RSVP Aggregation over MPLS TE tunnels       July 2005

   Internet Draft                                  Francois Le Faucheur
                                                       Michael Dibiasio
                                                            Bruce Davie
                                                    Cisco Systems, Inc.

                                                      Michael Davenport
                                                         Chris Christou
                                                    Booz Allen Hamilton

                                                              Jerry Ash
                                                              Bur Goode
   Expires: January 2006                                      July 2005

        Aggregation of RSVP Reservations over MPLS TE/DS-TE Tunnels

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                RSVP Aggregation over MPLS TE tunnels       July 2005

   This document provides specification for aggregation of RSVP end-to-
   end reservations over MPLS Traffic Engineering (TE) tunnels or MPLS
   Diffserv-aware MPLS Traffic Engineering (DS-TE) Tunnels. This
   approach is based on RFC 3175 and simply modifies the corresponding
   procedures for operations over MPLS TE tunnels instead of aggregated
   RSVP reservations. This approach can be used to achieve admission
   control of a very large number of flows in a scalable manner since
   the devices in the core of the network are unaware of the end-to-end
   RSVP reservations and are only aware of the MPLS TE tunnels.

Copyright Notice
      Copyright (C) The Internet Society. (2005)

Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

1.  Introduction

   The Integrated Services (Intserv) [INT-SERV] architecture provides a
   means for the delivery of end-to-end Quality of Service (QoS) to
   applications over heterogeneous networks.

   [RSVP] defines the Resource reSerVation Protocol which can be used by
   applications to request resources from the network. The network
   responds by explicitely admitting or rejecting these RSVP requests.
   Certain applications that have quantifiable resource requirements
   express these requirements using Intserv parameters as defined in the
   appropriate Intserv service specifications ([GUARANTEED],

   The Differentiated Services (DiffServ) architecture ([DIFFSERV]) was
   then developed to support differentiated treatment of packets in very
   large scale environments. In contrast to the per-flow orientation of
   Intserv and RSVP, Diffserv networks classify packets into one of a
   small number of aggregated flows or "classes", based on the Diffserv
   codepoint (DSCP) in the packet's IP header. At each Diffserv router,
   packets are subjected to a "per-hop behavior" (PHB), which is invoked
   by the DSCP.  The primary benefit of Diffserv is its scalability.
   Diffserv eliminates the need for per-flow state and per-flow
   processing and therefore scales well to large networks.

   However, DiffServ does not include any mechanism for communication
   between applications and the network. Thus, as detailed in [INT-DIFF],
   significant benefits can be achieved by using Intserv over Diffserv

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   including resource based admission control, policy based admission
   control, assistance in traffic identification /classification and
   traffic conditioning. As discussed in [INT-DIFF], Intserv can operate
   over Diffserv in multiple ways. For example, the Diffserv region may
   be statically provisioned or may be RSVP aware. When it is RSVP aware,
   several mechanisms may be used to support dynamic provisioning and
   topology aware admission control including aggregated RSVP
   reservations, per flow RSVP or a bandwidth broker. The advantage of
   using aggregated RSVP reservations is that it offers dynamic,
   topology-aware admission control over the Diffserv region without the
   scalability burden of per-flow reservations and the associated level
   of RSVP signaling in the Diffserv core. [RSVP-AGGR] describes in
   detail how to perform such aggregation of end to end RSVP
   reservations over aggregated RSVP reservations in a Diffserv cloud.
   It establishes an architecture where multiple end-to-end RSVP
   reservations sharing the same ingress router (Aggregator) and the
   same egress router (Deaggregator) at the edges of an "aggregation
   region", can be mapped onto a single aggregate reservation within the
   aggregation region. This considerably reduces the amount of
   reservation state that needs to be maintained by routers within the
   aggregation region. Furthermore, traffic belonging to aggregate
   reservations is classified in the data path purely using Diffserv

   [MPLS-TE] describes how MPLS TE Tunnels can be established via [RSVP-
   TE] and how these tunnels can be used to carry arbitrary aggregates
   of traffic. MPLS TE uses Constraint Based Routing to compute the path
   for a TE tunnel. Then, CAC (Call Admission Control) is performed
   during the establishment of TE Tunnels to ensure they are granted
   their requested resources.

