\
TSVWG                                                     F. Le Faucheur
Internet-Draft                                                     Cisco
Intended status: Informational                                 J. Manner
Expires: August 28, 2007                          University of Helsinki
                                                                 D. Wing
                                                                   Cisco
                                                              A. Guillou
                                                                    Neuf
                                                       February 24, 2007


                         RSVP Proxy Approaches
             draft-ietf-tsvwg-rsvp-proxy-approaches-00.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   RSVP signaling can be used to make end-to-end resource reservations
   in an IP network in order to guarantee the QoS required by certain
   flows.  With conventional RSVP, both the data sender and receiver of



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   a given flow take part in RSVP signaling.  Yet, there are many use
   cases where resource reservation is required, but the receiver, the
   sender, or both, is not RSVP-capable.  This document presents RSVP
   Proxy behaviors allowing RSVP routers to perform RSVP signaling on
   behalf of a receiver or a sender that is not RSVP-capable.  This
   allows resource reservations to be established on parts of the end-
   to-end path.  This document reviews conceptual approaches for
   deploying RSVP Proxies and discusses how those can synchronize RSVP
   reservations with application requirements.  This document also
   points out where extensions to RSVP (or to other protocols) may be
   needed for deployment of a given RSVP Proxy approach.  However, such
   extensions are outside the scope of this document.  Finally,
   practical use cases for RSVP Proxy are described.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  RSVP Proxy Behaviors . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  RSVP Receiver Proxy  . . . . . . . . . . . . . . . . . . .  4
     2.2.  RSVP Sender Proxy  . . . . . . . . . . . . . . . . . . . .  5
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  RSVP Proxy Approaches  . . . . . . . . . . . . . . . . . . . .  7
     4.1.  Path-Triggered Receiver Proxy  . . . . . . . . . . . . . .  7
     4.2.  Path-Triggered Sender Proxy for Reverse Direction  . . . . 10
     4.3.  Inspection-Triggered Proxy . . . . . . . . . . . . . . . . 13
     4.4.  STUN-Triggered Proxy . . . . . . . . . . . . . . . . . . . 15
     4.5.  Application-Signaling-Triggered On-Path Proxy  . . . . . . 17
     4.6.  Application-Signaling-Triggered Off-Path Source Proxy  . . 21
     4.7.  RSVP-Signaling-Triggered Proxy . . . . . . . . . . . . . . 23
     4.8.  Other Approaches . . . . . . . . . . . . . . . . . . . . . 24
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 25
   8.  Informative References . . . . . . . . . . . . . . . . . . . . 25
   Appendix A.  Use Cases for RSVP Proxies  . . . . . . . . . . . . . 27
     A.1.  RSVP-based VoD CAC in Broadband Aggregation Networks . . . 27
     A.2.  RSVP-based Voice/Video CAC in Enterprise WAN . . . . . . . 31
     A.3.  RSVP-based Voice CAC in TSP Domain . . . . . . . . . . . . 33
     A.4.  RSVP Proxies for Mobile Access Networks  . . . . . . . . . 34
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
   Intellectual Property and Copyright Statements . . . . . . . . . . 37









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1.  Introduction

   Guaranteed QoS for some applications with tight QoS requirements may
   be achieved by reserving resources in each node on the end-to-end
   path.  The main IETF protocol for these resource reservations is
   RSVP, specified in [RFC2205].  RSVP does not require that all
   intermediate nodes support RSVP, however it assumes that both the
   sender and the receiver of the data flow support RSVP.  There are
   environments where it would be useful to be able to reserve resources
   for a flow on at least a subset of the flow path even when the sender
   or the receiver (or both) is not RSVP capable.

   Since the data sender or receiver may be unaware of RSVP, there are
   two scenarios.  In the first case, an entity in the network must
   operate on behalf of the data sender, generate an RSVP Path message,
   and eventually receive, process and sink a Resv message.  We refer to
   this entity as the RSVP Sender Proxy.  In the latter case, an entity
   in the network must receive a Path message sent by a data sender (or
   by an RSVP Sender Proxy), and reply to it with a Resv message on
   behalf of the data receiver(s).  We refer to this entity as the RSVP
   Receiver Proxy.

   The flow sender and receiver generally have at least some (if not
   full) awareness of the application producing or consuming that flow.
   Hence, the sender and receiver are in a natural position to
   synchronize the establishment, maintenance and tear down of the RSVP
   reservation with the application requirements and to determine the
   characteristics of the reservation (bandwidth, QoS service,...) which
   best match the application requirements.  For example, before
   completing the establishment of a multimedia session, the endpoints
   may decide to establish RSVP reservations for the corresponding
   flows.  Similarly, when the multimedia session is torn down, the
   endpoints may decide to tear down the corresponding RSVP
   reservations.  For example, [RFC3312] discusses how RSVP reservations
   can be very tightly synchronised by SIP endpoints with SIP session
   control and SIP signaling.

   When RSVP reservation establishment, maintenance and tear down is to
   be handled by RSVP Proxy devices on behalf of an RSVP sender or
   receiver, a key challenge for the RSVP proxy is to determine when the
   RSVP reservations need to be established, maintained and torn down
   and to determine what are the characteristics (bandwidth, QoS
   Service,...) of the required RSVP reservations matching the
   application requirements.  We refer to this problem as the
   synchronization of RSVP reservations with application level
   requirements.

   The IETF Next Steps in Signaling (NSIS) working group is designing,



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   as one their many charter items, a new QoS signaling protocol.  This
   scheme already includes the notion of proxy operation, and
   terminating QoS signaling on nodes that are not the actual data
   senders or receivers.  This is the same concept as the proxy
   operation for RSVP discussed in this document.  One difference though
   is that the NSIS framework does not consider multicast resource
   reservations, which RSVP provides today.

   The next two sections introduce the notion of RSVP Sender Proxy and
   RSVP receiver Proxy.  The following section defines useful
   terminology.  The subsequent section then presents several
   fundamental RSVP Proxy approaches insisting on how they achieve the
   synchronization of RSVP reservations with application level
   requirements.  Appendix A includes more detailed use cases for the
   proxies in various deployment environments.


2.  RSVP Proxy Behaviors

   This section discusses the two types of proxies; the RSVP Sender
   Proxy operating on behalf of data senders, and the RSVP Receiver
   Proxy operating for data receivers.  The concepts presented in this
   document are not meant to replace the standard RSVP and end-to-end
   RSVP reservations are still expected to be used whenever possible.
   However, RSVP Proxies are intended to facilitate RSVP deployment
   where end-to-end RSVP signaling is not possible.

