an
Appendix, to ease updating.
All unused fields should be sent as zero and ignored on receipt.
A.1 SESSION Class
SESSION Class = 1.
o IPv4/UDP SESSION object: Class = 1, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 DestAddress (4 bytes) |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | DstPort |
+-------------+-------------+-------------+-------------+
o IPv6/UDP SESSION object: Class = 1, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 DestAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | DstPort |
+-------------+-------------+-------------+-------------+
DestAddress
The IP unicast or multicast destination address of the
session. This field must be non-zero.
Protocol Id
The IP Protocol Identifier for the data flow. This field
must be non-zero.
Braden, Zhang, et al. Expiration: September 1996 [Page 91]
Internet Draft RSVP Specification February 1996
Flags
0x01 = E_Police flag
The E_Police flag is used in Path messages to determine
the effective "edge" of the network, to control traffic
policing. If the sender host is not itself capable of
traffic policing, it will set this bit on in Path
messages it sends. The first node whose RSVP is capable
of traffic policing will do so (if appropriate to the
service) and turn the flag off.
0x10 = Non_RSVP flag
The Non_RSVP flag is turned on in the SESSION object of
a Path message whenever the RSVP daemon detects that the
previous RSVP hop included one or more non-RSVP-capable
routers. This flag is forwarded hop-by-hop and passed
to a receiver application. If it is on, it indicates to
the application that even a successful reservation
request may not install the requested QoS at every node
along the path.
0x20 = Maybe_RSVP flag
The Maybe_RSVP flag is turned on in the SESSION object
of a Path message whenever the RSVP daemon is unable to
ascertain whether or not the previous hop included one
or more non-RSVP-capable routers. This flag is
forwarded hop-by-hop and passed to a receiver
application. If it is on and the Non_RSVP flag is off,
the application cannot tell whether or not a successful
reservation request may not install the requested QoS at
every node along the path.
DstPort
The UDP/TCP destination port for the session. Zero may be
used to indicate `none'.
Other SESSION C-Types could be defined in the future to
support other demultiplexing conventions in the transport-
layer or application layer.
Braden, Zhang, et al. Expiration: September 1996 [Page 92]
Internet Draft RSVP Specification February 1996
A.2 RSVP_HOP Class
RSVP_HOP class = 3.
o IPv4 RSVP_HOP object: Class = 3, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 Next/Previous Hop Address |
+-------------+-------------+-------------+-------------+
| Logical Interface Handle |
+-------------+-------------+-------------+-------------+
o IPv6 RSVP_HOP object: Class = 3, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 Next/Previous Hop Address +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Logical Interface Handle |
+-------------+-------------+-------------+-------------+
This object provides the IP address of the interface through which
the last RSVP-knowledgeable hop forwarded this message. The
Logical Interface Handle is a 32-bit number which may be used to
distinguish logical outgoing interfaces as described in Section
3.2; it should be identically zero if there is no logical
interface handle.
Braden, Zhang, et al. Expiration: September 1996 [Page 93]
Internet Draft RSVP Specification February 1996
A.3 INTEGRITY Class
INTEGRITY class = 4.
See [Baker96].
A.4 TIME_VALUES Class
TIME_VALUES class = 5.
o TIME_VALUES Object: Class = 5, C-Type = 1
+-------------+-------------+-------------+-------------+
| Refresh Period R |
+-------------+-------------+-------------+-------------+
Refresh Period
The refresh timeout period R used to generate this message;
in milliseconds.
Braden, Zhang, et al. Expiration: September 1996 [Page 94]
Internet Draft RSVP Specification February 1996
A.5 ERROR_SPEC Class
ERROR_SPEC class = 6.
o IPv4 ERROR_SPEC object: Class = 6, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 Error Node Address (4 bytes) |
+-------------+-------------+-------------+-------------+
| Flags | Error Code | Error Value |
+-------------+-------------+-------------+-------------+
o IPv6 ERROR_SPEC object: Class = 6, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 Error Node Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Flags | Error Code | Error Value |
+-------------+-------------+-------------+-------------+
Error Node Address
The IP address of the node in which the error was detected.
Flags
0x01 = InPlace
This flag is used only for an ERROR_SPEC object in a
ResvErr message. If it on, this flag indicates that
there was, and still is, a reservation in place at the
failure point.