   [DSTE-REQ] presents the Service Providers requirements for support of
   Diff-Serv-aware MPLS Traffic Engineering (DS-TE). With DS-TE,
   separate DS-TE tunnels can be used to carry different Diffserv
   classes of traffic and different resource constraints can be enforced
   for these different classes. [DSTE-PROTO] specifies RSVP-TE signaling
   extensions as well as OSPF and ISIS extensions for support of DS-TE.

   In the rest of this document we will refer to both TE tunnels and DS-
   TE tunnels simply as "TE tunnels".

   TE tunnels have much in common with the aggregate RSVP reservations
   used in [RSVP-AGGR]:
      - a TE tunnel is subject to CAC and thus is effectively an
        aggregate bandwidth reservation
      - In the data plane, packet scheduling relies exclusively on
        Diff-Serv classification and PHBs
      - Both TE tunnels and Aggregate RSVP reservations are controlled
        by "intelligent" devices on the edge of the "aggregation core"

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        (Head-end and Tail-end in the case of TE tunnels, Aggregator
        and Deaggregator in the case of Aggregated RSVP reservations
      - Both TE tunnels and Aggregate RSVP reservations are signaled
        using the RSVP protocol (with some extensions defined in [RSVP-
        TE] and [DSTE-PROTO] respectively for TE tunnels and DS-TE

   This document provides a detailed specification for performing
   aggregation of end-to-end RSVP reservations over MPLS TE tunnels
   (which act as aggregated reservations in the core). This document
   builds on the RSVP Aggregation procedures defined in [RSVP-AGGR], and
   only changes those where necessary to operate over TE tunnels. With
   [RSVP-AGGR], a lot of responsibilities (such as mapping end-to-end
   reservations to Aggregate reservations and resizing the Aggregate
   reservations) are assigned to the Deaggregator (which is the
   equivalent of the Tunnel Tail-end) while with TE, the tunnels are
   controlled by the Tunnel Head-end. Hence, the main change over the
   RSVP Aggregations procedures defined in [RSVP-AGGR] is to modify
   these procedures to reassign responsibilities from the Deaggregator
   to the Aggregator (i.e. the tunnel Head-end).

   [LSP-HIER] defines how to aggregate MPLS TE Label Switched Paths
   (LSPs) by creating a hierarchy of such LSPs. This involves nesting of
   end-to-end LSPs into an aggregate LSP in the core (by using the label
   stack construct). Since end-to-end TE LSPs are themselves signaled
   with RSVP-TE and reserve resources at every hop, this can be looked
   at as a form of aggregation of RSVP(-TE) reservations over MPLS TE
   Tunnels. This document capitalizes on the similarities between
   nesting of TE LSPs over TE tunnels and RSVP aggregation over TE
   tunnels and reuses the procedures of [LSP-HIER] wherever possible.

   This document also builds on the "RSVP over Tunnels" concepts of RFC
   2746 [RSVP-TUN]. It differs from that specification in the following
     - Whereas RFC 2746 describes operation with IP tunnels, this
        draft describes operation over MPLS tunnels. One consequence of
        this difference is the need to deal with penultimate hop
        popping (PHP).
     - MPLS-TE tunnels inherently reserve resources, whereas the
        tunnels in RFC 2746 do not have resource reservations by
        default. This leads to some simplifications in the current
     - There is exactly one reservation per MPLS-TE tunnel, whereas
        RFC 2746 permits many reservations per tunnel.
     - We have assumed in the current draft that a given MPLS-TE
        tunnel will carry reserved traffic and nothing but reserved
        traffic, which negates the requirement of RFC 2746 to
        distinguish reserved and non-reserved traffic traversing the
        same tunnel by using distinct encapsulations.

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     - There may be several MPLS-TE tunnels that share common head and
        tail end routers, with head-end policy determining which tunnel
        is appropriate for a particular flow. This scenario does not
        appear to be addressed in RFC 2746.

   At the same time, this draft does have many similarities with RFC
   2746. MPLS-TE tunnels are "type 2 tunnels" in the nomenclature of RFC
      The (logical) link may be able to promise that some overall
      level of resources is available to carry traffic, but not to
      allocate resources specifically to individual data flows.

