[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 2205

Internet Draft                                            R. Braden, Ed.
Expiration: May 1996                                                 ISI
File: draft-ietf-rsvp-spec-08.txt                               L. Zhang
                                                                    PARC
                                                               S. Berson
                                                                     ISI
                                                               S. Herzog
                                                                     ISI
                                                           J. Wroclaswki
                                                                     MIT



                Resource ReSerVation Protocol (RSVP) --

                   Version 1 Functional Specification



                           November 22, 1995

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
   linebreak "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: May 1996                  [Page 1]


Internet Draft             RSVP Specification              November 1995


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 ............................................18
   2.1 RSVP Messages ...................................................18
   2.2 Port Usage ......................................................20
   2.3 Merging Flowspecs ...............................................21
   2.4 Soft State ......................................................22
   2.5 Teardown ........................................................24
   2.6 Errors and Acknowledgments ......................................25
   2.7 Policy and Security .............................................27
   2.8 Automatic RSVP Tunneling ........................................28
   2.9 Host Model ......................................................28
3. RSVP Functional Specification .......................................30
   3.1 RSVP Message Formats ............................................30
   3.2 Sending RSVP Messages ...........................................42
   3.3 Avoiding RSVP Message Loops .....................................44
   3.4 Local Repair ....................................................48
   3.5 Time Parameters .................................................48
   3.6 Traffic Policing and TTL ........................................50
   3.7 Multihomed Hosts ................................................51
   3.8 Future Compatibility ............................................52
   3.9 RSVP Interfaces .................................................55
4. Message Processing Rules ............................................65
APPENDIX A. Object Definitions .........................................82
APPENDIX B. Error Codes and Values .....................................97
APPENDIX C. UDP Encapsulation ..........................................101
APPENDIX D. Experimental and Open Issues ...............................103



















Braden, Zhang, et al.     Expiration: May 1996                  [Page 2]


Internet Draft             RSVP Specification              November 1995


   What's Changed

   The most important changes in this document from the rsvp-spec-07 draft
   are:


      o    The role and interpretation of the IP Protocol Id is changed.
           The Protocol Id is now a required part of the session
           definition, and filter specs and sender templates now assume
           the Protocol Id from the session rather than stating it
           explicitly.

      o    A "soft" reservation confirmation message is added.

      o    The text states explicitly that an erroneous reservation
           message is not forwarded.  A mechanism to allow a receiver
           more flexible control over forwarding of its messages after
           an admission control failure has not been designed and is
           therefore not included in this version of the protocol.

      o    A terminology confusion is eliminated.  The term "scope" was
           used both for a set of senders and for a set of sender hosts.
           A new term "sender selection" is introduced for the first,
           leaving "scope" for the second.

      o    The FILTER_SPEC object is dropped from a wildcard sender
           selection (WF) style reservation, which now selects "all
           senders" without qualification.

      o    The StyleID byte is dropped from a STYLE object, as
           redundant.

      o    An SE style flow descriptor is simplified to a single
           flowspec.

      o    The IP Router Alert option is now required in PATH, PTEAR,
           and RACK messages.

      o    The TIME_VALUES object is now required in RESV and PATH
           messages; there is no default.

      o    Policing at branch points is now defined in a new section on
           policing (3.6).

      o    A 2-second delay is inserted into local repair.

      o    Merging of SE with WF objects is no longer allowed.




Braden, Zhang, et al.     Expiration: May 1996                  [Page 3]


Internet Draft             RSVP Specification              November 1995


      o    The Rmax end-to-end bound on the refresh rate R is removed,
           since its utility was unclear.

      o    A rule for randomizing refresh timeouts is included.

      o    The suggestion that TCP could be used for carrying RSVP state
           through a congested non-RSVP cloud is removed.

      o    SENDER_TSPECS are now required in PATH| messages.

      o    There are new sections on multihomed hosts (3.7) and future
           compatibility (3.8).  The latter section makes clear that a
           message containing an object with unknown C-Type should be
           rejected.  Any more forgiving treatment seems too complex.

      o    Appendix C on UDP encapsulation is completely changed.

      o    Some text was rearranged in Sections 1 and 2.

































Braden, Zhang, et al.     Expiration: May 1996                  [Page 4]


Internet Draft             RSVP Specification              November 1995


1. Introduction

   This document defines RSVP, a resource reservation setup protocol
   designed for an integrated services Internet [RSVP93,ISInt93].

   On behalf of an application data stream, a host uses the RSVP
   protocol to request a specific quality of service (QoS) from the
   network.  RSVP delivers QoS requests to routers along the path(s) of
   the data stream and maintains router and host 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, a sender is 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, like ICMP, IGMP, and
   routing protocols, RSVP does not transport application data but is
   rather an Internet control protocol.  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.  The
   RSVP daemon consults the local routing protocol(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 only concerns
   with the QoS of those packets that are forwarded by routing.



















Braden, Zhang, et al.     Expiration: May 1996                  [Page 5]


Internet Draft             RSVP Specification              November 1995



            HOST                             ROUTER

 _________________________    RSVP  _____________________________
|                         |    .--------------.                  |
|  _______       ______   |   /    | ________  .   ______        |
| |       |     |      |  |  /     ||        |  . |      |       | RSVP
| |Applic-|     | RSVP <----/      ||Routing |   -> RSVP <---------->
| |  App  <----->daemon|  |        ||Protocol|    |daemon|       |
| |       |     |      |  |        || daemon <---->      |       |
| |_______|     |___.__|  |        ||_ ._____|    |__.__.|       |
|   |               |     |        |   |             |   .       |
|===|===============|=====|        |===|=============|====.======|
| data     .........|     |        |   |  ...........|     .____ |
|   |  ____V_   ____V____ |        |  _V__V_    _____V___ | Adm.||
|   | |Class-| |         ||  data  | |Class-|  |         ||Cntrl||
|   |=> ifier|=> Packet  ============> ifier|==> Packet  ||_____|| data
|     |______| |Scheduler||        | |______|  |Scheduler|===========>
|              |_________||        |           |_________|       |
|_________________________|        |_____________________________|

                  Figure 1: RSVP in Hosts and Routers


   Each router that is capable of resource reservation passes incoming
   data packets through a packet classifier and then queues them as
   necessary in a packet scheduler.  The packet classifier determines
   the route and the QoS class for each packet.  There is a scheduler
   for each interface, to allocate resources for transmission 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 resource reservations [RSVP93].  A QoS request, which
   typically originates from a receiver host application, is passed to
   the local RSVP implementation, shown as a user daemon 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).

   At each node, the RSVP daemon communicates with a local decision



Braden, Zhang, et al.     Expiration: May 1996                  [Page 6]


Internet Draft             RSVP Specification              November 1995


   module, called "admission control", to determine if the router can
   supply the requested QoS.  If the admission control check succeeds,
   the RSVP daemon sets parameters in the packet classifier and
   scheduler to obtain the desired QoS.  If the admission control check
   fails, the RSVP program immediately 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 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.

   o    RSVP provides several reservation models or "styles" (defined
        below) to fit a variety of applications.




Braden, Zhang, et al.     Expiration: May 1996                  [Page 7]


Internet Draft             RSVP Specification              November 1995


   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 for a
      particular 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
      extendible for greater generality, the present version supports
      only UDP/TCP ports as generalized ports.

      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 and
      each receiver Rj may be running in a unique Internet host, or a
      single host may contain multiple senders and/or receivers,
      distinguished by generalized ports.






Braden, Zhang, et al.     Expiration: May 1996                  [Page 8]


Internet Draft             RSVP Specification              November 1995



              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 session definition, specifies 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 flows.

      The flowspec in a reservation request will generally include a
      service class and two sets of numeric parameters: (1) an "Rspec"
      (R for `reserve') that defines the desired QoS, and (2) a "Tspec"
      (T for `traffic') that describes the data flow.  The formats and
      contents of Tspecs and Rspecs are determined by the integrated
      service model [ServTempl95a], and are generally opaque to RSVP.




Braden, Zhang, et al.     Expiration: May 1996                  [Page 9]


Internet Draft             RSVP Specification              November 1995


      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.  However, 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.

      RSVP reservation request messages originate at receivers and are
      passed upstream towards the sender(s).  When a reservation request
      is received at a node, two general actions are taken.

      1.   Make a reservation

           The flowspec and the filter spec are passed to traffic
           control.  Admission control determines the admissibility of
           the request (if it's new); if this test fails, the
           reservation is rejected and RSVP returns an error message to
           the appropriate receiver(s).  If admission control succeeds,
           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
      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; that is, 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



Braden, Zhang, et al.     Expiration: May 1996                 [Page 10]


Internet Draft             RSVP Specification              November 1995


      request propagates as far as the closest point(s) along the sink
      tree to the sender(s) where there is an existing reservation level
      equal or greater than that being requested.  At that point, the
      arriving request will be dropped in favor of the equal or larger
      reservation in place; 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) [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 control options, which are
      collectively called the reservation "style".

      One 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 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-selection
      reservation, each filter spec must match exactly one sender, while
      in a wildcard-selection no filter spec is needed.












Braden, Zhang, et al.     Expiration: May 1996                 [Page 11]


Internet Draft             RSVP Specification              November 1995



           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
           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, Zhang, et al.     Expiration: May 1996                 [Page 12]


Internet Draft             RSVP Specification              November 1995


           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.

           Symbolically, we can represent an SE reservation request by:

           SE( (S1,S2,...){Q} ),


           i.e., a flow descriptor composed of a flowspec Q and a list
           of senders S1, S2, etc.

      Both WF and SE are shared reservations, appropriate for those
      multicast applications whose application-specific constraints 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 appropriate for video signals.




Braden, Zhang, et al.     Expiration: May 1996                 [Page 13]


Internet Draft             RSVP Specification              November 1995


      The RSVP rules disallow merging of shared reservations with
      distinct reservations, since these modes are fundamentally
      incompatible.  They also disallow merging explict 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.

      Other reservation options and styles may be defined in the future
      (see Appendix D.4, for example).

   1.4 Examples of Styles

      This section presents examples of each of the reservation styles
      and show the effects of merging.

      Figure 4 shows schematically 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.

                         ________________
                     (a)|                | (c)
      ( S1 ) ---------->|                |----------> ( R1 )
                        |     Router     |
                     (b)|                | (d)
      ( S2,S3 ) ------->|                |----------> ( R2, R3 )
                        |________________|

                        Figure 4: Router Configuration






Braden, Zhang, et al.     Expiration: May 1996                 [Page 14]


Internet Draft             RSVP Specification              November 1995


      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



      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.






Braden, Zhang, et al.     Expiration: May 1996                 [Page 15]


Internet Draft             RSVP Specification              November 1995



                          |
            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.


                          |
            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



Braden, Zhang, et al.     Expiration: May 1996                 [Page 16]


Internet Draft             RSVP Specification              November 1995


      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).

                         _______________
                     (a)|               | (c)
      ( S1 ) ---------->| >-----------> |----------> ( R1 )
                        |    -          |
                        |      -        |
                     (b)|        -      | (d)
      ( S2,S3 ) ------->| >-------->--> |----------> ( R2, R3 )
                        |_______________|

                       Router Configuration


                             |
               Send          |       Reserve              Receive
                             |
                             |       _______
         WF( *{rB} ) <- (a)  |  (c) | * {B} |   (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: May 1996                 [Page 17]


Internet Draft             RSVP Specification              November 1995


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 2.8).  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 must be 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: May 1996                 [Page 18]


Internet Draft             RSVP Specification              November 1995


      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 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 all links on which the named
           sender is the only source sending to the session.

      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 downstream.

      For protocol efficiency, RSVP also allows multiple sets of
      reservation information for the same session to be "packed" into a
      single RESV message.  Unlike merging, packing preserves
      information.  For simplicity, however, the protocol currently
      prohibits packing reservations of different sessions into the same



Braden, Zhang, et al.     Expiration: May 1996                 [Page 19]


Internet Draft             RSVP Specification              November 1995


      RSVP message.

      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 2.8).  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 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 are defined by 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



Braden, Zhang, et al.     Expiration: May 1996                 [Page 20]


Internet Draft             RSVP Specification              November 1995


           assumption here is that the protocol does not have TCP/UDP-
           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
           Path" error.

   2.3 Merging Flowspecs

      As noted earlier, a single physical interface may receive multiple
      reservation request from different next hops for the same session
      and with the same filter spec, but RSVP should install only one
      reservation on that interface.  This reservation should an
      effective flowspec that is the "maximum" 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
      "maximum" of the flowspecs requested by the different next hops.
      Both cases represent flowspec merging.

      Merging flowspecs requires calculating the "largest" of a set of
      flowspecs, which are otherwise opaque to RSVP.  Since flowspecs
      are multi-dimensional vectors (they contain both Tspec and Rspec
      components, each of which may itself be multi-dimensional),
      generally speaking they cannot be strictly ordered.  However, in
      many cases one can easily determine the "larger" of two flowspecs,
      such as when both request the same bandwidth but one requests a
      tighter delay, or when one of the two requests both a higher
      bandwidth and a tighter delay bound.  When the "larger" of the two
      cannot be determined, RSVP must compute and use a third flowspec
      that is at least as large as each, i.e., a "least upper bound"
      (LUB).  If the two flowspecs are incomparable, their comparison
      will treated as an error.

      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: May 1996                 [Page 21]


Internet Draft             RSVP Specification              November 1995


      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.
           For Tspecs defined by token bucket parameters, this means to
           take the smaller of the bucket size and the rate parameters.

      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 LUB's, and summing Tspecs are outside the
      definition of RSVP [ServTempl95a].  Section 3.9.4 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.  It 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 RSVP
      messages.  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 should be
      an appropriate adjustment in the RSVP state in all nodes along the



Braden, Zhang, et al.     Expiration: May 1996                 [Page 22]


Internet Draft             RSVP Specification              November 1995


      path.

      In steady state, refreshing is performed hop-by-hop to allow
      merging.  If 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: May 1996                 [Page 23]


Internet Draft             RSVP Specification              November 1995


                         ________________
                      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, PTEAR and RTEAR.  A
      PTEAR message travels towards all receivers downstream from its
      point of initiation and deletes path state along the way.  An
      RTEAR message deletes reservation state and travels towards all
      senders upstream from its point of initiation.  A PTEAR (RTEAR)
      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 RTEAR message will prune the reservation state back
      (only) as far as possible.

      Like all other RSVP messages, teardown requests are not delivered



Braden, Zhang, et al.     Expiration: May 1996                 [Page 24]


Internet Draft             RSVP Specification              November 1995


      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 and Acknowledgments

      There are two RSVP error messages, RERR and PERR, and a
      reservation confirmation message RACK.

      There are a number of ways for a syntactically valid reservation
      request to fail at some node along the path, triggering a RERR
      message:

      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.

      In any of these cases, a RERR message is returned to the
      receiver(s) responsible for the erroneous request.  A node may
      also decide to preempt an established reservation.  A preemption
      will trigger a RERR message to all affected receivers.  An error
      message does not modify state in the nodes through which it
      passes.  Therefore, any reservations established downstream of the
      node where the failure occurred will persist until the responsible
      receiver(s) explicitly tear down the state or allow it to time
      out.

      In this version of RSVP, detection of an error in a reservation



Braden, Zhang, et al.     Expiration: May 1996                 [Page 25]


Internet Draft             RSVP Specification              November 1995


      request not only generates a RERR message, it also prevents the
      request from being forwarded further.  This may not always be the
      desirable behavior; for example, a receiver may want a reservation
      request to propagate all the way to the sender despite an
      admission control failure at a particular link along the path.
      However, design of the appropriate mechanism has proved difficult,
      and therefore this version take the simplest approach.

      When admission control fails for a reservation request, any
      existing reservation is left in place.  This prevents a new, very
      large, reservation from disrupting the existing QoS by merging
      with an existing reservation and then failing admission control
      (this has been called the "killer reservation" problem).

      To request a confirmation for its reservation request, a receiver
      Rj includes in the RESV message a confirmation-request object
      containing its 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 an
      confirmation-request object, a RACK 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 RERR or
           a RACK message back to the receiver from each sender.  In
           this case, the RACK message will be an end-to-end
           confirmation.

      o    The receipt of a RACK 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 RACK from
           that node while R1's request has not yet propagated all the
           way to a matching sender and may still fail.  In this case,
           R2 will receive a RACK although there is no end-to-end
           reservation in place.  Furthermore, if the two flowspecs are
           equal, R2 may receive a RACK followed by a RERR.  However, if
           its flowspec is smaller, R2 will receive only the RACK.

      o    Despite these uncertainties, receipt of a RACK indicates a
           high probability that the reservation is in place.

      o    Finally, note that RERR and/or RACK messages may be lost.






