RFC 2205 Network Working Group R. Braden, Ed. Request for Comments: 2205 ISI Category: Standards Track L. Zhang UCLA S. Berson ISI S. Herzog IBM Research S. Jamin Univ. of Michigan September 1997 Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. 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, Ed., et. al. Standards Track [Page 1] RFC 2205 RSVP September 1997 Table of Contents 1. Introduction ................................................... 4 1.1 Data Flows ................................................. 7 1.2 Reservation Model .......................................... 8 1.3 Reservation Styles .........................................11 1.4 Examples of Styles .........................................14 2. RSVP Protocol Mechanisms .......................................19 2.1 RSVP Messages ..............................................19 2.2 Merging Flowspecs ..........................................21 2.3 Soft State .................................................22 2.4 Teardown ...................................................24 2.5 Errors .....................................................25 2.6 Confirmation ...............................................27 2.7 Policy Control .............................................27 2.8 Security ...................................................28 2.9 Non-RSVP Clouds ............................................29 2.10 Host Model ................................................30 3. RSVP Functional Specification ..................................32 3.1 RSVP Message Formats .......................................32 3.2 Port Usage .................................................47 3.3 Sending RSVP Messages ......................................48 3.4 Avoiding RSVP Message Loops ................................50 3.5 Blockade State .............................................54 3.6 Local Repair ...............................................56 3.7 Time Parameters ............................................57 3.8 Traffic Policing and Non-Integrated Service Hops ...........58 3.9 Multihomed Hosts ...........................................59 3.10 Future Compatibility ......................................61 3.11 RSVP Interfaces ...........................................63 4. Acknowledgments ................................................76 APPENDIX A. Object Definitions ....................................77 APPENDIX B. Error Codes and Values ................................92 APPENDIX C. UDP Encapsulation .....................................98 APPENDIX D. Glossary .............................................102 REFERENCES .......................................................111 SECURITY CONSIDERATIONS ..........................................111 AUTHORS' ADDRESSES ...............................................112 Braden, Ed., et. al. Standards Track [Page 2] RFC 2205 RSVP September 1997 What's Changed This revision contains the following very minor changes from the ID14 version. o For clarity, each message type is now defined separately in Section 3.1. o We added more precise and complete rules for accepting Path messages for unicast and multicast destinations (Section 3.1.3). o We added more precise and complete rules for processing and forwarding PathTear messages (Section 3.1.5). o A note was added that a SCOPE object will be ignored if it appears in a ResvTear message (Section 3.1.6). o A note was added that a SENDER_TSPEC or ADSPEC object will be ignored if it appears in a PathTear message (Section 3.1.5). o The obsolete error code Ambiguous Filter Spec (09) was removed, and a new (and more consistent) name was given to error code 08 (Appendix B). o In the generic interface to traffic control, the Adspec was added as a parameter to the AddFlow and ModFlow calls (3.11.2). This is needed to accommodate a node that updates the slack term (S) of Guaranteed service. o An error subtype was added for an Adspec error (Appendix B). o Additional explanation was added for handling a CONFIRM object (Section 3.1.4). o The rules for forwarding objects with unknown class type were clarified. o Additional discussion was added to the Introduction and to Section 3.11.2 about the relationship of RSVP to the link layer. (Section 3.10). o Section 2.7 on Policy and Security was split into two sections, and some additional discussion of security was included. o There were some minor editorial improvements. Braden, Ed., et. al. Standards Track [Page 3] RFC 2205 RSVP September 1997 1. Introduction This document defines RSVP, a resource reservation setup protocol designed for an integrated services Internet [RSVP93, RFC 1633]. The RSVP protocol is used by a host to request specific qualities of service from the network for particular application data streams or flows. RSVP is also used by routers to deliver quality-of-service (QoS) requests to all nodes along the path(s) of the flows and to establish and maintain state to provide the requested service. RSVP requests will generally result in resources being reserved in each node along the data path. RSVP requests resources for simplex flows, 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 IPv4 or IPv6, occupying the place of a transport protocol in the protocol stack. However, RSVP does not transport application data but is rather an Internet control protocol, like ICMP, IGMP, or routing protocols. Like the implementations of routing and management protocols, an implementation of RSVP will typically execute in the background, not in the data forwarding path, as shown in Figure 1. RSVP is not itself a routing protocol; RSVP is designed to operate with current and future unicast and multicast routing protocols. An RSVP process 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. In order to efficiently accommodate large groups, dynamic group membership, and heterogeneous receiver requirements, RSVP makes receivers responsible for requesting a specific QoS [RSVP93]. A QoS request from a receiver host application is passed to the local RSVP process. 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), but only as far as the router where the receiver's data path joins the multicast distribution tree. As a result, RSVP's reservation overhead is in general logarithmic rather than linear in the number of receivers. Braden, Ed., et. al. Standards Track [Page 4] RFC 2205 RSVP September 1997 HOST ROUTER _____________________________ ____________________________ | _______ | | | | | | _______ | | _______ | | |Appli- | | | |RSVP | | | | | | cation| | RSVP <---------------------------> RSVP <----------> | | <--> | | | _______ | | | | | | |process| _____ | ||Routing| |process| _____ | | |_._____| | -->Polcy|| || <--> -->Polcy|| | | |__.__._| |Cntrl|| ||process| |__.__._| |Cntrl|| | |data | | |_____|| ||__.