   Aggregation of end-to-end RSVP reservations over TE tunnels combines
   the benefits of [RSVP-AGGR] with the benefits of MPLS including the
      - dynamic, topology-aware resource-based admission control can be
        provided to applications over any segment of the end to end
        path including the core
      - as per regular RSVP behavior, RSVP does not impose any burden
        on routers where such admission control is not needed (for
        example if the links upstream and downstream of the MPLS TE
        core are vastly over-engineered compared to the core capacity,
        admission control is not required on these links and RSVP need
        not be processed on the corresponding router hops)
      - the core scalability is not affected (relative to the standard
        MPLS TE deployment model) since the core remains unaware of
        end-to-end RSVP reservations and only has to maintain aggregate
        TE tunnels and since the datapath classification and scheduling
        in the core relies purely on Diffserv mechanism (or more
        precisely MPLS Diffserv mechanisms as specified in [DIFF-MPLS])
      - the aggregate reservation (and thus the traffic from the
        corresponding end to end reservations) can be network
        engineered via the use of Constraint based routing (e.g.
        affinity, optimization on different metrics) and when needed
        can take advantage of resources on other paths than the
        shortest path
      - the aggregate reservations (and thus the traffic from the
        corresponding end to end reservations) can be protected against
        failure through the use of MPLS Fast Reroute

   This document, like [RSVP-AGGR], covers aggregation of unicast
   sessions. Aggregation of multicast sessions is for further study.

1.1. Changes from previous versions

   The significant changes from version draft-lefaucheur-rsvp-dste-02
   to version draft-ietf-tsvwg-rsvp-dste-00.txt of this draft are:

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      - added a SHOULD for use of Make-Before-Break when resizing TE
      - added clarification text about E2E Resv hiding from Transit
      - added reference to [RSVP-AGG-IPSEC] in section 5.
      - added definition of E2E reservation in section 2.
      - removed the case where E2E reservation is a TE tunnel (already
        covered in [LSP-HIER])

   The significant changes from version draft-lefaucheur-rsvp-dste-01 to
   version draft-lefaucheur-rsvp-dste-02 of this draft are:
      - Alignment with RSVP operations of draft-ietf-mpls-lsp-hierarchy
      - Addition of an appendix providing an example usage scenario for
        information purposes

   The significant changes from version draft-lefaucheur-rsvp-dste-00 to
   version draft-lefaucheur-rsvp-dste-01 of this draft were:
      - added discussion of the relationship to RFC 2746 [RSVP-TUN]
      - added discussion of mapping policy at aggregator
      - added discussion of "RSVP proxy" behavior in conjunction with
        the aggregation scheme described here
      - added discussion on TTL processing on Deaggregator

2.  Definitions

   For readability, a number of definitions from [RSVP-AGGR] as well as
   definitions for commonly used MPLS TE terms are provided here:

   Aggregator   This is the router at the ingress edge of the
                 aggregation region (with respect to the end to end
                 RSVP reservation) and behaving in accordance with
                 [RSVP-AGG]. In this document, it is also the TE Tunnel

   Deaggregator This is the router at the egress edge of the
                 aggregation region (with respect to the end to end
                 RSVP reservation) and behaving in accordance with
                 [RSVP-AGG]. In this document, it is also the TE Tunnel

   E2E          End to end

   E2E reservation  This is an RSVP reservation such that:
                     (i)  corresponding Path messages are initiated
                            upstream of the Aggregator and terminated
                            downstream of the Deaggregator, and

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                     (ii) corresponding Resv messages are initiated
                            downstream of the Deaggregator and
                            terminated upstream of the Aggregator, and
                     (iii) this RSVP reservation is to be aggregated
                            over an MPLS TE tunnel between the
                            Aggregator and Deaggregator.
                     An E2E RSVP reservation may be a per-flow
                     reservation. Alternatively, the E2E reservation
                     may itself be an aggregate reservation of various
                     types (e.g. Aggregate IP reservation, Aggregate
                     IPsec reservation). See section 4 and 5 for more
                     details on the types of E2E RSVP reservations. As
                     per regular RSVP operations, E2E RSVP reservations
                     are unidirectional.

                 This is the Label Switch Router responsible for
                 establishing, maintaining and tearing-off a given TE

                 This is the Label Switch Router responsible for
                 terminating a given TE tunnel

   Transit LSR  This is a Label Switch router that is on the path of a
                 given TE tunnel and is neither the Head-end nor the

3.  Operations of RSVP Aggregation over TE with pre-established Tunnels

   [RSVP-AGG] supports operations both in the case where aggregate RSVP
   reservations are pre-established and in the case where Aggregating
   and De-aggregating routers have to dynamically discover each other
   and dynamically establish the necessary Aggregated RSVP reservations.

