Network Working Group Seisho Yasukawa (NTT)
Internet Draft Editor
Category: Informational
Expiration Date: December 2004 July 2004
Requirements for Point to Multipoint Traffic Engineered MPLS LSPs
<draft-ietf-mpls-p2mp-requirement-03.txt>
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Abstract
This document presents a set of requirements for
Point-to-Multipoint(P2MP) Traffic Engineered (TE) Multiprotocol
Label Switching (MPLS) Label Switched Paths (LSPs). It specifies
functional requirements for solutions in order to deliver P2MP
applications over a MPLS TE infrastructure. It is intended that
solutions that specify procedures for P2MP TE LSP setup satisfy
these requirements.
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There is no intent to either specify solution specific details in
this document or application specific requirements.
It is intended that the requirements presented in this document are
not limited to the requirements of packet switched networks, but
also encompass the requirements of L2SC, TDM, lambda and port
switching networks managed by Generalized MPLS (GMPLS) protocols.
Protocol solutions developed to meet the requirements set out in
this document must attempt to be equally applicable to MPLS and
GMPLS.
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Table of Contents
1. Introduction ................................................. 04
2. Definitions .................................................. 05
2.1 Acronyms ................................................. 05
2.2 Terminology .............................................. 06
2.3 Conventions .............................................. 07
3. Problem Statement ............................................ 07
3.1 Motivation ............................................... 07
3.2 Requirements Overview .................................... 08
4. Examples of candidate applications that may require
P2MP TE LSP ...................................................10
4.1 P2MP TE LSP for IP multicast data ....................... 10
4.2 P2MP TE backbone network for IP multicast network ....... 11
4.3 Layer 2 Multicast Over MPLS ............................. 13
4.4 VPN multicast network ................................... 13
4.5 GMPLS Networks .......................................... 14
5. Detailed requirements for P2MP TE extensions ................. 15
5.1 P2MP LSP tunnels ........................................ 15
5.2 P2MP explicit routing ................................... 15
5.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes.17
5.4 P2MP TE LSP establishment, teardown, and modification
mechanisms .............................................. 17
5.5 Fragmentation ........................................... 18
5.6 Failure Reporting and Error Recovery .................... 18
5.7 Record route of P2MP TE LSP tunnels ..................... 19
5.8 Call Admission Control (CAC) and QoS Control mechanism .. 19
5.9 Reoptimization of P2MP TE LSP ........................... 20
5.10 IPv4/IPv6 support ....................................... 20
5.11 P2MP MPLS Label ......................................... 21
5.12 Routing advertisement of P2MP capability ................ 21
5.13 Multi-Area/AS LSP ....................................... 21
5.14 P2MP MPLS OAM ........................................... 21
5.15 Scalability ............................................. 22
5.16 Backwards Compatibility ................................. 22
5.17 GMPLS ................................................... 23
5.18 Requirements for Hierarchical P2MP TE LSPs .............. 24
5.19 P2MP Crankback routing .................................. 24
6. Security Considerations ...................................... 24
7. Acknowledgements ............................................. 25
8. References ................................................... 25
8.1 Normative References ..................................... 25
8.2 Informational References ................................. 26
9. Editor's Address ............................................. 27
10. Authors' Addresses .......................................... 27
11. Intellectual Property Consideration ......................... 29
11.1 IPR Disclosure Acknowledgement .......................... 29
12. Full Copyright Statement .................................... 29
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1. Introduction
Existing MPLS Traffic Engineering (MPLS-TE) allows for strict QoS
guarantees, resources optimization, and fast failure recovery, but
is limited to P2P applications. There are P2MP applications like
Content Distribution, Interactive Multimedia and VPN multicast that
would also benefit from these TE capabilities. This clearly
motivates enhancements of the base MPLS-TE tool box in order to
support P2MP applications.
This document presents a set of requirements for
Point-to-Multipoint(P2MP) Traffic Engineering (TE) extensions to
Multiprotocol Label Switching (MPLS). It specifies functional
requirements for solutions to deliver P2MP TE LSPs. For the sake of
illustration, RSVP-TE [RFC3209] is one possible candidate to provide
such a solution so as to deliver P2MP TE LSPs.
It is intended that solutions that specify procedures for
P2MP TE LSP setup satisfy these requirements. There is no intent to
either specify solution specific details in this document or
application specific requirements.
It is intended that the requirements presented in this document are
not limited to the requirements of packet switched networks, but
also encompass the requirements of TDM, lambda and port switching
networks managed by Generalized MPLS (GMPLS) protocols. Protocol
solutions developed to meet the requirements set out in this
document must attempt to be equally applicable to MPLS and GMPLS.
Content Distribution (CD), Interactive multi-media (IMM), and VPN
multicast are applications that are best supported with multicast
capabilities. For some of them , there is a requirement to use P2MP
TE LSPs. One possible way to map P2MP flows onto LSPs in a MPLS
network is to setup multiple P2P TE LSPs, one to each of the
required egress LSRs. This requires replicating incoming packets to
all the P2P LSPs at the ingress LSR to accommodate multipoint
communication. This is sub-optimal as it places the replication
burden on the ingress LSR and hence has very poor scaling
characteristics. It also wastes bandwidth resources, memory and
MPLS (e.g. label) resources in the network.
Hence, to provide TE for a P2MP application in an efficient manner
(that is, with scalable impact on signaling and protocol state) in
a large-scale environment, P2MP TE mechanisms are required
specifically to support P2MP TE LSPs. As of now, existing MPLS TE
mechanisms such as [RFC3209] do not support P2MP TE LSPs so new
mechanisms must be developed.
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This should be achieved without requiring the use of a multicast
routing protocol in the network core, and with maximum re-use of the
existing MPLS protocols: in particular, MPLS Traffic
Engineering. That is, the separation between routing and signaling
that exists in the P2P TE network should be maintained within the
P2MP TE network, and the construction of the TEDB from which P2MP TE
LSP paths are computed should not be constrained to use a multicast
protocol.