____| | | |_____|| |===|===========|==|==========| |===|==========|==|==========| | | --------| | _____ | | | --------| | _____ | | | | | ---->Admis|| | | | | ---->Admis|| | _V__V_ ___V____ |Cntrl|| | _V__V_ __V_____ |Cntrl|| | | | | | |_____|| | | | | ||_____|| | |Class-| | Packet | | | |Class-| | Packet | | | | ifier|==>Schedulr|================> ifier|==>Schedulr|===========> | |______| |________| |data | |______| |________| |data | | | | |_____________________________| |____________________________| Figure 1: RSVP in Hosts and Routers Quality of service is implemented for a particular data flow by mechanisms collectively called "traffic control". These mechanisms include (1) a packet classifier, (2) admission control, and (3) a "packet scheduler" or some other link-layer-dependent mechanism to determine when particular packets are forwarded. The "packet classifier" determines the QoS class (and perhaps the route) for each packet. For each outgoing interface, the "packet scheduler" or other link-layer-dependent mechanism achieves the promised QoS. Traffic control implements QoS service models defined by the Integrated Services Working Group. During reservation setup, an RSVP QoS request is passed to 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 Braden, Ed., et. al. Standards Track [Page 5] RFC 2205 RSVP September 1997 determines whether the user has administrative permission to make the reservation. If both checks succeed, parameters are set in the packet classifier and in the link layer interface (e.g., in the packet 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. RSVP protocol mechanisms provide a general facility for creating and maintaining distributed reservation state across a mesh of multicast or unicast delivery paths. RSVP itself transfers and manipulates QoS and policy control parameters as opaque data, passing them to the appropriate traffic control and policy control modules for interpretation. The structure and contents of the QoS parameters are documented in specifications developed by the Integrated Services Working Group; see [RFC 2210]. The structure and contents of the policy parameters are under development. Since the membership of a large multicast group and the resulting multicast tree topology are likely to change with time, the RSVP design assumes that state for RSVP and traffic control state is to be built and destroyed incrementally in routers and hosts. For this purpose, RSVP establishes "soft" state; that is, RSVP sends periodic refresh messages to maintain the state along the reserved path(s). In the absence of refresh messages, the state automatically times out and is deleted. In summary, RSVP has the following attributes: o RSVP makes resource reservations for both unicast and many-to- many multicast applications, adapting dynamically to changing group membership as well as to changing routes. o RSVP is simplex, i.e., it makes reservations for unidirectional data flows. o RSVP is receiver-oriented, i.e., the receiver of a data flow initiates and maintains the resource reservation used for that flow. o RSVP maintains "soft" state in routers and hosts, providing graceful support for dynamic membership changes and automatic adaptation to routing changes. o RSVP is not a routing protocol but depends upon present and future routing protocols. o RSVP transports and maintains traffic control and policy control parameters that are opaque to RSVP. Braden, Ed., et. al. Standards Track [Page 6] RFC 2205 RSVP September 1997 o RSVP provides several reservation models or "styles" (defined below) to fit a variety of applications. o RSVP provides transparent operation through routers that do not support it. o RSVP supports both IPv4 and IPv6. Further discussion on the objectives and general justification for RSVP design are presented in [RSVP93] and [RFC 1633]. 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 a UDP encapsulation of RSVP messages, for hosts whose operating systems provide inadequate raw network I/O support. 1.1 Data Flows RSVP defines a "session" to be a data flow with a particular destination and transport-layer protocol. RSVP treats each session independently, and this document often omits the implied qualification "for the same session". An RSVP session is defined by the triple: (DestAddress, ProtocolId [, DstPort]). Here DestAddress, the IP destination address of the data packets, may be a unicast or multicast address. ProtocolId is the IP protocol ID. The optional DstPort parameter is a "generalized destination port", i.e., some further demultiplexing point in the transport or application protocol layer. DstPort could be defined by a UDP/TCP destination port field, by an equivalent field in another transport protocol, or by some application-specific information. Although the RSVP protocol is designed to be easily extensible for greater generality, the basic protocol documented here supports only UDP/TCP ports as generalized ports. Note that it is not strictly necessary to include DstPort in the session definition when DestAddress is multicast, since different sessions can always have different multicast addresses. However, DstPort is necessary to allow more than one unicast session addressed to the same receiver host. Braden, Ed., et. al. Standards Track [Page 7] RFC 2205 RSVP September 1997 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 multicast routing. Multicast distribution forwards a copy of each data packet from a sender Si to every receiver Rj; a unicast distribution session has a single receiver R. Each sender Si may be running in a unique Internet host, or a single host may contain multiple senders distinguished by "generalized source ports". Senders Receivers _____________________ ( ) ===> R1 S1 ===> ( Multicast ) ( ) ===> R2 ( distribution ) S2 ===> ( ) ( by Internet ) ===> R3 (_____________________) Figure 2: Multicast Distribution Session For unicast transmission, there will be a single destination host but there may be multiple senders; RSVP can set up reservations for multipoint-to-single-point transmission. 1.2 Reservation Model An elementary RSVP reservation request consists of a "flowspec" together with a "filter spec"; this pair is called a "flow descriptor". The flowspec specifies a desired QoS. The filter spec, together with a session specification, defines the set of data packets -- the "flow" -- to receive the QoS defined by the flowspec. The flowspec is used to set parameters in the node's packet scheduler or other link layer mechanism, 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. The flowspec in a reservation request will generally include a service class and two sets of numeric parameters: (1) an "Rspec" (R for `reserve') that defines the desired QoS, and (2) a "Tspec" (T for `traffic') that describes the data flow. The formats and contents of Tspecs and Rspecs are determined by the integrated service models [RFC 2210] and are generally opaque to RSVP. Braden, Ed., et. al. Standards Track [Page 8] RFC 2205 RSVP September 1997 The exact format of a filter spec depends upon whether IPv4 or IPv6 is in use; see Appendix A. In the most general approach [RSVP93], filter specs may select arbitrary subsets of the packets in a given session. Such subsets might be defined in terms of senders (i.e., sender IP address and generalized source port), in terms of a higher-level protocol, or generally in terms of any fields in any protocol headers in the packet. For example, filter specs might be used to select different subflows of a hierarchically-encoded video stream by selecting on fields in an application-layer header. In the interest of simplicity (and to minimize layer violation), the basic filter spec format defined in the present RSVP specification has a very restricted form: 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. This raises three potential problems. 1. It is necessary to avoid IP fragmentation of a data flow for which a resource reservation is desired. Document [RFC 2210] specifies a procedure for applications using RSVP facilities to compute the minimum MTU over a multicast tree and return the result to the senders. 