   Similarly, RSVP Aggregation over TE tunnels could operate both in the
   case where the TE tunnels are pre-established and in the case where
   the tunnels need to be dynamically established.

   In this document we provide a detailed description of the procedures
   in the case where TE tunnels are already established. These
   procedures are based on those defined in [LSP-HIER].

   Pre-establishment of the TE tunnels may be triggered by any
   mechanisms including for example manual configuration or automatic
   establishment of a TE tunnel mesh through dynamic discovery of TE
   Mesh membership as allowed in [AUTOMESH].

   Procedures in the case of dynamically established TE tunnels are for
   further studies.

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3.1.  Reference Model

      I----I                                          I----I
   H--I R  I\ I-----I                       I------I /I R  I--H
   H--I    I\\I     I       I---I           I      I//I    I--H
      I----I \I He/ I       I T I           I Te/  I/ I----I
              I Agg I=======================I Deag I
             /I     I       I   I           I      I\
   H--------//I     I       I---I           I      I\\--------H
   H--------/ I-----I                       I------I \--------H

   H       = Host requesting end-to-end RSVP reservations
   R       = RSVP router
   He/Agg  = TE tunnel Head-end/Aggregator
   Te/Deag = TE tunnel Tail-end/Deaggregator
   T       = Transit LSR

   --    = E2E RSVP reservation
   ==    = TE Tunnel

3.2.  Receipt of E2E Path message By the Aggregator

   The first event is the arrival of the E2E Path message at the
   Aggregator. Standard RSVP procedures are followed for this path
   message (including update of the PHOP field to a local Aggregator
   address) augmented with the extensions documented in this section.

   The Aggregator first attempts to map the E2E reservation onto a TE
   tunnel. This decision is made in accordance with routing information
   as well as any local policy information that may be available at the
   Aggregator. Examples of such policies appear in the following
   paragraphs. Just for illustration purposes, among many other criteria,
   such mapping policies might take into account the Intserv service
   type, the Application Identity [RSVP-APPID] and/or the signaled
   preemption [RSVP-PREEMP] of the E2E reservation (for example, the
   aggregator may take into account the E2E reservations RSVP preemption
   priority and the MPLS TE Tunnel set-up and/or hold priorities when
   mapping the E2E reservation onto an MPLS TE tunnel).

   There are situations where the Aggregator is able to make a final
   mapping decision. That would be the case, for example, if there is a
   single TE tunnel towards the destination and if the policy is to map
   any E2E RSVP reservation onto TE Tunnels.

   There are situations where the Aggregator is not able to make a final
   determination. That would be the case, for example, if routing

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   identifies two DS-TE tunnels towards the destination, one belonging
   to DS-TE Class-Type 1 and one to Class-Type 0, if the policy is to
   map Intserv Guaranteed Services reservations to a Class-Type 1 tunnel
   and Intserv Controlled Load reservations to a Class-Type 0 tunnel,
   and if the E2E RSVP Path message advertises both Guaranteed Service
   and Controlled Load.

   Whether final or tentative, the Aggregator makes a mapping decision
   and selects a TE tunnel. Before forwarding the E2E Path message
   towards the receiver, the Aggregator should update the ADSPEC inside
   the E2E Path message to reflect the impact of the MPLS TE cloud onto
   the QoS achievable by the E2E flow. This update is a local matter and
   may be based on configured information, on information available in
   the MPLS TE topology database, on the current TE tunnel path, on
   information collected via RSVP-TE signaling, or combinations of those.

   The Aggregator then forwards the E2E Path message. In accordance with
   [LSP-HIER], the E2E Path message is:
      - sent with an IF_ID RSVP_HOP object instead of an RSVP_HOP
        object. The data interface identification identifies the TE
      - addressed directly to the Deaggregator. The destination address
        of the E2E Path message is set to the Deaggregator address and
        the Router Alert is not set. Thus, the E2E Path message will
        not be visible to Transit routers along the path of the TE
        tunnel. Thus, in contrast to the procedures of [RSVP-AGGR], the
        IP Protocol number need not be modified to "RSVP-E2E-IGNORE";
        it is left as is (indicating "RSVP").

