HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 07:34:12 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Thu, 22 Feb 1996 23:00:00 GMT ETag: "305055-3af99-312cf570" Accept-Ranges: bytes Content-Length: 241561 Connection: close Content-Type: text/plain Internet Draft R. Braden, Ed. Expiration: August 1996 ISI File: draft-ietf-rsvp-spec-10.txt L. Zhang PARC S. Berson ISI S. Herzog ISI S. Jamin USC Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification February 21, 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: August 1996 [Page 1] Internet Draft RSVP Specification February 1996 Table of Contents 1. Introduction ........................................................5 1.1 Data Flows ......................................................8 1.2 Reservation Model ...............................................9 1.3 Reservation Styles ..............................................11 1.4 Examples of Styles ..............................................14 2. RSVP Protocol Mechanisms ............................................19 2.1 RSVP Messages ...................................................19 2.2 Port Usage ......................................................21 2.3 Merging Flowspecs ...............................................22 2.4 Soft State ......................................................23 2.5 Teardown ........................................................25 2.6 Errors ..........................................................26 2.7 Confirmation ....................................................28 2.8 Policy and Security .............................................28 2.9 Automatic RSVP Tunneling ........................................29 2.10 Host Model .....................................................30 3. RSVP Functional Specification .......................................32 3.1 RSVP Message Formats ............................................32 3.2 Sending RSVP Messages ...........................................45 3.3 Avoiding RSVP Message Loops .....................................47 3.4 Blockade State ..................................................50 3.5 Local Repair ....................................................52 3.6 Time Parameters .................................................53 3.7 Traffic Policing and Non-Integrated Service Hops ................54 3.8 Multihomed Hosts ................................................56 3.9 Future Compatibility ............................................57 3.10 RSVP Interfaces ................................................59 4. Message Processing Rules ............................................71 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: August 1996 [Page 2] Internet Draft RSVP Specification February 1996 What's Changed 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]. The most important changes in this document from the rsvp-spec-08 draft are: o The handling of reservation errors has been fundamentally changed, to prevent the "second killer reservation problem". A new kind of state has been introduced into a node, "blockade state", which is created by a ResvErr message with Error Code = 01, and which controls the merging process for generating reservation refresh messages [Sections 2.6 and 3.4]. o RSVP now carries two flag bits in the SESSION object to indicate to a receiver whether there are non-RSVP-capable nodes along the path to a given sender [Sections 2.9 and 3.7]. o The optional INTEGRITY object is now specified to immediately follow the common header and to appear in every fragment [Section 3.1]. o There are now two flag bits in an ERROR_SPEC object: InPlace and NotGuilty [Section 3.10]. o The text now states that implementations should be as permissive as possible in accepting objects in any order within a message (and required ordering is specified), but Braden, Zhang, et al. Expiration: August 1996 [Page 3] Internet Draft RSVP Specification February 1996 they should follow the BNF-implied order in creating a message. o The text now states that IP fragmentation of data packets is generally not possible when RSVP is in use, since the TCP/UDP port fields may be required for classification [Section 1.2]. o The rules for handling an unrecognized object class are changed to include a third possibility: ignore and do not forward the object [Section 3.9]. o All generic Traffic Control calls are modified to include an interface specification, allowing the Thandle to be interface-specific [Section 3.10.2]. o Disabling an interface for RSVP is allowed [Section 3.10.3]. Braden, Zhang, et al. Expiration: August 1996 [Page 4] 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 IP6), 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: August 1996 [Page 5] 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. For each outgoing interface, a " packet scheduler" then makes forwarding decisions for each 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 heterogeneous receivers and dynamic group membership, 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: August 1996 [Page 6] 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 succeeds, 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. RSVP transfers reservation parameters as opaque data (except for certain well-defined operations on the data), which it simply passes to traffic control for interpretation. Although the RSVP protocol mechanisms are largely independent of the encoding of these parameters, the encodings must be defined in the reservation model that is presented to an application; see Appendix A for more details. 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 changing routes. o RSVP is simplex, i.e., it reserves for a data flow in one direction only. 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. Braden, Zhang, et al. Expiration: August 1996 [Page 7] Internet Draft RSVP Specification February 1996 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. 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. Finally, some experimental RSVP features are documented in Appendix D for future reference. 