A P2MP TE LSP will be set up with TE constraints and will allow
efficient packet or data replication at various branching points in
the network. Note that the notion of "efficient" packet replication
is relative and may have different meanings depending on the
objectives (see section 5.2).
For instance, RSVP-TE could be used for setting up a P2MP TE LSP
with enhancements to existing P2P TE LSP procedures.
P2MP TE LSP setup mechanisms MUST include the ability to add/remove
receivers to/from an existing P2MP TE LSP.
Note that with existing multicast routing mechanisms, multicast
traffic cannot currently benefit from P2P TE LSPs. Hence, Call
Admission Control for P2P TE LSP cannot take into account the
bandwidth used for multicast traffic. P2MP TE will allow the
bandwidth used by both the unicast and multicast traffics to be
counted by means of CAC.
This document is organized as follows: Section 2 provides a set of
definitions used throughout the document. The problem statement is
then discussed in Section 3. for the sake of illustration, this
document lists various applications that could make use P2MP TE
LSP. Detailed application-specific requirements as far as
P2MP TE LSP is concerned are out of the scope of this document.
Detailed requirements for the support of applications that require
P2MP MPLS TE LSPs are described in section 4.
The requirement for Multipoint-to-Point and Multipoint-to-Multipoint
TE LSPs are outside of the scope of this document.
2. Definitions
2.1 Acronyms
P2P:
Point-to-point
P2MP:
Point-to-multipoint
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2.2 Terminology
The reader is assumed to be familiar with the terminology in
[RFC3031] and [RFC3209].
P2MP TE LSP:
A traffic engineered label switched path that has one unique
ingress LSR (also referred to as the root) and one or more
egress LSRs (also referred to as the leaf).
P2MP tree:
The ordered set of LSRs and links that comprise the path of a
P2MP TE LSP from its ingress LSR to all of its egress LSRs.
sub-P2MP tree:
A sub-P2MP tree is a portion of a P2MP tree starting at
a particular LSR that is a member of the P2MP tree and includes
ALL downstream LSRs that are also members of the P2MP tree.
P2P sub-LSP:
The path from the ingress LSR to a particular egress LSR.
ingress LSR:
The LSR that is responsible for initiating the signaling
messages that set up the P2MP TE LSP.
egress LSR:
One of potentially many destinations of the P2MP TE LSP.
Egress LSRs may also be referred to as leaf nodes or leaves.
bud LSR:
An LSR that is an egress, but also has one or more directly
connected downstream LSRs.
branch LSR:
An LSR that has more than one directly connected downstream LSR.
graft LSR:
An LSR that is already a member of the P2MP tree and is in
process of signaling a new sub-P2MP tree.
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prune LSR:
An LSR that is a member of the P2MP tree and is in
process of tearing down an existing sub-P2MP tree.
P2MP-ID (Pid):
The ID that can be used to map a set of P2P sub-LSPs to a
particular P2MP LSP.
2.3 Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC2119].
3. Problem Statement
3.1 Motivation
Content Distribution (CD), Interactive multi-media (IMM), and VPN
multicast are applications that are best supported with multicast
capabilities.
IP Multicast provides P2MP communication. However, there are no
Traffic Engineering (TE) capabilities or QoS guarantees with
existing IP multicast protocols. Note that Diff-serv
(see [RFC2475],[RFC2597] and [RFC3246]) combined with IP multicast
routing may not be sufficient for P2MP applications for many of the
same reasons that it is not sufficient for unicast applications.
Note also that multicast trees provided by existing IP multicast
routing protocols are not optimal from a bandwidth usage
perspective, which may lead to significant bandwidth wasting.
TE and Constraint Based Routing, including Call Admission
Control(CAC), explicit source routing and bandwidth reservation, is
required to enable efficient resource usage and strict QoS
guarantees.
Furthermore there are no existing P2MP mechanisms for carrying layer
2 or SONET/SDH multicast traffic over MPLS. TE capabilities are
desirable for both these applications; the related set of application
requirements are outside of the scope of this document and might
require special pseudowire encapsulation.
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One possible solution would be to setup multiple P2P TE LSPs, one to
each of the required egress LSRs. This requires replicating incoming
traffic to all the P2P LSPs at the ingress LSR to accommodate
multipoint communication. This is clearly sub-optimal as it places
the replication burden on the ingress LSR and hence has very poor
scaling characteristics. It also wastes bandwidth resources, memory
and MPLS(e.g. label) resources in the network.
Hence, to provide MPLS TE [RFC2702] for a P2MP application in an
efficient manner (that is, with scalable impact on signaling and
protocol state) in a large scale environment, P2MP TE mechanisms
are required. Existing MPLS P2P TE mechanisms have to be enhanced
to support P2MP TE LSP.
3.2. Requirements Overview
This document states basic requirements for the setup of P2MP TE
LSPs and a solution SHOULD satisfy them without requiring that a
multicast routing protocol is used, although such a protocol
MUST NOT be prohibited. It is desirable to maximize the re-use of
existing MPLS TE techniques and protocols. Note that the use of
MPLS forwarding to carry the multicast traffic may also be useful
in the context of some network designs where it might be desired to
avoid running some multicast routing protocol like PIM [PIM-SM] or
BGP (which might be required for the use of PIM).
A P2MP TE LSP path will be computed taking into account various
constraints such as bandwidth, affinities, required level of
protection and so on. The solution MUST allow for the computation
of P2MP TE LSP paths satisfying constraints with the objective of
supporting various optimization criteria such as delays, bandwidth
consumption in the network, or any other combinations.