2. IPv6 inserts a variable number of variable-length Internet- layer headers before the transport header, increasing the difficulty and cost of packet classification for QoS. Efficient classification of IPv6 data packets could be obtained using the Flow Label field of the IPv6 header. The details will be provided in the future. 3. IP-level Security, under either IPv4 or IPv6, may encrypt the entire transport header, hiding the port numbers of data packets from intermediate routers. A small extension to RSVP for IP Security under IPv4 and IPv6 is described separately in [RFC 2207]. RSVP messages carrying reservation requests originate at receivers and are passed upstream towards the sender(s). Note: in this document, we define the directional terms "upstream" vs. "downstream", "previous hop" vs. "next hop", and "incoming interface" vs "outgoing interface" with respect to the direction of data flow. Braden, Ed., et. al. Standards Track [Page 9] RFC 2205 RSVP September 1997 At each intermediate node, a reservation request triggers two general actions, as follows: 1. Make a reservation on a link The RSVP process passes the request to admission control and policy control. If either test fails, the reservation is rejected and the RSVP process returns an error message to the appropriate receiver(s). If both succeed, the node sets the packet classifier to select the data packets defined by the filter spec, and it interacts with the appropriate link layer to obtain the desired QoS defined by the flowspec. The detailed rules for satisfying an RSVP QoS request depend upon the particular link layer technology in use on each interface. Specifications are under development in the ISSLL Working Group for mapping reservation requests into popular link layer technologies. For a simple leased line, the desired QoS will be obtained from the packet scheduler in the link layer driver, for example. If the link-layer technology implements its own QoS management capability, then RSVP must negotiate with the link layer to obtain the requested QoS. Note that the action to control QoS occurs at the place where the data enters the link-layer medium, i.e., at the upstream end of the logical or physical link, although an RSVP reservation request originates from receiver(s) downstream. 2. Forward the request upstream A 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. The traffic control mechanism may modify the flowspec hop-by-hop. More importantly, reservations from different downstream branches of the multicast tree(s) from the same sender (or set of senders) must be " merged" as reservations travel upstream. 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 Braden, Ed., et. al. Standards Track [Page 10] RFC 2205 RSVP September 1997 than that being requested. At that point, the arriving request is merged with the reservation in place and need not be forwarded further; the node may then send a reservation confirmation message back to the receiver. Note that the receipt of a confirmation is only a high-probability indication, not a guarantee, that the requested service is in place all the way to the sender(s), as explained in Section 2.6. The basic RSVP reservation model is "one pass": a receiver sends a reservation request upstream, and each node in the path either accepts or rejects the request. This scheme provides no easy way for a receiver to find out the resulting end-to-end service. Therefore, RSVP supports an enhancement to one-pass service known as "One Pass With Advertising" (OPWA) [OPWA95]. With OPWA, RSVP control packets are sent downstream, following the data paths, to gather information that may be used to predict the end-to-end QoS. The results ("advertisements") are delivered by RSVP to the receiver hosts and perhaps to the receiver applications. The advertisements may then be used by the receiver to construct, or to dynamically adjust, an appropriate reservation request. 1.3 Reservation Styles A reservation request includes a set of options that are collectively called the reservation "style". One reservation option concerns the treatment of reservations for different senders within the same session: establish a "distinct" reservation for each upstream sender, or else make a single reservation that is "shared" among all packets of selected senders. Another reservation option controls the selection of senders; it may be an "explicit" list of all selected senders, or a "wildcard" that implicitly selects all the senders to the session. In an explicit sender-selection reservation, each filter spec must match exactly one sender, while in a wildcard sender-selection no filter spec is needed. Braden, Ed., et. al. Standards Track [Page 11] RFC 2205 RSVP September 1997 Sender || Reservations: Selection || Distinct | Shared _________||__________________|____________________ || | | Explicit || Fixed-Filter | Shared-Explicit | || (FF) style | (SE) Style | __________||__________________|____________________| || | | Wildcard || (None defined) | Wildcard-Filter | || | (WF) Style | __________||__________________|____________________| Figure 3: Reservation Attributes and Styles The following styles are currently defined (see Figure 3): o Wildcard-Filter (WF) Style The WF style implies the options: "shared" reservation and "wildcard" sender selection. Thus, a WF-style reservation creates a single reservation shared by flows from all upstream senders. This reservation may be thought of as a shared "pipe", whose "size" is the largest of the resource requests from all receivers, independent of the number of senders using it. A WF-style reservation is propagated upstream towards all sender hosts, and it automatically extends to new senders as they appear. Symbolically, we can represent a WF-style reservation request by: WF( * {Q}) where the asterisk represents wildcard sender selection and Q represents the flowspec. o Fixed-Filter (FF) Style The FF style implies the options: "distinct" reservations and "explicit" sender selection. Thus, an elementary FF-style reservation request creates a distinct reservation for data packets from a particular sender, not sharing them with other senders' packets for the same session. Braden, Ed., et. al. Standards Track [Page 12] RFC 2205 RSVP September 1997 Symbolically, we can represent an elementary FF reservation request by: FF( S{Q}) where S is the selected sender and Q is the corresponding flowspec; the pair forms a flow descriptor. RSVP allows multiple elementary FF-style reservations to be requested at the same time, using a list of flow descriptors: FF( S1{Q1}, S2{Q2}, ...) The total reservation on a link for a given session is the `sum' of Q1, Q2, ... for all requested senders. o Shared Explicit (SE) Style The SE style implies the options: "shared" reservation and "explicit" sender selection. Thus, an SE-style reservation creates a single reservation shared by selected upstream senders. Unlike the WF style, the SE style allows a receiver to explicitly specify the set of senders to be included. We can represent an SE reservation request containing a flowspec Q and a list of senders S1, S2, ... by: SE( (S1,S2,...){Q} ) Shared reservations, created by WF and SE styles, are appropriate for those multicast applications in which multiple data sources are unlikely to transmit simultaneously. Packetized audio is an example of an application suitable for shared reservations; since a limited number of people talk at once, each receiver might issue a WF or SE reservation request for twice the bandwidth required for one sender (to allow some over-speaking). On the other hand, the FF style, which creates distinct reservations for the flows from different senders, is