1.1 Data Flows RSVP defines a "session" as a data flow with a particular destination and transport-layer protocol. The destination of a session is generally 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 assumes the 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 present version supports only UDP/TCP ports as generalized ports. Note that it is not strictly necessary to include ports in the session definition when DestAddress is multicast, since different sessions can always have different multicast addresses. However, destination ports are necessary to allow more than one unicast session to the same receiver host. Figure 2 illustrates the flow of data packets in a single RSVP session, assuming multicast data distribution. The arrows indicate data flowing from senders S1 and S2 to receivers R1, R2, and R3, and the cloud represents the distribution mesh created by Braden, Zhang, et al. Expiration: August 1996 [Page 8] Internet Draft RSVP Specification February 1996 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 to 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 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. The flowspec in a reservation request will generally include a Braden, Zhang, et al. Expiration: August 1996 [Page 9] Internet Draft RSVP Specification February 1996 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 [ServTempl95a], and are generally opaque to RSVP. 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. RSVP reservation request messages originate at receivers and are passed upstream towards the sender(s). At each intermediate node, two general actions are taken on the 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, it is possible in theory for the traffic control Braden, Zhang, et al. Expiration: August 1996 [Page 10] Internet Draft RSVP Specification February 1996 mechanism to modify the flowspec hop-by-hop, although none of the currently defined services does so. 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; 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, and 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) [Shenker94]. With OPWA, RSVP control packets are sent downstream, following the data paths, to 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, which 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: 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 Braden, Zhang, et al. Expiration: August 1996 [Page 11] Internet Draft RSVP Specification February 1996 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 styles currently defined are as follows (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 into which flows from all upstream senders are mixed. 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 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 Braden, Zhang, et al. Expiration: August 1996 [Page 12] Internet Draft RSVP Specification February 1996 reservation request creates a distinct reservation for data packets from a particular sender, not sharing them with other senders' packets for the same session. The total reservation on a link for a given session is the total of the FF reservations for all requested senders. On the other hand, FF reservations requested by different receivers Rj but selecting the same sender Si must be merged to share a single reservation. 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}, ...) 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 into which flows from all upstream senders are mixed. However, like the FF style, the SE style allows a receiver to explicitly specify the set of senders. We can represent an SE reservation request containing a flowspec Q and a list of senders S1, S2, ... by: SE( (S1,S2,...){Q} ) Both WF and SE styles create shared reservations, appropriate for those multicast applications whose properties make it unlikely that multiple data sources will 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 independent reservations for the flows from different senders, is Braden, Zhang, et al. Expiration: August 1996 [Page 13] Internet Draft RSVP Specification February 1996 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 path 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 through which data streams will arrive, labeled (a) and (b), and two outgoing interfaces through which data will be forwarded, labeled (c) and (d). This topology will be assumed in the examples that follow. There are three upstream senders; packets from 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 R2 and R3 arrive via different next hops, e.g., via the two routers D and D' in Figure 9. This illustrates the effect of a non-RSVP cloud or a broadcast LAN on interface (d). In addition to the connectivity shown in 4, we must also specify the multicast routes within this node. 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. Braden, Zhang, et al. Expiration: August 1996 [Page 14] Internet Draft RSVP Specification February 1996 ________________ (a)| | (c) ( S1 ) ---------->| |----------> ( R1 ) | Router | (b)| | (d) ( S2,S3 ) ------->| |----------> ( R2, 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 the two possible merging situations. Each of the two next hops on interface (d) results in a separate RSVP reservation request, as shown. These two requests are merged into the effective flowspec 3B, which is used to make the reservation on interface (d). To forward the reservation requests upstream, the reservations on the interfaces (c) and (d) are merged; as a result, the larger flowspec 4B is forwarded upstream to each previous hop. | 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 Braden, Zhang, et al. Expiration: August 1996 [Page 15] Internet Draft RSVP Specification February 1996 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 into the request forwarded to previous hop (b). On the other hand, the three different flow descriptors for sender S1 are merged into the single request FF( S1{4B} ), which 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 is 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 reservations. When SE-style reservations are merged, the resulting filter spec is the union of the original filter specs. Braden, Zhang, et al. Expiration: August 1996 [Page 16] Internet Draft RSVP Specification February 1996 | 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: August 1996 [Page 17] 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: August 1996 [Page 18] 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). An RSVP daemon preserves the next and previous hop addresses in its reservation and path state, respectively. There are two fundamental RSVP message types: Resv and Path. Each receiver host sends RSVP reservation request (Resv) messages upstream towards the senders. These reservation messages must follow exactly the reverse of the routes the data packets will use, upstream to all the sender hosts included in the sender selection. Resv messages are delivered to the sender hosts themselves so that the hosts can set up appropriate traffic control parameters for the first hop. Braden, Zhang, et al. Expiration: August 1996 [Page 19] 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. Like a filter spec, the Sender Template is less than fully general at present, specifying only the sender IP address and optionally the UDP/TCP sender port. 