3.3.  Handling of E2E Path message By Transit LSRs

   Since the E2E Path message is addressed directly to the Deaggreagtor
   and does not have Router Alert set, it is hidden from all transit

3.4.  Receipt of E2E Path Message by Deaggregator

   On receipt of the E2E Path message addressed to it, the Deaggregator
   will notice that the IP Protocol number is set to "RSVP" and will
   thus perform RSVP processing of the E2E Path message.

   As with [LSP-HIER], the IP TTL vs. RSVP TTL check must not be made.
   The Deaggregator is informed that this check must not be made because
   of the presence of the IF_ID RSVP HOP object. As with [LSP-HIER], the
   following checks should be made by the receiver Y of the IF_ID
   RSVP_HOP object:

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         1. Make sure that the data interface identified in the IF_ID
            RSVP_HOP object actually terminates on Y.
         2. Find the "other end" of the above data interface, say X.
            Make sure that the PHOP in the IF_ID RSVP_HOP object is a
            control channel address that belongs to the same node as X.

3.5.  Handling of E2E Resv Message by Deaggregator

   The Deaggregator follows standard RSVP procedures on receipt of the
   E2E Resv message. This includes performing admission control for the
   segment downstream of the Deaggregator and forwarding the E2E Resv
   message to the PHOP signaled earlier in the E2E Path message and
   which identifies the Aggregator. Since the E2E Resv message is
   directly addressed to the Aggregator and does not carry the Router
   Alert option (as per regular RSVP Resv procedures), the E2E Resv
   message is hidden from the transit LSRs which handle the E2E Resv
   message as a regular IP packet.

3.6.  Handling of E2E Resv Message by the Aggregator

   The Aggregator is responsible for ensuring that there is sufficient
   bandwidth available and reserved over the appropriate TE tunnel to
   the Deaggregator for the E2E reservation.

   On receipt of the E2E Resv message, the Aggregator first performs the
   final mapping onto the final TE tunnels (if it was only a tentative
   mapping). If needed the Aggregator updates the ADSPEC and immediately
   generates an E2E Path refresh in order to provide the accurate ADSPEC
   information to the receiver as soon as possible.

   The aggregator then calculates the size of the resource request using
   standard RSVP procedures. That is, it follows the procedures in
   [RFC2205] to determine the resource requirements from the Sender
   Tspec and the Flowspec contained in the Resv. It them compares the
   resource requests with the available resources of the selected TE

   If sufficient bandwidth is available on the final TE tunnel, the
   Aggregator updates its internal understanding of how much of the TE
   Tunnel is in use and forwards the E2E Resv messages to the
   corresponding PHOP.

   As noted in [RSVP-AGGR], a range of policies may be applied to the
   re-sizing of the aggregate reservation (in this case, the TE tunnel.)
   For example, the policy may be that the reserved bandwidth of the
   tunnel can only be changed by configuration. More dynamic policies
   are also possible, whereby the aggregator may attempt to increase the
   reserved bandwidth of the tunnel in response to the amount of

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   allocated bandwidth that has been used by E2E reservations.
   Furthermore, to avoid the delay associated with the increase of the
   Tunnel size, the Aggregator may attempt to anticipate the increases
   in demand and adjust the TE tunnel size ahead of actual needs by E2E
   reservations. In order to reduce disruptions, the aggregator SHOULD
   use "make-before-break" procedures as described in [RSVP-TE] to alter
   the TE tunnel bandwidth".

   If sufficient bandwidth is not available on the final TE Tunnel, the
   Aggregator must follow the normal RSVP procedure for a reservation
   being placed with insufficient bandwidth to support this reservation.
   That is, the reservation is not installed and a ResvError is sent
   back towards the receiver.

3.7.  Removal of E2E reservations

   E2E reservations are removed in the usual way via PathTear, ResvTear,
   timeout, or as the result of an error condition. When a reservation
   is removed, the Aggregator updates its local view of the
   resources available on the corresponding TE tunnel accordingly.