appropriate for video signals. The RSVP rules disallow merging of shared reservations with distinct reservations, since these modes are fundamentally incompatible. They also disallow merging explicit sender selection with wildcard sender selection, since this might produce an unexpected service for a receiver that specified explicit selection. As a result of these prohibitions, WF, SE, and FF styles are all mutually incompatible. Braden, Ed., et. al. Standards Track [Page 13] RFC 2205 RSVP September 1997 It would seem possible to simulate the effect of a WF reservation using the SE style. When an application asked for WF, the RSVP process on the receiver host could use local state to create an equivalent SE reservation that explicitly listed all senders. However, an SE reservation forces the packet classifier in each node to explicitly select each sender in the list, while a WF allows the packet classifier to simply "wild card" the sender address and port. When there is a large list of senders, a WF style reservation can therefore result in considerably less overhead than an equivalent SE style reservation. For this reason, both SE and WF are included in the protocol. Other reservation options and styles may be defined in the future. 1.4 Examples of Styles This section presents examples of each of the reservation styles and shows the effects of merging. Figure 4 illustrates a router with two incoming interfaces, labeled (a) and (b), through which flows will arrive, and two outgoing interfaces, labeled (c) and (d), through which data will be forwarded. This topology will be assumed in the examples that follow. There are three upstream senders; packets from sender S1 (S2 and S3) arrive through previous hop (a) ((b), respectively). There are also three downstream receivers; packets bound for R1 (R2 and R3) are routed via outgoing interface (c) ((d), respectively). We furthermore assume that outgoing interface (d) is connected to a broadcast LAN, i.e., that replication occurs in the network; R2 and R3 are reached via different next hop routers (not shown). We must also specify the multicast routes within the node of Figure 4. Assume first that data packets from each Si shown in Figure 4 are routed to both outgoing interfaces. Under this assumption, Figures 5, 6, and 7 illustrate Wildcard-Filter, Fixed-Filter, and Shared-Explicit reservations, respectively. Braden, Ed., et. al. Standards Track [Page 14] RFC 2205 RSVP September 1997 ________________ (a)| | (c) ( S1 ) ---------->| |----------> ( R1 ) | Router | | (b)| | (d) |---> ( R2 ) ( S2,S3 ) ------->| |------| |________________| |---> ( R3 ) | Figure 4: Router Configuration For simplicity, these examples show flowspecs as one-dimensional multiples of some base resource quantity B. The "Receives" column shows the RSVP reservation requests received over outgoing interfaces (c) and (d), and the "Reserves" column shows the resulting reservation state for each interface. The "Sends" column shows the reservation requests that are sent upstream to previous hops (a) and (b). In the "Reserves" column, each box represents one reserved "pipe" on the outgoing link, with the corresponding flow descriptor. Figure 5, showing the WF style, illustrates two distinct situations in which merging is required. (1) Each of the two next hops on interface (d) results in a separate RSVP reservation request, as shown; these two requests must be merged into the effective flowspec, 3B, that is used to make the reservation on interface (d). (2) The reservations on the interfaces (c) and (d) must be merged in order to forward the reservation requests upstream; as a result, the larger flowspec 4B is forwarded upstream to each previous hop. Braden, Ed., et. al. Standards Track [Page 15] RFC 2205 RSVP September 1997 | Sends | Reserves Receives | | _______ WF( *{4B} ) <- (a) | (c) | * {4B}| (c) <- WF( *{4B} ) | |_______| | -----------------------|---------------------------------------- | _______ WF( *{4B} ) <- (b) | (d) | * {3B}| (d) <- WF( *{3B} ) | |_______| <- WF( *{2B} ) Figure 5: Wildcard-Filter (WF) Reservation Example Figure 6 shows Fixed-Filter (FF) style reservations. For each outgoing interface, there is a separate reservation for each source that has been requested, but this reservation will be shared among all the receivers that made the request. The flow descriptors for senders S2 and S3, received through outgoing interfaces (c) and (d), are packed (not merged) into the request forwarded to previous hop (b). On the other hand, the three different flow descriptors specifying sender S1 are merged into the single request FF( S1{4B} ) that is sent to previous hop (a). | Sends | Reserves Receives | | ________ 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 Braden, Ed., et. al. Standards Track [Page 16] RFC 2205 RSVP September 1997 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, and the resulting flowspec is the largest flowspec. | Sends | Reserves Receives | | ________ 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, Ed., et. al. Standards Track [Page 17] RFC 2205 RSVP September 1997 _______________ (a)| | (c) ( S1 ) ---------->| >-----------> |----------> ( R1 ) | > | | > | (b)| > | (d) ( S2,S3 ) ------->| >-------->--> |----------> ( R2, R3 ) |_______________| Router Configuration | Sends | Reserves Receives | | _______ 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, Ed., et. al. Standards Track [Page 18] RFC 2205 RSVP September 1997 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 flow arrives from a "previous hop" through a corresponding "incoming interface" and departs through one or more "outgoing interface"(s). The same 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; for example, the figure implies that D and D' are connected to (d) with a broadcast LAN. There are two fundamental RSVP message types: Resv and Path. Each receiver host sends RSVP reservation request (Resv) messages upstream towards the senders. These messages must follow exactly the reverse of the path(s) the data packets will use, upstream to all the sender hosts included in the sender selection. They create and maintain "reservation state" in each node along the path(s). Resv messages must finally be delivered to the sender hosts themselves, so that the hosts can set up appropriate traffic control parameters for the first hop. The processing of Resv messages was discussed previously in Section 1.2. Braden, Ed., et. al. Standards Track [Page 19] RFC 2205 RSVP September 1997 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 contains the following information in addition to the previous hop address: o Sender Template A Path message is required to carry a Sender Template, which describes the format of data packets that the sender will originate. This template is in the form of a filter spec that could be used to select this sender's packets from others in the same session on the same link. Sender Templates have exactly the same expressive power and format as filter specs that appear in Resv messages. Therefore a Sender Template may specify only the sender IP address and optionally the UDP/TCP sender port, and it assumes the protocol Id specified for the session. o Sender Tspec A Path message is required to carry a Sender Tspec, which defines the traffic characteristics of the data flow that the sender will generate. This Tspec is used by traffic control to prevent over-reservation, and perhaps unnecessary Admission Control failures. o Adspec A Path message may 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. Braden, Ed., et. al. Standards Track [Page 20] RFC 2205 RSVP September 1997 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. 