Braden, Zhang, et al.     Expiration: May 1996                 [Page 26]


Internet Draft             RSVP Specification              November 1995


   2.7 Policy and Security

      RSVP-mediated QoS requests will result in particular user(s)
      getting preferential access to network resources.  To prevent
      abuse, some form of back pressure on users is likely to be
      required.  This back pressure might take the form of
      administrative rules, or of some form of real or virtual billing
      for the "cost" of a reservation.  The form and contents of such
      back pressure is a matter of administrative policy that may be
      determined independently by each administrative domain in the
      Internet.

      Therefore, admission control at each node is likely to contain a
      policy component in addition to a resource reservation component.
      As input to the policy-based admission decision, RSVP messages may
      carry policy data.  This data may include credentials identifying
      users or user classes, account numbers, limits, quotas, etc.

      To protect the integrity of the policy-based admission 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 are expected to contain an encrypted part and to assume a
      shared secret between neighbors.

      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 an integrity field will allow upstream
      nodes to accept these tokens.

      In summary, different administrative domain 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.






Braden, Zhang, et al.     Expiration: May 1996                 [Page 27]


Internet Draft             RSVP Specification              November 1995


   2.8 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
      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.

      Some interconnection topologies of RSVP and non-RSVP routers can
      cause RESV messages to arrive at the wrong RSVP-capable node, or
      to arrive at the wrong interface at the correct node.  An RSVP
      daemon must be prepared to handle either situation.  When a RESV
      message arrives, its IP destination address should normally be the
      address of one of the local interfaces.  If so, the reservation
      should be made on the addressed interface, even if it is not the
      one on which the message arrived.  If the destination address does
      not match any local interface and the message is not a PATH or
      PTEAR, it should be forwarded without further processing by this
      node.

   2.9 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.




Braden, Zhang, et al.     Expiration: May 1996                 [Page 28]


Internet Draft             RSVP Specification              November 1995


      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.  [LZ: should recommend that a receiver
           wait for at least PATH messages to arrive 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 3.9.1 discusses the general requirements and
      presen








Braden, Zhang, et al.     Expiration: May 1996                 [Page 29]


Internet Draft             RSVP Specification              November 1995


3. RSVP Functional Specification

   3.1 RSVP Message Formats

      An RSVP message consists of a common header followed by a variable
      number of variable-length, typed "objects".  The subsections that
      follow 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 and ordering of object types.  These rules are
      specified using Backus-Naur Form (BNF) augmented with square
      brackets surrounding optional sub-sequences.

      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

              (None defined yet)

         Type: 8 bits

              1 = PATH

              2 = RESV

              3 = PERR

              4 = RERR



Braden, Zhang, et al.     Expiration: May 1996                 [Page 30]


Internet Draft             RSVP Specification              November 1995


              5 = PTEAR

              6 = RTEAR

              7 = RACK

         RSVP Checksum: 16 bits

              A standard TCP/UDP checksum over the contents of the RSVP
              message, with the checksum field replaced by zero.

         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 is the length of the current fragment of
              a larger message.

         Send_TTL: 8 bits

              The IP TTL value with which the message was sent.

         Message ID: 32 bits

              A label shared by all fragments of one message from a
              given next/previous RSVP hop.  An RSVP implementation
              assigns a unique Message ID to each message it sends.

         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 fragment in the
              message.

      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    |



Braden, Zhang, et al.     Expiration: May 1996                 [Page 31]


Internet Draft             RSVP Specification              November 1995


         +-------------+-------------+-------------+-------------+
         |                                                       |
         //                  (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.

         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 3.5.  Required in



Braden, Zhang, et al.     Expiration: May 1996                 [Page 32]


Internet Draft             RSVP Specification              November 1995


                   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

                   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 PERR or RERR message.

              POLICY_DATA

                   Carries information that will allow a local policy
                   module to decide whether an associated reservation is
                   administratively permitted.  May appear in a PATH or
                   RESV message.

              INTEGRITY

                   Contains cryptographic data to authenticate the
                   originating node, and perhaps to verify the contents,



Braden, Zhang, et al.     Expiration: May 1996                 [Page 33]


Internet Draft             RSVP Specification              November 1995


                   of this RSVP message.

              SCOPE

                   An explicit list of sender hosts towards which to
                   forward a message.  May appear in a RESV, RERR, or
                   RTEAR message.

              RESV_CONFIRM

                   Carries the IP address of a receiver that requested a
                   confirmation.  May appear in a RESV or RACK 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 bit 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 3.8.

      3.1.3 Path Message

         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: May 1996                 [Page 34]


Internet Draft             RSVP Specification              November 1995


           <Path Message> ::= <Common Header> <SESSION> <RSVP_HOP>

                                     [ <INTEGRITY> ]  <TIME_VALUES>

                                     <sender descriptor>

           <sender descriptor> ::= <SENDER_TEMPLATE>   <SENDER_TSPEC>

                                    [ <POLICY_DATA> ]   [ <ADSPEC> ]


         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 a POLICY_DATA object
         specifying user credential and accounting information and/or 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 PERR 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, any ADSPEC or
         POLICY_DATA 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



Braden, Zhang, et al.     Expiration: May 1996                 [Page 35]


Internet Draft             RSVP Specification              November 1995


         messages that have arrived on the wrong interface.

      3.1.4 Resv Messages

         RESV messages carry reservation requests hop-by-hop from
         receivers to senders, along the reverse paths of data flows for
         the session.  The IP destination address of a RESV message is
         the unicast address of a previous-hop node, obtained from the
         path state.  The IP source address is an address of the node
         that sent the message.

         The RESV message format is as follows:

           <Resv Message> ::= <Common Header> <SESSION>  <RSVP_HOP>

                                     [ <INTEGRITY> ] <TIME_VALUES>

                                     [ <S_POLICY_DATA> ]

                                     [ <RESV_CONFIRM> ]  [ <SCOPE> ]

                                     <STYLE> <flow descriptor list>

           <S_POLICY_DATA> ::=  <POLICY_DATA>

           <flow descriptor list> ::=  <flow descriptor> |

                              <flow descriptor list>  <flow descriptor>


         The NHOP (i.e., the RSVP_HOP) object contains the IP address of
         the (incoming) interface through which the RESV message is
         sent.  The appearance of a RESV_CONFIRM object signals a
         request for a reservation confirmation and carries the IP
         address of the receiver to which the RACK should be sent.  The
         S_POLICY_DATA object is a POLICY_DATA object that is associated
         with the entire session.  There may also be flow-specific
         POLICY_DATA objects, as described below.

         The BNF above defines a flow descriptor list as simply a list
         of flow descriptors.  The following style-dependent rules
         specify in more detail the composition of a valid flow
         descriptor list for each of the reservation styles.

         o    WF Style:

                <flow descriptor list> ::=  <WF flow descriptor>




Braden, Zhang, et al.     Expiration: May 1996                 [Page 36]


Internet Draft             RSVP Specification              November 1995


                <WF flow descriptor> ::= <FLOWSPEC> [ <F_POLICY_DATA> ]

                <F_POLICY_DATA> ::=  <POLICY_DATA>


         o    FF style:

                <flow descriptor list> ::=   <First FF flow descriptor>  |

                              <flow descriptor list> <FF flow descriptor>

                <First FF flow descriptor> ::=

                           <FLOWSPEC>  [ <F_POLICY_DATA> ] <FILTER_SPEC>

                <FF flow descriptor> ::=

                          [ <FLOWSPEC> ] [ <F_POLICY_DATA> ] <FILTER_SPEC>



              Each elementary FF style request is defined by a single
              (FLOWSPEC, FILTER_SPEC) pair, and multiple such requests
              may be packed into the flow descriptor list of a single
              RESV message.  A FLOWSPEC object can be omitted if it is
              identical to the most recent such object that appeared in
              the list; the first FF flow descriptor must contain a
              FLOWSPEC.

         o    SE style:

                <flow descriptor list> ::= <SE flow descriptor>

                <SE flow descriptor> ::=

                         <FLOWSPEC> [ <F_POLICY_DATA> ] <filter spec list>

                <filter spec list> ::=  <FILTER_SPEC>

                                  |  <filter spec list> <FILTER_SPEC>


              Each elementary SE style request is defined by a single SE
              descriptor, which includes a FLOWSPEC defining the shared
              reservation, optionally a POLICY_DATA object, and a list
              of FILTER_SPEC objects.

         The reservation scope, i.e., the set of senders towards which a



Braden, Zhang, et al.     Expiration: May 1996                 [Page 37]


Internet Draft             RSVP Specification              November 1995


         particular reservation is to be forwarded, is determined as
         follows:

         o    Explicit sender selection

              Match each FILTER_SPEC object against the path state
              created from SENDER_TEMPLATE objects to select a
              particular sender.  An ambiguous match, i.e., a
              FILTER_SPEC matching more than one SENDER_TEMPLATE (e.g.
              through use of a wildcard port), is an error.  Any SCOPE
              object associated with the reservation should be ignored
              in this case.

         o    Wildcard sender selection

              All senders that route to the given outgoing interface
              match this request.  A SCOPE object, if present, contains
              an explicit list of sender IP addresses.  If there is no
              SCOPE object, the scope is determined by the relevant set
              of senders in the path state.  Whenever a RESV message
              with wildcard sender selection is forwarded to more than
              one previous hop, a SCOPE object must be included in the
              message.  See Section 3.3 below.

      3.1.5 Error and Confirmation Messages

         There are three types of RSVP error/confirmation messages.

         o    PERR messages result from PATH messages and travel towards
              senders.  PERR messages are routed hop-by-hop using the
              path state; at each hop, the IP destination address is the
              unicast address of a previous hop.

         o    RERR messages result from RESV messages and travel towards
              the appropriate receivers.  They are routed hop-by-hop
              using the reservation state; at each hop, the IP
              destination address is the unicast address of a next-hop
              node.

         o    RACK messages are sent to (probabilistically) acknowledge
              reservation requests.  A RACK message is sent as the
              result of the appearance of a RESV_CONFIRM object in a
              RESV message, and contains a copy of that RESV_CONFIRM.
              The RACK message is sent to the unicast address of a
              receiver host; the address is obtained from the
              RESV_CONFIRM object.  A RACK message is forwarded to the
              receiver hop-by-hop by (to accommodate the hop-by-hop
              integrity check mechanism).



Braden, Zhang, et al.     Expiration: May 1996                 [Page 38]


Internet Draft             RSVP Specification              November 1995


         Errors encountered while processing error messages must cause
         the error message to be discarded without creating further
         error messages; however, logging of such events may be useful.

         None of these messages modify the state of any node through
         which they pass; instead, they are only reported to the end
         application.


           <PathErr message> ::= <Common Header> <SESSION>

                                       [ <INTEGRITY> ]  <ERROR_SPEC>

                                       <sender descriptor>

           <sender descriptor> ::= (see earlier definition)


           <ResvErr Message> ::= <Common Header> <SESSION>

                                       [ <INTEGRITY> ]  <ERROR_SPEC>

                                       [S_POLICY_DATA]  [ <SCOPE> ]

                                      <STYLE> <error flow descriptor>


           <ResvConf Message> ::= <Common Header> <SESSION>

                                       [ <INTEGRITY> ]  <ERROR_SPEC>

                                       <RESV_CONFIRM>

                                       <STYLE> <flow descriptor list>

           <flow descriptor list> ::= (see earlier definition)


         The RESV_CONFIRM object in a RACK message is a copy of the
         object from the RESV message that triggered the confirmation.

         The following style-dependent rules define the composition of a
         valid error flow descriptor:

         o    WF Style:

                  <error flow descriptor> ::= <WF flow descriptor>




Braden, Zhang, et al.     Expiration: May 1996                 [Page 39]


Internet Draft             RSVP Specification              November 1995


         o    FF style:

                  <error flow descriptor> ::= <FF flow descriptor>


         o    SE style:

                  <error flow descriptor> ::= <SE flow descriptor>


         The ERROR_SPEC object specifies the error and includes the IP
         address of the node that detected the error (Error Node
         Address).  POLICY_DATA objects are included in error messages
         in cases where they may provide relevant information (i.e.,
         when an administrative failure is being reported).  In a RACK
         message, the ERROR_SPEC is used only to carry the IP address of
         the originating node, in the Error Node Address; the error
         specification is a special value that indicates a confirmation.

         When a RESV message contains a list of flow descriptors (e.g.,
         FF style), the RSVP implementation should process each flow
         descritor independently and return a separate RERR message for
         each that is in error.

         Generally speaking, a RERR message should be forwarded towards
         all receivers that may have caused the error being reported.
         More specifically:

         o    The node that detects an error in a reservation request
              sends a RERR message to the next hop from which the
              erroneous reservation came.

              The message must contain the information required to
              define the error and to route the error message.  Routing
              requires at least a STYLE object and one or more
              FILTER_SPEC object(s) from the erroneous RESV message.
              For an admission control failure, for example, the
              erroneous FLOWSPEC must be included.

         o    Succeeding nodes forward the RERR message using their
              local reservation state, to the next hops of reservations
              that match the FILTER_SPEC(s) in the message.  For
              reservations with wildcard scope, there is an additional
              limitation on forwarding RERR messages, to avoid loops;
              see Section 3.3.

         When the error is an admission control failure, a node is
         allowed (but not required) to match the FLOWSPEC as well as the



Braden, Zhang, et al.     Expiration: May 1996                 [Page 40]


Internet Draft             RSVP Specification              November 1995


         FILTER_SPEC object(s), to limit the distribution of a RERR
         message to those receivers that `caused' the error.  Suppose
         that a RERR message contains a FLOWSPEC Qerr that is being
         matched against the FLOWSPEC Qlocal in the local reservation
         state in node N.  Qerr, which originated in a node upstream
         from N, resulted from merging of flowspecs that included
         Qlocal.  Generally, a RERR message can be forwarded to the
         receiver(s) that specified the `biggest' flowspec.  The
         comparison of Qerr against a particular Qlocal to determine
         whether Qlocal qualifies as (one of) the `biggest', may be
         called `de-merging'.  As with merging, the  details of de-
         merging depend upon the service and the FLOWSPEC format, and
         are outside RSVP itself.

         A RERR message that is forwarded should carry the FILTER_SPEC
         from the corresponding reservation state (thus `de-merging' the
         filter spec).

         When a RERR or RACK message reaches a receiver, the STYLE
         object, flow descriptor list, and ERROR_SPEC object (which
         contains the LUB-Used flag) should be delivered to the receiver
         application.  In the case of an Admission Control error, the
         flow descriptor list will contain the FLOWSPEC object that
         failed.  If the LUB-Used flag is off, this should be
         semantically equivalent (but not necessarily identical) to the
         FLOWSPEC originated by this application; otherwise, they may
         differ.

      3.1.6 Teardown Messages

         There are two types of RSVP Teardown message, PTEAR and RTEAR.

         o    A PTEAR message deletes path state (which in turn deletes
              the reservation state for that sender, if there is any)
              and travels towards all receivers that are downstream from
              the point of initiation.  A PTEAR message is routed like a
              PATH message, and its IP destination address is
              DestAddress for the session.

         o    A RTEAR message deletes reservation state and travels
              towards all matching senders upstream from the point of
              teardown initiation.  A RTEAR message is routed in the
              same way as a corresponding RESV message (using the same
              scope rules).  Its IP destination address is the unicast
              address of a previous hop.

             <PathTear Message> ::= <Common Header> <SESSION> <RSVP_HOP>




Braden, Zhang, et al.     Expiration: May 1996                 [Page 41]


Internet Draft             RSVP Specification              November 1995


                                         [ <INTEGRITY> ]

                                         <sender descriptor>

             <sender descriptor> ::= (see earlier definition)

             <ResvTear Message> ::= <Common Header> <SESSION> <RSVP_HOP>

                                         [ <INTEGRITY> ] [ <SCOPE> ]

                                         <STYLE> <flow descriptor list>

             <flow descriptor list> ::= (see earlier definition)


         FLOWSPEC or POLICY_DATA objects in the flow descriptor list of
         a RTEAR message will be ignored and may be omitted.

         Note that, unless it is accidentally dropped along the way, a
         PTEAR message will reach all the receivers down stream from its
         origination.  On the other hand, a RTEAR message will cease to
         be forwarded at the same node where merging suppresses
         forwarding of the corresponding RESV messages.  In each node N
         along the way, if the RTEAR message causes the removal of all
         state for this session, N will create a new teardown message to
         be propagated further upstream; otherwise, the RTEAR message
         may result in the immediate forwarding of a modified RESV
         refresh message.

         Deletion of path state as the result of a PTEAR message or a
         timeout may force adjustments in related reservation state, to
         maintain state consistency in the local node.  The adjustment
         in reservation state depends upon the style.  For example,
         suppose a PTEAR deletes the path state for a sender S.  If the
         style specifies explicit sender selection (FF or SE), delete
         any reservation with a filter spec matching S; otherwise, the
         style is wildcard sender selection (WF) and the reservation
         should be deleted if S is the last sender to the session.
         These reservation changes should not trigger an immediate RESV
         refresh message, since the PTEAR message have already made the
         required changes upstream.  However, at the node in which a
         RTEAR message stops, the change of reservation state may
         trigger a RESV refresh starting at that node.