This document does not restrict the choice of signaling protocol
used to set up a P2MP TE LSP, but it should be noted that [RFC3468]
states
... the consensus reached by the Multiprotocol Label Switching
(MPLS) Working Group within the IETF to focus its
efforts on "Resource Reservation Protocol (RSVP)-TE: Extensions to
RSVP for Label-Switched Paths (LSP) Tunnels" (RFC 3209) as the MPLS
signaling protocol for traffic engineering applications...
The P2MP TE LSP setup mechanism MUST include the ability to
add/remove egress LSRs to/from an existing P2MP TE LSP and MUST allow
for the support of all the TE LSP management procedures already
defined for P2P TE LSP such as the non disruptive rerouting (the so
called "Make before break" procedure).
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The computation of P2MP TE trees is implementation dependent and is
beyond the scope of the solutions that are built with this document
as a guideline.
A separate document(s) will specify how to build P2MP TE LSPs.
The usage of those solutions will be application dependent and is
out of the scope of this document. However, it is a requirement that
those solutions attempt to be applicable to GMPLS as well as to MPLS
so that only a single set of solutions are developed.
Consider the following figure.
Source 1 (S1)
|
I-LSR1
| |
| |
R2----E-LSR3--LSR1 LSR2---E-LSR2--Receiver 1 (R1)
| :
R3----E-LSR4 E-LSR5
| :
| :
R4 R5
Figure 1
Figure 1 shows a single ingress (I-LSR1), and four egresses(E-LSR2,
E-LSR3, E-LSR4 and E-LSR5). I-LSR1 is attached to a traffic source
that is generating traffic for a P2MP application.
Receivers R1, R2, R3 and R4 are attached to E-LSR2, E-LSR3 and
E-LSR4.
The following are the objectives of P2MP LSP establishment and use.
a) A P2MP TE LSP tree which satisfies various constraints is
pre-determined and supplied to ingress I-LSR1.
Note that no assumption is made on whether the tree is provided
to I-LSR1 or computed by I-LSR1. Note that the solution SHOULD
also allow for the support of partial path by means of loose
routing.
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Typical constraints are bandwidth requirements, resource class
affinities, fast rerouting, preemption, to mention a few of
them. There should not be any restriction on the possibility
to support the set of constraints already defined for point to
point TE LSPs. A new constraint may specify which LSRs should
be used as branch points for the P2MP LSR in order to take
into account some LSR capabilities or network constraints.
b) A P2MP TE LSP is set up from I-LSR1 to E-LSR2, E-LSR3 and
E-LSR4 using the tree information.
c) In this case, the branch LSR1 should replicate incoming
packets or data and send them to E-LSR3 and E-LSR4.
d) If a new receiver (R5) expresses an interest in receiving
traffic, a new tree is determined and a sub-P2MP tree from
LSR2 to E-LSR5 is grafted onto the P2MP tree. LSR2 becomes a
branch LSR.
4. Examples of candidate applications that may require P2MP TE LSP
This section describes some of the candidate applications that P2MP
MPLS TE is applicable to.
The purpose of this section is not to mandate how P2MP TE LSPs must
be used in certain application scenarios. Rather it is to illustrate
some of the potential application scenarios so as to highlight the
features and functions that any P2MP solution must provide in order
to be of wide use and applicability. This section is not meant to be
exhaustive, and P2MP is not limited to the described applications.
4.1 P2MP TE LSP for IP multicast data
One typical scenario is to use P2MP TE LSPs as P2MP tunnels carrying
multicast data traffic (e.g. IP mcast). In this scenario, a P2MP TE
LSP is established between an ingress LSR which supports IP
multicast source and several egress LSRs which support several IP
multicast receivers. A P2MP TE LSP is established over the network
and IP multicast data are tunneled from an ingress LSR node to
multiple egress leaf LSRs with data replication at the branch LSRs
in the network core. Figure 2 shows an example.
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Note that a P2MP TE LSP can be established over multiple areas/ASs
and that the egress LSRs may deliver data into an IP multicast
network.
Mcast Source
|
+---------------I-LSR0----------------+
| | |
| LSR0 +----E-LSR2---R2
| / \ / |
R1---E-LSR1---LSR2-----LSR1 LSR3----LSR4----E-LSR3---R3
| / \ \ |
| / \ +----E-LSR4---R4
+-------B-LSR1---------B-LSR2---------+
+-------- / ------++------ \ ---------+
| | || |
R5---E-LSR5--------LSR5 || IPmcast Network |
| / \ || |
+-E-LSR6---E-LSR7-++----MR0--MR1------+
| | | |
R6 R7 R8 R9
Figure 2
4.2 P2MP TE backbone network for IP multicast network
P2MP TE LSPs are applicable in a backbone network to construct or
support a multicast network(e.g. IPmcast network).
The IP multicast access networks are interconnected by P2MP TE LSPs.
A P2MP TE LSP is established from an ingress LSR which accommodates
an IP multicast network that has a multicast source to multiple
egress LSRs which each accommodate an IP multicast network.
In this scenario, ingress/egress LSRs placed at the edge of
multicast network handle an IP multicast routing protocol.
This means that the ingress/egress LSRs exchange IP multicast
routing messages as neighbor routers. Figure 3 shows a network
example of this scenario.
A P2MP TE LSP is established from a I-LSR1 to E-LSR2, E-LSR3, E-LSR4
and the ingress/egress LSR exchanges the multicast routing messages
with each other.
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As specified in the section related to the problem statement it
should be possible for a solution to add/remove egress LSRs to/from
the P2MP MPLS TE LSP. IP multicast group membership distribution
between the egress LSRs may change frequently. This in turn may
require a potential P2MP MPLS TE solution, that is suitable for IP
multicast, to handle additions/deletions of egress LSRs with an
appropriate reactiveness.
It is recommended to support a message exchange mechanism on top of
P2MP LSP setup mechanism to support multicast (S, G) Join/Leave.