2.2 Merging Flowspecs A Resv message forwarded to a previous hop carries a flowspec that is the "largest" of the flowspecs requested by the next hops to which the data flow will be sent (however, see Section 3.5 for a different merging rule used in certain cases). We say the flowspecs have been "merged". The examples shown in Section 1.4 illustrated another case of merging, when there are 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. Here again, the installed reservation should have an effective flowspec that is the "largest" of the flowspecs requested by the different next hops. Since flowspecs are opaque to RSVP, the actual rules for comparing flowspecs must be defined and implemented outside RSVP proper. The comparison rules are defined in the appropriate integrated service specification document. An RSVP implementation will need to call service-specific routines to perform flowspec merging. Note that flowspecs are generally multi-dimensional vectors; they may contain both Tspec and Rspec components, each of which may itself be multi-dimensional. Therefore, 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, the service-specific merging routines must be able to return a third flowspec that is at least as large as each; mathematically, this is the "least upper bound" (LUB). In some cases, a flowspec at least as small is needed; this is the "greatest lower bound" (GLB) GLB (Greatest Lower Bound). The following steps are used to calculate the effective flowspec (Re, Te) to be installed on an interface [RFC 2210]. Here Te is the effective Tspec and Re is the effective Rspec. Braden, Ed., et. al. Standards Track [Page 21] RFC 2205 RSVP September 1997 1. An effective flowspec is determined for the outgoing interface. Depending upon the link-layer technology, this may require merging flowspecs from different next hops; this means computing the effective flowspec as the LUB of the flowspecs. Note that what flowspecs to merge is determined by the link layer medium (see Section 3.11.2), while how to merge them is determined by the service model in use [RFC 2210]. The result is a flowspec that is opaque to RSVP but actually consists of the pair (Re, Resv_Te), where is Re is the effective Rspec and Resv_Te is the effective Tspec. 2. A service-specific calculation of Path_Te, the sum of all Tspecs that were supplied in Path messages from different previous hops (e.g., some or all of A, B, and B' in Figure 9), is performed. 3. (Re, Resv_Te) and Path_Te are passed to traffic control. Traffic control will compute the effective flowspec as the "minimum" of Path_Te and Resv_Te, in a service-dependent manner. Section 3.11.6 defines a generic set of service-specific calls to compare flowspecs, to compute the LUB and GLB of flowspecs, and to compare and sum Tspecs. 2.3 Soft State RSVP takes a "soft state" approach to managing the reservation state in routers and hosts. RSVP soft state is created and periodically refreshed by Path and Resv messages. The state is deleted if no matching refresh messages arrive before the expiration of a "cleanup timeout" interval. State may also be deleted by an explicit "teardown" message, described in the next section. At the expiration of each "refresh timeout" period and after a state change, RSVP scans its state to build and forward Path and Resv refresh messages to succeeding hops. Path and Resv messages are idempotent. When a route changes, the next Path message will initialize the path state on the new route, and future Resv messages will establish reservation state there; the state on the now-unused segment of the route will time out. Thus, whether a message is "new" or a "refresh" is determined separately at each node, depending upon the existence of state at that node. Braden, Ed., et. al. Standards Track [Page 22] RFC 2205 RSVP September 1997 RSVP sends its messages as IP datagrams with no reliability enhancement. Periodic transmission of refresh messages by hosts and routers is expected to handle the occasional loss of an RSVP message. If the effective cleanup timeout is set to K times the refresh timeout period, then RSVP can tolerate K-1 successive RSVP packet losses without falsely deleting state. The network traffic control mechanism should be statically configured to grant some minimal bandwidth for RSVP messages to protect them from congestion losses. The state maintained by RSVP is dynamic; to change the set of senders Si or to change any QoS request, a host simply starts sending revised Path and/or Resv messages. The result will be an appropriate adjustment in the RSVP state in all nodes along the path; unused state will time out if it is not explicitly torn down. In steady state, state is refreshed hop-by-hop to allow merging. When the received state differs from the stored state, the stored state is updated. If this update results in modification of state to be forwarded in refresh messages, these refresh messages must be generated and forwarded immediately, so that state changes can be propagated end-to-end without delay. However, propagation of a change stops when and if it reaches a point where merging causes no resulting state change. This minimizes RSVP control traffic due to changes and is essential for scaling to large multicast groups. State that is received through a particular interface I* should never be forwarded out the same interface. Conversely, state that is forwarded out interface I* must be computed using only state that arrived on interfaces different from I*. A trivial example of this rule is illustrated in Figure 10, which shows a transit router with one sender and one receiver on each interface (and assumes one next/previous hop per interface). Interfaces (a) and (c) serve as both outgoing and incoming interfaces for this session. Both receivers are making wildcard-style reservations, in which the Resv messages are forwarded to all previous hops for senders in the group, with the exception of the next hop from which they came. The result is independent reservations in the two directions. There is an additional rule governing the forwarding of Resv messages: state from Resv messages received from outgoing interface Io should be forwarded to incoming interface Ii only if Path messages from Ii are forwarded to Io. Braden, Ed., et. al. Standards Track [Page 23] RFC 2205 RSVP September 1997 ________________ 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 2.4 Teardown RSVP "teardown" messages remove path or reservation state immediately. Although it is not necessary to explicitly tear down an old reservation, we recommend that all end hosts send a teardown request as soon as an application finishes. There are two types of RSVP teardown message, PathTear and ResvTear. A PathTear message travels towards all receivers downstream from its point of initiation and deletes path state, as well as all dependent reservation state, along the way. An ResvTear message deletes reservation state and travels towards all senders upstream from its point of initiation. A PathTear (ResvTear) message may be conceptualized as a reversed-sense Path message (Resv message, respectively). A teardown request may be initiated either by an application in an end system (sender or receiver), or by a router as the result of state timeout or service preemption. Once initiated, a teardown request must be forwarded hop-by-hop without delay. A teardown message deletes