2.1.  RSVP Receiver Proxy

   With conventional RSVP operations, RSVP reservations are controlled
   by receivers of data.  After a data sender has sent an RSVP Path
   message towards the intended recipient(s), each recipient that
   requires a reservation generates a Resv message.  If, however, a data
   receiver is not running the RSVP protocol, the last hop RSVP router
   will still send the Path message to the data receiver, which will
   silently drop this message as an IP packet with an unknown protocol
   number.

   In order for reservations to be made in such a scenario, one of the
   RSVP routers on the data path must somehow know that the data
   receiver will not be participating in the resource reservation
   signaling.  This RSVP router should, thus, perform RSVP Receiver
   Proxy functionality on behalf of the data receiver.  This is
   illustrated in the figure below.  Various mechanisms by which the
   RSVP proxy router can gain the required information are discussed
   later in the document.





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    |----|         ***          ***         |----------|          |----|
    | S  |---------*r*----------*r*---------| RSVP     |----------| R  |
    |----|         ***          ***         | Receiver |          |----|
                                            | Proxy    |
                                            |----------|

      *************************************************************>

      ===================RSVP======================>


 |----| RSVP-capable     |----| non-RSVP-capable       ***
 | S  | Sender           | R  | Receiver               *r* regular RSVP
 |----|                  |----|                        *** router


 ***> unidirectional media flow

 ==>  segment of flow path protected by RSVP reservation


                       Figure 1: RSVP Receiver Proxy

2.2.  RSVP Sender Proxy

   With conventional RSVP operations, If a data sender is not running
   the RSVP protocol, a resource reservation can not be set up; a data
   receiver can not alone reserve resources without Path messages first
   being sent.  Thus, even if the data receiver is running RSVP, it
   still needs some node on the data path to send a Path message towards
   the data receiver.

   In that case, in a similar manner to the RSVP Receiver Proxy
   described before, an RSVP node on the data path must somehow know
   that it should generate a Path message for setting up a resource
   reservation.  This case is more complex than the Receiver Proxy,
   since the RSVP Sender Proxy must be able to generate all the
   information in the Path message (such as the Sender TSpec) without
   the benefit of having previously seen any RSVP messages.  An RSVP
   Receiver Proxy, by contrast only needs to formulate an appropriate
   Resv message in response to an incoming Path message.  Mechanisms to
   operate an RSVP Sender Proxy are discussed later in this document.









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    |----|         |----------|         ***          ***          |----|
    | S  |---------| RSVP     |---------*r*----------*r*----------| R  |
    |----|         | Sender   |         ***          ***          |----|
                   | Proxy    |
                   |----------|

      *************************************************************>

                         ================RSVP======================>


 |----| non-RSVP-capable     |----| RSVP-capable       ***
 | S  | Sender               | R  | Receiver           *r* regular RSVP
 |----|                      |----|                    *** router


 ***> unidirectional media flow

 ==>  segment of flow path protected by RSVP reservation


                        Figure 2: RSVP Sender Proxy


3.  Terminology

   On-Path: located on the datapath of the actual flow of data from the
   application (regardless of where it is located on the application
   level signaling path)

   Off-Path: not On-Path

   RSVP-capable (or RSVP-aware): which supports the RSVP protocol as per
   [RFC2205]

   RSVP Receiver Proxy: an RSVP capable router performing, on behalf of
   a receiver, the RSVP operations which would normally be performed by
   an RSVP-capable receiver if end-to-end RSVP signaling was used.  Note
   that while RSVP is used upstream of the RSVP Receiver Proxy, RSVP is
   not used downstream of the RSVP Receiver Proxy.

   RSVP Sender Proxy: an RSVP capable router performing, on behalf of a
   sender, the RSVP operations which would normally be performed by an
   RSVP-capable sender if end-to-end RSVP signaling was used.  Note that
   while RSVP is used downstream of the RSVP Sender Proxy, RSVP is not
   used upstream of the RSVP Sender Proxy.

   Regular RSVP Router: an RSVP-capable router which is not behaving as



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   a RSVP Receiver Proxy nor as a RSVP Sender Proxy.

   Note that the roles of RSVP Receiver Proxy, RSVP Sender Proxy,
   Regular RSVP Router are all relative to one unidirectional flow.  A
   given router may act as the RSVP Receiver Proxy for a flow, as the
   RSVP Sender Proxy for another flow and as a Regular RSVP router for
   yet another flow.

   Application level signaling: signaling between entities operating
   above the IP layer and which are aware of the QoS requirements for
   actual media flows.  SIP and RTSP are examples of application level
   signaling protocol.  RSVP is clearly not an application level
   signaling.


4.  RSVP Proxy Approaches

   This section specifies several fundamental RSVP Proxy approaches.

4.1.  Path-Triggered Receiver Proxy

   In this approach, it is assumed that the sender is RSVP capable and
   takes full care of the synchronisation between application
   requirements and RSVP reservations.  With this approach, the RSVP
   Receiver Proxy uses the RSVP Path messages generated by the sender as
   the cue for establishing the RSVP reservation on behalf of the
   receiver.  The RSVP Receiver Proxy is effectively acting as a slave
   making reservations (on behalf of the receiver) under the sender's
   control.  This changes somewhat the usual RSVP reservation model
   where reservations are normally controlled by receivers.  Such a
   change greatly facilitates operations in the scenario of interest
   here, which is where the receiver is not RSVP capable.  Indeed it
   allows the RSVP Receiver Proxy to remain application unaware by
   taking advantage of the application awareness and RSVP awareness of
   the sender.

   With the Path-Triggered RSVP Receiver Proxy approach, the RSVP router
   may be configured to use receipt of a regular RSVP Path message as
   the trigger for RSVP Receiver Proxy behavior.

   On receipt of the RSVP Path message, the RSVP Receiver Proxy:

   1.  establishes the RSVP Path state as per regular RSVP processing

   2.  identifies the downstream interface towards the receiver

   3.  sinks the Path message




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   4.  behaves as if a Resv message (whose details are discussed below)
       was received on the downstream interface.  This includes
       performing admission control on the downstream interface,
       establishing a Resv state (in case of successful admission
       control) and forwarding the Resv message upstream, sending
       periodic refreshes of the Resv message and tearing down the
       reservation if the Path state is torn down.

   In order to build the Resv message, the RSVP Receiver Proxy can take
   into account information received in the Path message.  For example,
   the RSVP Receiver Proxy may compose a FLOWSPEC object for the Resv
   message which mirrors the SENDER_TSPEC object in the received Path
   message.