0x02 = NotGuilty
This flag is used only for an ERROR_SPEC object in a
ResvErr message, and it is only set in the interface to
Braden, Zhang, et al. Expiration: September 1996 [Page 95]
Internet Draft RSVP Specification February 1996
the receiver application. If it on, this flag indicates
that the FLOWSPEC that failed was strictly greater than
the FLOWSPEC requested by this receiver.
Error Code
A one-octet error description.
Error Value
A two-octet field containing additional information about the
error. Its contents depend upon the Error Type.
The values for Error Code and Error Value are defined in Appendix
B.
Braden, Zhang, et al. Expiration: September 1996 [Page 96]
Internet Draft RSVP Specification February 1996
A.6 SCOPE Class
SCOPE class = 7.
This object contains a list of IP addresses, used for routing
messages with wildcard scope without loops. The addresses must be
listed in ascending numerical order.
o IPv4 SCOPE List object: Class = 7, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 Src Address (4 bytes) |
+-------------+-------------+-------------+-------------+
// //
+-------------+-------------+-------------+-------------+
| IPv4 Src Address (4 bytes) |
+-------------+-------------+-------------+-------------+
o IPv6 SCOPE list object: Class = 7, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 Src Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
// //
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 Src Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
Braden, Zhang, et al. Expiration: September 1996 [Page 97]
Internet Draft RSVP Specification February 1996
A.7 STYLE Class
STYLE class = 8.
o STYLE object: Class = 8, C-Type = 1
+-------------+-------------+-------------+-------------+
| Flags | Option Vector |
+-------------+-------------+-------------+-------------+
Flags: 8 bits
(None assigned yet)
Option Vector: 24 bits
A set of bit fields giving values for the reservation
options. If new options are added in the future,
corresponding fields in the option vector will be assigned
from the least-significant end. If a node does not recognize
a style ID, it may interpret as much of the option vector as
it can, ignoring new fields that may have been defined.
The option vector bits are assigned (from the left) as
follows:
19 bits: Reserved
2 bits: Sharing control
00b: Reserved
01b: Distinct reservations
10b: Shared reservations
11b: Reserved
3 bits: Sender selection control
000b: Reserved
001b: Wildcard
010b: Explicit
Braden, Zhang, et al. Expiration: September 1996 [Page 98]
Internet Draft RSVP Specification February 1996
011b - 111b: Reserved
The low order bits of the option vector are determined by the
style, as follows:
WF 10001b
FF 01010b
SE 10010b
Braden, Zhang, et al. Expiration: September 1996 [Page 99]
Internet Draft RSVP Specification February 1996
A.8 FLOWSPEC Class
FLOWSPEC class = 9.
o Class = 9, C-Type = 2: int-serv flowspec
The contents of this object will be specified in documents
prepared by the int-serv working group.
Braden, Zhang, et al. Expiration: September 1996 [Page 100]
Internet Draft RSVP Specification February 1996
A.9 FILTER_SPEC Class
FILTER_SPEC class = 10.
o IPv4 FILTER_SPEC object: Class = 10, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 SrcAddress (4 bytes) |
+-------------+-------------+-------------+-------------+
| ////// | ////// | SrcPort |
+-------------+-------------+-------------+-------------+
o IPv6 FILTER_SPEC object: Class = 10, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 SrcAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| ////// | ////// | SrcPort |
+-------------+-------------+-------------+-------------+
o IPv6 Flow-label FILTER_SPEC object: Class = 10, C-Type = 3
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 SrcAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| /////// | Flow Label (24 bits) |
+-------------+-------------+-------------+-------------+
SrcAddress
The IP source address for a sender host. Must be non-zero.
Braden, Zhang, et al. Expiration: September 1996 [Page 101]
Internet Draft RSVP Specification February 1996
SrcPort
The UDP/TCP source port for a sender, or zero to indicate
`none'.
Flow Label
A 24-bit Flow Label, defined in IPv6. This value may be used
by the packet classifier to efficiently identify the packets
belonging to a particular (sender->destination) data flow.