   3.2 Sending RSVP Messages

      RSVP messages are sent hop-by-hop between RSVP-capable routers as
      "raw" IP packets with protocol number 46.  Raw IP packets are



Braden, Zhang, et al.     Expiration: May 1996                 [Page 42]


Internet Draft             RSVP Specification              November 1995


      intended to be used between an end system and the first/last hop
      router, although it is also possible to encapsulate RSVP messages
      as UDP datagrams for end-system communication, as described in
      Appendix C.  UDP encapsulation is needed for systems that cannot
      do raw network I/O.

      PATH, PTEAR, and RACK messages must be sent with the Router Alert
      IP option [Katz95] in their IP headers.  This option may be used
      by in the fast forwarding path of a high-speed router to detect
      datagrams that require special processing.

      Upon the arrival of an RSVP message M that changes the state, a
      node must forward the modified state immediately.  However, this
      must not trigger sending an message out the interface through
      which M arrived (as could happen if the implementation simply
      triggered an immediate refresh of all state for the session).
      This rule is necessary to prevent packet storms on broadcast LANs.

      An RSVP message must be fragmented when necessary to fit into the
      MTU of the interface through which it will be sent.  All fragments
      of the message should carry the same unique value of the Message
      ID field, as well as appropriate Fragment Offset and MF bits, in
      their common headers.  When an RSVP message arrives, it must be
      reassembled before it can be processed.  The refresh period R can
      be used as an appropriate reassembly timeout time.

      Since RSVP messages are normally generated and sent hop-by-hop,
      using the RSVP-level fragmentation mechanism should avoid further
      fragmentation at the IP level.  However, IP fragmentation may
      still occur when RSVP messages travel through a non-RSVP cloud.
      In case of IP6, which does not support IP fragmentation at
      routers, an RSVP implementation must use Path MTU Discovery or
      hand configuration to obtain an appropriate MTU between adjacent
      RSVP neighbors.

      RSVP recovers from occasional packet losses by its periodic
      refresh mechanism.  Under network overload, however, substantial
      losses of RSVP messages could cause a failure of resource
      reservations.  To control the queueing delay and dropping of RSVP
      packets, routers should be configured to offer them a preferred
      class of service.  If RSVP packets experience noticeable losses
      when crossing a congested non-RSVP cloud, a larger value can be
      used for the timeout factor K (see section 3.5 below).

      Some multicast routing protocols provide for "multicast tunnels",
      which encapsulate multicast packets for transmission through
      routers that do not have multicast capability.  A multicast tunnel
      looks like a logical outgoing interface that is mapped into some



Braden, Zhang, et al.     Expiration: May 1996                 [Page 43]


Internet Draft             RSVP Specification              November 1995


      physical interface.  A multicast routing protocol that supports
      tunnels will describe a route using a list of logical rather than
      physical interfaces.  RSVP can run through multicast tunnels in
      the following manner:

      1.   When a node N forwards a PATH message out a logical outgoing
           interface L, it includes in the message some encoding of the
           identity of L, called the "logical interface handle" or LIH.
           The LIH value is carried in the RSVP_HOP object.

      2.   The next hop node N' stores the LIH value in its path state.

      3.   When N' sends a RESV message to N, it includes the LIH value
           from the path state (again, in the RSVP_HOP object).

      4.   When the RESV message arrives at N, its LIH value provides
           the information necessary to attach the reservation to the
           appropriate logical interface.  Note that N creates and
           interprets the LIH; it is an opaque value to N'.

   3.3 Avoiding RSVP Message Loops

      Forwarding of RSVP messages must avoid looping.  In steady state,
      PATH and RESV messages are forwarded only once per refresh period
      on each hop.  This avoids looping packets, but there is still the
      possibility of an " auto-refresh" loop, clocked by the refresh
      period.  Such auto-refresh loops keep state active "forever", even
      if the end nodes have ceased refreshing it, until either the
      receivers leave the multicast group and/or the senders stop
      sending PATH messages.  On the other hand, error and teardown
      messages are forwarded immediately and are therefore subject to
      looping.

      Consider each message type.

      o    PATH Messages

           PATH messages are forwarded in exactly the same way as IP
           data packets.  Therefore there should be no loops of PATH
           messages, even in a topology with cycles.

      o    PTEAR Messages

           PTEAR messages use the same routing as PATH messages and
           therefore cannot loop.

      o    PERR Messages




Braden, Zhang, et al.     Expiration: May 1996                 [Page 44]


Internet Draft             RSVP Specification              November 1995


           Since PATH messages do not loop, they create path state
           defining a loop-free reverse path to each sender.  PERR
           messages are always directed to particular senders and
           therefore cannot loop.

      o    RESV Messages

           RESV messages directed to particular senders (i.e., with
           explicit sender selection) cannot loop.  However, RESV
           messages with wildcard sender selection (WF style) have a
           potential for auto-refresh looping.

      o    RTEAR Messages

           Although RTEAR messages are routed the same as RESV messages,
           during the second pass around a loop there will be no state
           so any RTEAR message will be dropped.  Hence there is no
           looping problem here.

      o    RERR Messages

           RERR messages for WF style reservations may loop for
           essentially the same reasons that RESV messages loop.

      o    RACK Messages

           RACK messages are forwarded towards a fixed unicast receiver
           address and cannot loop.

      If the topology has no loops, then looping of "wildcard" RESV and
      RERR messages, i.e., messages with wildcard sender selection, can
      be avoided by simply enforcing the rule given earlier: state that
      is received through a particular interface must never be forwarded
      out the same interface.  However, when the topology does have
      cycles, further effort is needed to prevent auto-refresh loops of
      wildcard RESV messages and fast loops of wildcard RERR messages.
      The solution to this problem adopted by this protocol
      specification is for such messages to carry an explicit sender
      address list in a SCOPE object.


      When a RESV message with WF style is to be forwarded to a
      particular previous hop, a new SCOPE object is computed from the
      SCOPE objects that were received in matching RESV messages.  If
      the computed SCOPE object is empty, the message is not forwarded
      to the previous hop; otherwise, the message is sent containing the
      new SCOPE object.  The rules for computing a new SCOPE object for
      a RESV message are as follows:



Braden, Zhang, et al.     Expiration: May 1996                 [Page 45]


Internet Draft             RSVP Specification              November 1995


      1.   The union is formed of the sets of sender IP addresses listed
           in all SCOPE objects in the reservation state for the given
           session.

           If reservation state from some NHOP does not contain a SCOPE
           object, a substitute sender list must be created and included
           in the union.  For a message that arrived on outgoing
           interface OI, the substitute list is the set of senders that
           route to OI.

      2.   Any local senders (i.e., any sender applications on this
           node) are removed from this set.

      3.   If the SCOPE object is to be sent to PHOP, remove from the
           set any senders that did not come from PHOP.

      Figure 11 shows an example of wildcard-scoped (WF style) RESV
      messages.  The address lists within SCOPE objects are shown in
      square brackets.  Note that there may be additional connections
      among the nodes, creating looping topology that is not shown.































Braden, Zhang, et al.     Expiration: May 1996                 [Page 46]


Internet Draft             RSVP Specification              November 1995



                         ________________
                      a |                | c
           R4, S4<----->|     Router     |<-----> R2, S2, S3
                        |                |
                      b |                |
           R1, S1<----->|                |
                        |________________|

          Send on (a):           |    Receive on (c):
                                 |
             <-- WF( [S4] )      |       <-- WF( [S4, S1])
                                 |
          Send on (b):           |
                                 |
             <-- WF( [S1] )      |
                                 |
          Receive on (a):        |    Send on (c):
                                 |
             WF( [S1,S2,S3]) --> |       WF( [S2, S3]) -->
                                 |
          Receive on (b):        |
                                 |
             WF( [S2,S3,S4]) --> |
                                 |

           Figure 11: SCOPE Objects in Wildcard-Scope Reservations


      SCOPE objects are not necessary if the multicast routing uses
      shared trees or if the reservation style has explicit sender
      selection.  Furthermore, attaching a SCOPE object to a reservation
      may be deferred to a node which has more than one previous hop
      upstream.

      The following rules are used for SCOPE objects in RERR messages
      with WF style:

      1.   The node that detected the error initiates an RERR message
           containing a copy of the SCOPE object associated with the
           reservation state or message in error.

      2.   Suppose a wildcard-scoped RERR message arrives at a node with
           a SCOPE object containing the sender host address list L.
           The node forwards the RERR message using the rules of Section
           3.1.5.  However, the RERR message forwarded out OI must
           contain a SCOPE object derived from L by including only those
           senders that route to OI.  If this SCOPE object is empty, the



Braden, Zhang, et al.     Expiration: May 1996                 [Page 47]


Internet Draft             RSVP Specification              November 1995


           RERR message should not be sent out OI.

   3.4 Local Repair

      When a route changes, the next PATH or RESV refresh message will
      establish path or reservation state (respectively) along the new
      route.  To provide fast adaptation to routing changes without the
      overhead of short refresh periods, the local routing protocol
      module can notify the RSVP daemon of route changes for particular
      destinations.  The RSVP daemon should use this information to
      trigger a quick refresh of state for these destinations, using the
      new route.

      More specifically, the rules are as follows:

      o    When routing detects a change of the set of outgoing
           interfaces for destination G, RSVP should wait for a short
           period W, and then send PATH refreshes for all sessions G/*
           (i.e., for any session with destination G, regardless of
           destination port).

           The short wait period before sending PATH refreshes is to
           allow the routing protocol getting settled with the new
           change(s), and the exact value for W should be chosen
           accordingly.  Currently W = 2 sec is suggested; however, this
           value should be configurable per interface.

      o    When a PATH message arrives with a Previous Hop address that
           differs from the one stored in the path state, RSVP should
           send immediate RESV refreshes for that session.

   3.5 Time Parameters

      There are two time parameters relevant to each element of RSVP
      path or reservation state in a node: the refresh period R between
      generation of successive refreshes for the state by the neighbor
      node, and the local state's lifetime L.  Each RSVP RESV or PATH
      message may contain a TIME_VALUES object specifying the R value
      that was used to generate this (refresh) message.  This R value is
      then used to determine the value for L when the state is received
      and stored.  The values for R and L may vary from hop to hop.

      In more detail:

      1.   Floyd and Jacobson [FJ94] have shown that periodic messages
           generated by independent network nodes can become
           synchronized.  This can lead to disruption in network
           services as the periodic messages contend with other network



Braden, Zhang, et al.     Expiration: May 1996                 [Page 48]


Internet Draft             RSVP Specification              November 1995


           traffic for link and forwarding resources.  Since RSVP sends
           periodic refresh messages, it must avoid message
           synchronization and ensure that any synchronization that may
           occur is not stable.

           For this reason, the refresh timer should be randomly set to
           a value in the range [0.5R, 1.5R].

      2.   To avoid premature loss of state, L must satisfy L >= (K +
           0.5)*1.5*R, where K is a small integer.  Then in the worst
           case, K-1 successive messages may be lost without state being
           deleted.  To compute a lifetime L for a collection of state
           with different R values R0, R1, ..., replace R by max(Ri).

           Currently K = 3 is suggested as the default.  However, it may
           be necessary to set a larger K value for hops with high loss
           rate.  K may be set either by manual configuration per
           interface, or by some adaptive technique that has not yet
           been specified.

      3.   Each message that creates state (PATH or RESV message)
           carries a TIME_VALUES object containing the R used to
           generate refreshes; the recipient node uses this R to
           determine L of the stored state.

      4.   R is chosen locally by each node.  If the node does not
           implement local repair of reservations disrupted by route
           changes, a smaller R speeds up adaptation to routing changes,
           while increasing the RSVP overhead.  With local repair, a
           router can be more relaxed about R since the periodic refresh
           becomes only a backstop robustness mechanism.  A node may
           therefore adjust the effective R dynamically to control the
           amount of overhead due to refresh messages.

           The current suggested default for R is 30 seconds.  However,
           the default should be configurable per interface.



      5.   When R is changed dynamically, there is a limit to how fast
           it may increase.  Specifically, the ratio of two successive
           values R2/R1 must not exceed 1 + Slew.Max.

           Currently, Slew.Max is 0.30.  With K = 3, one packet may be
           lost without state timeout while R is increasing 30 percent
           per refresh cycle.

      6.   To improve robustness, a node may temporarily send refreshes



Braden, Zhang, et al.     Expiration: May 1996                 [Page 49]


Internet Draft             RSVP Specification              November 1995


           more often than R after a state change (including initial
           state establishment).

      7.   The values of Rdef, K, and Slew.Max used in an implementation
           should be easily modifiable per interface, as experience may
           lead to different values.  The possibility of dynamically
           adapting K and/or Slew.Max in response to measured loss rates
           is for future study.

   3.6 Traffic Policing and TTL

      RSVP is required to compute and pass several service-related flags
      to traffic control: policing flags and a non-RSVP flag.

      Some QoS services may require traffic policing at some or all of
      (1) the edge of the network, (2) a merging point for data from
      multiple senders, and/or (3) a branch point where traffic flow
      from upstream may be greater than the downstream reservation.
      RSVP knows where such points occur and must so indicate to the
      traffic control mechanism.  On the other hand, RSVP does not
      interpret the service embodied in the flowspec and therefore does
      not know whether policing will actually be applied in any
      particular case.

      The RSVP daemon passes to traffic control a separate policing flag
      for each of these three situations.

      o    E_Police_Flag -- Entry Policing

           This flag is set in the first-hop RSVP node that implements
           traffic control (and is therefore capable of policing).

           For example, sender hosts must implement RSVP but currently
           many of them do not implement traffic control.  In this case,
           the E_Police_Flag should be off in the sender host, and it
           should only be set on when the first hop capable of traffic
           control is reached.  This is controlled by the E_Police flag
           in SESSION objects.

      o    M_Police_Flag -- Merge Policing

           This flag should be set on for a reservation using a shared
           style (WF or SE) when flows from more than one sender are
           being merged.

      o    B_Police_Flag -- Branch Policing

           This flag should be set on when the flowspec being installed



Braden, Zhang, et al.     Expiration: May 1996                 [Page 50]


Internet Draft             RSVP Specification              November 1995


           is smaller than, or incomparable to, a FLOWSPEC in place on
           any other interface, for the same FILTER_SPEC and SESSION.

      RSVP must also detect and report to receivers the presence of
      non-RSVP hops in the path.  For this purpose, an RSVP daemon must
      place into each PATH message that it sends the value of the IP TTL
      with which the message was sent.  The RSVP-capable node that
      receives this message compares this field to the TTL with which
      the message was actually received, and if they differ it turns on
      the Non_RSVP flag.  This flag is carried forward to receivers in
      the ADSPEC [??].

   3.7 Multihomed Hosts

      Accommodating multihomed hosts requires some special rules in
      RSVP.  We use the term `multihomed host' to cover both hosts (end
      systems) with more than one network interface [could ref. section
      3.3.4 of RFC-1122], and routers that are supporting local
      application programs.

      An application executing on a multihomed host may explicitly
      specify which interface any given flow will use for sending and/or
      for receiving data packets, to override the system-specified
      default interface.  The RSVP daemon must be aware of the default,
      and if an application sets a specific interface, it must also pass
      that information to RSVP.

      o    Sending Data

           A sender application uses an API call (SENDER in Section
           3.9.1) to declare to RSVP the characteristics of the data
           flow it will originate.  This call may optionally include the
           local IP address of the sender. If it is set by the
           application, this parameter must be the interface address for
           sending the data packets; otherwise, the system default
           interface is implied.

           The RSVP daemon on the host then sends PATH messages for this
           application out the specified interface (only).

      o    Making Reservations

           A receiver application uses an API call (called RESERVE in
           Section 3.9.1) to request a reservation from RSVP.  This call
           may optionally include the local IP address of the receiver,
           i.e., the interface address for receiving data packets.  In
           the case of multicast sessions, this is the interface on
           which the group has been joined.  If the parameter is



Braden, Zhang, et al.     Expiration: May 1996                 [Page 51]


Internet Draft             RSVP Specification              November 1995


           omitted, the system default interface is used.

           In general, the RSVP daemon should send RESV messages for
           application out the specified interface.  However, when the
           application is executing on a router and the session is
           multicast, a more complex situation arises.   Suppose in this
           case that a receiver application joins the group on an
           interface Iapp that differs from Isp, the shortest-path
           interface to the sender.  Then there are two possible ways
           for multicast routing to deliver data packets to the
           application.  The RSVP daemon must determine which case holds
           by examining the path state, to decide which incoming
           interface to use for sending RESV messages.

           1.   The multicast routing protocol may create a separate
                branch of the multicast distribution `tree' to deliver
                to Iapp.  In this case, there will be path state for
                both Isp and Iapp.  The path state on Iapp should only
                match a reservation from the local application; it must
                be marked "Local_only" by the RSVP daemon.  If
                "Local_only" path state for Iapp exists, the RESV
                message should be sent out Iapp.