   Operation of the Path-Triggered Receiver Proxy in the case of a
   successful reservation is illustrated in the Figure below.


    |----|         ***          ***         |----------|          |----|
    | S  |---------*r*----------*r*---------| RSVP     |----------| R  |
    |----|         ***          ***         | Receiver |          |----|
                                            | Proxy    |
                                            |----------|

      *************************************************************>

      ===================RSVP======================>

         ---Path---> ----Path----> ---Path---->

         <--Resv---> <---Resv----- <--Resv----


 |----| RSVP-capable     |----| Non-RSCP-capable        ***
 | S  | Sender           | R  | Receiver                *r* regular RSVP
 |----|                  |----|                         *** router


 ***> media flow

 ==>  segment of flow path protected by RSVP reservation


               Figure 3: Path-Triggered RSVP Receiver Proxy

   In case the reservation establishment is rejected (for example
   because of an admission control failure on a regular RSVP router on
   the path between the RSVP-capable sender and the RSVP Receiver



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   Proxy), a ResvErr message will be generated as per conventional RSVP
   operations and will travel downstream towards the RSVP Receiver
   Proxy.  While this ensures that the RSVP Receiver Proxy is aware of
   the reservation failure, conventional RSVP procedures do not cater
   for notification of the sender of the reservation failure.  Operation
   of the Path-Triggered RSVP Receiver Proxy in the case of an admission
   control failure is illustrated in the Figure below.


    |----|         ***          ***         |----------|          |----|
    | S  |---------*r*----------*r*---------| RSVP     |----------| R  |
    |----|         ***          ***         | Receiver |          |----|
                                            | Proxy    |
                                            |----------|

      *************************************************************>

      ===================RSVP======================>

         ---Path---> ----Path----> ---Path---->

                    <---Resv----- <--Resv------

                    ---ResvErr---> --ResvErr--->




 |----| RSVP-capable     |----| Non-RSCP-capable       ***
 | S  | Sender           | R  | Receiver               *r* regular RSVP
 |----|                  |----|                        *** router

 ***> media flow

 ==>  segment of flow path protected by RSVP reservation


         Figure 4: Path-Triggered RSVP Receiver Proxy with Failure

   Since, as explained above, in this scenario involving the RSVP
   Receiver Proxy, synchronisation between application and RSVP
   reservation is generally performed by the sender, notifying the
   sender of reservation failure is needed.
   [I-D.ietf-tsvwg-rsvp-proxy-proto] specifies RSVP extensions allowing
   such sender notification in case of reservation failure.






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4.2.  Path-Triggered Sender Proxy for Reverse Direction

   In this approach, it is assumed that one endpoint is RSVP capable and
   takes full care of the synchronisation between application
   requirements and RSVP reservations.  This endpoint is the sender for
   one flow direction (which we refer to as the "forward" direction) and
   is the receiver for the flow in the opposite direction (which we
   refer to as the "reverse" direction).

   With the Path-Triggered Sender Proxy for Reverse Direction approach,
   the RSVP Proxy uses the RSVP signaling generated by the sender as the
   cue for initiating RSVP signaling for the reservation in the reverse
   direction.  Thus, the RSVP Proxy is effectively acting as a Sender
   Proxy for the reverse direction under the control of the sender for
   the forward direction.  Note that this assumes a degree of symmetry
   for the two directions of the flow (as is currently typical for IP
   telephony, for example).

   This is illustrated in the Figure below.
































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    |----|         ***          ***         |----------|          |----|
    | E  |---------*r*----------*r*---------| RSVP     |----------| E  |
    |----|         ***          ***         | Sender   |          |----|
                                            | Proxy    |
                                            |----------|

      *************************************************************>

      <===================RSVP======================

         ---Path---> ----Path----> ---Path---->

         <--Path---> <---Path----- <--Path----

         ---Resv---> ----Resv----> ---Resv---->


 |----|                     ***
 | E  | Endpoint            *r* regular RSVP
 |----|                     *** router


 ***> media flow

 ==>  segment of flow path protected by RSVP reservation
      in reverse direction


        Figure 5: Path-Triggered Sender Proxy for Reverse Direction

   Of course, the RSVP Proxy may simultaneously (and typically will)
   also act as the Path-Triggered Receiver Proxy for the forward
   direction, as defined in Section 4.1.  Such an approach is most
   useful in situations involving RSVP reservations in both directions
   for symmetric flows.  This is illustrated in the Figure below
















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    |----|         ***          ***         |----------|          |----|
    | E  |---------*r*----------*r*---------| RSVP     |----------| E  |
    |----|         ***          ***         | Receiver |          |----|
                                            | & Sender |
                                            | Proxy    |
                                            |----------|

      *************************************************************>

      <===================RSVP=====================>

         ---Path---> ----Path----> ---Path---->

         <--Resv---> <---Resv----- <--Resv----

         <--Path---> <---Path----- <--Path----

         ---Resv---> ----Resv----> ---Resv---->


 |----|                     ***
 | E  | Endpoint            *r* regular RSVP
 |----|                     *** router


 <***> media flow

 <==>  segment of flow path protected by RSVP reservation
       in forward and in reverse direction


             Figure 6: Path Triggered Receiver & Sender Proxy

   With the Path-Triggered Sender Proxy for Reverse Direction approach,
   the RSVP router may be configurable to use receipt of a regular RSVP
   Path message as the trigger for Sender Proxy for Reverse Direction
   behavior.

   On receipt of the RSVP Path message for the forward direction, the
   RSVP Sender Receiver Proxy :

   1.  sinks the Path message

   2.  behaves as if a Path message for reverse direction (whose details
       are discussed below) had been received by the Sender Proxy.  This
       includes establishing the corresponding Path state, forwarding
       the Path message downstream, sending periodic refreshes of the
       Path message and tearing down the Path in reverse direction when



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       the Path state in forward direction is torn down.

   In order to build the Path message for the reverse direction, the
   RSVP Sender Proxy can take into account information in the received
   Path message for the forward direction.  For example, the RSVP Sender
   Proxy may mirror the SENDER_TSPEC object in the received Path
   message.

   We observe that this approach does not require any extensions to the
   existing RSVP protocol.

4.3.  Inspection-Triggered Proxy

   In this approach, it is assumed that the RSVP Proxy device is on the
   datapath of "packets of interest", that it can inspect such packets
   on the fly as they transit through it, and that it can infer
   information from these packets of interest to determine what RSVP
   reservations need to be established, when and with what
   characteristics (possibly also using some configured information).

   One example of "packets of interest" could be application level
   signaling.  An RSVP Proxy device capable of inspecting SIP signaling
   for multimedia session or RTSP signaling for Video streaming, can
   obtain from such signaling information about when a multimedia
   session is up or when a Video is going to be streamed.  It can also
   identify the addresses and ports of senders and receivers and can
   determine the bandwidth of the corresponding flows.  Thus, such an
   RSVP Proxy device can determine all necessary information to
   synchronise RSVP reservations to application requirements.  This is
   illustrated in the Figure below.





