Braden, Zhang, et al. Expiration: September 1996 [Page 102]
Internet Draft RSVP Specification February 1996
A.10 SENDER_TEMPLATE Class
SENDER_TEMPLATE class = 11.
o IPv4 SENDER_TEMPLATE object: Class = 11, C-Type = 1
Definition same as IPv4/UDP FILTER_SPEC object.
o IPv6 SENDER_TEMPLATE object: Class = 11, C-Type = 2
Definition same as IPv6/UDP FILTER_SPEC object.
A.11 SENDER_TSPEC Class
SENDER_TSPEC class = 12.
o Intserv SENDER_TSPEC object: Class = 12, C-Type = 1
The contents of this object are specified in service
specification documents prepared by the int-serv working
group.
Braden, Zhang, et al. Expiration: September 1996 [Page 103]
Internet Draft RSVP Specification February 1996
A.12 ADSPEC Class
ADSPEC class = 13.
o Intserv ADSPEC object: Class = 13, C-Type = 2
The contents of this object are specified in service
specification documents prepared by the int-serv working
group.
Braden, Zhang, et al. Expiration: September 1996 [Page 104]
Internet Draft RSVP Specification February 1996
A.13 POLICY_DATA Class
POLICY_DATA class = 14.
o Type 1 POLICY_DATA object: Class = 14, C-Type = 1
The contents of this object are for further study.
Braden, Zhang, et al. Expiration: September 1996 [Page 105]
Internet Draft RSVP Specification February 1996
A.14 Resv_CONFIRM Class
RESV_CONFIRM class = 15.
o IPv4 RESV_CONFIRM object: Class = 15, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 Receiver Address (4 bytes) |
+-------------+-------------+-------------+-------------+
o IPv6 RESV_CONFIRM object: Class = 15, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 Receiver Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
Braden, Zhang, et al. Expiration: September 1996 [Page 106]
Internet Draft RSVP Specification February 1996
APPENDIX B. Error Codes and Values
The following Error Codes may appear in ERROR_SPEC objects and be
passed to end systems. Except where noted, these Error Codes may
appear only in ResvErr messages.
o Error Code = 00: Confirmation
This code is reserved for use in the ERROR_SPEC object of a
ResvConf message. The Error Value will also be zero.
o Error Code = 01: Admission Control failure
Reservation request was rejected by Admission Control due to
unavailable resources.
For this Error Code, the 16 bits of the Error Value field are:
ssur cccc cccc cccc
where the bits are:
ss = 00: Low order 12 bits contain a globally-defined sub-code
(values listed below).
ss = 10: Low order 12 bits contain a organization-specific sub-
code. RSVP is not expected to be able to interpret this
except as a numeric value.
ss = 11: Low order 12 bits contain a service-specific sub-code.
RSVP is not expected to be able to interpret this except as
a numeric value.
Since the traffic control mechanism might substitute a
different service, this encoding may include some
representation of the service in use.
u = 0: RSVP rejects the message without updating local
state.
u = 1: RSVP may use message to update local state and forward
the message. This means that the message is informational.
Braden, Zhang, et al. Expiration: September 1996 [Page 107]
Internet Draft RSVP Specification February 1996
r: Reserved bit, should be zero.
cccc cccc cccc: 12 bit code.
The following globally-defined sub-codes may appear in the low-
order 12 bits when ssur = 0000:
- Sub-code = 1: Delay bound cannot be met
- Sub-code = 2: Requested bandwidth unavailable
o Error Code = 02: Policy Control failure
Reservation has been rejected for administrative reasons, for
example, required credentials not submitted, insufficient quota
or balance, or administrative preemption. This Error Code may
appear in a PathErr or ResvErr message.
Contents of the Error Value field are to be determined in the
future.
o Error Code = 03: No path information for this Resv message.
No path state for this session. Resv message cannot be
forwarded.
o Error Code = 04: No sender information for this Resv message.