                Note that it is possible for the path state blocks for
                Isp and Iapp to have the same next hop, if there is an
                intervening non-RSVP cloud.

           2.   The multicast routing protocol may forward data within
                the router from Isp to Iapp.  In this case, Iapp will
                appear in the list of outgoing interfaces of the path
                state for Isp, and the RESV message should be sent out
                Isp.

   3.8 Future Compatibility

      We may expect that in the future new object C-Types will be
      defined for existing object classes, and perhaps new object
      classes will be defined.  It will be desirable to employ such new
      objects within the Internet using older implementations that do
      not recognize them.  Unfortunately, this is only possible to a
      limited degree with reasonable complexity.  The rules are as
      follows.

      1.   Unknown Class

           There are two possible ways that an RSVP implementation can
           treat an object with unknown class.  This choice is
           determined by the high-order bit of the Class-Num octet, as



Braden, Zhang, et al.     Expiration: May 1996                 [Page 52]


Internet Draft             RSVP Specification              November 1995


           follows.

           o    Class-Num >= 128

                In this case, the entire message should be rejected and
                an "Unknown Object Class" error returned.

           o    Class-Num < 128

                In this case, the node should ignore the object but
                forward it, unexamined and unmodified, in all messages
                resulting from the state contained in this message.

                For example, suppose that a RESV message that is
                received contains an object of unknown class.  Such an
                object should be saved in the reservation state without
                further examination; however, only the latest object
                with a given (unknown class, C-Type) pair should be
                saved.  When a RESV message is forwarded, it should
                include copies of such saved unknown-class objects from
                all reservations that are merged to form the new RESV
                message.

                Note that objects with unknown class cannot be merged;
                however, unmerged objects may be forwarded until they
                reach a node that knows how to merge them.  Forwarding
                objects with unknown class enables incremental
                deployment of new objects; however, the scaling
                limitations of doing so must be carefully examined
                before a new object class is deployed with Class-Num <
                128.

           These rules should be considered when any new Class-Num is
           defined.

      2.   Unknown C-Type for Known Class

           One might expect the known Class-Num to provide information
           that could allow intelligent handling of such an object.
           However, in practice such class-dependent handling is
           complex, and in many cases it is not useful.

           Generally, the appearance of an object with unknown C-Type
           should result in rejection of the entire message and
           generation of an error message (RERR or PERR as appropriate).
           The error message will include the Class-Num and C-Type that
           failed (see Appendix B); the end system that originated the
           failed message may be able to use this information to retry



Braden, Zhang, et al.     Expiration: May 1996                 [Page 53]


Internet Draft             RSVP Specification              November 1995


           the request using a different C-Type object, repeating this
           process until it runs out of alternatives or succeeds.

           Objects of certain classes (FLOWSPEC, ADSPEC, and
           POLICY_DATA) are opaque to RSVP, which simply hands them to
           traffic control or policy modules.  Depending upon its
           internal rules, either of the latter modules may reject a C-
           Type and inform the RSVP daemon; RSVP should then reject the
           message and send an error, as described in the previous
           paragraph.









































Braden, Zhang, et al.     Expiration: May 1996                 [Page 54]


Internet Draft             RSVP Specification              November 1995


   3.9 RSVP Interfaces

      RSVP on a router has interfaces to routing and to traffic control.
      RSVP on a host has an interface to applications (i.e, an API) and
      also an interface to traffic control (if it exists on the host).

      3.9.1 Application/RSVP Interface

         This section describes a generic interface between an
         application and an RSVP control process.  The details of a real
         interface may be operating-system dependent; the following can
         only suggest the basic functions to be performed.  Some of
         these calls cause information to be returned asynchronously.

         o    Register Session

              Call: SESSION( DestAddress , ProtocolId, DstPort ,

                         [ , SESSION_object ]

                         [ , Upcall_Proc_addr ] )  -> Session-id


              This call initiates RSVP processing for a session, defined
              by DestAddress together with ProtocolId and possibly a
              port number DstPort.  If successful, the SESSION call
              returns immediately with a local session identifier
              Session-id, which may be used in subsequent calls.

              The Upcall_Proc_addr parameter defines the address of an
              upcall procedure to receive asynchronous error or event
              notification; see below.  The SESSION_object parameter is
              included as an escape mechanism to support some more
              general definition of the session ("generalized
              destination port"), should that be necessary in the
              future.  Normally SESSION_object will be omitted.

         o    Define Sender

              Call: SENDER( Session-id,

                         [ , Source_Address ]  [ , Source_Port ]

                         [ , Sender_Template ]

                         [ , Sender_Tspec ]   [ , Data_TTL ]

                         [ , Sender_Policy_Data ] )



Braden, Zhang, et al.     Expiration: May 1996                 [Page 55]


Internet Draft             RSVP Specification              November 1995


              A sender uses this call to define, or to modify the
              definition of, the attributes of the data stream.  The
              first SENDER call for the session registered as `Session-
              id' will cause RSVP to begin sending PATH messages for
              this session; later calls will modify the path
              information.

              The SENDER parameters are interpreted as follows:

              -    Source_Address

                   This is the address of the interface from which the
                   data will be sent.  If it is omitted, a default
                   interface will be used.  This parameter is needed on
                   a multihomed sender host.

              -    Source_Port

                   This is the UDP/TCP port from which the data will be
                   sent.  If it is omitted or zero, the port is "wild"
                   and can match any port in a FILTER_SPEC.

              -    Sender_Template

                   This parameter is included as an escape mechanism to
                   support a more general definition of the sender
                   ("generalized source port").  Normally this parameter
                   may be omitted.

              -    Sender_Tspec

                   This optional parameter describes the traffic flow to
                   be sent.  It may be included to prevent over-
                   reservation on the initial hops.

              -    Data_TTL

                   This is the (non-default) IP Time-To-Live parameter
                   that is being supplied on the data packets.  It is
                   needed to ensure that Path messages do not have a
                   scope larger than multicast data packets.

              -    Sender_Policy_Data

                   This optional parameter passes policy data for the
                   sender.  This data may be supplied by a system
                   service, with the application treating it as opaque.




Braden, Zhang, et al.     Expiration: May 1996                 [Page 56]


Internet Draft             RSVP Specification              November 1995


         o    Reserve

              Call: RESERVE( session-id, [ receiver_address , ]

                        [ ACK_flag, ] style, style-dependent-parms )


              A receiver uses this call to make or to modify a resource
              reservation for the session registered as `session-id'.
              The first RESERVE call will initiate the periodic
              transmission of RESV messages.  A later RESERVE call may
              be given to modify the parameters of the earlier call (but
              note that changing existing reservations may result in
              admission control failure).

              The optional `receiver_address' parameter may be used by a
              receiver on a multihomed host (or router); it is the IP
              address of one of the node's interfaces.  The ACK_flag
              should be set on if a reservation ACK is desired, off
              otherwise.  The `style' parameter indicates the
              reservation style.  The rest of the parameters depend upon
              the style, but generally these will include appropriate
              flowspecs, filter specs, and possibly receiver policy data
              objects.

              The RESERVE call returns immediately.  Following a RESERVE
              call, an asynchronous ERROR/EVENT upcall may occur at any
              time.

         o    Release

              Call: RELEASE( session-id )

              This call removes RSVP state for the session specified by
              session-id.  The node then sends appropriate teardown
              messages and ceases sending refreshes for this session-id.

         o    Error/Event Upcalls

              Upcall: <Upcall_Proc>( ) -> session-id, Info_type,

                            [ Error_code , Error_value ,

                                 Error_Node , LUB-Used, ]

                            List_count, [ Flowspec_list,]

                            [ Filter_spec_list, ] [ Advert_list, ]



Braden, Zhang, et al.     Expiration: May 1996                 [Page 57]


Internet Draft             RSVP Specification              November 1995


                            [ Policy_data ]


              Here "Upcall_Proc" represents the upcall procedure whose
              address was supplied in the SESSION call.

              This upcall may occur asynchronously at any time after a
              SESSION call and before a RELEASE call, to indicate an
              error or an event.  Currently there are five upcall types,
              distinguished by the Info_type parameter:

              1.   Info_type = Path Event

                   A Path Event upcall results from receipt of the first
                   PATH message for this session, indicating to a
                   receiver application that there is at least one
                   active sender.

                   This upcall provides synchronizing information to the
                   receiver application, and it may also provide
                   parallel lists of senders (in Filter_spec_list),
                   traffic descriptions (in Flowspec_list), and service
                   advertisements (in Advert_list).  `List_count' will
                   be the number in each list;  where these objects are
                   missing, corresponding null objects must appear.  The
                   Error_code, Error_value, LUB-Used flag, and
                   Policy_data parameters will be undefined in this
                   upcall.

              2.   Info_type = Resv Event

                   A Resv Event upcall is triggered by the receipt of
                   the first reservation message or by modification of a
                   previous reservation state, for this session.

                   `List_count' will be 1, and Flowspec_list will
                   contain one FLOWSPEC, the effective QoS that would be
                   applicable to the application itself.
                   Filter_spec_list and Advert_list will contain one
                   NULL object.  The Error_code, Error_value, LUB-Used
                   flag, and Policy_data parameters will be undefined in
                   this upcall.

              3.   Info_type = Path Error

                   An Path Error event indicates an error in sender
                   information that was specified in a SENDER call.




Braden, Zhang, et al.     Expiration: May 1996                 [Page 58]


Internet Draft             RSVP Specification              November 1995


                   The Error_code parameter will define the error, and
                   Error_value may supply some additional (perhaps
                   system-specific) data about the error.  The
                   Error_Node parameter will specify the IP address of
                   the node that detected the error.

                   `List_count' will be 1, and Filter_spec_list will
                   contain the Sender_Template supplied in the SENDER
                   call; Flow_Spec_list and Advert_list will each
                   contain one NULL object.  The Policy_data parameter
                   will contain any POLICY_DATA objects in the PERR
                   message.

              4.   Info_type = Resv Error/Confirmation

                   An Resv Error/Confirmation event indicates an error
                   in a reservation message to which this application
                   contributed, or the receipt of a RACK message.  The
                   Error_code parameter will define the error or
                   confirmation.  For an error, Error_value may supply
                   some additional (perhaps system-specific) data.  The
                   Error_Node parameter will specify the IP address of
                   the node that detected the event being reported.

                   Filter_spec_list and Flowspec_list will contain the
                   FILTER_SPEC and FLOWSPEC objects from the error flow
                   descriptor (see Section 3.1.5).  List_count will
                   specify the number of FILTER_SPECS in
                   Filter_spec_list, while there will be one FLOWSPEC in
                   Flowspec_list.  For an error, the Policy_data
                   parameter will contain any POLICY_DATA objects in the
                   RERR message.




              Although RSVP messages indicating path or resv events may
              be received periodically, the API should make the
              corresponding asynchronous upcall to the application only
              on the first occurrence or when the information to be
              reported changes.  All error and confirmation events
              should be reported to the application.


      3.9.2 RSVP/Traffic Control Interface

         In an RSVP-capable node, enhanced QoS is achieved by a group of
         inter-related traffic control functions:  a packet classifier,



Braden, Zhang, et al.     Expiration: May 1996                 [Page 59]


Internet Draft             RSVP Specification              November 1995


         an admission control module, and a packet scheduler.  This
         section describes a generic RSVP interface to traffic control.

         o    Make a Reservation

              Call: Rhandle =  TC_AddFlowspec( Interface, TC_Flowspec,

                                     TC_Tspec, E_Police_Flag,

                                     M_Police_Flag, B_Police_Flag )


              The TC_Flowspec parameter defines the desired effective
              QoS to admission control; its value is computed as the
              maximum over the flowspecs of different next hops (see the
              Compare_Flowspecs call below).  It contains the effective
              reservation Tspec Resv_Te (although the RSVP daemon itself
              has no means to extract the Tspec).  The TC_Tspec
              parameter defines the effective sender Tspec Path_Te (see
              Section 2.3).  We assume that traffic control takes the
              min of Resv_Te and Path_Te (see step (4) in Section 2.3).

              E_Police_Flag, M_Police_Flag, and B_Police_Flag are
              Boolean parameters whose values should be set as described
              in Section 3.6.

              The TC_AddFlowspec call returns an error code if Flowspec
              is malformed or if the requested resources are
              unavailable.  Otherwise, it establishes a new reservation
              channel corresponding to Rhandle.  It returns the opaque
              number Rhandle for subsequent references to this
              reservation.

         o    Modify Reservation

              Call: TC_ModFlowspec( Rhandle, new_Flowspec,

                                    Sender_Tspec,  E_Police_flag,

                                     M_Police_Flag, B_Police_Flag )


              This call can modify an existing reservation.  If
              new_Flowspec is included, it is passed to Admission
              Control; if it is rejected, the current flowspec is left
              in force.  The corresponding filter specs, if any, are not
              affected.  The other parameters are defined as in
              TC_AddFlowspec.



Braden, Zhang, et al.     Expiration: May 1996                 [Page 60]


Internet Draft             RSVP Specification              November 1995


         o    Delete Flowspec

              Call: TC_DelFlowspec( Rhandle )


              This call will delete an existing reservation, including
              the flowspec and all associated filter specs.

         o    Add Filter Spec

              Call: FHandle = TC_AddFilter( Rhandle, Session , FilterSpec )


              This call is used to associate an additional filter spec
              with the reservation specified by the given Rhandle,
              following a successful TC_AddFlowspec call.  This call
              returns a filter handle FHandle.

         o    Delete Filter Spec

              Call: TC_DelFilter( FHandle )


              This call is used to remove a specific filter, specified
              by FHandle.

         o    OPWA Update

              Call: TC_Advertise( interface, Adspec,

                              [ , Non_RSVP_flag ] ) -> New_Adspec


              This call is used for OPWA to compute the outgoing
              advertisement New_Adspec for a specified interface.

         o    Preemption Upcall

              Upcall: TC_Preempt() -> RHandle, Reason_code


              In order to grant a new reservation request, the admission
              control and/or policy modules may be allowed to preempt an
              existing reservation.  This might be reflected in an
              upcall to RSVP, passing the RHandle of the preempted
              reservation, and some indication of the reason.





Braden, Zhang, et al.     Expiration: May 1996                 [Page 61]


Internet Draft             RSVP Specification              November 1995


      3.9.3 RSVP/Routing Interface

         An RSVP implementation needs the following support from the
         packet forwarding and routing mechanisms of the node.

         o    Promiscuous Receive Mode for RSVP Messages

              Any packet received for IP protocol 46 must be diverted to
              the RSVP program for processing, without being forwarded.
              On a router, the identity of the interface, real or
              virtual, on which it is received must also be available to
              the RSVP daemon.

         o    Route Query

              To forward PATH and PTEAR messages, an RSVP daemon must be
              able to query the routing daemon(s) for routes.

                 Ucast_Route_Query( [ SrcAddress, ] DestAddress, Notify_flag )

                                        -> OutInterface

                 Mcast_Route_Query( [ SrcAddress, ] DestAddress, Notify_flag )

                                        -> [ IncInterface, ] OutInterface_list


              Depending upon the routing protocol, the query may or may
              not depend upon SrcAddress, i.e., upon the sender host IP
              address, which is also the IP source address of the
              message.  Here IncInterface is the interface through which
              the packet is expected to arrive; some multicast routing
              protocols may not provide it.

              If the Notify_flag is True, routing will save state
              necessary to issue unsolicited route change notification
              callbacks (see below) whenever the specified route
              changes.  Such callbacks will be enabled until routing
              receives a route query call with the Notify_Flag set
              False.

              A multicast route query may return an empty
              OutInterface_list if there are no receivers downstream of
              a particular router.  A route query may also return a `No
              such route' error, probably as a result of a transient
              inconsistency in the routing (since a PATH or PTEAR
              message for the requested route did arrive at this node).
              In either case, the local state should be updated as



Braden, Zhang, et al.     Expiration: May 1996                 [Page 62]


Internet Draft             RSVP Specification              November 1995


              requested by the message, although it cannot be forwarded
              further.  Updating local state will make path state
              available immediately for a new local receiver, or it will
              tear down path state immediately.

         o    Route Change Notification

              If requested by a route query with the Notify_flag True,
              the routing daemon may provide an asynchronous callback to
              the RSVP daemon that a specified route has changed.

                 Ucast_Route_Change( ) -> DestAddress, OutInterface

                 Mcast_Route_Change( ) -> [ SrcAddress, ] DestAddress,

                               [ IncInterface, ] OutInterface_list


         o    Outgoing Link Specification

              RSVP must be able to force a (multicast) datagram to be
              sent on a specific outgoing virtual link, bypassing the
              normal routing mechanism.  A virtual link may be a real
              outgoing link or a multicast tunnel.  Outgoing link
              specification is necessary to send different versions of
              an outgoing PATH message on different interfaces.  It is
              also necessary in some cases to avoid routing loops.

         o    Source Address Specification

              RSVP must be able to specify the IP source address to be
              used when sending PATH messages.

         o    Interface List Discovery

              RSVP must be able to learn what real and virtual
              interfaces are active, with their IP addresses.