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                               |-------------|
                               | Application |
                               | Signaling   |
                               | Entity      |
                               |-------------|
                                   // \\
                                  //   \\
                                 //     \\
       <//////////////////////////       \\\\\\\\\\\\\\\\\\\\\\\\\\>

     |----|        |--------|      ***        |--------|          |----|
     | E  |--------| RSVP   |------*r*--------| RSVP   |----------| E  |
     |----|        | Proxy  |      ***        | Proxy  |          |----|
                   |--------|                 |--------|

       <************************************************************>

                      <=========RSVP=============>



  |----|
  | E  | End system (sender, or receiver, or both)
  |----|

  ***
  *r*   Regular RSVP router
  ***

  <///> application level signaling

  <***> media flow

  <==>  segment of flow path protected by RSVP reservation


                 Figure 7: Inspection-Triggered RSVP Proxy

   Another example of "packets of interest" could be packets belonging
   to the application flow itself (e.g. media packets).  An RSVP Proxy
   device capable of detecting the transit of packets from a particular
   flow, can attempt to establish a reservation corresponding to that
   flow.  Characteristics of the reservation may be derived from
   configuration, flow measurement or a combination of those.

   Note however, that in case of reservation failure, the inspection-
   triggered RSVP Proxy does not have a direct mechanism for notifying
   the application (since it is not participating itself actively in



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   application signaling) so that the application takes appropriate
   action (for example terminate the corresponding session).  To
   mitigate this problem, the inspection-triggered RSVP Proxy may mark
   differently the DSCP of flows for which an RSVP reservation has been
   successfully proxied from the flows for which a reservation is not in
   place.  In some situations, the Inspection-Triggered Proxy might be
   able to modify the "packets of interest" (e.g. application signaling
   messages) to convey some hint to applications that the corresponding
   flows cannot be guaranteed by RSVP reservations.

   With the inspection-triggered Proxy approach, the RSVP Receiver Proxy
   is effectively required to attempt to build application awareness by
   traffic inspection and then is somewhat limited in the actions in can
   take in case of reservation failure.  However, this may be a useful
   approach in some environments.  Note also that this approach does not
   require any change to the RSVP protocol.

   With the "Inspection-Triggered" RSVP Proxy approach, the RSVP router
   may be configurable to use and interpret some specific "packets of
   interest" as the trigger for RSVP Receiver Proxy behavior.

4.4.  STUN-Triggered Proxy

   In this approach, the RSVP Proxy entity takes advantage of the
   application awareness provided by the STUN signaling to synchronise
   RSVP reservations with application requirements.  The STUN signaling
   is sent from endpoint to endpoint.  This is illustrated in the figure
   below.























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                                  |---------|
                                  | SIP     |
                                  | Server  |
                                  |---------|
                                 //         \\
                                //           \\
                               //             \\
                              //               \\
                             //                 \\
     |----|        |--------|      ***        |--------|          |----|
     | E  |--------| RSVP   |------*r*--------| RSVP   |----------| E  |
     |----|        | Proxy  |      ***        | Proxy  |          |----|
                   |--------|                 |--------|


       <**************************************************************>

                          <=========RSVP=============>

  |----|
  | E  | End system (sender, or receiver, or both) also STUN Clients
  |----|

  ***
  *r*   Regular RSVP router
  ***

  <***> STUN message flow and RTP media flow (over same UDP ports)

  <==>  segment of flow path protected by RSVP reservation

  //    signaling


                      Figure 8: STUN-Triggered Proxy

   In this approach, a STUN [I-D.ietf-behave-rfc3489bis] message
   triggers the RSVP proxy.  Using a STUN message eases the RSVP proxy
   agent's computational burden because it need only look for STUN
   messages rather than maintain state of all flows.  More importantly,
   the STUN message can also include a STUN attribute describing the
   bandwidth and describing the application requesting the flow, which
   allows the RSVP proxy agent to authorize an appropriately-sized
   reservation for each flow.

   For unicast flows, [I-D.ietf-mmusic-ice] is an already widely-adopted
   emerging standard for NAT traversal.  For our purposes, we are not
   interested in its NAT traversal capabilities.  Rather, ICE's useful



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   characteristic is its connectivity check -- the exchange of STUN
   Binding Request messages between hosts to verify connectivity (see
   Connectivity Check Usage in [I-D.ietf-behave-rfc3489bis]).  By
   including new STUN attributes in those messages an RSVP proxy agent
   could perform its functions more effectively.  Additionally, the RSVP
   proxy agent can inform endpoints of an RSVP reservation failure by
   dropping the ICE connectivity check message.  This provides very
   RSVP-like call admission control and signaling to the endpoints,
   without implementing RSVP on the endpoints.

   For multicast flows (or certain kinds of unicast flows that don't or
   can't use ICE), a STUN Indication message
   [I-D.ietf-behave-rfc3489bis] could be used for similar purposes.  The
   STUN Indication message is not acknowledged by its receiver and has
   the same scalability as the underlying multicast flow itself.

   The corresponding extensions to ICE and STUN for such a STUN-
   triggered RSVP Proxy approach are beyond the scope of this document.
   They may be defined in the future in a separate document.

4.5.  Application-Signaling-Triggered On-Path Proxy

   In this approach, it is assumed that an entity involved in the
   application level signaling controls an RSVP Proxy device which is
   located in the datapath of the application flows (i.e. "on-path").
   In this case, the RSVP Proxy entity does not attempt to understand
   the application reservation requirements, but instead is instructed
   by the entity participating in application level signaling to
   establish, maintain and tear down reservations as needed by the
   application flows.  In other words, with this approach, the solution
   for synchronising RSVP signaling with application-level signaling is
   to rely on an application-level signaling entity which controls an
   RSVP Proxy function that sits in the flow datapath.

   In some instantiations, the application-level signaling entity may be
   collocated with the on-path RSVP Proxy device.  The figure below
   illustrates such an environment in the case where the application-
   level signaling protocol is SIP.













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                    |--------|                |--------|
         -----------|SIP     |----------------|SIP     |----------
        /           |Server/ |                |Server/ |          \
       /            |Proxy   |                |Server/ |           \
   |----|           |--------|      ***       |--------|          |----|
   | E  |-----------| Bearer |------*r*-------| Bearer |----------| E  |
   |----|           | Path   |      ***       | Path   |          |----|
                    | Entity |                | Entity |
                    |  +     |                |    +   |
                    | RSVP   |                | RSVP   |
                    | Proxy  |                | Proxy  |
                    |--------|                |--------|

     <******************> <***********************> <***************>

                        <=========RSVP=============>

|----|
| E  | End system (sender, or receiver, or both)
|----|

***
*r*   Regular RSVP router
***

<***> media flow

<==>  segment of flow path protected by RSVP reservation

/    SIP signaling


          Figure 9: Application-Signaling-Triggered On-Path Proxy

   This RSVP Proxy approach does not require any protocol extensions.
   We also observe that when multiple sessions are to be established
   between two given such RSVP Proxy, the RSVP Proxy have the option to
   establish aggregate RSVP reservations (as defined in ([RFC3175] or
   [I-D.ietf-tsvwg-rsvp-ipsec]) for a group of sessions, instead of
   establishing one RSVP reservation per session.