There is path state for this session, but it does not include
the sender matching some flow descriptor contained in the Resv
message. RESV message cannot be forwarded.
o Error Code = 05: Conflicting reservation style
Reservation style conflicts with style(s) of existing
reservation state. The Error Value field contains the low-order
16 bits of the Option Vector of the existing style with which
the conflict occurred. This Resv message cannot be forwarded.
o Error Code = 06: Unknown reservation style
Reservation style is unknown. This Resv message cannot be
forwarded.
o Error Code = 07: Conflicting dest port
Sessions for same destination address and protocol have appeared
Braden, Zhang, et al. Expiration: September 1996 [Page 108]
Internet Draft RSVP Specification February 1996
with both zero and non-zero dest port fields. This Error Code
may appear in a PathErr or ResvErr message.
o Error Code = 08: Ambiguous path
Sender port appears both zero and non-zero in same session in a
Path message. This Error Code may appear only in a PathErr
message.
o Error Code = 09: Ambiguous Filter Spec
Message contains a filter spec that matches more than one
sender, but an explicit style that requires an exact match.
o Error Code = 10, 11: (reserved)
o Error Code = 12: Service preempted
The service request defined by the STYLE object and the flow
descriptor has been administratively preempted.
For this Error Code, the 16 bits of the Error Value field are:
ssur cccc cccc cccc
Here the high-order bits ssur are as defined under Error Code
01. The following globally-defined sub-codes may appear in the
low-order 12 bits when ssur = 0000 are to be defined in the
future.
o Error Code = 13: Unknown object class
Error Value contains 16-bit value composed of (Class-Num, C-
Type) of unknown object. This error should be sent only if RSVP
is going to reject the message, as determined by the high-order
bits of the Class-Num. This Error Code may appear in a PathErr
or ResvErr message.
o Error Code = 14: Unknown object C-Type
Error Value contains 16-bit value composed of (Class-Num, C-
Type) of object.
o Error Code = 15-19: (reserved)
o Error Code = 20: Reserved for API
Braden, Zhang, et al. Expiration: September 1996 [Page 109]
Internet Draft RSVP Specification February 1996
Error Value field contains an API error code, for an API error
that was detected asynchronously and must be reported via an
upcall.
o Error Code = 21: Traffic Control Error
Reservation request was rejected by Traffic Control due to the
format or contents of the request. This Resv message cannot be
forwarded, and continued attempts would be futile.
For this Error Code, the 16 bits of the Error Value field are:
ss00 cccc cccc cccc
Here the high-order bits ss are as defined under Error Code 01.
The following globally-defined sub-codes may appear in the low
order 12 bits (cccc cccc cccc) when ssr = 000:
- Sub-code = 01: Service conflict
Trying to merge two incompatible service requests.
- Sub-code = 02: Service unsupported
Traffic control can provide neither the requested service
nor an acceptable replacement.
- Sub-code = 03: Bad Flowspec value
Mal-formed or unreasonable request.
- Sub-code = 04: Bad Tspec value
Mal-formed or unreasonable request.
o Error Code = 22: Traffic Control System error
A system error was detected and reported by the traffic control
modules. The Error Value will contain a system-specific value
giving more information about the error. RSVP is not expected
to be able to interpret this value.
o Error Code = 23: RSVP System error
The Error Value field will provide implementation-dependent
information on the error. RSVP is not expected to be able to
Braden, Zhang, et al. Expiration: September 1996 [Page 110]
Internet Draft RSVP Specification February 1996
interpret this value.
In general, every RSVP message is rebuilt at each hop, and the node
that creates an RSVP message is responsible for its correct
construction. Similarly, each node is required to verify the correct
construction of each RSVP message it receives. Should a programming
error allow an RSVP to create a malformed message, the error is not
generally reported to end systems in an ERROR_SPEC object; instead,
the error is simply logged locally, and perhaps reported through
network management mechanisms.
The only message formatting errors that are reported to end systems
are those that may reflect version mismatches, and which the end
system might be able to circumvent, e.g., by falling back to a
previous CType for an object; see code 12 and 13 above.
The choice of message formatting errors that an RSVP may detect and
log locally is implementation-specific, but it will typically include
the following:
o Wrong-length message: RSVP Length field does not match message
length.
o Unknown or unsupported RSVP version.
o Bad RSVP checksum
o Illegal RSVP message Type
o Illegal object length: not a multiple of 4, or less than 4.
o Next hop/Previous hop address in HOP object is illegal.
o Conflicting source port: Source port is non-zero in a filter
spec or sender template for a session with destination port
zero.
o Required object class (specify) missing
o Illegal object class (specify) in this message type.
o Violation of required object order
o Flow descriptor count wrong for style
o Logical Interface Handle invalid
o Unknown object Class-Num.