Though several schemes exist to handle this scenario, these are out
of scope of this document. This document only describes requirements
to setup a P2MP TE LSP.
Mcast Source
|
+-----MR-----+
| | |
| MR |
+------|-----+
+---------------I-LSR1----------------+
| // ||| \\ |
| // ||| \\ |
| // |LSR| \\ |
| ___//____/|_____\\____ |
| / // ||| \\ \ |
| | // ||| \\ | |
+-----E-LSR2----E-LSR3-----E-LSR4-----+
+---- / ---++------|------++--- \ ----+
| | || | || | |
R1---MR---MR || MR || MR__ |
| / \ || / \ || / \ \MR---R8
+--MR--MR--++----MR--MR---++--MR--MR--+
| | | | | |
R2 R3 R4 R5 R6 R7
Figure 3
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4.3 Layer 2 Multicast Over MPLS
Existing layer 2 networks offer multicast video services. These are
typically carried using layer 2 NBMA technology such as ATM or
layer 2 Broadcast Access technology such as Ethernet. It may be
desirable to deliver these layer 2 multicast services over
a converged MPLS infrastructure where P2MP TE LSPs are used instead.
For instance, several SPs provision P2MP ATM VCs for TV/ADSL
services. These P2MP VCs are setup between a video server and a set
of ATM DSLAMs. Each channel is carried in a distinct P2MP VC. These
VC maybe be routed independently, or may all be nested into a unique
PVC, connecting the video sever to all DSLAMs.
Such service could benefit from a P2MP MPLS-TE control plane. An
option is to setup a permanent P2MP TE LSP between the video server
and all DSLAMs, that would correspond to a PVC carrying all channel
VCs. In this case each DSLAM receives all channels, even if there
are no receivers that are registered for a given channel.
This ensure fast zapping, but lead to significant bandwidth wasting.
A second option is to setup a distinct P2MP TE LSP per channel. If a
client, behind a DSLAM, zaps to a new channel, then the DSLAM has
to be added to the P2MP TE LSP carrying this channel using a P2MP TE
grafting procedure, if it is not already egress LSR for that LSP.
Pruning procedure has to be used to remove a DSLAM from the P2MP TE
LSP when there is no longer any client behind the DSLAM, watching
the channel.
4.4 VPN multicast network
In this scenario, P2MP TE LSPs could be utilized to construct a
provider network which can deliver VPN multicast service(s) to its
customers.
A P2MP TE LSP is established between all the PE routers which
accommodate the customer private network(s) that handle the IP
multicast packets. Each PE router must handle a VPN instance.
For example, in Layer3 VPNs like BGP/MPLS based IP VPNs
[BGPMPLS-VPN], this means that each PE router must handle both
private multicast VRF tables and common multicast routing and
forwarding table. And each PE router exchanges private multicast
routing information between the corresponding PE routers. In case
of high rate source, the need for P2MP TE LSP can be envisaged for
Layer3 VPN data transmission.
Another example is a Layer2 VPN that supports multipoint LAN
connectivity service. In an Ethernet network environment, IP
multicast data is flooded to the appropriate Ethernet port(s).
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An Ethernet multipoint Layer2 VPN service provided by MPLS, this
function is achieved by switching MPLS encapsulated frames towards
the relevant PE nodes. But if existing P2P TE LSPs are used as
tunnels between PEs, any ingress PE must duplicate the frames and
send them to the corresponding PEs. This means the data stream is
flooded just from the ingress PE, which will waste the provider's
network resources.
So, for Layer 2 VPNs that are required to support multicast traffic,
it might be desirable that P2MP MPLS TE LSPs are used for data
transmission with an appropriate layer 2 encapsulation technique
(for example, pseudo wire) instead of P2P MPLS TE LSPs, contributing
in turn to savings of network resources.
This document does not set requirements for how multicast VPNs are
provided, but it does set requirements for the function that must be
available in P2MP MPLS solutions. Therefore, it is not a requirement
that multicast VPNs utilize P2MP TE LSPs, but it is a requirement
that P2MP MPLS solutions should be capable of supporting multicast
VPNs.
As already pointed out, application-specific requirements are out of
the scope of this document.
4.5 GMPLS Networks
GMPLS currently supports only P2P TE-LSPs just like MPLS. GMPLS
enhances MPLS to support four new classes of interfaces: Layer-2
Switch Capable (L2SC), Time-Division Multiplex (TDM), Lambda Switch
Capable (LSC) and Fiber-Switch Capable (FSC) in addition to Packet
Switch Capable (PSC) already supported by MPLS. All of these
interface classes have so far been limited to P2P TE LSPs
(see [RFC3473] and [RFC 3471]).
The requirement for P2MP services for non-packet switch interfaces
is similar to that for PSC interfaces. In particular, cable
distribution services such as video distribution are prime
candidates to use P2MP features. Therefore, it is a requirement that
reasonable attempts must be made to make all the features/mechanisms
(and protocol extensions) that will be defined to provide MPLS P2MP
TE LSPs equally applicable to P2MP PSC and non-PSC TE-LSPs. If the
requirements of non-PSC networks over-complicate the PSC solution a
decision may be taken to separate the solutions. This decision must
be taken in full consultation with the MPLS and CCAMP working
groups.
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5. Detailed requirements for P2MP TE extensions
5.1 P2MP LSP tunnels
The P2MP TE extensions MUST be applicable to the signaling of LSPs
of different traffic types. For example, it MUST be possible to
signal a P2MP TE LSP to carry any kind of payload being packet or
non-packet based (including frame, cell, TDM un/structured, etc.)
Carrying IP multicast or Ethernet traffic within a P2MP tunnel are
typical examples.
As with P2P MPLS technology [RFC3031], traffic is classified with a
FEC in this extension. All packets which belong to a particular FEC
and which travel from a particular node MUST follow the same P2MP
tree.