   Consider an environment involving decomposed Session Border
   Controllers (SBCs).  The SBC function may be broken up into a
   Signaling Border Element (SBE) and Datapath Border Elements (DBEs).
   The DBEs are remotely controled by the SBE.  This may be achieved
   using a protocol like [RFC3525].  Where admission control and
   bandwidth reservation is required between the SBEs for QoS guarantees
   of the sessions, the SBE could implement RSVP Proxy functionality.



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   In that case, the application-level signaling entity (the SBE) is
   remotely located from the on-path RSVP Proxy devices (located in the
   DBEs).  Such an environment is illustrated in the Figure below.
















































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                                |---------|
               -----------------| SBE     |------------------
              /                 |         |                  \
             /                  |---------|                   \
            /                  //         \\                   \
           /                  //           \\                   \
          /                  //             \\                   \
         /                  //               \\                   \
        /                  //                 \\                   \
   |----|           |--------|      ***       |--------|          |----|
   | E  |-----------| DBE    |------*r*-------| DBE    |----------| E  |
   |----|           |        |      ***       |        |          |----|
                    |  +     |                |    +   |
                    | RSVP   |                | RSVP   |
                    | Proxy  |                | Proxy  |
                    |--------|                |--------|

     <******************> <***********************> <***************>

                        <=========RSVP=============>

|----|
| E  | End system (sender, or receiver, or both)
|----|

***
*r*   Regular RSVP router
***

SBE  Signaling Border Element
DBE  Datapath Border Element
SBE + DBE = decomposed Session Border Controller (decomposed SBC)

<***> media flow

<==>  segment of flow path protected by RSVP reservation

/    SIP signaling

//   control interface between the SBE and DBE


                Figure 10: Remote Signaling Border Element

   This RSVP Proxy approach does not require any extension to the RSVP
   protocol.  However, it may require extensions to the protocol (e.g.
   that may be based on [RFC3525]) used by the application level
   signaling entity to control the remote on-path RSVP Proxy entities.



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4.6.  Application-Signaling-Triggered Off-Path Source Proxy

   In this approach, it is assumed that an entity involved in the
   application level signaling also behaves as the RSVP Source Proxy
   device.  However, since such an application level signaling entity is
   generally not on the datapath of the actual application flows, the
   RSVP messages need to be logically "tunnelled" between the off-path
   RSVP Source Proxy and a router in the datapath and upstream of the
   segment of the path to be protected by RSVP reservations.  This is to
   ensure that the RSVP messages follow the exact same path as the flow
   they protect (as required by RSVP operations) on the segment of the
   end-to-end path which is to be subject to RSVP reservations.

   With this approach, the solution for synchronising RSVP signaling
   with application-level signaling is to co-locale the RSVP Proxy
   function with a (typically) off-path application-level signaling
   entity and then "tunnel" the RSVP signaling towards the appropriate
   router in the datapath.

   The figure below illustrates such an environment.































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                                |-------------|
                  --------------| Application |-----------
                 /              | Signaling   |           \
                /               | Entity  +   |            \
               /                | RSVP Sender |             \
              /                 | Proxy       |              \
             /                  |-------------|               \
            /                  /=/                             \
           /                  /=/                               \
          /                  /=/                                 \
         /                  /=/                                   \
        /                  /=/                                     \
   |----|           |--------|           ***                      |----|
   | S  |-----------| RSVP   |-----------*r*----------------------| R  |
   |----|           | Router |           ***                      |----|
                    |--------|

     ****************************************************************>

                        =========RSVP==============================>


|----|                  |----|               ***
| S  | Sender           | R  | Receiver      *r* regular RSVP
|----|                  |----|               *** router

<***> media flow

==>  segment of flow path protected by RSVP reservation
     in forward direction

/    Application level signaling

/*/  GRE-tunnelled RSVP (Path messages)


     Figure 11: Application-Signaling-Triggered Off-Path Source Proxy

   With the "Application-Triggered Off-Path Source Proxy" approach, the
   RSVP Source Proxy :

   o  generates a Path message on behalf of the sender, corresponding to
      the reservation needed by the application and maintains the
      corresponding Path state.  The Path message built by the Source
      Proxy is exactly the same as would be built by the actual sender
      (if it was RSVP capable), with one single exception which is that
      the RSVP Sender Proxy put its own IP address as the RSVP Previous
      Hop. In particular, it is recommended that the source address of



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      the Path message built by the RSVP Source Proxy be set to the IP
      address of the sender (not of the Sender Proxy).  This helps
      ensuring that, in the presence of non-RSVP routers and of load-
      balancing in the network where the load-balancing algorithm takes
      into account the source IP address, the Path message generated by
      the Sender Proxy follows the exact same path that the actual
      stream sourced by the sender.

   o  encapsulates the Path message into a GRE tunnel whose destination
      address is an RSVP Router sitting on the datapath for the flow
      (and upstream of the segment which requires QoS guarantees via
      RSVP reservation).

   o  processes the corresponding received RSVP messages (including Resv
      messages) as per regular RSVP.

   o  synchronises the RSVP reservation state with application level
      requirements and signaling.

   Note that since the Off-Path Source Proxy encodes its own IP address
   as the RSVP PHOP in the Path message, the RSVP Router terminating the
   GRE tunnel naturally addresses all the RSVP messages travelling
   upstream hop-by-hop (such as Resv messages) to the Off-Path Source
   Proxy (without having to encapsulate those in a reverse-direction GRE
   tunnel to the Off-Path Proxy).

   This RSVP Proxy approach does not require any extension to the RSVP
   protocol.  It only requires tunneling of the downstream end-to-end
   routed RSVP messages (in particular the Path messages) in a GRE
   tunnel.

4.7.  RSVP-Signaling-Triggered Proxy

   An RSVP proxy can also be triggered and controlled through extended
   RSVP signaling from the remote end that is RSVP-capable (and supports
   these RSVP extensions for Proxy control).  For example, an RSVP
   capable sender could send a new or extended RSVP message explicitely
   requesting an RSVP Proxy device on the path towards the receiver to
   behave as an RSVP Receiver Proxy and also to trigger a reverse
   direction reservation thus also behaving as a sender proxy.  The new
   or extended RSVP message sent by the sender could also include
   attributes (e.g. bandwidth) for the reservations to be signaled by
   the RSVP Proxy.