Braden, Zhang, et al. Expiration: September 1996 [Page 111]
Internet Draft RSVP Specification February 1996
APPENDIX C. UDP Encapsulation
An RSVP implementation will generally require the ability to perform
"raw" network I/O, i.e., to send and receive IP datagrams using
protocol 46. However, some important classes of host systems may not
support raw network I/O. To use RSVP, such hosts must encapsulate
RSVP messages in UDP.
The basic UDP encapsulation scheme makes two assumptions:
1. All hosts are capable of sending and receiving multicast packets
if multicast destinations are to be supported.
2. The first/last-hop routers are RSVP-capable.
A method of relaxing the second assumption is given later.
Let Hu be a "UDP-only" host that requires UDP encapsulation, and Hr a
host that can do raw network I/O. The UDP encapsulation scheme must
allow RSVP interoperation among an arbitrary topology of Hr hosts, Hu
hosts, and routers.
Resv, ResvErr, ResvTear, and PathErr messages are sent to unicast
addresses learned from the path or reservation state in the node. If
the node keeps track of which previous hops and which interfaces need
UDP encapsulation, these messages can be sent using UDP encapsulation
when necessary. On the other hand, Path and PathTear messages are
send to the destination address for the session, which may be unicast
or multicast.
The tables in Figures 13 and 14 show the basic rules for UDP
encapsulation of Path and PathTear messages, for unicast DestAddress
and multicast DestAddress, respectively. Under the `Send' column,
the notation is `mode(destaddr, destport)'; destport is omitted for
raw packets. The `Receive' column shows the group that is joined
and, where relevant, the UDP Listen port.
It is useful to define two flavors of UDP encapsulation, one to be
sent by Hu and the other to be sent by Hr and R, to avoid double
processing by the recipient. In practice, these two flavors are
distinguished by differing UDP port numbers Pu and Pu'.
The following symbols are used in the tables.
o D is the DestAddress for the particular session.
o G* is a well-known group address of the form 224.0.0.x, i.e., a
group that is limited to the local connected network. [TO BE
Braden, Zhang, et al. Expiration: September 1996 [Page 112]
Internet Draft RSVP Specification February 1996
DEFINED]
o Pu and Pu' are two well-known UDP ports for UDP encapsulation of
RSVP. [TO BE DEFINED]
o Ra is the IP address of the router interface `a'.
o Tr is the TTL value of the specific Path message.
o Router interface `a' is on the local network connected to Hu and
Hr.
o [RA] indicates that the Router Alert option is sent.
UNICAST DESTINATION D:
RSVP RSVP
Node Send Receive
___ _____________ _______________
Hu UDP(D/Ra,Pu) UDP(D,Pu)
[Note 1] and UDP(D,Pu')
[Note 2]
Hr Raw(D,Tr)[RA] Raw()
and if (UDP) and UDP(D, Pu)
then UDP(D,Pu') [Note 2]
(Ignore Pu')
R (Interface a):
Raw(D,Tr)[RA] Raw()
and if (UDP) and UDP(Ra, Pu)
then UDP(D,Pu') (Ignore Pu')
Figure 13: UDP Unicast Encapsulation Rules for Path Messages
Braden, Zhang, et al. Expiration: September 1996 [Page 113]
Internet Draft RSVP Specification February 1996
MULTICAST DESTINATION D:
RSVP RSVP
Node Send Receive
___ _____________ _________________
Hu UDP(G*,Pu) UDP(D,Pu')
[Note 3]
and UDP(G*,Pu)
Hr Raw(D,Tr)[RA] Raw()
and if (UDP) and UDP(G*,Pu)
then UDP(D,Pu') (Ignore Pu')
R (Interface a):
Raw(D,Tr)[RA] Raw()
and if (UDP) and UDP(G*,Pu)
then UDP(D,Pu') (Ignore Pu')
Figure 14: UDP Multicast Encapsulation Rules for Path Messages
[Note 1] Hu sends a unicast Path message either to the destination
address D, if D is local, or to the address Ra of the first-hop
router. Ra is presumably known to the host.
[Note 2] Here D is the address of the local interface through which
the message arrived.
[Note 3] This assumes that the application has joined the group D.