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 failure) on upstream links. 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 hop. Braden, Zhang, et al. Expiration: August 1996 [Page 20] Internet Draft RSVP Specification February 1996 2.2 Port Usage At present an RSVP session is 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 must know about the values for UDP and TCP (17 and 6, respectively). An end system should 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/or reservation state for the same DestAddress and ProtocolId must 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. A sender host must not send path state both with and without a zero SrcPort. Violation of this condition is an "Ambiguous Braden, Zhang, et al. Expiration: August 1996 [Page 21] Internet Draft RSVP Specification February 1996 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 all 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 several cases, the GLB (Greatest Lower Bound) is used instead of the LUB; this simply interchanges max and min operations. We can now give the complete rules for calculating 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. Re is calculated as the largest (using an LUB if necessary) of the Rspecs in Resv messages from different next hops (e.g., D and D') but the same outgoing interface (d). 2. 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) are summed; call this sum Path_Te. Braden, Zhang, et al. Expiration: August 1996 [Page 22] Internet Draft RSVP Specification February 1996 3. The maximum Tspec supplied in Resv messages from different next hops (e.g., D and D') is calculated; call this Resv_Te. 4. Te is the GLB (greatest lower bound) of Path_Te and Resv_Te. Flowspecs, Tspecs, and Adspecs are opaque to RSVP. Therefore, the last of these steps is actually performed by traffic control. The definition and implementation of the rules for comparing flowspecs, calculating LUBs and GLBs, and summing Tspecs are outside the definition of RSVP [ServTempl95a]. 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 existing 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 erasing a reservation. We recommend that the network traffic control mechanism 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 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. Braden, Zhang, et al. Expiration: August 1996 [Page 23] Internet Draft RSVP Specification February 1996 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-scope 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: August 1996 [Page 24] 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. 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: August 1996 [Page 25] 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. 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, for example: 1. The effective flowspec that is computed using the new request may fail admission control. 2. Administrative policy may prevent the requested reservation. 3. There may be no matching path state, so that the request cannot be forwarded towards the sender(s). 4. A reservation style that requires the explicit selection of a unique sender may have a filter spec that is ambiguous, i.e., that matches more than one sender in the path state, due to the use of wildcard fields in the filter spec. 5. The requested style may be incompatible with the style(s) of existing reservations. The incompatibility may occur among reservations for the same session on the same outgoing interface, or among effective reservations on different outgoing interfaces. 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 Braden, Zhang, et al. Expiration: August 1996 [Page 26] Internet Draft RSVP Specification February 1996 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 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 will succeed. 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, in general the downstream reservations will not be "wasted". 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. Braden, Zhang, et al. Expiration: August 1996 [Page 27] Internet Draft RSVP Specification February 1996 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 Td seconds. Such on/off behavior might be very distressing for users. 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. This 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. Braden, Zhang, et al. Expiration: August 1996 [Page 28] Internet Draft RSVP Specification February 1996 Therefore, there will 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 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 Automatic RSVP Tunneling 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 Braden, Zhang, et al. Expiration: August 1996 [Page 29] Internet Draft RSVP Specification February 1996 resource reservation. However, if such a cloud has sufficient capacity, it may still provide acceptable realtime service. RSVP automatically tunnels through such a non-RSVP 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. This effectively constructs a tunnel through the cloud for Resv messages, which can then be 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 addessed 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 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. Braden, Zhang, et al. Expiration: August 1996 [Page 30] Internet Draft RSVP Specification February 1996 H4 A receiver starts sending appropriate Resv messages, specifying the desired flow descriptors. 