the specified state in the node where it is received. As always, this state change will be propagated immediately to the next node, but only if there will be a net change after merging. As a result, a ResvTear message will prune the reservation state back (only) as far as possible. Braden, Ed., et. al. Standards Track [Page 24] RFC 2205 RSVP September 1997 Like all other RSVP messages, teardown requests are not delivered reliably. The loss of a teardown request message will not cause a protocol failure because the unused state will eventually time out even though it is not explicitly deleted. If a teardown message is lost, the router that failed to receive that message will time out its state and initiate a new teardown message beyond the loss point. Assuming that RSVP message loss probability is small, the longest time to delete state will seldom exceed one refresh timeout period. It should be possible to tear down any subset of the established state. For path state, the granularity for teardown is a single sender. For reservation state, the granularity is an individual filter spec. For example, refer to Figure 7. Receiver R1 could send a ResvTear message for sender S2 only (or for any subset of the filter spec list), leaving S1 in place. A ResvTear message specifies the style and filters; any flowspec is ignored. Whatever flowspec is in place will be removed if all its filter specs are torn down. 2.5 Errors There are two RSVP error messages, ResvErr and PathErr. PathErr messages are very simple; they are simply sent upstream to the sender that created the error, and they do not change path state in the nodes though which they pass. There are only a few possible causes of path errors. However, there are a number of ways for a syntactically valid reservation request to fail at some node along the path. A node may also decide to preempt an established reservation. The handling of ResvErr messages is somewhat complex (Section 3.5). Since a request that fails may be the result of merging a number of requests, a reservation error must be reported to all of the responsible receivers. In addition, merging heterogeneous requests creates a potential difficulty known as the "killer reservation" problem, in which one request could deny service to another. There are actually two killer-reservation problems. 1. The first killer reservation problem (KR-I) arises when there is already a reservation Q0 in place. If another receiver now makes a larger reservation Q1 > Q0, the result of merging Q0 and Q1 may be rejected by admission control in some upstream node. This must not deny service to Q0. Braden, Ed., et. al. Standards Track [Page 25] RFC 2205 RSVP September 1997 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 would succeed if not merged with Q1. To solve this problem, a ResvErr message establishes additional state, called "blockade state", in each node through which it passes. Blockade state in a node modifies the merging procedure to omit the offending flowspec (Q1 in the example) from the merge, allowing a smaller request to be forwarded and established. The Q1 reservation state is said to be "blockaded". Detailed rules are presented in Section 3.5. A reservation request that fails Admission Control creates blockade state but is left in place in nodes downstream of the failure point. It has been suggested that these reservations downstream from the failure represent "wasted" reservations and should be timed out if not actively deleted. However, the downstream reservations are left in place, for the following reasons: o There are two possible reasons for a receiver persisting in a failed reservation: (1) it is polling for resource availability along the entire path, or (2) it wants to obtain the desired QoS along as much of the path as possible. Certainly in the second case, and perhaps in the first case, the receiver will want to hold onto the reservations it has made downstream from the failure. o If these downstream reservations were not retained, the responsiveness of RSVP to certain transient failures would be impaired. For example, suppose a route "flaps" to an alternate route that is congested, so an existing reservation suddenly fails, then quickly recovers to the original route. The blockade state in each downstream router must not remove the state or prevent its immediate refresh. o If we did not refresh the downstream reservations, they might time out, to be restored every Tb seconds (where Tb is the blockade state timeout interval). Such intermittent behavior might be very distressing for users. Braden, Ed., et. al. Standards Track [Page 26] RFC 2205 RSVP September 1997 2.6 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 is not forwarded further, and if the Resv included a confirmation- request object, a ResvConf message is sent back to Rj. If the confirmation request is forwarded, it is forwarded immediately, and no more than once for each request. This confirmation mechanism has the following consequences: o A new reservation request with a flowspec larger than any in place for a session will normally result in either a ResvErr or a ResvConf message back to the receiver from each sender. In this case, the ResvConf message will be an end-to-end confirmation. o The receipt of a ResvConf gives no guarantees. Assume the first two reservation requests from receivers R1 and R2 arrive at the node where they are merged. R2, whose reservation was the second to arrive at that node, may receive a ResvConf from that node while R1's request has not yet propagated all the way to a matching sender and may still fail. Thus, R2 may receive a ResvConf although there is no end-to-end reservation in place; furthermore, R2 may receive a ResvConf followed by a ResvErr. 2.7 Policy Control RSVP-mediated QoS requests allow particular user(s) to obtain preferential access to network resources. To prevent abuse, some form of back pressure will generally be required on users who make reservations. For example, such back pressure may be accomplished by administrative access policies, or it may depend upon some form of user feedback such as real or virtual billing for the "cost" of a reservation. In any case, reliable user identification and selective admission will generally be needed when a reservation is requested. The term "policy control" is used for the mechanisms required to support access policies and back pressure for RSVP reservations. When a new reservation is requested, each node must answer two questions: "Are enough resources available to meet this request?" Braden, Ed., et. al. Standards Track [Page 27] RFC 2205 RSVP September 1997 and "Is this user allowed to make this reservation?" These two decisions are termed the "admission control" decision and the "policy control" decision, respectively, and both must be favorable in order for RSVP to make a reservation. Different administrative domains in the Internet may have different reservation policies. The input to policy control is referred to as "policy data", which RSVP carries in POLICY_DATA objects. Policy data may include credentials identifying users or user classes, account numbers, limits, quotas, etc. Like flowspecs, policy data is opaque to RSVP, which simply passes it to policy control when required. Similarly, merging of policy data must be done by the policy control mechanism rather than by RSVP itself. Note that the merge points for policy data are likely to be at the boundaries of administrative domains. It may therefore be necessary to carry accumulated and unmerged policy data upstream through multiple nodes before reaching one of these merge points. Carrying user-provided policy data in Resv messages presents a potential 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. The policy data will have to be administratively merged at places near the receivers, to avoid excessive policy data. Further discussion of these issues and an example of a policy control scheme will be found in [PolArch96]. Specifications for the format of policy data objects and RSVP processing rules for them are under development. 