A router may determine if its interface X needs UDP encapsulation by
listening for UDP-encapsulated Path messages that were sent to either
G* (multicast D) or to the address of interface X (unicast D). There
is one failure mode for this scheme: if no host on the connected
network acts as an RSVP sender, there will be no Path messages to
trigger UDP encapsulation. In this (unlikely) case, it will be
necessary to explicitly configure UDP encapsulation on the local
network interface of the router.
When a UDP-encapsulated packet is received, the IP TTL is not
available to the application on most systems. The RSVP daemon that
receives a UDP-encapsulated Path or PathTear message should therefore
use the Send_TTL field of the RSVP common header as the effective
receive TTL. This may be overridden by manual configuration.
Braden, Zhang, et al. Expiration: September 1996 [Page 114]
Internet Draft RSVP Specification February 1996
We have assumed that the first-hop RSVP-capable router R is on the
directly-connected network. There are several possible approaches if
this is not the case.
1. Hu can send both unicast and multicast sessions to UDP(Ra,Pu)
with TTL=Ta
Here Ta must be the TTL to exactly reach R. If Ta is too small,
the Path message will not reach R. If Ta is too large,
multicast routing in R will forward the UDP packet into the
Internet until its hop count expires. This will turn on UDP
encapsulation between routers within the Internet, perhaps
causing bogus UDP traffic. The host Hu must be explicitly
configured with Ra and Ta.
2. A particular host on the LAN connected to Hu could be designated
as an "RSVP relay host". A relay host would listen on (G*,Pu)
and forward any Path messages directly to R, although it would
not be in the data path. The relay host would have to be
configured with Ra and Ta.
References
[Baker96] Baker, Fred, "RSVP Cryptographic Authentication", Work in
Progress, February 1996.
[ISInt93] Braden, R., Clark, D., and S. Shenker, "Integrated Services
in the Internet Architecture: an Overview", RFC 1633, ISI, MIT, and
PARC, June 1994.
[FJ94] Floyd, S. and V. Jacobson, "Synchronization of Periodic Routing
Messages", IEEE/ACM Transactions on Networking, Vol. 2, No. 2,
April, 1994.
[IPSEC96] Berger, L., O'Malley, T., and R. Atkinson, "RSVP Extensions
for IPSEC IPv4 Data Flows", Work in Progress, 1996.
[Katz95] Katz, D., "IP Router Alert Option", Work in Progress, November
1995.
[ISdata95] Wroclawski, J., "Standard Data Encoding for Integrated
Services Objects", Work in Progress, November 1995.
[RSVP93] Zhang, L., Deering, S., Estrin, D., Shenker, S., and D.
Zappala, "RSVP: A New Resource ReSerVation Protocol", IEEE Network,
September 1993.
Braden, Zhang, et al. Expiration: September 1996 [Page 115]
Internet Draft RSVP Specification February 1996
[ServTempl95] Shenker, S., "Network Element Service Specification
Template", Internet Draft draft-ietf-intserv-svc-template-00.txt,
Integrated Services Working Group, March 1995.
[OPWA95] Shenker, S. and L. Breslau, "Two Issues in Reservation
Establishment", Proc. ACM SIGCOMM '95, Cambridge, MA, August 1995.
Security Considerations
See Section 2.8.
Authors' Addresses
Lixia Zhang
Xerox Palo Alto Research Center
3333 Coyote Hill Road
Palo Alto, CA 94304
Phone: (415) 812-4415
EMail: Lixia@PARC.XEROX.COM
Bob Braden
USC Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
Phone: (310) 822-1511
EMail: Braden@ISI.EDU
Steve Berson
USC Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
Phone: (310) 822-1511
EMail: Berson@ISI.EDU
Braden, Zhang, et al. Expiration: September 1996 [Page 116]
Internet Draft RSVP Specification February 1996
Shai Herzog
USC Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
Palo Alto, CA 94304
Phone: (310) 822 1511
EMail: Herzog@ISI.EDU
Sugih Jamin
Computer Science Department
University of Southern California
Los Angeles, CA 90089-0871
Phone: (213) 740-6578
EMail: jamin@catarina.usc.edu
Braden, Zhang, et al. Expiration: September 1996 [Page 117]