      3.9.4 Service-Dependent Manipulations

         Flowspecs, Tspecs, and Adspecs are opaque objects to RSVP;
         their contents are defined in service specification documents.
         In order to manipulate these objects, RSVP daemon must have
         available to it the following service-dependent routines.

         o    Compare Flowspecs





Braden, Zhang, et al.     Expiration: May 1996                 [Page 63]


Internet Draft             RSVP Specification              November 1995


                 Compare_Flowspecs( Flowspec_1, Flowspec_2 ) -> result_code


              The possible result_codes indicate: flowspecs are equal,
              Flowspec_1 is greater, Flowspec_2 is greater, flowspecs
              are incomparable but LUB can be computed, or flowspecs are
              incompatible.

              Note that comparing two flowspecs implicitly compares the
              Tspecs that are contained.  Although the RSVP daemon
              cannot itself parse a flowspec to extract the Tspec, it
              can use the Compare_Flowspecs call to implicitly calculate
              Resv_Te (see Section 2.3).

         o    Compute LUB of Flowspecs


                 LUB_of_Flowspecs( Flowspec_1, Flowspec_2 ) ->
                   Flowspec_LUB


         o    Compare Tspecs


                 Compare_Tspecs( Tspec_1, Tspec_2 ) -> result_code


              The possible result_codes indicate: Tspecs are equal, or
              Tspecs are unequal.

         o    Sum Tspecs


                 Sum_Tspecs( Tspec_1, Tspec_2 ) -> Tspec_sum


              This call is used to compute Path_Te (see Section 2.3).














Braden, Zhang, et al.     Expiration: May 1996                 [Page 64]


Internet Draft             RSVP Specification              November 1995


4. Message Processing Rules

   This section provides a generic description of the rules for RSVP
   operation.  It is intended to outline a set of algorithms that will
   accomplish the needed function.  An actual implementation may use
   different but equivalent algorithms.  This section assumes the
   generic interface calls defined in Section 3.9 and the following data
   structures.  An actual implementation may use additional or different
   data structures and interfaces.

   [NOTE: This section is always the last to be updated when changes are
   made, and it is neither correct nor complete at the present time.
   Therefore, when this section disagrees with the rest of the text, you
   should believe the rest of the text!]

   o    PSB -- Path State Block

        Each PSB holds path state for a particular (session, sender)
        pair, defined by SESSION and SENDER_TEMPLATE objects,
        respectively, received in a PATH message.

        PSB contents include the following values from a PATH message:

        -    The previous hop IP address from a PHOP object (required)

        -    LIH, the Logical Interface Handle from the previous hop,
             from a PHOP object (required).

        -    The remaining IP TTL (required)

        -    SENDER_TSPEC (required)

        -    POLICY_DATA and/or ADSPEC objects (optional)

        -    Non_RSVP flag (required); see Section 3.6.

        In addition, the PSB contains the following information provided
        by routing: OutInterface_list, the list of outgoing interfaces
        for this (sender, destination), and IncInterface, the expected
        incoming interface.  For a unicast destination,
        OutInterface_list contains one entry and IncInterface is
        undefined.

   o    RSB -- Reservation State Block

        Each RSB holds a reservation request that arrived in a
        particular RESV message, corresponding to the triple:  (session,
        next hop, filter_spec_list).  Here "filter_spec_list" may be a



Braden, Zhang, et al.     Expiration: May 1996                 [Page 65]


Internet Draft             RSVP Specification              November 1995


        list of FILTER_SPECs (for SE style), a single FILTER_SPEC (FF
        style), or empty (WF style).  We use the symbol "FILTER_SPEC*"
        to indicate such a FILTER_SPEC list.

        RSB contents include:

        -    The outgoing (logical) interface OI on which the
             reservation is to be made or has been made (required).

        -    FLOWSPEC*, list of FLOWSPEC objects (required)

        -    The style (required)

        -    A POLICY_DATA object (optional)

        -    A SCOPE object (optional, depending on style)

        -    A RESV_CONFIRM object (optional)

   o    TCSB -- Traffic Control State Block

        TCSB's hold the reservation specifications that have been handed
        to traffic control for specific outgoing interfaces.  In
        general, information in TCSB's is derived from RSB's for the
        same outgoing interface.  Each TCSB defines a single reservation
        for a particular triple: (session, OI, filter_spec_list).   TCSB
        contents include:

        -    TC_Flowspec, the effective flowspec, i.e., the maximum over
             the corresponding FLOWSPEC values from matching RSB's.
             TC_Flowspec is passed to traffic control to make the actual
             reservation.  The Tspec part of TC_Flowspec is the
             effective reservation Tspec Resv_Te (Section 2.3).

        -    TC_Tspec, equal to the effective sender Tspec Path_Te.

        -    Police Flags

             The flags E_Police_Flag, M_Police_Flag,and B_Police_Flag
             are defined in Section 3.6.

        -    Rhandle, F_Handle_list

             Handles returned by the traffic control interface,
             corresponding to the reservation (flowspec) and to the list
             of filter specs.

   Boolean flags Path_Refresh_Needed, Resv_Refresh_Needed, and



Braden, Zhang, et al.     Expiration: May 1996                 [Page 66]


Internet Draft             RSVP Specification              November 1995


   Tear_Needed will also be used in this section.

   [LZ: It might be very helpful to have a short section to summarize
   the management of all the timers.]

   MESSAGE ARRIVES

   Verify version number and checksum fields of common header, and
   discard message if any mismatch is found.

   Reassemble a fragmented message.

   Parse the sequence of objects in the message to verify the length
   field of the common header; discard message if there is a mismatch.

   If the message type is not PATH or PTEAR and if the IP destination
   address does not match any of the addresses of the local interfaces,
   then forward the message to IP destination address and return.

   Verify the INTEGRITY object, if any.  If the check fails, discard the
   message and return.

   Further processing depends upon message type.

   PATH MESSAGE ARRIVES

        Process the sender descriptor object sequence in the message as
        follows.  The flags Path_Refresh_Needed and Resv_Refresh_Needed
        flags are initially off.

        o    If there is a POLICY_DATA object, verify it; if it is
             unacceptable, build and send a "Administrative Rejection"
             PERR message, drop the PATH message, and return.

        o    If the DstPort in the SESSION object is zero but the
             SrcPort in the SENDER_TEMPLATE object is non-zero, build a
             send a "Conflicting Src Port"  PERR message, drop the PATH
             message, and return.

        o    Search for a path state block (PSB) whose (SESSION,
             SENDER_TEMPLATE) pair matches the corresponding objects in
             the message, considering any wildcard ports.

        o    If, during the PSB search, a PSB is found whose session
             matches the DestAddress and Protocol Id fields of the
             received SESSION object, but the DstPorts differ and one is
             zero, then build and send a "Conflicting Dst Port" PERR
             message, drop the PATH message, and return.



Braden, Zhang, et al.     Expiration: May 1996                 [Page 67]


Internet Draft             RSVP Specification              November 1995


        o    If, during the PSB search, a PSB is found with a matching
             sender host (in SENDER_TEMPLATE) but the SrcPorts differ
             and one is zero, then build and send a "Ambiguous Path"
             PERR message, drop the PATH message, and return.

        o    If there was no matching PSB, then:

             1.   Create a new PSB.

             2.   Call the appropriate Route_Query routine, using
                  DestAddress from SESSION and (for multicast routing)
                  SrcAddress from SENDER_TEMPLATE.  Store the values of
                  OutInterface_list and IncInterface into the PSB.
                  However, if the sender is from the local API, then
                  instead of invoking routing, set OutInterface_List to
                  the single interface whose address matches the sender
                  address; IncInterface is undefined in this case.

             3.   If IncInterface is defined and if a multicast message
                  arrived on an interface different from IncInterface,
                  drop the message and return.

             4.   Set a cleanup timer for the PSB.  If this is the first
                  PSB for the session, set a refresh timer for the
                  session.

             5.   Copy contents of the SESSION, SENDER_TEMPLATE,
                  SENDER_TSPEC, and PHOP (IP address and LIH) objects
                  into the PSB.  Store the received TTL into the PSB.
                  Copy into the PSB either of the following objects that
                  are present: POLICY_DATA and ADSPEC.

             6.   Turn on the Path_Refresh_Needed flag.

        o    Otherwise (there is a matching PSB and there is no dest
             port conflict):

             1.   If there is no route change notification in place,
                  call the appropriate Route_Query routine using
                  DestAddress from SESSION and (for multicast routing)
                  SrcAddress from SENDER_TEMPLATE.

                  -    If the OutInterface_list that is returned differs
                       from that in the PSB, execute the PATH LOCAL
                       REPAIR event sequence below.

                  -    If a multicast message arrived on an interface
                       different from IncInterface, drop the message and



Braden, Zhang, et al.     Expiration: May 1996                 [Page 68]


Internet Draft             RSVP Specification              November 1995


                       return.

             2.   If the PHOP IP address, the LIH, or SENDER_TSPEC
                  differs between the message and the PSB, copy the new
                  value into the PSB, execute the RESV REFRESH event
                  sequence for the sender defined by the PSB, and turn
                  on the Path_Refresh_Needed flag.

                  [LZ: [When] should ADSPEC change trigger a refresh?]

                  However, if the PATH message being processed came from
                  a local application and if there is reservation state
                  for this session, then make a Resv Event upcall to
                  that application instead of executing the RESV REFRESH
                  sequence.

                      Call: <Upcall_Proc>( session-id, Resv Event, 1,
                                  {Flowspec}, NULL, NULL, NULL )


             3.   Restart the cleanup timer.

        o    If the message arrived with a TTL different from Send_TTL
             in the RSVP common header, set the Non_RSVP flag on in the
             PSB.

        o    If the Path_Refresh_Needed flag is now set then:

             1.   If this PATH message came from a network interface and
                  not from a local application, make a Path Event upcall
                  for each local application for this session:

                      Call: <Upcall_Proc>( session-id, Path Event, 1,
                                  {SENDER_TSPEC}, {SENDER_TEMPLATE},
                                  {ADSPEC}, {POLICY_DATA} )


             2.   Execute the PATH REFRESH event sequence (below) for
                  the sender defined by the PSB.


   PATH TEAR MESSAGE ARRIVES

        o    Search for a PSB whose (SESSION, SENDER_TEMPLATE) pair
             matches the corresponding objects in the message.  If no
             matching PSB is found, drop the PTEAR message and return.

        o    Forward a copy of the PTEAR message to each outgoing



Braden, Zhang, et al.     Expiration: May 1996                 [Page 69]


Internet Draft             RSVP Specification              November 1995


             interface listed in OutInterface_list of the PSB.

        o    Find each RSB that matches this PSB, i.e., whose
             FILTER_SPEC object matches the SENDER_TEMPLATE in the PSB
             and whose OI is included in OutInterface_list.

             If this RSB matches no other PSB, then tear down the RSB,
             as described below under RESV TEAR MESSAGE ARRIVES.

        o    Delete the PSB.

        o    Drop the PTEAR message and return.


   PATH ERROR MESSAGE ARRIVES

        o    Search for a PSB whose (SESSION, SENDER_TEMPLATE) pair
             matches the corresponding objects in the message.  If no
             matching PSB is found, drop the PERR message and return.

        o    If the previous hop address in the PSB is the local API,
             make an error upcall to the application:

                 Call: <Upcall_Proc>( session-id, Path Error,
                               Error_code, Error_value, Node_Addr,
                               0, 1, NULL, SENDER_TEMPLATE,
                               NULL, Policy_Data)


             Any POLICY_DATA, SENDER_TSPEC, or ADSPEC object in the
             message is ignored.  [LZ: Why we don't send these objects
             up to application?  They might of some help to understand
             the errors.]  Drop the PERR message and return.

        o    Otherwise, send a copy of the PERR message to the PHOP IP
             address, drop the PERR message, and return.


   RESV MESSAGE ARRIVES

        Initially, the Resv_Refresh_PHOP* list is empty and the
        Resv_Refresh_Needed flag is off.  These variables are used to
        control immediate reservation refreshes.

        o    Process the NHOP object

             The logical outgoing interface OI is taken from the LIH in
             the NHOP object.  (If the physical interface is not implied



Braden, Zhang, et al.     Expiration: May 1996                 [Page 70]


Internet Draft             RSVP Specification              November 1995


             by the LIH, it can be learned from the interface matching
             the IP destination address).

        o    Check the SESSION object.

             If there are no existing PSB's for SESSION then build and
             send a RERR message (as described later) specifying "No
             path information", drop the RESV message, and return.
             However, do not send the RERR message if the style has
             wildcard reservation scope and this is the receiver host
             itself.

             [LZ: Explain this?]

        o    Check the S_POLICY_DATA object.

             If there is an S_POLICY_DATA object in the message, check
             permission to create a reservation for the session.  If the
             check fails, build and send an "Administrative rejection"
             RERR message, drop the RESV message, and return.
             Otherwise, copy the S_POLICY_DATA object into the RSB.

        Now process the STYLE object and the flow descriptor list to
        make reservations, as follows.

        For FF style, execute the following steps independently for each
        b flow descriptor, i.e., for each (FLOWSPEC, FILTER_SPEC) pair.
        For FF style, FILTER_SPEC* consists of the single FILTER_SPEC
        from the flow descriptor.

        For SE style, execute the following steps once, with
        FILTER_SPEC* consisting of the list of FILTER_SPEC objects from
        the flow descriptor.

        For WF style, execute the following steps once, with
        FILTER_SPEC* consisting of a single internal placeholder
        "WILD_FILTER".

        o    If the DstPort in the SESSION object is zero but the
             SrcPort in the FILTER_SPEC object is non-zero, build a send
             a "Conflicting Src Port" RERR message, drop the RESV
             message, and return.

        o    Find or create a reservation state block (RSB) for the
             triple: (SESSION, NHOP, FILTER_SPEC*).  Call this the
             "active RSB".

        o    If the RSB is not new and if its style is incompatible with



Braden, Zhang, et al.     Expiration: May 1996                 [Page 71]


Internet Draft             RSVP Specification              November 1995


             the STYLE object in the message, build and send a RERR
             message specifying "Conflicting Style", drop the RESV
             message, and return.

        o    Start or restart the cleanup timer on the the active RSB.

        o    If the active RSB is not new, check whether FLOWSPEC or
             SCOPE objects have changed.  If not, continue with the next
             flow descriptor in the RESV message, if any.

        o    If the active RSB is new, set its OI and style, and copy
             any FLOWSPEC, POLICY_DATA, and/or SCOPE objects into it.

        o    If there is a RESV_CONFIRM in the message, turn on
             Resv_Refresh_Needed and save the object in the RSB.

        o    The active RSB must be new or changed.  Compute the traffic
             control parameters, using the following steps.

             1.   Locate the set of PSBs (senders) whose
                  SENDER_TEMPLATEs match FILTER_SPEC* in the active RSB
                  and whose OutInterface_list includes OI.

                  If this set is empty, build and send an error message
                  specifying "No sender information", and continue with
                  the next flow descriptor in the RESV message.

             2.   If this set contains more than one PSB and if the
                  style has explicit sender selection (e.g., FF or SE),
                  build and send an error message specifying "Ambiguous
                  filter spec" and continue with the next flow
                  descriptor.

             3.   Add the PHOP from the PSB to the Resv_Refresh_PHOP*
                  list, if the PHOP is not already on the list.

             4.   Set TC_E_Police_flag on if any of these PSBs have
                  their E_Police flag on.  Set TC_M_Police_flag on if it
                  is a shared style and there is more than one PSB in
                  the set.

             5.   Compute Path_Te as the sum of the SENDER_TSPEC objects
                  in this set of PSBs.

             6.   Scan all RSB's matching the SESSION and
                  Filter_Spec_list from the message.

                  -    If any of these RSB's has a style that is



Braden, Zhang, et al.     Expiration: May 1996                 [Page 72]


Internet Draft             RSVP Specification              November 1995


                       incompatible with the specifying "Conflicting
                       Style", drop the RESV message, delete the RSB if
                       it has just been created, and return.

                  -    Set TC_B_Police_flag on if TC_Flowspec is smaller
                       than, or incomparable to, any FLOWSPEC in those
                       RSB's.

             7.   Consider the set of RSB's for the same (SESSION, OI,
                  Filter_Spec_list) triple from the message.

                  -    Compute the effective kernel flowspec,
                       TC_Flowspec, as the maximum of the FLOWSPEC
                       values in these RSB's.

                  -    Compute the effective kernel filter spec (list),
                       TC_Filter*. by merging the FILTER_SPEC* object
                       (lists) from these RSB's.

        o    Search for a TCSB matching the triple (SESSION, OI,
             FILTER_SPEC*), taken from the RSB.

             1.   If none is found but style is SE, search for a TCSB
                  matching (SESSION, OI).  If find one and if TCSB's
                  TC_Flowspec, Path_Te, and police flags match the
                  computed values, then

                  -    Make an appropriate set of TC_DelFilter and
                       TC_AddFilter calls to transform the
                       Filter_Spec_list in the TCSB into the
                       Filter_Spec_list from the message.