2.8 Security RSVP raises the following security issues. o Message integrity and node authentication Corrupted or spoofed reservation requests could lead to theft of service by unauthorized parties or to denial of service caused by locking up network resources. RSVP protects against such attacks with a hop-by-hop authentication mechanism using an encrypted hash function. The mechanism is supported by INTEGRITY objects that may appear in any RSVP message. These objects use a keyed cryptographic digest technique, which assumes that RSVP neighbors share a secret. Although this mechanism is part of the base RSVP specification, it is described in a companion document [Baker96]. Braden, Ed., et. al. Standards Track [Page 28] RFC 2205 RSVP September 1997 Widespread use of the RSVP integrity mechanism will require the availability of the long-sought key management and distribution infrastructure for routers. Until that infrastructure becomes available, manual key management will be required to secure RSVP message integrity. o User authentication Policy control will depend upon positive authentication of the user responsible for each reservation request. Policy data may therefore include cryptographically protected user certificates. Specification of such certificates is a future issue. Even without globally-verifiable user certificates, it may be possible to provide practical user authentication in many cases by establishing a chain of trust, using the hop-by-hop INTEGRITY mechanism described earlier. o Secure data streams The first two security issues concerned RSVP's operation. A third security issue concerns resource reservations for secure data streams. In particular, the use of IPSEC (IP Security) in the data stream poses a problem for RSVP: if the transport and higher level headers are encrypted, RSVP's generalized port numbers cannot be used to define a session or a sender. To solve this problem, an RSVP extension has been defined in which the security association identifier (IPSEC SPI) plays a role roughly equivalent to the generalized ports [RFC 2207]. 2.9 Non-RSVP Clouds It is impossible to deploy RSVP (or any new protocol) at the same moment throughout the entire Internet. Furthermore, RSVP may never be deployed everywhere. RSVP must therefore provide correct protocol operation even when two RSVP-capable routers are joined by an arbitrary "cloud" of non-RSVP routers. Of course, an intermediate cloud that does not support RSVP is unable to perform resource reservation. However, if such a cloud has sufficient capacity, it may still provide useful realtime service. RSVP is designed to operate correctly through such a non-RSVP 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 Braden, Ed., et. al. Standards Track [Page 29] RFC 2205 RSVP September 1997 unaffected by non-RSVP routers in the path. When a Path message traverses a non-RSVP cloud, it carries to the next RSVP-capable node the IP address of the last RSVP-capable router before entering the cloud. An Resv message is then forwarded directly to the next RSVP-capable router on the path(s) back towards the source. Even though RSVP operates correctly through a non-RSVP cloud, the non-RSVP-capable nodes will in general perturb the QoS provided to a receiver. Therefore, RSVP passes a `NonRSVP' flag bit to the local traffic control mechanism when there are non-RSVP-capable hops in the path to a given sender. Traffic control combines this flag bit with its own sources of information, and forwards the composed information on integrated service capability along the path to receivers using Adspecs [RFC 2210]. 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 process 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. To handle the wrong interface case, a "Logical Interface Handle" (LIH) is used. The previous hop information included in a Path message includes not only the IP address of the previous node but also an LIH defining the logical outgoing interface; both values are stored in the path state. A Resv message arriving at the addressed node carries both the IP address and the LIH of the correct outgoing interface, i.e, the interface that should receive the requested reservation, regardless of which interface it arrives on. The LIH may also be useful when RSVP reservations are made over a complex link layer, to map between IP layer and link layer flow entities. 2.10 Host Model Before a session can be created, the session identification (DestAddress, ProtocolId [, DstPort]) 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. Braden, Ed., et. al. Standards Track [Page 30] RFC 2205 RSVP September 1997 H1 A receiver joins the multicast group specified by DestAddress, using IGMP. H2 A potential sender starts sending RSVP Path messages to the DestAddress. H3 A receiver application receives a Path message. H4 A receiver starts sending appropriate Resv messages, specifying the desired flow descriptors. 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 3.11.1 discusses the general requirements and outlines a generic interface. Braden, Ed., et. al. Standards Track [Page 31] RFC 2205 RSVP September 1997 3. RSVP Functional Specification 3.1 RSVP Message Formats An RSVP message consists of a common header, followed by a body consisting of a variable number of variable-length, typed "objects". The following subsections define the formats of the common header, the standard object header, and each of the RSVP message types. For each RSVP message type, there is a set of rules for the permissible choice of object types. These rules are specified using Backus-Naur Form (BNF) augmented with square brackets surrounding optional sub-sequences. The BNF implies an order for the objects in a message. However, in many (but not all) cases, object order makes no logical difference. An implementation should create messages with the objects in the order shown here, but accept the objects in any permissible order. 3.1.1 Common Header 0 1 2 3 +-------------+-------------+-------------+-------------+ | Vers | Flags| Msg Type | RSVP Checksum | +-------------+-------------+-------------+-------------+ | Send_TTL | (Reserved) | RSVP Length | +-------------+-------------+-------------+-------------+ The fields in the common header are as follows: Vers: 4 bits Protocol version number. This is version 1. Flags: 4 bits 0x01-0x08: Reserved No flag bits are defined yet. Msg Type: 8 bits 1 = Path 2 = Resv Braden, Ed., et. al. Standards Track [Page 32] RFC 2205 RSVP September 1997 3 = PathErr 4 = ResvErr 5 = PathTear 6 = ResvTear 7 = ResvConf RSVP Checksum: 16 bits The one's complement of the one's complement sum of the message, with the checksum field replaced by zero for the purpose of computing the checksum. An all-zero value means that no checksum was transmitted. Send_TTL: 8 bits The IP TTL value with which the message was sent. See Section 3.8. RSVP Length: 16 bits The total length of this RSVP message in bytes, including the common header and the variable-length objects that follow. 