In order to scale to a large number of branches, P2MP TE LSPs SHOULD
be identified by a unique identifier (the P2MP ID or Pid) that is
constant for the whole LSP regardless of the number of branches
and/or leaves. Therefore, the identification of the P2MP session by
its destination addresses is not adequate.
5.2 P2MP explicit routing
Various optimizations in P2MP tree formation need to be applied to
meet various QoS requirements and operational constraints.
Some P2MP applications may request a bandwidth guaranteed P2MP tree
which satisfies end-to-end delay requirements. And some operators
may want to set up a cost minimum P2MP tree by specifying branch LSRs
explicitly.
The P2MP TE solution therefore MUST provide a means of establishing
arbitrary P2MP trees under the control of an external tree
computation process or path configuration process or dynamic tree
computation process located on the ingress LSR. Figure 4 shows two
typical examples.
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A A
| / \
B B C
| / \ / \
C D E F G
| / \ / \/ \ / \
D--E*-F*-G*-H*-I*-J*-K*--L H I J KL M N O
Steiner P2MP tree SPF P2MP tree
Figure 4 Examples of P2MP TE LSP topology
One example is the Steiner P2MP tree (Cost minimum P2MP tree)
[STEINER]. This P2MP tree is suitable for constructing a cost
minimum P2MP tree so as to minimize the bandwidth consumption in
the core. To realize this P2MP tree, several intermediate LSRs must
be both MPLS data terminating LSRs and transit LSRs (LSRs E, F, G,
H, I, J and K in the figure 4). This means that the LSRs must
perform both label swapping and popping at the same time. Therefore,
the P2MP TE solution MUST support a mechanism that can setup this
kind of bud LSR between an ingress LSR and egress LSRs. Note that
this includes constrained Steiner trees that allow for the
computation of a minimal cost trees with some other constraints such
as a bounded delay between the source and every receiver.
Another example is a CSPF (Constraint Shortest Path First) P2MP
tree. By some metric (which can be set upon any specific criteria
like the delay, bandwidth, a combination of those), one can
calculate a shortest path P2MP tree. This P2MP tree is suitable for
carrying real time traffic.
The solution MUST allow the operator to make use of any tree
computation technique. In the former case an efficient/optimal tree
is defined as a minimal cost tree (Steiner tree) whereas in the
later case it is defined as the tree that provides shortest path
between the source and any receiver.
To support explicit setup of any reasonable P2MP tree shape, a P2MP
TE solution MUST support some form of explicit source-based control
of the P2MP tree which can explicitly include particular LSRs as
branch nodes. This can be used by the ingress LSR to setup the P2MP
TE LSP. For instance, a P2MP TE LSP can be simply represented as a
whole tree or by its individual branches.
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5.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes
A P2MP tree is completely specified if all of the required branches
and hops between a sender and leaf LSR are indicated.
A P2MP tree is partially specified if only a subset of intermediate
branches and hops are indicated. This may be achieved using loose
hops in the explicit path, or using widely scoped abstract nodes
such as IPv4 prefixes shorter than 32 bits, or AS numbers.
A partially specified P2MP tree might be particularly useful in
inter-area and inter-AS situations although P2MP requirements for
inter-area and inter-AS are beyond the scope of this document.
Protocol solutions SHOULD include a way to specify loose hops and
widely scoped abstract nodes in the explicit source-based control
of the P2MP tree as defined in the previous section. Where this
support is provided, protocol solutions MUST allow downstream LSRs
to apply further explicit control to the P2MP tree to resolve a
partially specified tree into a (more) completely specified tree.
Protocol solutions MUST allow the P2MP tree to be completely
specified at the ingress where sufficient information exists to
allow the full tree to be computed.
In all cases, the egress nodes of the P2MP TE LSP must be fully
specified.
In case of a tree being computed by some downstream LSRs (e.g. the
case of hops specified as loose hops), the solution MUST provide
the ability for the ingress LSR of the P2MP TE LSP to learn the full
P2MP tree. Note that this requirement MAY be relaxed in some
environments (e.g. Inter-AS) where confidentiality must be preserved.
5.4 P2MP TE LSP establishment, teardown, and modification mechanisms
The P2MP TE solution MUST support establishment, maintenance and
teardown of P2MP TE LSPs in a scalable manner. This MUST include
both the existence of very many LSPs at once, and the existence of
very many destinations for a single P2MP LSP.
In addition to P2MP TE LSP establishment and teardown mechanism, it
SHOULD implement partial P2MP tree modification mechanism.
For the purpose of adding sub-P2MP TE LSPs to an existing P2MP TE
LSP, the extensions SHOULD support a grafting mechanism. For the
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purpose of deleting a sub-P2MP TE LSPs from an existing P2MP TE LSP,
the extensions SHOULD support a pruning mechanism.
It is RECOMMENDED that these grafting and pruning operations do not
cause any additional processing in nodes except along the path to
the grafting and pruning node and its downstream nodes. Moreover,
both grafting and pruning operations MUST not be traffic disruptive
for the traffic currently forwarded along the P2MP tree.
5.5 Fragmentation
The P2MP TE solution MUST handle the situation where a single
protocol message cannot contain all of the information necessary to
signal the establishment of the P2MP LSP. It MUST be possible to
establish the LSP in these circumstances.
This situation may arrise in either of the following circumstances.
a. The ingress LSR cannot signal the whole tree in a single
message.
b. The information in a message expands to be too large (or is
discovered to be too large) at some transit node. This may
occur because of some increase in the information that needs
to be signaled or because of a reduction in the size of
signaling message that is supported.
5.6 Failure Reporting and Error Recovery
Failure events may cause egress nodes or sub-P2MP LSPs to become
detached from the P2MP TE LSP. These events MUST be reported
upstream as for a P2P LSP.