                  -    Set Resv_Refresh_Needed on, drop the RESV
                       message, and return.

             2.   Otherwise, if none is found:

                  -    Create a new TCSB.

                  -    Store TC_Flowspec, Filter_Spec_list, Path_Te, and
                       the police flags into TCSB.

                       [SCOPE?]

                  -    Set Resv_Refresh_Needed on.

                  -    Make the traffic control call:




Braden, Zhang, et al.     Expiration: May 1996                 [Page 73]


Internet Draft             RSVP Specification              November 1995


                          Rhandle = TC_AddFlowspec( OI, TC_flowspec, Path_Te,
                                              TC_E_Police_flag, TC_M_Police_flag,
                                              TC_B_Police_flag )


                       If this call fails, build and send a RERR message
                       specifying "Admission control failed", and
                       continue with the next flow descriptor.
                       Otherwise, record Rhandle in the TCSB.

                  -    For each filter_spec F in Filter_Spec_list, call:


                          Fhandle = TC_AddFilter( Rhandle, SESSION, F)

                       and record the returned Fhandle in the TCSB.

                  -    Continue with the next flow descriptor.

             3.   Otherwise (found existing TCSB), check whether
                  TC_Flowspec, Path_Te, and/or any of the police flags
                  has changed, and if so:

                  -    Store TC_Flowspec, Filter_Spec_list, Path_Te, and
                       the police flags into it.

                       [SCOPE?]

                  -    Set Resv_Refresh_Needed on.

                  -    Make the traffic control call:

                          TC_ModFlowspec( Rhandle, K_Flowspec, Path_Te,
                                       TC_E_Police_flag, TC_M_Police_flag,
                                       TC_B_Police_flag )


             4.   Continue with the next flow descriptor.

        o    If the Resv_Refresh_Needed flag is now on, execute the RESV
             REFRESH sequence (below) for each PHOP in the
             Resv_Refresh_PHOP* set.

        If processing a RESV message finds an error, a RERR message is
        created containing flow descriptor and an ERRORS object.  The
        Error Node field of the ERRORS object (see Appendix A) is set to
        the IP address of OI, and the message is sent unicast to NHOP.




Braden, Zhang, et al.     Expiration: May 1996                 [Page 74]


Internet Draft             RSVP Specification              November 1995


   RESV TEAR MESSAGE ARRIVES

        A RTEAR message arrives with an IP destination address matching
        outgoing interface OI.  Flags Tear_Needed and
        Resv_Refresh_Needed are initially off and Resv_Refresh_PHOP*
        list is empty.

        o    Process the STYLE object and the flow descriptor list in
             the RTEAR message to tear down local reservation state, as
             follows.

             For FF style, execute the following steps for each b flow
             descriptor, i.e., for each (FLOWSPEC, FILTER_SPEC) pair
             independently, with Filter_Spec_list consisting of a single
             FILTER_SPEC object.

             For SE style, execute the following steps once, with
             Filter_Spec_list consisting of a list of FILTER_SPEC
             objects.

             For WF style, execute the following steps once, with
             Filter_Spec_list consisting of a single internal
             placeholder "WILD_FILTER".

             1.   Find matching RSB for the 4-tuple: (SESSION, NHOP,
                  style, Filter_Spec_list); call this the active RSB.
                  If no active RSB is found, continue with next flow
                  descriptor.

             2.   Delete the active RSB.

             3.   Find TCSB for the triple: (SESSION, OI,
                  Filter_Spec_list).

             4.   Consider the set of RSB's matching this TCSB.  If
                  there are none:

                  -    Call the traffic control interface routine:


                          TC_DelFlowspec( Rhandle )


                  -    Delete the TCSB and set Tear_Needed flag on.

                  -    Continue with the next flow descriptor.

             5.   Otherwise (there are other RSB's for the same TCSB),



Braden, Zhang, et al.     Expiration: May 1996                 [Page 75]


Internet Draft             RSVP Specification              November 1995


                  recompute TC_Flowspec and Path_Te (see RESV MESSAGE
                  ARRIVES).  (This also adds the appropriate PHOP
                  addresses to the Resv_Refresh_PHOP* list>) If either
                  changed, update the TCSB, set flag Resv_Refresh_Needed
                  on, and call the traffic control interface module:


                     TC_ModFlowspec( Rhandle, TC_Flowspec, Path_Te)
                                  TC_E_Police_flag, TC_M_Police_flag,
                                  TC_B_Police_flag )


                  This kernel call should not fail, since the
                  reservation can only be reduced.

             [LZ: Suppose receiver R has the credential to make the
             reservation and others took a ride on top of R's
             credential.  Now R tears down its request, what should
             happen?  Shouldn't TEAR take policy data as input?]

        o    If Tear_Needed and Resv_Refresh_Needed flags are both off,
             then drop the RTEAR message and return.

        o    If Tear_Needed is off but Resv_Refresh_Needed is on, then
             execute the RESV REFRESH sequence for each PHOP in the
             Resv_Refresh_PHOP* set, drop the RTEAR message, and return.

        o    Otherwise (Tear_Needed is on), need to forward RTEAR and/or
             RESV refresh messages.

             Do the following for each PSB whose OutInterface_list
             includes the outgoing interface OI:

             1.   Pick each flow descriptor Fj in the RTEAR message
                  whose FILTER_SPEC matches the PSB, and do the
                  following.

                  -    If there is no RSB whose FILTER_SPEC matches the
                       PSB, then add Fj to the new RTEAR message being
                       built.

                  -    Otherwise (there is a matching RSB), note the PSB
                       as needing a RESV refresh message and set the
                       Resv_Refresh_Needed flag True.

             2.   If the new RTEAR message contains any flow
                  descriptors, send it to PHOP in the PSB.




Braden, Zhang, et al.     Expiration: May 1996                 [Page 76]


Internet Draft             RSVP Specification              November 1995


        o    If the Resv_Refresh_Needed flag is now on, execute the RESV
             REFRESH sequence (below) for each PHOP in the
             Resv_Refresh_PHOP* set.

             If the Refresh_Needed flag is true, then execute the RESV
             REFRESH sequence for the PSB's that have been noted.

        o    Drop the RTEAR message and return.


   RESV ERROR MESSAGE ARRIVES

        A RERR message arrives through the (real) incoming interface
        In_If.

        o    If there is no path state for SESSION, drop the RERR
             message and return.

        o    Do the following with each RSB for this SESSION whose OI
             does not match In_If and whose FILTER_SPEC matches that in
             the RERR message.

             1.   Copy the error flow descriptor from the incoming RERR
                  message.

             2.   Compare the FLOWSPEC in the RERR message with the
                  FLOWSPEC in the RSB.  If they don't match along any
                  coordinate (i.e., if the RSB FLOWSPEC is strictly
                  `smaller'), continue with the next RSB.

                  If they agree on some but not all coordinates, turn on
                  the LUB-used flag.

             3.   If NHOP in RSB is the local API, deliver an error
                  upcall to application:


                           Call: <Upcall_Proc>( session-id, Resv Error,
                                     Error_code, Error_value, Node_Addr,
                                        LUB-Used,
                                        Flowspec, Filter_Spec_List,
                                        NULL, NULL)


                  and continue with the next RSB.  Here k,
                  Filter_Spec_List, and Flowspec_List are constructed
                  from the error flow descriptor.




Braden, Zhang, et al.     Expiration: May 1996                 [Page 77]


Internet Draft             RSVP Specification              November 1995


             4.   If the RESV message has wildcard sender selection, use
                  its SCOPE object SC.In to construct a SCOPE object
                  SC.Out to be forwarded.  SC.Out should contain those
                  sender addresses that appeared in SC.In and that route
                  to OI [LIH?], as determined by scanning the PSB's.  If
                  SC.Out is empty, continue with the next RSB.

             5.   Create a new RERR message containing the error flow
                  descriptor and send to the NHOP address specified by
                  the RSB.  Include SC.Out if the sender selection is
                  wildcard.

             6.   Continue with the next RSB.

        o    Drop the RERR message and return.


   RESV CONFIRMATION ARRIVES

        If the (unicast) IP address found in its RESV_CONFIRM object
        matches an interface of the node, a confirmation upcall is made
        to the matching application:


                    Call: <Upcall_Proc>( session-id, Resv Confirm,
                              Error_code, Error_value, Node_Addr,
                              LUB-Used, nlist, Flowspec,
                              Filter_Spec_List, NULL, NULL )


        Otherwise, the RACK message is forwarded immediately to the
        address in the IP address in its RESV_CONFIRM object.

   PATH REFRESH

        This sequence sends a path refresh for a particular sender,
        i.e., a PSB.  This sequence may be entered by either the
        expiration of the path refresh timer or directly as the result
        of the Path_Refresh_Needed flag being turned on during the
        processing of a received PATH message.

        o    Compute the IP TTL for the PATH message as one less than
             the maximum of the TTL values from the senders included in
             the message.  However, if the result is zero, return
             without sending the PATH message.

        o    Insert TIME_VALUES and PHOP objects into the PATH message
             being built.



Braden, Zhang, et al.     Expiration: May 1996                 [Page 78]


Internet Draft             RSVP Specification              November 1995


        o    Create a sender descriptor containing the SENDER_TEMPLATE,
             SENDER_TSPEC, and POLICY_DATA objects, if present in the
             PSB, and pack it into the PATH message being built.

        o    Pass any ADSPEC and SENDER_TSPEC objects present in the PSB
             to the traffic control call TC_Advertise.  Insert the
             modified ADSPEC object that is returned into the PATH
             message being built.

        o    If the PSB has the E_Police flag on and if interface OI is
             not capable of policing, turn the E_Police flag on in the
             PATH message being built.

        o    Send a copy of the PATH message to each interface in
             OutInterfact_list.  Before sending each copy, insert into
             its PHOP object the interface address and the LIH for the
             interface.


   RESV REFRESH

        This sequence sends a reservation refresh towards a particular
        previous hop with IP address PH.  This sequence may be entered
        by either the expiration of a reservation refresh timer or
        directly as the result of the Resv_Refresh_Needed flag being
        turned on as the result of processing a RESV or RTEAR message.

        In general, this sequence considers each of the PSB's with PHOP
        address PH.  For a given PSB, it scans the RSBs for matching
        reservations and merges the styles, FLOWSPECs and FILTER_SPEC*'s
        appropriately.  It then builds a RESV message and sends it to
        PH.  The details depend upon the attributes of the style(s)
        included in the reservations.

        o    If there are PSB's from more than one PHOP and if the
             multicast routing protocol does not use shared trees, set
             the Need_Scope flag on, otherwise set it off.

        o    Create an output message containing SESSION, RSVP_HOP,
             INTEGRITY, and TIME_VALUES objects.

        o    Select each sender PSB whose PHOP has address PH.

             1.   Select all RSB's whose FILTER_SPEC*'s match the
                  SENDER_TEMPLATE object in the PSB and whose OI appears
                  in the OutInterface_list of the PSB.

             2.   Get a STYLE object from the first RSB and move it into



Braden, Zhang, et al.     Expiration: May 1996                 [Page 79]


Internet Draft             RSVP Specification              November 1995


                  the output message.  (Note that the present set of
                  styles are never themselves merged; if future styles
                  can be merged, these rules will become more complex).

             3.   Compute the maximum/LUB over the FLOWSPEC objects of
                  this set of RSB's.

             4.   While computing the maximum/LUB, check for a
                  RESV_CONFIRM object in each RSB.  If a RESV_CONFIRM
                  object is found and if the FLOWSPEC in that RSB is
                  larger than all other flowspecs being compared, then
                  save this RESV_CONFIRM object.  If a RESV_CONFIRM
                  object is found but the corresponding FLOWSPEC is
                  equal or smaller than the largest, or if the result of
                  merging was a LUB, then create and send a RACK message
                  to the address in the RESV_CONFIRM object.

                  -    Include the RESV_CONFIRM object in the RACK
                       message.

                  -    Build a confirmation ERROR_SPEC object and
                       include it in the RACK message.  The Error_Node
                       parameter in this object should be the IP address
                       of OI from the RSB.

                  Then delete the RESV_CONFIRM object from the RSB.

             5.   Merge the matching FILTER_SPEC objects from this set
                  of RSB's.  The merging rule depend upon the style:


                  Explicit sender selection (FF, SE) styles:

                       Use the SENDER_TEMPLATE as the merged
                       FILTER_SPEC.


                  Wildcard sender selection (WF) style:

                       There is no filter spec to merge.

             6.   If the Need_Scope flag is on, compute a new SCOPE
                  object as the union of the SCOPE objects found in the
                  RSB's.

             7.   Merge the F_POLICY_DATA objects from the RSB's.

             8.   (All matching RSB's have been processed).  The next



Braden, Zhang, et al.     Expiration: May 1996                 [Page 80]


Internet Draft             RSVP Specification              November 1995


                  step depends upon the style attributes.


                  Distinct reservation (FF) style

                       Pack the merged (FLOWSPEC, FILTER_SPEC,
                       F_POLICY_DATA) triplet into the message as a flow
                       descriptor.


                  Shared reservation (SE, WF) styles

                       Merge (take the maximum) across all PSB's the
                       merged FLOWSPECS from the RSB's.

                       If the sender selection is not wildcard (i.e., if
                       it is SE), form the union of the FILTER_SPECs
                       obtained from the RSB's.  For Wildcard sender
                       selection (WF) style, there is not filter spec to
                       merge.

             9.   If the Need_Scope flag is on, remove from the merged
                  SCOPE object all sender addresses that do not match
                  the set of PSB's for PH, and all senders addresses
                  that are local.  If the resulting set is empty, no
                  RESV should be forwarded to this PHOP; return;
                  otherwise (set is not empty), move the new SCOPE
                  object into the message.

        o    (All PSB's have been processed).  If a shared reservation
             style is being built, move the final merged FLOWSPEC,
             F_POLICY_DATA, and FILTER_SPEC (if SE) objects into the
             message.

        o    If a RESV_CONFIRM object was saved earlier, copy it into
             the new RESV message and delete it from the RSB in which it
             was found.

        o    Set the RSVP_HOP object in the message to contain the
             IncInterface address through which it will be sent and the
             LIH from (one of) the PSB's.

        o    Send the message to the address PH.








Braden, Zhang, et al.     Expiration: May 1996                 [Page 81]


Internet Draft             RSVP Specification              November 1995


APPENDIX A. Object Definitions

   C-Types are defined for the two Internet address families IPv4 and
   IP6.  To accommodate other address families, additional C-Types could
   easily be defined.  These definitions are contained as an Appendix,
   to ease updating.

   All unused fields should be sent as zero and ignored on receipt.

   A.1 SESSION Class

      SESSION Class = 1.

      o    IPv4/UDP SESSION object: Class = 1, C-Type = 1

           +-------------+-------------+-------------+-------------+
           |             IPv4 DestAddress (4 bytes)                |
           +-------------+-------------+-------------+-------------+
           | Protocol Id |    Flags    |          DstPort          |
           +-------------+-------------+-------------+-------------+


      o    IP/UDP SESSION object: Class = 1, C-Type = 2

           +-------------+-------------+-------------+-------------+
           |                                                       |
           +                                                       +
           |                                                       |
           +               IP6 DestAddress (16 bytes)              +
           |                                                       |
           +                                                       +
           |                                                       |
           +-------------+-------------+-------------+-------------+
           | Protocol Id |     Flags   |          DstPort          |
           +-------------+-------------+-------------+-------------+



      DestAddress

           The IP unicast or multicast destination address of the
           session.  This parameter must be supplied.

      Protocol Id

           The IP Protocol Identifier for the data flow.  This parameter
           must be supplied.




Braden, Zhang, et al.     Expiration: May 1996                 [Page 82]


Internet Draft             RSVP Specification              November 1995


      Flags

           0x01 = E_Police flag

                The E_Police flag is used in PATH messages to determine
                the effective "edge" of the network, to control traffic
                policing.  If the sender host is not itself capable of
                traffic policing, it will set this bit on in PATH
                messages it sends.  The first node whose RSVP is capable
                of traffic policing will do so (if appropriate to the
                service) and turn the flag off.

                [It might make more sense to include this flag in ADSPEC
                object.]

      DstPort

           The UDP/TCP destination port for the session.  Zero may be
           used to indicate a `wildcard', i.e., any port.

           Other SESSION C-Types could be defined in the future to
           support other demultiplexing conventions in the transport-
           layer or application layer.




