   The challenges in these explicit signaling schemes are:

   o  How does the proxy differentiate between reservation requests that
      must be proxied, from requests that should go end-to-end?



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   o  How does the node sending the explicit messages know where the
      proxy is located, e.g., an IP address of the proxy that should
      reply to the signaling?

   o  How are sender and receiver proxy operations differentiated?

   An example of such a mechanism is presented in
   [I-D.manner-tsvwg-rsvp-proxy-sig].  This scheme is primarily targeted
   to local access network reservations whereby an end host can request
   resource reservations for both incoming and outgoing flows only over
   the access network.  This may be useful in environments where the
   access network is typically the bottleneck while the core is
   comparatively over-provisioned, as may be the case with a number of
   radio access technologies.  In this proposal, messages targeted to
   the proxy are flagged with one bit in all RSVP message.  Similarly,
   all messages sent by the proxy back are marked.  The use of one bit
   allows differentiating between proxied and end-to-end reservations.
   For triggering an RSVP receiver proxy, the sender of the data sends a
   PATH message which is marked with the mentioned one bit.  The
   receiver proxy is located on the signaling and data path, eventually
   gets the PATH message, and replies back with a RESV.  A node triggers
   an RSVP sender proxy with a new PATH_REQUEST message, which instructs
   the proxy to send a PATH messages towards the triggering node.  The
   node then replies back with a RESV.  More details can be found in
   [I-D.manner-tsvwg-rsvp-proxy-sig].

   Such RSVP-Signaling-Triggered Proxy approaches require RSVP signaling
   extensions which are outside the scope of the present document,
   however they can provide more flexibility in the control of the Proxy
   behavior (e.g. control of reverse reservation parameters).

4.8.  Other Approaches

   In some cases, having a full RSVP implementation running on an end
   host can be seen to produce excessive overhead.  In end-hosts that
   are low in processing power and functionality, having an RSVP daemon
   run and take care of the signaling may introduce unnecessary
   overhead.  One article [Kars01] proposes to create a remote API so
   that the daemon would in fact run on the end-host's default router
   and the end-host application would send its requests to that daemon.
   Thus, we can have deployments, where an end host uses some
   proprietary simple protocol to communicate with its pre-defined RSVP
   router - a form of RSVP proxy.


5.  Security Considerations

   In the environments concerned by this document, RSVP messages are



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   used to control resource reservations on a segment of the end-to-end
   path of flows.  To ensure the integrity of the associated reservation
   and admission control mechanisms, the mechanisms defined in
   [RFC2747]] and [RFC3097] can be used.  Those protect RSVP messages
   integrity hop-by-hop and provide node authentication, thereby
   protecting against corruption and spoofing of RSVP messages.

   An important issue regarding the various types of proxy functionality
   is authorization: which node is authorized to send messages on behalf
   of the data sender or receiver, and how is the authorization
   verified?  RFC 3520 [RFC3520] presents a mechanism to include
   authorization information within RSVP signaling messages.  Subsequent
   versions of this document will discuss in more details how such
   mechanisms can be used to address security of RSVP Proxy approaches.


6.  IANA Considerations

   This document does not make any request to IANA registration.


7.  Acknowledgments

   This document benefited from earlier work on the concept of RSVP
   Proxy including the one documented by Silvano Gai, Dinesh Dutt,
   Nitsan Elfassy and Yoram Bernet.  It also benefited from discussions
   with Pratik Bose, Chris Christou and Michael Davenport.


8.  Informative References

   [I-D.ietf-behave-rfc3489bis]
              Rosenberg, J., "Simple Traversal Underneath Network
              Address Translators (NAT) (STUN)",
              draft-ietf-behave-rfc3489bis-05 (work in progress),
              October 2006.

   [I-D.ietf-mmusic-ice]
              Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Methodology for Network  Address Translator (NAT)
              Traversal for Offer/Answer Protocols",
              draft-ietf-mmusic-ice-13 (work in progress), January 2007.

   [I-D.ietf-tsvwg-rsvp-ipsec]
              Le Faucheur, L., "Generic Aggregate Resource ReSerVation
              Protocol (RSVP) Reservations", February 2007.

   [I-D.ietf-tsvwg-rsvp-proxy-proto]



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              Le Faucheur, L., "RSVP Extensions For Path-Triggered RSVP
              Receiver Proxy", February 2007.

   [I-D.manner-tsvwg-rsvp-proxy-sig]
              Manner, J., "Localized RSVP for Controlling RSVP Proxies",
              October 2006.

   [Kars01]   Karsten, M., "Experimental Extensions to RSVP -- Remote
              Client and One-Pass Signalling", IWQoS Karlsruhe, Germany,
              2006.

   [RFC1633]  Braden, B., Clark, D., and S. Shenker, "Integrated
              Services in the Internet Architecture: an Overview",
              RFC 1633, June 1994.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC2210]  Wroclawski, J., "The Use of RSVP with IETF Integrated
              Services", RFC 2210, September 1997.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, December 1998.

   [RFC2747]  Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
              Authentication", RFC 2747, January 2000.

   [RFC2961]  Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
              and S. Molendini, "RSVP Refresh Overhead Reduction
              Extensions", RFC 2961, April 2001.

   [RFC3097]  Braden, R. and L. Zhang, "RSVP Cryptographic
              Authentication -- Updated Message Type Value", RFC 3097,
              April 2001.

   [RFC3175]  Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
              "Aggregation of RSVP for IPv4 and IPv6 Reservations",
              RFC 3175, September 2001.

   [RFC3312]  Camarillo, G., Marshall, W., and J. Rosenberg,
              "Integration of Resource Management and Session Initiation
              Protocol (SIP)", RFC 3312, October 2002.

   [RFC3520]  Hamer, L-N., Gage, B., Kosinski, B., and H. Shieh,
              "Session Authorization Policy Element", RFC 3520,
              April 2003.



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   [RFC3525]  Groves, C., Pantaleo, M., Anderson, T., and T. Taylor,
              "Gateway Control Protocol Version 1", RFC 3525, June 2003.