The solution SHOULD provide recovery techniques such as protection
and restoration allowing recovery of any impacted sub-P2MP TE
LSPs. In particular, a solution MUST provide fast protection
mechanisms applicable to P2MP TE LSP similar to the solutions
specified in [FRR] for P2P TE LSPs. Note also that no assumption is
made on whether backup paths for P2MP TE LSPs should or should not
be shared with P2P TE LSPs backup paths.
Note that other application-specific requirement documents may
introduce even more stringent requirement such as non packet loss,
at the cost of some increased bandwidth consumption.
The solution SHOULD also support the ability to meet other network
recovery requirements such as bandwidth protection and bounded
propagation delay increase along the backup path during failure.
A P2MP TE solution MUST support P2MP fast protection mechanism to
handle P2MP applications sensitive to traffic disruption.
The report of the failure of delivery to fewer than all of the
egress nodes SHOULD NOT cause automatic teardown of the P2MP TE LSP.
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That is, while some egress nodes remain connected to the P2MP tree
it should be a matter of local policy at the ingress whether the
P2MP LSP is retained.
When all egress nodes downstream of a branch node have become
disconnected from the P2MP tree, and the some branch node is unable
to restore connectivity to any of them by means of some recovery or
protection mechanisms, the branch node MAY remove itself from the
P2MP tree provided that it is not also an egress LSR. Since the
faults that severed the various downstream egress nodes from the
P2MP tree may be disparate, the branch node MUST report all such
errors to its upstream neighbor. The ingress node can then decide
to re-compute the path to those particular egress nodes, around the
failure point.
Solutions MAY include the facility for transit LSRs and particularly
branch nodes to recompute sub-P2MP trees to restore them after
failures. In the event of successful repair, error notifications
SHOULD NOT be reported to upstream nodes, but the new paths are
reported if route recording is in use. Crankback requirements are
discussed in Section 5.18.
5.7 Record route of P2MP TE LSP tunnels
Being able to identify the established topology of P2MP TE LSP is
very important for various purposes such as management and operation
of some local recovery mechanisms like Fast Reroute [FRR]. A network
operator uses this information to manage P2MP TE LSPs. Therefore,
topology information MUST be collected and updated after P2MP TE LSP
establishment and modification process.
The P2MP TE solution MUST support a mechanism which can collect and
update P2MP tree topology information after P2MP LSP establishment
and modification process. For example, the P2P MPLS TE mechanism of
route recording could be extended and used if RSVP-TE was used as
the P2MP signaling protocol.
It is RECOMMENDED that the information is collected in a data format
by which the sender node can recognize the P2MP tree topology
without involving some complicated data calculation process.
The solution MUST support the recording of both outgoing interfaces
and node-id [NODE-ID].
5.8 Call Admission Control (CAC) and QoS Control mechanism
of P2MP TE LSPs
P2MP TE LSPs may share network resource with P2P TE LSPs. Therefore
it is important to use CAC and QoS in the same way as P2P TE LSPs
for easy and scalable operation.
In particular, it should be highlighted that because Multicast
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traffic cannot make use of P2P TE LSP, multicast traffic cannot be
easily taken into account by P2P TE LSPs when performing CAC.
The use of P2MP TE LSP will now allow for an accounting of the
unicast and multicast traffic for bandwidth reservation.
P2MP TE solutions MUST support both resource sharing and exclusive
resource utilization to facilitate co-existence with other LSPs to
the same destination(s).
P2MP TE solution MUST be applicable to DiffServ-enabled networks
that can provide consistent QoS control in P2MP LSP traffic.
Any solution SHOULD also satisfy the DS-TE requirements [RFC3564]
and interoperate smoothly with current P2P DS-TE protocol
specifications.
Note that this requirement document does not make any assumption on
the type of bandwidth pool used for P2MP TE LSPs which can either be
shared with P2P TE LSP or be dedicated for P2MP use.
5.9 Reoptimization of P2MP TE LSP
The detection of a more optimal path (for example, one with a lower
overall cost) is an example of a situation where P2MP TE LSP
re-routing may be required. While re-routing is in progress, an
important requirement is avoiding double bandwidth reservation
(over the common parts between the old and new LSP) thorough the use
of resource sharing.
Make-before-break MUST be supported for a P2MP TE LSP to ensure that
there is no traffic disruption when the P2MP TE LSP is re-routed.
For example, the P2P MPLS TE make-before-break mechanism could be
extended and used if RSVP-TE was used as the P2MP signaling protocol.
It is possible to achieve make-before-break that only applies to a
sub-P2MP tree without impacting the data on all of the other parts
of the P2MP tree.
The solution SHOULD allow for make-before-break reoptimization of a
sub-tree with no impact on the rest of the tree (no label
reallocation, no change in identifiers, etc.).
The solution SHOULD also provide the ability for the ingress LSR to
have a strict control on the reoptimization process.
Such reoptimization MAY be initiated by the sub-tree root branch
node (that is, the branch node MAY setup a new sub-tree, then splice
traffic on the new subtree and delete the former sub-tree).
5.10 IPv4/IPv6 support
Any P2MP TE solution MUST be equally applicable to IPv4 and IPv6.
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5.11 P2MP MPLS Label
A P2MP TE solution MUST support establishment of both P2P and P2MP
TE LSPs and MUST NOT impede the operation of P2P TE LSPs within the
same network. A P2MP TE solution MUST be specified in such a way
that it allows P2MP and P2P TE LSPs to be signaled on the same
interface. Labels for P2MP TE LSPs and P2P TE LSPs MAY be assigned
from shared or dedicated label space(s). Label space shareability is
implementation specific.
5.12 Routing advertisement of P2MP capability
Several high-level requirements have been identified to determine
the capabilities of LSRs within a P2MP network. The aim of such
information is to facilitate the computation of P2MP trees using TE
constraints within a network that contains LSRs that do not all have
the same capabilities levels with respect to P2MP signaling and data
forwarding.