Braden, Zhang, et al.     Expiration: May 1996                 [Page 83]


Internet Draft             RSVP Specification              November 1995


   A.2 RSVP_HOP Class

      RSVP_HOP class = 3.

      o    IPv4 RSVP_HOP object: Class = 3, C-Type = 1

           +-------------+-------------+-------------+-------------+
           |             IPv4 Next/Previous Hop Address            |
           +-------------+-------------+-------------+-------------+
           |                 Logical Interface Handle              |
           +-------------+-------------+-------------+-------------+

      o    IP6 RSVP_HOP object: Class = 3, C-Type = 2

           +-------------+-------------+-------------+-------------+
           |                                                       |
           +                                                       +
           |                                                       |
           +             IP6 Next/Previous Hop Address             +
           |                                                       |
           +                                                       +
           |                                                       |
           +-------------+-------------+-------------+-------------+
           |                 Logical Interface Handle              |
           +-------------+-------------+-------------+-------------+


      This object provides the IP address of the interface through which
      the last RSVP-knowledgeable hop forwarded this message.  The
      Logical Interface Handle is a 32-bit number which may be used to
      distinguish logical outgoing interfaces as described in Section
      3.2; it should be identically zero if there is no logical
      interface handle.


















Braden, Zhang, et al.     Expiration: May 1996                 [Page 84]


Internet Draft             RSVP Specification              November 1995


   A.3 INTEGRITY Class

      INTEGRITY class = 4.

      See draft-ietf-rsvp-md5-00.txt.

   A.4 TIME_VALUES Class

      TIME_VALUES class = 5.

      o    TIME_VALUES Object: Class = 5, C-Type = 1


           +-------------+-------------+-------------+-------------+
           |                    Refresh Period                     |
           +-------------+-------------+-------------+-------------+



      Refresh Period

           The refresh timeout period R used to generate this message;
           in milliseconds.




























Braden, Zhang, et al.     Expiration: May 1996                 [Page 85]


Internet Draft             RSVP Specification              November 1995


   A.5 ERROR_SPEC Class

      ERROR_SPEC class = 6.

      o    IPv4 ERROR_SPEC object: Class = 6, C-Type = 1


           +-------------+-------------+-------------+-------------+
           |            IP4 Error Node Address (4 bytes)           |
           +-------------+-------------+-------------+-------------+
           |    Flags    |  Error Code |        Error Value        |
           +-------------+-------------+-------------+-------------+


      o    IP6 ERROR_SPEC object: Class = 6, C-Type = 2


           +-------------+-------------+-------------+-------------+
           |                                                       |
           +                                                       +
           |                                                       |
           +           IP6 Error Node Address (16 bytes)           +
           |                                                       |
           +                                                       +
           |                                                       |
           +-------------+-------------+-------------+-------------+
           |    Flags    |  Error Code |        Error Value        |
           +-------------+-------------+-------------+-------------+



      Error Node Address

           The IP address of the node in which the error was detected.

      Flags

           0x01 = LUB-Used

                The use of this flag is described in section 3.1.5.

      Error Code

           A one-octet error description.

      Error Value

           A two-octet field containing additional information about the



Braden, Zhang, et al.     Expiration: May 1996                 [Page 86]


Internet Draft             RSVP Specification              November 1995


                error.  Its contents depend upon the Error Type.

      The values for Error Code and Error Value are defined in Appendix
      B.

   A.6 SCOPE Class

      SCOPE class = 7.

      This object contains a list of IP addresses, used for routing
      messages with wildcard scope without loops.  The addresses must be
      listed in ascending numerical order.

      o    IPv4 SCOPE List object: Class = 7, C-Type = 1


           +-------------+-------------+-------------+-------------+
           |                IP4 Src Address (4 bytes)              |
           +-------------+-------------+-------------+-------------+
           //                                                      //
           +-------------+-------------+-------------+-------------+
           |                IP4 Src Address (4 bytes)              |
           +-------------+-------------+-------------+-------------+


      o    IP6  SCOPE list object: Class = 7, C-Type = 2


           +-------------+-------------+-------------+-------------+
           |                                                       |
           +                                                       +
           |                                                       |
           +                IP6 Src Address (16 bytes)             +
           |                                                       |
           +                                                       +
           |                                                       |
           +-------------+-------------+-------------+-------------+
           //                                                      //
           +-------------+-------------+-------------+-------------+
           |                                                       |
           +                                                       +
           |                                                       |
           +                IP6 Src Address (16 bytes)             +
           |                                                       |
           +                                                       +
           |                                                       |
           +-------------+-------------+-------------+-------------+




Braden, Zhang, et al.     Expiration: May 1996                 [Page 87]


Internet Draft             RSVP Specification              November 1995


   A.7 STYLE Class

      STYLE class = 8.

      o    STYLE object: Class = 8, C-Type = 1

           +-------------+-------------+-------------+-------------+
           |                    Option Vector                      |
           +-------------+-------------+-------------+-------------+



      Option Vector

           A set of bit fields giving values for the reservation
           options.  If new options are added in the future,
           corresponding fields in the option vector will be assigned
           from the least-significant end.  If a node does not recognize
           a style ID, it may interpret as much of the option vector as
           it can, ignoring new fields that may have been defined.

           The option vector bits are assigned (from the left) as
           follows:

           27 bits: Reserved

           2 bits: Sharing control

                00b: Reserved

                01b: Distinct reservations

                10b: Shared reservations

                11b: Reserved

           3 bits: Sender selection control

                000b: Reserved

                001b: Wildcard

                010b: Explicit

                011b - 111b: Reserved

      The low order bits of the option vector are determined by the
      style, as follows:



Braden, Zhang, et al.     Expiration: May 1996                 [Page 88]


Internet Draft             RSVP Specification              November 1995


              WF 10001b
              FF 01010b
              SE 10010b
















































Braden, Zhang, et al.     Expiration: May 1996                 [Page 89]


Internet Draft             RSVP Specification              November 1995


   A.8 FLOWSPEC Class

      FLOWSPEC class = 9.

      o    Class = 9, C-Type = 1:  int-serv flowspec

           The contents of this object will be specified in documents
           prepared by the int-serv working group.

      o    Class = 9, C-Type = 254:  Unmerged Flowspec List

           +-------------+-------------+-------------+-------------+
           |                                                       |
           //                 FLOWSPEC object  1                  //
           |                                                       |
           +-------------+-------------+-------------+-------------+
           |                                                       |
           //                 FLOWSPEC object  2                  //
           |                                                       |
           +-------------+-------------+-------------+-------------+
           //                                                     //
           //                                                     //
           +-------------+-------------+-------------+-------------+
           |                                                       |
           //                 FLOWSPEC object  k                  //
           |                                                       |
           +-------------+-------------+-------------+-------------+


           This is a container C-Type, used to enclose a set of FLOWSPEC
           objects that could not be merged at the next hop downstream
           because they include unrecognized C-Types.  The node that
           receives this object may merge those it recognizes and
           forward the rest in another Unmerged Flowspec List object.

















Braden, Zhang, et al.     Expiration: May 1996                 [Page 90]


Internet Draft             RSVP Specification              November 1995


   A.9 FILTER_SPEC Class

      FILTER_SPEC class = 10.

      o    IPv4 FILTER_SPEC object: Class = 10, C-Type = 1

           +-------------+-------------+-------------+-------------+
           |               IPv4 SrcAddress (4 bytes)               |
           +-------------+-------------+-------------+-------------+
           |    //////   |    //////   |          SrcPort          |
           +-------------+-------------+-------------+-------------+


      o    IP6 FILTER_SPEC object: Class = 10, C-Type = 2

           +-------------+-------------+-------------+-------------+
           |                                                       |
           +                                                       +
           |                                                       |
           +               IP6 SrcAddress (16 bytes)               +
           |                                                       |
           +                                                       +
           |                                                       |
           +-------------+-------------+-------------+-------------+
           |    //////   |    //////   |          SrcPort          |
           +-------------+-------------+-------------+-------------+


      o    IP6 Flow-label FILTER_SPEC object: Class = 10, C-Type = 3

           +-------------+-------------+-------------+-------------+
           |                                                       |
           +                                                       +
           |                                                       |
           +               IP6 SrcAddress (16 bytes)               +
           |                                                       |
           +                                                       +
           |                                                       |
           +-------------+-------------+-------------+-------------+
           |   ///////   |         Flow Label (24 bits)            |
           +-------------+-------------+-------------+-------------+



      SrcAddress

           The IP source address for a sender host, or zero to indicate
           a `wildcard'.



Braden, Zhang, et al.     Expiration: May 1996                 [Page 91]


Internet Draft             RSVP Specification              November 1995


      SrcPort

           The UDP/TCP source port for a sender, or zero to indicate a
           `wildcard' (i.e., any port).

      Flow Label

           A 24-bit Flow Label, defined in IP6.  This value may be used
           by the packet classifier to efficiently identify the packets
           belonging to a particular (sender->destination) data flow.









































Braden, Zhang, et al.     Expiration: May 1996                 [Page 92]


Internet Draft             RSVP Specification              November 1995


   A.10 SENDER_TEMPLATE Class

      SENDER_TEMPLATE class = 11.

      o    IPv4/UDP SENDER_TEMPLATE object: Class = 11, C-Type = 1

           Definition same as IPv4/UDP FILTER_SPEC object.

      o    IP6/UDP SENDER_TEMPLATE object: Class = 11, C-Type = 2

           Definition same as IP6/UDP FILTER_SPEC object.

   A.11 SENDER_TSPEC Class

      SENDER_TSPEC class = 12.

      o    Token Bucket SENDER_TSPEC object: Class = 12, C-Type = 1

           The contents of this object will be specified in documents
           prepared by the int-serv working group.































Braden, Zhang, et al.     Expiration: May 1996                 [Page 93]


Internet Draft             RSVP Specification              November 1995


   A.12 ADSPEC Class

      ADSPEC class = 13.

      The contents of this object will be specified in documents
      prepared by the int-serv working group.













































Braden, Zhang, et al.     Expiration: May 1996                 [Page 94]


Internet Draft             RSVP Specification              November 1995


   A.13 POLICY_DATA Class

      POLICY_DATA class = 14.

      o    Type 1 POLICY_DATA object: Class = 14, C-Type = 1

           The contents of this object are for further study.

      o    Unmerged POLICY_DATA object: Class = 14, C-Type = 254

           This object is a container for a list of POLICY_DATA objects
           (none of which may have C-Type = 254).  The contained objects
           have not yet been merged.

           +-------------+-------------+-------------+-------------+
           |                                                       |
           //                 POLICY_DATA object  1              //
           |                                                       |
           +-------------+-------------+-------------+-------------+
           |                                                       |
           //                 POLICY_DATA object  2              //
           |                                                       |
           +-------------+-------------+-------------+-------------+
           //                                                     //
           //                                                     //
           +-------------+-------------+-------------+-------------+
           |                                                       |
           //                 POLICY_DATA object  k              //
           |                                                       |
           +-------------+-------------+-------------+-------------+





















Braden, Zhang, et al.     Expiration: May 1996                 [Page 95]


Internet Draft             RSVP Specification              November 1995


   A.14 RESV_CONFIRM Class

      RESV_CONFIRM class = 15.

      o    IPv4 RESV_CONFIRM object: Class = 15, C-Type = 1

           +-------------+-------------+-------------+-------------+
           |            IPv4 Receiver Address (4 bytes)            |
           +-------------+-------------+-------------+-------------+


      o    IP6 RESV_CONFIRM object: Class = 15, C-Type = 2

           +-------------+-------------+-------------+-------------+
           |                                                       |
           +                                                       +
           |                                                       |
           +            IP6 Receiver Address (16 bytes)            +
           |                                                       |
           +                                                       +
           |                                                       |
           +-------------+-------------+-------------+-------------+





























Braden, Zhang, et al.     Expiration: May 1996                 [Page 96]


Internet Draft             RSVP Specification              November 1995


APPENDIX B. Error Codes and Values

   The following Error Codes are defined.

   o    Error Code = 01: Admission failure

        Reservation rejected by admission control.

        For this Error Code, the 16 bits of the Error Value field are:


           ussr cccc cccc cccc

        where the bits are:


        u = 0: RSVP rejects the message without updating local state.


        u = 1: RSVP may use message to update local state and forward
             the message.


        ss = 00: Low order 12 bits contain a globally-defined sub-code
             (values listed below).


        ss = 10: Low order 12 bits contain a sub-code that is specific
             to local organization.  RSVP is not expected to be able to
             interpret this except as a numeric value.


        ss = 11: Low order 12 bits contain a sub-code that is specific
             to the service.  RSVP is not expected to be able to
             interpret this except as a numeric value.  Since the
             traffic control mechanism might substitute a different
             service, this encoding may include some representation of
             the service in use.


        r: Reserved bit, should be zero.


        cccc cccc cccc: 12 bit code.

        The following globally-defined sub-codes may appear in the low-
        order 12 bits when ss = 00:




Braden, Zhang, et al.     Expiration: May 1996                 [Page 97]


Internet Draft             RSVP Specification              November 1995


        -    Sub-code = 1: Delay bound cannot be met

        -    Sub-code = 2: Requested bandwidth unavailable

        -    Sub-code = 11: Service conflict

        -    Sub-code = 12: Service unsupported

             Traffic control can provide neither the requested service
             nor an acceptable replacement.

        -    Sub-code = 13: Bad Flowspec or Tspec value

             Unreasonable request.  High order bit u = 0, i.e., RSVP
             will reject the message.

        -    Sub-code = 14: Rmax value too small.

             Rmax would result in excessive refresh overhead.

   o    Error Code = 02: Administrative rejection

        Reservation has been rejected for administrative reasons.

        The high order 4 bits of the Error Value field are assigned as
        for Error Code = 01 (above).  For Error Code = 02, the following
        global sub-codes are defined:

        -    Sub-code = 1: Required credential(s) not presented.

        -    Sub-code = 2: Request too large

             Reservation request exceeds allowed value for this user
             class.

        -    Sub-code = 3: Insufficient quota or balance.

        -    Sub-code = 4: Administrative preemption

   o    Error Code = 03: No path information for this Resv

        RSVP should reject the message.

   o    Error Code = 04: No sender information for this Resv

        There is path information, but it does not include the sender
        specified in one of the Filterspecs listed in the Resv message.
        RSVP should reject the message.



Braden, Zhang, et al.     Expiration: May 1996                 [Page 98]


Internet Draft             RSVP Specification              November 1995


   o    Error Code = 05: Ambiguous path

        Sender port appears both zero and non-zero in same session.
        RSVP should reject the message.

   o    Error Code = 06: Ambiguous filter spec

        Filter spec matches more than one sender, in a style that
        requires a unique match.  RSVP should reject the message.

   o    Error Code = 07: Conflicting or unknown style

        Reservation style conflicts with style(s) of existing
        reservation state, or it is unknown.  If the high-order bit of
        Error Value is zero, RSVP should reject the message.

   o    Error Code = 08: Conflicting dest port

        Sessions for same destination address and protocol have appeared
        with both zero and non-zero dest port fields.

   o    Error Code = 09: Conflicting source port

        The source port is non-zero in a filter spec or sender template
        for a session with destination port zero.

   o    Error Code = 11: Missing required object

        RSVP was unable to find or construct required object data from
        message.  Error Value will be Class-Num that is missing.  RSVP
        should reject the message.

   o    Error Code = 12: Unknown object class

        Error Value will contain 16-bit value composed of (Class-Num,
        C-Type) of unknown object.  This error should be sent only if
        RSVP is going to reject the message.

   o    Error Code = 13: Unknown object C-Type

        Error Value will contain 16-bit value composed of (Class-Num,
        C-Type) of object.  This error should be sent only if RSVP is
        going to reject the message.

   o    Error Code = 14: Object error

        A non-specific error indicating bad format or contents of an
        object.  The Error Value will contain 16-bits value (Class-Num,



Braden, Zhang, et al.     Expiration: May 1996                 [Page 99]


Internet Draft             RSVP Specification              November 1995


        C-Type) from header of bad object.  RSVP should reject the
        message.

   o    Error Code = 21: Traffic Control error

        Some system error was detected and reported by the traffic
        control modules.  The Error Value will contain a system-specific
        value giving more information about the error.  RSVP is not
        expected to be able to interpret this value.

   o    Error Code = 22: RSVP System error

        The Error Value field will provide implementation-dependent
        information on the error.  RSVP is not expected to be able to
        interpret this value.




































Braden, Zhang, et al.     Expiration: May 1996                [Page 100]


Internet Draft             RSVP Specification              November 1995


APPENDIX C. UDP Encapsulation

   An RSVP implementation will generally require the ability to perform
   "raw" network I/O, i.e., to send and receive IP datagrams using
   protocol 46.  However, some important classes of host systems may not
   support raw network I/O.  To use RSVP, such hosts must encapsulate
   RSVP messages in UDP.

   The basic UDP encapsulation scheme makes two assumptions:

   1.   All hosts are capable of sending and receiving multicast
        packets.

   2.   The first/last-hop routers are RSVP-capable.

   A method of relaxing the second assumption is given later.

   Let Hu be a "UDP-only" host that requires UDP encapsulation, and Hr a
   host that can do raw network I/O.  The UDP encapsulation scheme must
   allow RSVP interoperation among an arbitrary topology of Hr hosts, Hu
   hosts, and routers.