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: August 1996 [Page 31] Internet Draft RSVP Specification February 1996 3. RSVP Functional Specification 3.1 RSVP Message Formats An RSVP message or message fragment consists of a common header, an optional integrity-check data structure, and a body consisting of a variable number of variable-length, typed "objects". The integrity-check data structure is itself an object, of class INTEGRITY [Baker96]. In a fragmented message, INTEGRITY objects must occur either in every fragment or else in no fragment. Fragmentation of a message allows division of an object across two (or more) successive fragments. The following subsections define the formats of the common header, the object structures, 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 order except where the order is logically required (as noted in the following). 3.1.1 Common Header 0 1 2 3 +-------------+-------------+-------------+-------------+ | Vers | Flags| Type | RSVP Checksum | +-------------+-------------+-------------+-------------+ | RSVP Length | (Reserved) | Send_TTL | +-------------+-------------+-------------+-------------+ | Message ID | +----------+--+-------------+-------------+-------------+ |(Reserved)|MF| Fragment offset | +----------+--+-------------+-------------+-------------+ The fields in the common header are as follows: Vers: 4 bits Protocol version number. This is version 1. Flags: 4 bits Braden, Zhang, et al. Expiration: August 1996 [Page 32] Internet Draft RSVP Specification February 1996 0x01 = INTEGRITY object present This flag indicates that an INTEGRITY object follows immediately after the common header. The use of the INTEGRITY object is described in [Baker96]. 0x02-0x80: Reserved Type: 8 bits 1 = PATH 2 = RESV 3 = PERR 4 = RERR 5 = PTEAR 6 = RTEAR 7 = RACK RSVP Checksum: 16 bits The one's complement of the one's complement sum of the message (fragment), with the checksum field replaced by zero for the purpose of computing the checksum. An all- zero value means that no checksum was transmitted. RSVP Length: 16 bits The total length of this RSVP packet in bytes, including the common header and the variable-length objects that follow. If the MF flag is on or the Fragment Offset field is non-zero, this will generally differ from the length of the current fragment. Send_TTL: 8 bits The IP TTL value with which the message was sent. Message ID: 32 bits An unique identifying value that is used to identify and reassemble the fragments of a single message. It is assigned to the RSVP message by the node whose address is Braden, Zhang, et al. Expiration: August 1996 [Page 33] Internet Draft RSVP Specification February 1996 the IP source address of the message (fragment). MF: More Fragments Flag: 1 bit This flag is the low-order bit of a byte; the seven high- order bits are reserved. It is on for all but the last fragment of a message. Fragment Offset: 24 bits This field gives the byte offset of the current fragment in the complete message. For a Path or PathTear message, the Message Id is assigned by the sender host, and it must be copied at each successive node into forwarded messages. For other messages, it is assigned at the most recent RSVP hop to forward the message. When a message is fragmented, the Messsage Id must be copied into each fragment. When a fragmented packet is received, it may be reassembled by RSVP out of fragments carrying the same Message Id and IP source address. RSVP messages that exceed the MTU of the interface on which they are being sent must be split into fragments, each of which will fit into an MTU. 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 bytes. Must always be a multiple of 4, and at least 4. Braden, Zhang, et al. Expiration: August 1996 [Page 34] Internet Draft RSVP Specification February 1996 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 a 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. 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 Defines a desired QoS, in a Resv message. FILTER_SPEC Braden, Zhang, et al. Expiration: August 1996 [Page 35] Internet Draft RSVP Specification February 1996 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, in a Path message. SENDER_TSPEC Defines the traffic characteristics of a sender's data stream, in a Path message. ADSPEC Carries OPWA data, in a Path message. ERROR_SPEC Specifies an error, in a PathErr or ResvErr 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 Contains cryptographic data to authenticate the originating node and to verify the contents of this RSVP message. See [Baker96]. SCOPE An explicit list of sender hosts towards which to forward a message. May appear in a Resv, ResvErr, or ResvTear message. RESV_CONFIRM Carries the IP address of a receiver that requested a confirmation. May appear in a Resv or ResvConf message. Braden, Zhang, et al. Expiration: August 1996 [Page 36] Internet Draft RSVP Specification February 1996 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. Each RSVP-capable node along the path(s) captures Path messages and processes them to build local path state. The node then forwards the Path messages towards the receiver(s), replicating it as dictated by multicast routing, while preserving the original 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 format of a Path message is as follows: ::= [ ] [ ... ] ::= [ ] Braden, Zhang, et al. Expiration: August 1996 [Page 37] Internet Draft RSVP Specification February 1996 If the INTEGRITY object is present, there must be an INTEGRITY object immediately following the common header in every fragment of the message, in this and all other messages. 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 address of the interface through which the Path message was most recently sent. 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. A Path message received at a node is processed 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 downstream. Each message contains a sender descriptor defining one sender. The RSVP daemon forwards these messages 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 interface of each Path message and immediately discard those messages that have arrived on the wrong interface. Braden, Zhang, et al. Expiration: August 1996 [Page 38] Internet Draft RSVP Specification February 1996 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: ::= [ ] [ ... ] [ ] [ ]