These capabilities include, but are not limited to:
- the ability of an LSR to support branching.
- the ability of an LSR to act as an egress and a branch for the
same LSP.
- the ability of an LSR to support P2MP MPLS-TE signalling.
It is expected that it may be appropriate to gather this information
through extensions to TE IGPs (see [RFC3630] and [IS-IS-TE]), but
the precise requirements and mechanisms are out of the scope of this
document. It is expected that a separate document will cover this
requirement.
5.13 Multi-Area/AS LSP
P2MP TE solutions SHOULD support multi-area/AS P2MP TE LSPs.
The precise requirements in support of multi-area/AS P2MP TE LSPs is
out of the scope of this document. It is expected that a separate
document will cover this requirement.
5.14 P2MP MPLS OAM
Management of P2MP LSPs is as important as the management of P2P
LSPs.
The MPLS and GMPLS MIB modules MUST be enhanced to provide P2MP TE
LSP management.
In order to facilitate correct management, P2MP TE LSPs MUST have
unique identifiers.
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OAM facilities will have special demands in P2MP environments
especially within the context of tracing the paths and connectivity
of P2MP TE LSPs. The precise requirements and mechanisms for OAM are
out of the scope of this document. It is expected that a separate
document will cover these requirements.
5.15 Scalability
Scalability is a key requirement in P2MP MPLS systems. Solutions
MUST be designed to scale well with an increase in the number of any
of the following:
- the number of recipients
- the number of branch points
- the number of branches.
Both scalability of performance and operation MUST be considered.
Key considerations SHOULD include:
- the amount of refresh processing associated with maintaining
a P2MP TE LSP.
- the amount of protocol state that must be maintained by ingress
and transit LSRs along a P2MP tree.
- the number of protocol messages required to set up or tear down a
P2MP LSP as a function of the number of egress LSRs.
- the number of protocol messages required to repair a P2MP LSP
after failure or perform make-before-break.
- the amount of protocol information transmitted to manage
a P2MP TE LSP (i.e. the message size).
- the amount of potential routing extensions.
- the amount of control plane processing required by the ingress,
transit and egress LSRs to add/delete a branch LSP to/from an
existing P2MP LSP.
It is expected that the applicability of each solution will be
evaluated with regards to the aforementioned scalability criteria.
5.16 Backwards Compatibility
It SHOULD be an aim of any P2MP solution to offer as much backward
compatibility as possible. An ideal which is probably impossible to
achieve would be to offer P2MP services across legacy MPLS networks
without any change to any LSR in the network.
If this ideal cannot be achieved, the aim SHOULD be to use legacy
nodes as both transit non-branch LSRs and egress LSRs.
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It is a further requirement for the solution that any LSR that
implements the solution SHALL NOT be prohibited by that act from
supporting P2P TE LSPs using existing signaling mechanisms. That is,
unless administratively prohibited, P2P TE LSPs MUST be supported
through a P2MP network.
Also, it is a requirement that P2MP TE LSPs MUST be able to co-exist
with IP unicast and IP multicast networks.
5.17 GMPLS
Solutions for MPLS P2MP TE-LSPs when applied to GMPLS P2MP PSC or
non-PSC TE-LSPs MUST be backward and forward compatible with the
other features of GMPLS including:
- control and data plane separation (IF_ID RSVP_HOP and IF_ID
ERROR_SPEC),
- full support of numbered and unnumbered TE links (see [RFC 3477]
and [GMPLS-ROUTE]),
- use of the GENERALIZED_LABEL_REQUEST, the GENERALIZED_LABEL
(C-Type 2 and 3), the SUGGESTED_LABEL and the RECOVERY_LABEL,
in conjunction with the LABEL_SET and the ACCEPTABLE_LABEL_SET
object,
- processing of the ADMIN_STATUS object,
- processing of the PROTECTION object,
- support of Explicit Label Control,
- processing of the Path_State_Removed Flag,
- handling of Graceful Deletion procedures.
- E2E and Segment Recovery procedures.
In addition, since non-PSC TE-LSPs may have to be processed in
environments where the "P2MP capability" could be limited, specific
constraints may also apply during the P2MP TE Path computation.
Being technology specific, these constraints are outside the scope
of this document. However, technology independent constraints
(i.e. constraints that are applicable independently of the LSP
class) SHOULD be allowed during P2MP TE LSP message processing.
It has to be emphasized that path computation and management
techniques shall be as close as possible to those being used for
PSC P2P TE LSPs and P2MP TE LSPs.
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5.18 Requirements for Hierarchical P2MP TE LSPs
[LSP-HIER] defines concepts and procedures for P2P LSP hierarchy.
These procedures SHOULD be extended to support P2MP LSP hierarchy.
The P2MP MPLS-TE solution SHOULD support the concept of region and
region hierarchy (PSC1<PSC2<PSC3<PSC4<L2SC<TDM<LSC<FSC).
Particularly it SHOULD allow a Region i P2MP TE LSP to be nested
into a region j P2MP TE LSP or multiple region j P2P TE LSPs,
providing that i<j.
The precise requirements and mechanisms for this function are out of
the scope of this document. It is expected that a separate document
will cover these requirements.
5.19 P2MP Crankback routing
P2MP solutions SHOULD support crankback requirements as defined in
[CRANKBACK]. In particular, they SHOULD provide sufficient
information to a branch LSR from downstream LSRs to allow the branch
LSR to re-route a sub-tree around any failures or problems in the
network.
6. Security Considerations
This requirements document does not define any protocol extensions
and does not, therefore, make any changes to any security models.
It should be noted that P2MP signaling mechanisms built on P2P
RSVP-TE signaling are likely to inherit all of the security
techniques and problems associated with RSVP-TE. These problems may
be exacerbated in P2MP situations where security relationships may
need to maintained between an ingress and multiple egresses. Such
issues are similar to security issues for IP multicast.