   RESV, RERR, RTEAR, and PERR messages are sent to unicast addresses
   learned from the path or reservation state in the node.  If the node
   keeps track of which previous hops and which interfaces need UDP
   encapsulation, these messages message can be sent using UDP
   encapsulation when necessary.

   On the other hand, PATH and PTEAR messages are send to the unicast or
   multicast destination address for the session.  The table in Figure
   12 shows the basic rules for UDP encapsulation of such messages.
   Under the `Send' column, the notation is `mode(destaddr, destport,
   TTL)', where TTL is the IP-layer hop count.  The `Receive' column
   shows the group that is joined and, where relevant, the UDP Listen
   port.  The following symbols are also used:

   o    D is the DestAddress for the particular session.

   o    G* is a well-known group address of the form 224.0.0.x, i.e., a
        group that is limited to the local connected network.  [TO BE
        DEFINED]

   o    Pu is the well-known UDP port for UDP encapsulation of RSVP:
        3455.

   o    Ra is the IP address of the router interface `a'.

   o    Tr is the TTL value of the specific PATH message.



Braden, Zhang, et al.     Expiration: May 1996                [Page 101]


Internet Draft             RSVP Specification              November 1995


   o    Router interface `a' is on the local network connected to Hu and
        Hr, while interface `b' is connected only to another router.


                            RSVP             RSVP
   Node  Node Type          Send             Receive
   ___   __________     _____________     _______________
   Hu   UDP-only host    UDP(G*,Pu,1)     UDP(G*,Pu)
                        or UDP(Ra,Pu,1)   and UDP(D,Pu)
                        [Note 1]          [Note 3]

   Hr   Raw-mode host    UDP(G*,Pu,1)     UDP(G*,Pu)
                        and Raw(D,,Tr)    and Raw()

   R    Router
         Interface a:    UDP(D,Pu,Tr)     UDP(G*,Pu) [Note 2]
                        and Raw(D,,Tr)    and UDP(Ra,Pu)
                                          and Raw()

         Interface b:    Raw(D,,Tr)           Raw()

           Figure 12: UDP Encapsulation Rules for Path Messages


   [Note 1] Hu sends a PATH message to Ra only if session destination
   address D is unicast.

   [Note 2] R ignores PATH messages addressed to G* if D is unicast.
   (This is necessary to prevent routing and reservation anomalies).

   [Note 3] The DestAddress D is the IP address of Hu in this case.

   R and Hr send their PATH messages twice, once with UDP encapsulation
   and once in raw mode.  In two cases (Hr -> R and Hr -> Hr), each PATH
   message will be delivered twice.  The destination may take steps to
   ignore the duplicates, although this redundancy has no ill effect
   other than overhead for processing the extra messages.

   A router may determine if its interface X needs UDP encapsulation by
   listening for UDP-encapsulated PATH messages that were sent to either
   G* (multicast D) or to the address of interface X (unicast D).  There
   is one failure mode for this scheme:  if no host on the connected
   network acts as an RSVP sender, there will be no PATH messages to
   trigger UDP encapsulation.  In this (unlikely) case, it will be
   necessary to explicitly configure UDP encapsulation on the local
   network interface of the router.

   A UDP-only host Hu supporting unicast RSVP sessions must somehow know



Braden, Zhang, et al.     Expiration: May 1996                [Page 102]


Internet Draft             RSVP Specification              November 1995


   the address Ra, presumably by configuration.

   When a UDP-encapsulated packet is received, the IP TTL is not
   available to the application on most systems.  The RSVP daemon that
   receives a UDP-encapsulated PATH or PTEAR message should therefore
   use the Send_TTL field of the RSVP common header as the effective
   receive TTL.

   We have assumed that the first-hop RSVP-capable router R is on the
   directly-connected network.  There are several possible approaches if
   this is not the case.

   1.   Hu can send both unicast and multicast sessions to
        UDP(Ra,Pu,Ta).

        Here Ta must be the TTL to exactly reach R.  If Ta is too small,
        the PATH message will not reach R.  If Ta is too large,
        multicast routing in R will forward the UDP packet into the
        Internet until its hop count expires.  This will turn on UDP
        encapsulation between routers within the Internet, causing bogus
        UDP traffic.  The host Hu must be explicitly configured with Ra
        and Ta.

   2.   A particular host on the LAN connected to Hu could be designated
        as an "RSVP relay host".  A relay host would listen on (G*,Pu)
        and forward any PATH messages directly to R, although it would
        not be in the data path.  The relay host would have to be
        configured with Ra and Ta.


APPENDIX D. Experimental and Open Issues

   D.1 Reservation Compatibility

      How strong is the requirement for compatibility of reservations in
      different directions?  For example, see Figure 10; should it be
      possible to have incompatible reservation styles on the two
      interfaces?  If R1 requests a WF reservation and R2 requests a FF
      reservation, it is logically possible to make the corresponding
      reservations on the two different interfaces.  The current
      implementation does NOT allow this; instead, it prevents mixing of
      incompatible styles in the same session on a node, even if they
      are on different interfaces.

   D.2 Session Groups (Experimental)

      Section 1.2 explained that a distinct destination address, and
      therefore a distinct session, will be used for each of the



Braden, Zhang, et al.     Expiration: May 1996                [Page 103]


Internet Draft             RSVP Specification              November 1995


      subflows in a hierarchically encoded flow.  However, these
      separate sessions are logically related.  For example it may be
      necessary to pass reservations for all subflows to Admission
      Control at the same time (since it would be nonsense to admit high
      frequency components but reject the baseband component of the
      session data).  Such a logical grouping is indicated in RSVP by
      defining a "session group", an ordered set of sessions.

      To declare that a set of sessions form a session group, a receiver
      includes a data structure we call a SESSION_GROUP object in the
      RESV message for each of the sessions.  A SESSION_GROUP object
      contains four fields: a reference address, a session group ID, a
      count, and a rank.

      o    The reference address is an agreed-upon choice from among the
           DestAddress values of the sessions in the group, for example
           the smallest numerically.

      o    The session group ID is used to distinguish different groups
           with the same reference address.

      o    The count is the number of members in the group.

      o    The rank, an integer between 1 and count, is different in
           each session of the session group.

      The SESSION_GROUP objects for all sessions in the group will
      contain the same values of the reference address, the session
      group ID, and the count value.  The rank values establishes the
      desired order among them.

      If RSVP at a given node receives a RESV message containing a
      SESSION_GROUP object, it should wait until RESV messages for all
      `count' sessions have appeared (or until the end of the refresh
      cycle) and then pass the RESV requests to Admission Control as a
      group.  It is normally expected that all sessions in the group
      will be routed through the same nodes.  However, if not, only a
      subset of the session group reservations may appear at a given
      node; in this case, the RSVP should wait until the end of the
      refresh cycle and then perform Admission Control on the subset of
      the session group that it has received.  The rank values will
      identify which are missing.

      Note that routing different sessions of the session group
      differently will generally result in delays in establishing or
      rejecting the desired QoS.  A "bundling" facility could be added
      to multicast routing, to force all sessions in a session group to
      be routed along the same path.



Braden, Zhang, et al.     Expiration: May 1996                [Page 104]


Internet Draft             RSVP Specification              November 1995


      D.2.1 Resv Messages

         Add:


          [ <SESSION_GROUP> ]


         after the SESSION object.

      D.2.2 SESSION_GROUP Class

         SESSION_GROUP class = 2.

         o    IPv4 SESSION_GROUP Object: Class = 2, C-Type = 1:


              +-------------+-------------+-------------+-------------+
              |               IPv4 Reference DestAddress              |
              +-------------+-------------+-------------+-------------+
              |      Session_Group ID     |    Count    |     Rank    |
              +-------------+-------------+-------------+-------------+


         o    IP6 SESSION_GROUP Object: Class = 2, C-Type = 2:


              +-------------+-------------+-------------+-------------+
              |                                                       |
              +                                                       +
              |                                                       |
              +               IP6 Reference DestAddress               +
              |                                                       |
              +                                                       +
              |                                                       |
              +-------------+-------------+-------------+-------------+
              |      Session-Group ID     |    Count    |     Rank    |
              +-------------+-------------+-------------+-------------+


         The variables are defined in above.

   D.3 DF Style (Experimental)

      In addition to the WF and FF styles defined in this specification,
      a Dynamic Filter (DF) style has also been proposed.  The following
      describes this style and gives examples of its usage.  At this
      time, DF style is experimental.



Braden, Zhang, et al.     Expiration: May 1996                [Page 105]


Internet Draft             RSVP Specification              November 1995


      D.3.1 Reservation Styles

         A Dynamic-Filter (DF) style reservation makes "distinct"
         reservations with "wildcard" scope, but it decouples
         reservations from filters.

         o    Each DF reservation request specifies a number D of
              distinct reservations using the same specified flowspec.
              These reservations are distributed with wildcard  scope,
              i.e., to all senders.

              The number of reservations that are actually made in a
              particular node is D' = min(D,Ns), where Ns is the total
              number of senders upstream of the node.

         o    In addition to D and the flowspec, a DF style reservation
              may also specify a list of K filterspecs, for some K in
              the range: 0 <= K <= D'.  These filterspecs define
              particular senders to use the D' reservations, and this
              list establishes the scope for the filter specs.

              Once a DF reservation has been established, the receiver
              may change the set of filterspecs to specify a different
              selection of senders, without a new admission control
              check (assuming D' and the common flowspec remain
              unchanged).  This is known as "channel switching", in
              analogy with a television set.

         In order to provide assured channel switching, each node along
         the path must reserve enough bandwidth for all D' channels,
         even though some of this bandwidth may be unused at any one
         time.  If D' changes (because the receiver changed D or because
         the number Ns of upstream sources changed), or if the common
         flowspec changes, the refresh message is treated as a new
         reservation that is subject to admission control and may fail.

         The DF style allows a receiver to switch channels without
         danger of an admission denial due to limited resources (unless
         a topology change reroutes traffic along a lower-capacity path
         or new senders appear), once the initial reservations have been
         made.  This in turn implies that the DF style creates
         reservations that may not be in use at any given time.

         The DF style is compatible with the FF style but not the WF or
         SE style.






Braden, Zhang, et al.     Expiration: May 1996                [Page 106]


Internet Draft             RSVP Specification              November 1995


      D.3.2 Examples

         To give an example of the DF style, we use the following
         notation:

         o    DF Style

              DF( n, {r} ; ) or DF( n, {r} ; S1, S2, ...)

         This message carries the count n of channels to be reserved,
         each using common flowspec r.  It also carries a list, perhaps
         empty, of filterspecs defining senders.

         Figure 13 shows an example of Dynamic-Filter reservations.  The
         receivers downstream from interface (d) have requested two
         reserved channels, but selected only one sender, S1.  The node
         reserves min(2,3) = 2 channels of size B on interface (d), and
         it then applies any specified filters to these channels.  Since
         only one sender was specified, one channel has no corresponding
         filter, as shown by `?'.

         Similarly, the receivers downstream of interface (c) have
         requested two channels and selected senders S1 and S2.  The two
         channels might have been one channel each from R1 and R2, or
         two channels requested by one of them, for example.

                           |
            Send           |      Reserve              Receive
                           |
                           |       ________
    DF( 1,{B}; S1) <- (a)  |  (c) |  S1{B} |  (c) <- DF( 2,{B}; S1, S2)
                           |      |________|
                           |      |  S2{B} |
                           |      |________|
                           |
   ------------------------|-------------------------------------------
                           |       ________
    DF( 2,{B}; S2) <- (b)  |  (d) |  S1{B} |   (d) <- DF( 2,{B}; S1)
                           |      |________|
                           |      |   ?{B} |
                           |      |________|


               Figure 13: Dynamic-Filter Reservation Example


         A router should not reserve more Dynamic-Filter channels than
         the number of upstream sources (three, in the router of Figure



Braden, Zhang, et al.     Expiration: May 1996                [Page 107]


Internet Draft             RSVP Specification              November 1995


         13).
          Since there is only one source upstream from previous hop (a),
         the first parameter of the DF message (the count of channels to
         be reserved) was decreased to 1 in the forwarded reservations.
         However, this is unnecessary, because the routers upstream will
         reserve only one channel, regardless.

         When a DF reservation is received, it is labeled with the IP
         address of the next hop (RSVP-capable) router, downstream from
         the current node.  Since the outgoing interface may be directly
         connected to a shared medium network or to a non-RSVP-capable
         router, there may be more than one next-hop node downstream; if
         so, each sends independent DF RESV messages for a given
         session.  The number N' of DF channels reserved on an outgoing
         interface is given by the formula:

         N' = min( D1+D2+...Dn, Ns),

         where Di is the D value (channel reservation count) in a RESV
         from the ith next-hop node.

         For a DF reservation request with a Dynamic Reservation Count =
         C, RSVP should call TC_AddFlowspec C times.

      D.3.3 Resv Messages

         Add the following sequence:

             <flow descriptor list> ::=

                         <FLOWSPEC> <filter spec list>


      D.3.4 STYLE Class

         o    STYLE-DF object: Class = 8, C-Type = 2

              +-------------+-------------+-------------+-------------+
              | Style ID=4  |   Attribute Vector  0...0101001b        |
              +-------------+-------------+-------------+-------------+
              |    //////       ///////   |    Dynamic Resv Count     |
              +-------------+-------------+---------------------------+

              Style ID

                   4 = Dynamic-Filter (DF)

              Attribute Vector



Braden, Zhang, et al.     Expiration: May 1996                [Page 108]


Internet Draft             RSVP Specification              November 1995


                   18 bits: Reserved

                   1 bit: Decoupled if 1.

                   2 bits: Sharing control (as before)

                   3 bits: Scope control (as before)

              Dynamic Resv Count

                   The number of channels to be reserved for a Dynamic
                   Filter style reservation.  This integer value must
                   not less than the number of FILTER_SPEC objects in
                   filter spec list.


References

[CSZ92]  Clark, D., Shenker, S., and L. Zhang, "Supporting Real-Time
    Applications in an Integrated Services Packet Network: Architecture
    and Mechanisms", Proc. SIGCOMM '92, Baltimore, MD, August 1992.

[FJ94]  Floyd, S. and V. Jacobson, "Synchronization of Periodic Routing
    Messages", IEEE/ACM Transactions on Networking, Vol. 2, No. 2,
    April, 1994.

[ISInt93]  Braden, R., Clark, D., and S. Shenker, "Integrated Services
    in the Internet Architecture: an Overview", RFC 1633, ISI, MIT, and
    PARC, June 1994.

[IServ93]  Shenker, S., Clark, D., and L. Zhang, "A Service Model for an
    Integrated Services Internet", Work in Progress, October 1993.

[Katz95]  Katz, D., "IP Router Alert Option", Internet Draft draft-
    katz-router-alert-01.txt, Cisco Systems, November 16, 1995.

[Partridge92]  Partridge, C., "A Proposed Flow Specification", RFC 1363,
    BBN, September 1992.

[RSVP93]  Zhang, L., Deering, S., Estrin, D., Shenker, S., and D.
    Zappala, "RSVP: A New Resource ReSerVation Protocol", IEEE Network,
    September 1993.

[ServTempl95a]  Shenker, S., "Network Element Service Specification
    Template", Internet Draft draft-ietf-intserv-svc-template-00.txt,
    Integrated Services Working Group, March 1995.

[Shenker94]  Shenker, S., "Two-Pass or Not Two-Pass", Current Meeting



Braden, Zhang, et al.     Expiration: May 1996                [Page 109]


Internet Draft             RSVP Specification              November 1995


    Report, RSVP Working Group, Proceedings of the Thirtieth Internet
    Engineering Task Force, Toronto, Canada, July 1994.



Security Considerations

   See Section 2.7.

Authors' Addresses

   Lixia Zhang
   Xerox Palo Alto Research Center
   3333 Coyote Hill Road
   Palo Alto, CA 94304

   Phone: (415) 812-4415
   EMail: Lixia@PARC.XEROX.COM


   Bob Braden
   USC Information Sciences Institute
   4676 Admiralty Way
   Marina del Rey, CA 90292

   Phone: (310) 822-1511
   EMail: Braden@ISI.EDU


   Deborah Estrin
   Computer Science Department
   University of Southern California
   Los Angeles, CA 90089-0871

   Phone: (213) 740-4524
   EMail: estrin@USC.EDU


   Shai Herzog
   USC Information Sciences Institute
   4676 Admiralty Way
   Marina del Rey, CA 90292
   Palo Alto, CA 94304

   Phone: (310) 822 1511
   EMail: Herzog@ISI.EDU





Braden, Zhang, et al.     Expiration: May 1996                [Page 110]


Internet Draft             RSVP Specification              November 1995


   Sugih Jamin
   Computer Science Department
   University of Southern California
   Los Angeles, CA 90089-0871

   Phone: (213) 740-6578
   EMail: jamin@catarina.usc.edu












































Braden, Zhang, et al.     Expiration: May 1996                [Page 111]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/