Appendix A.  Use Cases for RSVP Proxies

A.1.  RSVP-based VoD CAC in Broadband Aggregation Networks

   As broadband services for residential are becoming more and more
   prevalent, next generation aggregation networks are being deployed in
   order to aggregate traffic from broadband users (whether attached via
   Digital Subscriber Line technology aka DSL, Fiber To The Home/Curb
   aka FTTx, Cable or other broadband access technology) and service
   providers core network or service delivery platforms.  Video on
   Demand (VoD) services which may be offered to broadband users present
   significant capacity planning challenges for the aggregation network
   because each VoD stream requires significant dedicated sustained
   bandwidth (typically 2-4 Mb/s in Standard Definition TV and 8-12 Mb/s
   in High Definition TV), the VoD codec algorithms are very sensitive
   to packet loss and the load resulting from such services is very hard
   to predict (e.g. it can vary very suddenly with block-buster titles
   made available as well as with commercial offerings).  As a result,
   transport of VoD streams on the aggregation network usually translate
   into a strong requirement for admission control, so that the quality
   of established VoD sessions can be protected at all times by
   rejecting the excessive session attempts during unpredictable peaks,
   during link or node failures, or combination of those factors.

   RSVP can be used in the aggregation network for admission control of
   the VoD sessions.  However, since Customer Premises equipment such as
   Set Top Boxes (which behave as the receiver for VoD streams) often do
   not yet support RSVP, the last IP hop in the aggregation network can
   behave as an RSVP Receiver Proxy.  This way, RSVP can be used between
   VoD Pumps and the Last IP hop in the Aggregation network to perform
   accurate admission control of VoD streams over the resources set
   aside for VoD in the aggregation network (typically a certain
   percentage of the bandwidth of any link).  As VoD streams are
   unidirectional, a simple "Path-Triggered" RSVP Receiver Proxy (as
   described in Section 4.1) is all that is required in this use case.

   The Figure below illustrates operation of RSVP-based admission
   control of VoD sessions in an Aggregation network involving RSVP
   support on the VoD Pump (the senders) and RSVP Receiver Proxy on the
   last IP hop of the aggregation network.  All the customer premises
   equipment remain RSVP unaware.






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                         |-------------|
                     ----| VoD  SRM    |-----------
                    /    |             |           \
                   /     |             |            \
                  /      |             |             \
                 /       |             |              \
                /        |-------------|               \
               /                                        \
              /                                          \
             /                                            \
            /                                              \
           /                                                \
      |----|  |------|    ***  ***  |--------|  |-----|    |---|
      | VoD|--|RSVP  |----*r*--*r*--|RSVP    |--|DSLAM|~~~~|STB|--TV
      |Pump|  |Router|    ***  ***  |Receiver|  |-----|    |---|
      |----|  |------|              |Proxy   |
                                    |--------|

               <---Aggregation Net------------->

        ******************************************************>

         ====================RSVP==============>


   SRM Systems Resource Manager

   ***                       |---|
   *r* regular RSVP          |STB| Set Top Box
   *** router                |---|

   <***> media flow

   ==>  segment of flow path protected by RSVP reservation
        in forward direction

   /    VoD Application level signaling



                Figure 12: VoD Use Case with Receiver Proxy

   In the case where the VoD Pumps are not RSVP-capable, an Application-
   Signaling-triggered Off-Path Source Proxy (as described in
   Section 4.6) can also be implemented on the VoD Controller or Systems
   Resource Manager (SRM) devices typically involved in VoD deployments.
   The Figure below illustrates operation of RSVP-based admission
   control of VoD sessions in an Aggregation network involving such



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   Application-Signaling-triggered Off-Path Source Proxy on the SRM and
   RSVP Receiver Proxy on the Last IP hop of the aggregation network.
   All the customer premises equipment, as well as the VoD pumps, remain
   RSVP unaware.















































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                         |-------------|
                     ----| VoD  SRM    |-----------
                    /    |             |           \
                   /     |     +       |            \
                  /      | RSVP Sender |             \
                 /       | Proxy       |              \
                /        |-------------|               \
               /        /=/                             \
              /        /=/                               \
             /        /=/                                 \
            /        /=/                                   \
           /        /=/                                     \
      |----|  |------|    ***  ***  |--------|  |-----|    |---|
      | VoD|--|RSVP  |----*r*--*r*--|RSVP    |--|DSLAM|~~~~|STB|--TV
      |Pump|  |Router|    ***  ***  |Receiver|  |-----|    |---|
      |----|  |------|              |Proxy   |
                                    |--------|

               <---Aggregation Net------------->

        ******************************************************>

               ==============RSVP==============>


   SRM Systems Resource Manager

   ***                       |---|
   *r* regular RSVP          |STB| Set Top Box
   *** router                |---|

   <***> media flow

   ==>  segment of flow path protected by RSVP reservation
        in forward direction

   /    VoD Application level signaling

   /*/  GRE-tunnelled RSVP (Path messages)


     Figure 13: VoD Use Case with Receiver Proxy and SRM-based Sender
                                   Proxy

   The RSVP Proxy entities specified in this document play a significant
   role here since they allow immediate deployment of an RSVP-based
   admission control solution for VoD without requiring any upgrade to
   the huge installed base of non-RSVP-capable customer premises



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   equipment.  In one mode described above, they also avoid upgrade of
   non-RSVP-capable VoD pumps.  In turn, this means that the benefits of
   on-path admission control can be offered to VoD services over
   broadband aggregation networks.  Those include accurate bandwidth
   accounting regardless of topology (hub-and-spoke, ring, mesh, star,
   arbitrary combinations) and dynamic adjustment to any change in
   topology (such as failure, routing change, additional links...).

A.2.  RSVP-based Voice/Video CAC in Enterprise WAN

   More and more enterprises are migrating their telephony and
   videoconferencing applications onto IP.  When doing so, there is a
   need for retaining admission control capabilities of existing TDM-
   based systems to ensure the QoS of these applications is maintained
   even when transiting through the enterprise's Wide Area Network
   (WAN).  Since many of the endpoints already deployed (such as IP
   Phones or Videoconferencing terminals) are not RSVP capable, RSVP
   Proxy approaches are very useful by allowing deployment of an RSVP-
   based admission control solution over the WAN without requiring
   upgrade of the existing terminals.

   A common deployment architecture for such environments involves
   Application-Signaling-Triggered On-Path RSVP Proxy as defined in
   Section 4.5.  Routers sitting at the edges of the WAN network behave
   as Media Relay in the datapath.  For example, such a Media Relay
   router on the WAN Edge may terminate a call-leg from the calling IP
   phone and relay it to another call-leg setup on the WAN side towards
   another Media Relay router on the egress side of the WAN towards the
   called IP phone.  Finally that egress Media Relay router may
   terminate the call leg from the ingress Media Relay router and relay
   it onto a call-leg setup to the called IP Phone.  The Media Relay
   routers setup, maintain and tear down the call-legs on the WAN
   segment under the control of the SIP Server/Proxy.  They also
   establish, maintain and tear-down RSVP reservations over the WAN
   segment for these call-legs also under the control of the SIP Server/
   Proxy.  The SIP Server/Proxy synchronises the RSVP reservation status
   with the status of end-to-end calls.  For example, the called IP
   phone will only be instructed to play a ring tone if the RSVP
   reservations for the corresponding WAN call leg has been successfully
   established.