It is a requirement that documents offering solutions for P2MP LSPs
MUST have detailed security sections.
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7. Acknowledgements
The authors would like to thank George Swallow, Ichiro Inoue, Dean
Cheng, and Eric Rosen for their review and suggestions.
8. References
8.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC2597] Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597, June 1999.
[RFC2702] D. Awduche, J. Malcolm, J. Agogbua, M. O'Dell, J.
McManus, "Requirements for Traffic Engineering Over
MPLS", RFC2702, September 1999.
[RFC3031] Rosen, E., Viswanathan, A. and R. Callon,
"Multiprotocol Label Switching Architecture", RFC 3031,
January 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3246] Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le
Boudec, J.Y., Davari, S., Courtney, W., Firioiu, V. and
D. Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, March 2002.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78,
RFC 3667, February 2004.
[RFC3668] Bradner, S., Ed., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004.
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8.2 Informational References
[RFC3471] Berger, L., Editor, "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description",
RFC 3471, January 2003.
[RFC3473] Berger, L., Editor, "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling - Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions",
RFC 3473, January 2003.
[RFC3477] K. Kompella, Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol -Traffic Engineering
(RSVP-TE)", RFC3477, January 2003.
[RFC3564] F. Le Faucheur, W. Lai, "Requirements for Support of
Differentiated Services-aware MPLS Traffic
Engineering", RFC 3564, July 2003.
[RFC3630] D. Katz, D. Yeung, K. Kompella, "Traffic Engineering
Extensions to OSPF Version 2", RFC 3630, September
2003.
[PIM-SM] B. Fenner, M. Hadley, H. Holbrook, I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", draft-ietf-pim-sm-
v2-new-08.txt, October 2003.
[BGPMPLS-VPN] E. Rosen, Y.Rekhter, Editor, "BGP/MPLS IP VPNs",
draft-ietf-l3vpn-rfc2547bis-01.txt, September 2003.
[GMPLS-ROUTE] K. Kompella, Y. Rekhter, Editor, "Routing Extensions
in Support of Generalized Multi-Protocol Label
Switching", draft-ietf-ccamp-gmpls-routing-08.txt,
October 2003.
[STEINER] H. Salama, et al., "Evaluation of Multicast Routing
Algorithm for Real-Time Communication on High-Speed
Networks," IEEE Journal on Selected Area in
Communications, pp.332-345, 1997.
[FRR] P. Pan, D. Gan, G. Swallow, J. P. Vasseur, D. Cooper,
A. Atlas, M. Jork,"Fast Reroute Extensions to RSVP-TE
for LSP Tunnels",
draft-ietf-mpls-rsvp-lsp-fastreroute-03.txt, July
2003.
[IS-IS-TE] Henk Smit, Tony Li, "IS-IS extensions for Traffic
Engineering", draft-ietf-isis-traffic-04.txt, December
2002.
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Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004
[CRANKBACK] A. Farrel, A. Satyanarayana, A. Iwata, N. Fujita, G.
Ash, S. Marshall, "Crankback Signaling Extensions for
MPLS Signaling", draft-ietf-ccamp-crankback-01.txt,
January 2004.
[LSP-HIER] K. Kompella, Y. Rekhter, "LSP Hierarchy with
Generalized MPLS TE", draft-ietf-mpls-lsp-hierarchy-
08.txt, September 2002.
[NODE-ID] Vasseur, Ali and Sivabalan, "Definition of an RRO node-
id subobject", draft-ietf-mpls-nodeid-subobject-01.txt,
June 2003.
9. Editor's Address
Seisho Yasukawa
NTT Corporation
9-11, Midori-Cho 3-Chome
Musashino-Shi, Tokyo 180-8585,
Japan
Phone: +81 422 59 4769
Email: yasukawa.seisho@lab.ntt.co.jp
10. Authors' Addresses
Dimitri Papadimitriou
Alcatel
Francis Wellensplein 1,
B-2018 Antwerpen,
Belgium
Phone : +32 3 240 8491
Email: dimitri.papadimitriou@alcatel.be
JP Vasseur
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough, MA 01719,
USA
Email: jpv@cisco.com
Yuji Kamite
NTT Communications Corporation
Tokyo Opera City Tower
3-20-2 Nishi Shinjuku, Shinjuku-ku,
Tokyo 163-1421,
Japan
Email: y.kamite@ntt.com
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Internet Draft draft-ietf-mpls-p2mp-requirement-03.txt July 2004
Rahul Aggarwal
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: rahul@juniper.net
Alan Kullberg
Motorola Computer Group
120 Turnpike Rd.
Southborough, MA 01772
Email: alan.kullberg@motorola.com
Adrian Farrel
Old Dog Consulting
Phone: +44 (0) 1978 860944
Email: adrian@olddog.co.uk
Markus Jork
Avici Systems
101 Billerica Avenue
N. Billerica, MA 01862
Phone: +1 978 964 2142
Email: mjork@avici.com
Andrew G. Malis
Tellabs
2730 Orchard Parkway
San Jose, CA 95134
Phone: +1 408 383 7223
Email: andy.malis@tellabs.com
Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
France
Email: jeanlouis.leroux@francetelecom.com
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11. Intellectual Property Consideration
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology
described in this document or the extent to which any license
under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any
such rights. Information on the procedures with respect to rights
in RFC documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use
of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be required
to implement this standard. Please address the information to the
IETF at ietf-ipr@ietf.org.
11.1 IPR Disclosure Acknowledgement
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance
with RFC 3668.
12. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is
subject to the rights, licenses and restrictions contained in BCP
78, and except as set forth therein, the authors retain all their
rights.
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This document and the information contained herein are provided
on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE.
Yasukawa,et. al. [Page 30]