3.1.2 Object Formats Every object consists of one or more 32-bit words with a one- word header, with the following format: 0 1 2 3 +-------------+-------------+-------------+-------------+ | Length (bytes) | Class-Num | C-Type | +-------------+-------------+-------------+-------------+ | | // (Object contents) // | | +-------------+-------------+-------------+-------------+ Braden, Ed., et. al. Standards Track [Page 33] RFC 2205 RSVP September 1997 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. Class-Num Identifies the object class; values of this field are defined in Appendix A. Each object class has a name, which is always capitalized in this document. An RSVP implementation must recognize the following classes: NULL A NULL object has a Class-Num of zero, and its C-Type is ignored. Its length must be at least 4, but can be any multiple of 4. A NULL object may appear anywhere in a sequence of objects, and its contents will be ignored by the receiver. SESSION Contains the IP destination address (DestAddress), the IP protocol id, and some form of generalized destination port, to define a specific session for the other objects that follow. Required in every RSVP message. RSVP_HOP Carries the IP address of the RSVP-capable node that sent this message and a logical outgoing interface handle (LIH; see Section 3.3). 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 Section 3.7. Required in every Path and Resv message. Braden, Ed., et. al. Standards Track [Page 34] RFC 2205 RSVP September 1997 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 Defines a subset of session data packets that should receive the desired QoS (specified by a FLOWSPEC object), in a Resv message. SENDER_TEMPLATE Contains a sender IP address and perhaps some additional demultiplexing information to identify a sender. Required in a Path message. SENDER_TSPEC Defines the traffic characteristics of a sender's data flow. Required in a Path message. ADSPEC Carries OPWA data, in a Path message. ERROR_SPEC Specifies an error in a PathErr, ResvErr, or a confirmation in a ResvConf message. POLICY_DATA Carries information that will allow a local policy module to decide whether an associated reservation is administratively permitted. May appear in Path, Resv, PathErr, or ResvErr message. The use of POLICY_DATA objects is not fully specified at this time; a future document will fill this gap. Braden, Ed., et. al. Standards Track [Page 35] RFC 2205 RSVP September 1997 INTEGRITY Carries cryptographic data to authenticate the originating node and to verify the contents of this RSVP message. The use of the INTEGRITY object is described in [Baker96]. SCOPE Carries an explicit list of sender hosts towards which the information in the message is to be forwarded. May appear in a Resv, ResvErr, or ResvTear message. See Section 3.4. RESV_CONFIRM Carries the IP address of a receiver that requested a confirmation. May appear in a Resv or ResvConf message. C-Type Object type, unique within Class-Num. Values are defined in Appendix A. The maximum object content length is 65528 bytes. The Class- Num and C-Type fields may be used together as a 16-bit number to define a unique type for each object. The high-order two bits of the Class-Num is used to determine what action a node should take if it does not recognize the Class-Num of an object; see Section 3.10. 3.1.3 Path Messages Each sender host periodically sends a Path message for each data flow it originates. It contains a SENDER_TEMPLATE object defining the format of the data packets and a SENDER_TSPEC object specifying the traffic characteristics of the flow. Optionally, it may contain may be an ADSPEC object carrying advertising (OPWA) data for the flow. A 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 must be an address of the sender it describes, while the destination address must be the DestAddress for the session. These addresses assure that the message will be correctly routed through a non-RSVP cloud. Braden, Ed., et. al. Standards Track [Page 36] RFC 2205 RSVP September 1997 The format of a Path message is as follows:::= [ ] [ ... ] [ ] ::= [ ] If the INTEGRITY object is present, it must immediately follow the common header. There are no other requirements on transmission order, although the above order is recommended. Any number of POLICY_DATA objects may appear. The PHOP (i.e., RSVP_HOP) object of each Path message contains the previous hop address, i.e., the IP address of the interface through which the Path message was most recently sent. It also carries a logical interface handle (LIH). Each RSVP-capable node along the path(s) captures a Path message and processes it to create path state for the sender defined by the SENDER_TEMPLATE and SESSION objects. Any POLICY_DATA, SENDER_TSPEC, and ADSPEC objects are also saved in the path state. If an error is encountered while processing a Path message, a PathErr message is sent to the originating sender of the Path message. Path messages must satisfy the rules on SrcPort and DstPort in Section 3.2. Periodically, the RSVP process at a node scans the path state to create new Path messages to forward towards the receiver(s). Each message contains a sender descriptor defining one sender, and carries the original sender's IP address as its IP source address. Path messages eventually reach the applications on all receivers; however, they are not looped back to a receiver running in the same application process as the sender. The RSVP process forwards Path messages and replicates them as required by multicast sessions, using routing information it obtains from the appropriate uni-/multicast routing process. The route depends upon the session DestAddress, and for some Braden, Ed., et. al. Standards Track [Page 37] RFC 2205 RSVP September 1997 routing protocols also upon the source (sender's IP) address. The routing information generally includes the list of zero or more outgoing interfaces to which the Path message is 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. Path state for a given session and sender may not necessarily have a unique PHOP or unique incoming interface. There are two cases, corresponding to multicast and unicast sessions. o Multicast Sessions Multicast routing allows a stable distribution tree in which Path messages from the same sender arrive from more than one PHOP, and RSVP must be prepared to maintain all such path state. The RSVP rules for handling this situation are contained in Section 3.9. RSVP must not forward (according to the rules of Section 3.9) Path messages that arrive on an incoming interface different from that provided by routing. o Unicast Sessions For a short period following a unicast route change upstream, a node may receive Path messages from multiple PHOPs for a given (session, sender) pair. The node cannot reliably determine which is the right PHOP, although the node will receive data from only one of the PHOPs at a time. One implementation choice for RSVP is to ignore PHOP in matching unicast past state, and allow the PHOP to flip among the candidates. Another implementation choice is to maintain path state for each PHOP and to send Resv messages upstream towards all such PHOPs. In either case, the situation is a transient; the unused path state will time out or be torn down (because upstream path state timed out). 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. Braden, Ed., et. al. Standards Track [Page 38] RFC 2205 RSVP September 1997 The Resv message format is as follows: ::= [ ] [ ] [ ] [ ... ]