   This architecture allowing RSVP-based admission control of voice and
   video on the Enterprise WAN is illustrated in the Figure below.








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                                 |---------|
                   --------------| SIP     |------------
                  /              | Server/ |            \
                 /               | Proxy   |             \
                /                |---------|              \
               /                //       \\                \
              /                //         \\                \
             /                //           \\                \
            /                //             \\                \
           /                //               \\                \
      |-----|      |--------|   ***   ***   |--------|       |-----|
      | IP  |------| Media  |---*r*---*r*---| Media  |-------|IP   |
      |Phone|      | Relay  |   ***   ***   | Relay  |       |Phone|
      |-----|      |  +     |               |    +   |       |-----|
                   | RSVP   |               | RSVP   |
                   | Proxy  |               | Proxy  |
                   |--------|               |--------|

        <--campus-->                               <--campus-->
          network                                    network

                        <---------WAN----------->

        <*************> <***********************> <**************>

                       <=========RSVP===========>



   ***
   *r*   Regular RSVP router
   ***

   <***> media flow

   <==>  segment of flow path protected by RSVP reservation

   /    SIP signaling

   //   control interface between the SIP Server/Proxy and
        Media Relay/RSVP Proxy


                 Figure 14: CAC on Enterprise WAN Use Case







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A.3.  RSVP-based Voice CAC in TSP Domain

   Let us consider an environment involving multiple Telephony Service
   Providers (TSPs).  Those may be interconnected through Session Border
   Controllers (SBC) which are on-path i.e. on the datapath of the voice
   media streams.  The SBCs may be remotely controlled by a SIP Server/
   Proxy.  Support of RSVP Proxy on one side of the SBC may be used to
   perform RSVP-based admission control through one of the TSP Domain,
   even if it is not used end-to-end (and in particular when another TSP
   domain remains entirely non-RSVP-aware).  This relies on the
   Application-Signaling-Triggered On-Path RSVP Proxy presented in
   Section 4.5.  This is illustrated in the Figure below.







































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                                 |---------|
                   --------------| SIP     |------------
                  /              | Server/ |            \
                 /               | Proxy   |             \
                /                |---------|              \
               /                     ||                    \
              /                      ||                     \
             /                       ||                      \
            /                        ||                       \
           /                         ||                        \
      |-----|      |---------|     |--------|     |---------|  |-----|
      | IP  |------| TSP     |-----| SBC    |-----| TSP     |--|IP   |
      |Phone|      | Domain1 |     |   +    |     | Domain2 |  |Phone|
      |-----|      |         |     | RSVP   |     |         |  |-----|
                   |         |     | Proxy  |     |         |
                   |         |     |--------|     |         |
                   |---------|                    |---------|

        <******************************> <*************************>

                                         <=========RSVP===========>


   <***> media flow

   <==>  segment of flow path protected by RSVP reservation

   /    SIP signaling

   ||   control interface between the SIP Server/Proxy and
        SBC/RSVP Proxy


                    Figure 15: Voice CAC in TSP Domain

A.4.  RSVP Proxies for Mobile Access Networks

   Mobile access networks are increasingly based on IP technology.  This
   implies that, on the network layer, all traffic, both traditional
   data and streamed data like audio or video, is transmitted as
   packets.  Increasingly popular multimedia applications would benefit
   from better than best-effort service from the network, a forwarding
   service with strict Quality of Service (QoS) with guaranteed minimum
   bandwidth and bounded delay.  Other applications, such as electronic
   commerce, network control and management, and remote login
   applications, would also benefit from a differentiated treatment.

   The IETF has two main models for providing differentiated treatment



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   of packets in routers.  The Integrated Services (IntServ) model
   [RFC1633] together with the Resource Reservation Protocol (RSVP)
   [RFC2205] [RFC2210] [RFC2961] provides per-flow guaranteed end-to-end
   transmission service.  The Differentiated Services (DiffServ)
   framework [RFC2475] provides non- signaled flow differentiation that
   usually provides, but does not guarantee, proper transmission
   service.

   However, these architectures have weaknesses, for example, RSVP
   requires support from both communication end points, and the protocol
   may have potential performance issues in mobile environments.
   DiffServ can only provide statistical guarantees and is not well
   suited for dynamic environments.

   Let us consider a scenario, where a fixed network correspondent node
   (CN) would be sending a multimedia stream to an end host behind a
   wireless link.  If the correspondent node does not support RSVP it
   cannot signal its traffic characteristics to the network and request
   specific forwarding services.  Likewise, if the correspondent node is
   not able to mark its traffic with a proper DiffServ Code Point (DSCP)
   to trigger service differentiation, the multimedia stream will get
   only best-effort service which may result in poor visual and audio
   quality in the receiving application.  Even if the connecting wired
   network is over-provisioned, an end host would still benefit from
   local resource reservations, especially in wireless access networks,
   where the bottleneck resource is most probably the wireless link.

   RSVP proxies would be a very beneficial solution to this problem.  It
   would allow distinguishing local network reservations from the end-
   to-end reservations.  The end host does not need to know the access
   network topology or the nodes that will reserve the local resources.
   The access network would do resource reservations for both incoming
   and outgoing flows based on certain criterion, e.g., filters based on
   application protocols.  Another option is that the mobile end host
   makes an explicit reservation that identifies the intention and the
   access network will find the correct local access network node(s) to
   respond to the reservation.  RSVP proxies would, thus, allow resource
   reservation over the segment which is the most likely bottleneck, the
   wireless connectivity.  If the wireless access network uses a local
   mobility management mechanism, where the IP address of the mobile
   node does not change during handover, RSVP reservations would follow
   the mobile node movement.









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Authors' Addresses

   Francois Le Faucheur
   Cisco Systems
   Greenside, 400 Avenue de Roumanille
   Sophia Antipolis  06410
   France

   Phone: +33 4 97 23 26 19
   Email: flefauch@cisco.com


   Jukka Manner
   University of Helsinki
   P.O. Box 68
   University of Helsinki  FIN-00014 University of Helsinki
   Finland

   Phone: +358 9 191 51298
   Email: jmanner@cs.helsinki.fi
   URI:   http://www.cs.helsinki.fi/u/jmanner/


   Dan Wing
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   United States

   Email: dwing@cisco.com


   Allan Guillou
   Neuf Cegetel
   40-42 Quai du Point du Jour
   Boulogne-Billancourt,   92659
   France

   Email: allan.guillou@neufcegetl.fr












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Full Copyright Statement

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