3.8.  Removal of TE Tunnel

   Should a TE Tunnel go away (presumably due to a configuration change,
   route change, or policy event), the aggregator behaves much like a
   conventional RSVP router in the face of a link failure. That is, it
   may try to forward the Path messages onto another tunnel, if routing
   and policy permit, or it may send Path_Error messages to the sender
   if no suitable tunnel exists. In case the Path messages are forwarded
   onto another tunnel which terminates on a different Deaggregator, or
   the reservation is torn-down via Path Error messages, the reservation
   state established on the router acting as the Deaggregator before the
   TE tunnel went away, will time out since it will no longer be

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3.9.  Example Signaling Flow

                Aggregator                      Deaggregator

                              RSVP-TE Path

                              RSVP-TE Resv

    E2E Path
                              E2E Path
                                                        E2E Path

                                                            E2E Resv
                              E2E Resv
          E2E Resv

      (*)  Aggregator is triggered to pre-establish the TE Tunnel(s)

      (**) TE Tunnel(s) are pre-established

      (1)  Aggregator tentatively selects the TE tunnel and forwards
           E2E path to Deaggregator

      (2)  Deaggregator forwards the E2E Path towards receiver

      (3)  Deaggregator forwards the E2E Resv to the Aggregator

      (4)  Aggregator selects final TE tunnel, check there is
           sufficient bandwidth on TE tunnel and forwards E2E Resv to

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4.  IPv4 and IPv6 Applicability

   The procedures defined in this document are applicable to all the
   following cases:

      (1)  Aggregation of E2E IPv4 RSVP reservations over IPv4 TE
      (2)  Aggregation of E2E IPv6 RSVP reservations over IPv6 TE
      (3)  Aggregation of E2E IPv6 RSVP reservations over IPv4 TE
           tunnels, provided a mechanism such as [6PE] is used by the
           Aggregator and Deaggregator for routing of IPv6 traffic over
           an IPv4 MPLS core,
      (4)  Aggregation of E2E IPv4 RSVP reservations over IPv6 TE
           tunnels, provided a mechanism is used by the Aggregator and
           Deaggregator for routing IPv4 traffic over IPv6 MPLS.

5.  E2E Reservations Applicability

   The procedures defined in this document are applicable to many types
   of E2E RSVP reservations including the following cases:
      (1)  the E2E RSVP reservation is a per-flow reservation where the
           flow is characterized by the usual 5-tuple
      (2)  the E2E reservation is an aggregate reservation for multiple
           flows as described in [RSVP-AGG] where the set of flows is
           characterized by the <source address, destination address,
      (3)  the E2E reservation is a reservation for an IPSec protected
           flow. For example, where the flow is characterized by the
           <source address, destination address, SPI> as described in
      (4)  the E2E reservation is an aggregate reservation for multiple
           flows and where the set of flows are protected by IPSec

6.  Example Deployment Scenarios

6.1.  Voice and Video Reservations Scenario

   An example application of the procedures specified in this document
   is admission control of voice and video in environments with very
   high numbers of hosts. In the example illustrated below, hosts
   generate end-to-end per-flow reservations for each of their video
   streams associated with a video-conference, each of their audio
   streams associated with a video-conference and each of their voice

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   calls. These reservations are aggregated over MPLS DS-TE tunnels over
   the packet core. The mapping policy defined by the user maybe that
   all the reservations for audio and voice streams are mapped onto DS-
   TE tunnels of Class-Type 1 while reservations for video streams are
   mapped onto DS-TE tunnels of Class-Type 0.

   ------                                             ------
   I H  I# -------                          -------- #I H  I
   I    I\#I     I          -----           I      I#/I    I
   -----I \I Agg I          I T I           I Deag I/ ------
           I     I==========================I      I
   ------ /I     I::::::::::I   I:::::::::::I      I\ ------
   I H  I/#I     I          -----           I      I#\I H  I
   I    I# -------                          -------- #I    I
   ------                                             ------

   H     = Host
   Agg   = Aggregator (TE Tunnel Head-end)
   Deagg = Deaggregator (TE Tunnel Tail-end)
   T     = Transit LSR

   /     = E2E RSVP reservation for a Voice flow
   #     = E2E RSVP reservation for a Video flow
   ==    = DS-TE Tunnel from Class-Type 1
   ::    = DS-TE Tunnel from Class-Type 0

6.2.  PSTN/3G Voice Trunking Scenario

   An example application of the procedures specified in this document
   is voice call admission control in large scale telephony trunking
   environments. A Trunk VoIP Gateway may generate one aggregate RSVP
   reservation for all the calls in place towards another given remote
   Trunk VoIP Gateway (with resizing of this aggregate reservation in a
   step function depending on current number of calls). In turn, these
   reservations may be aggregated over MPLS TE tunnels over the packet
   core so that tunnel Head-ends act as Aggregators and perform
   admission control of Trunk Gateway reservations into MPLS TE Tunnels.
   The MPLS TE tunnels may be protected by MPLS Fast Reroute.
   This scenario is illustrated below:

Le Faucheur, et al.                                          [Page 14]

                RSVP Aggregation over MPLS TE tunnels       July 2005

   ------                                             ------
   I GW I\ -------                          -------- /I GW I
   I    I\\I     I          -----           I      I//I    I
   -----I \I Agg I          I T I           I Deag I/ ------
           I     I==========================I      I
   ------ /I     I          I   I           I      I\ ------
   I GW I//I     I          -----           I      I\\I GW I
   I    I/ -------                          -------- \I    I
   ------                                             ------

   GW    = VoIP Gateway
   Agg   = Aggregator (TE Tunnel Head-end)
   Deagg = Deaggregator (TE Tunnel Tail-end)
   T     = Transit LSR

   /     = Aggregate Gateway to Gateway E2E RSVP reservation
   ==    = TE Tunnel

7.  Optional Use of RSVP Proxy on RSVP Aggregator

   A number of approaches ([RSVP-PROXY], [L-RSVP]) have been, or are
   being, discussed in the IETF in order to allow a network node to
   behave as an RSVP proxy which:
      - originates the Resv Message (in response to the Path message) on
   behalf of the destination node
      - originates the Path message (in response to some trigger) on
   behalf of the source node.

   We observe that such approaches may optionally be used in conjunction
   with the aggregation of RSVP reservations over MPLS TE tunnels as
   specified in this document. In particular, we consider the case where
   the RSVP Aggregator/Deaggregator also behaves as the RSVP proxy.

   As discussed in [RSVP-PROXY]:

   "The proxy functionality does not imply merely generating a single
   Resv message. Proxying the Resv involves installing state in the node
   doing the proxy i.e. the proxying node should act as if it had
   received a Resv from the true endpoint. This involves reserving
   resources (if required), sending periodic refreshes of the Resv
   message and tearing down the reservation if the Path is torn down."

   Hence, when behaving as the RSVP Proxy, the RSVP Aggregator may
   effectively perform resource reservation over the MPLS TE Tunnel (and
   hence over the whole segment between the RSVP Aggregator and the RSVP

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                RSVP Aggregation over MPLS TE tunnels       July 2005

   Deaggregator) even if the RSVP signaling only takes place upstream of
   the MPLS TE Tunnel (i.e. between the host and the RSVP aggregator).

   Also, the RSVP Proxy can generate the Path message on behalf of the
   remote source host in order to achieve reservation in the return
   direction (i.e. from RSVP aggregator/Deaggregator to host).

   The resulting Signaling Flow is illustrated below, covering
   reservations for both directions:

   I----I       I--------------I  I------I   I--------------I     I----I
   I    I       I Aggregator/  I  I MPLS I   I Aggregator/  I     I    I
   IHostI       I Deaggregator/I  I cloudI   I Deaggregator/I     IHostI
   I    I       I RSVP Proxy   I  I      I   I RSVP Proxy   I     I    I
   I----I       I--------------I  I------I   I--------------I     I----I

                      ==========TE Tunnel==========>
                      <========= TE Tunnel==========

     Path                                                      Path
    ------------> (1)-\                          /-(i)  <----------
           Resv       I                         I        Resv
    <------------ (2)-/                          \-(ii) ------------>
           Path                                        Path
    <------------ (3)                          (iii) ------------>
     Resv                                                    Resv
    ------------>                                    <------------

   (1)(i)  : Aggregator/Deaggregator/Proxy receives Path message,
   selects the TE tunnel, performs admission control over the TE Tunnel.
   (1) and (i) happens independently of each other.

   (2)(ii)  : Aggregator/Deaggregator/Proxy generates the Resv message
   towards Host. (2) is triggered by (1) and (ii) is triggered by (i).
   Before generating this Resv message, the Aggregator/Proxy performs
   admission control of the corresponding reservation over the TE tunnel
   that will eventually carry the corresponding traffic.

   (3)(iii) : Aggregator/Deaggregator/Proxy generates the Path message
   towards Host for reservation in return direction. The actual trigger
   for this depends on the actual RSVP proxy solution. As an example,
   (3) and (iii) may simply be triggered respectively by (1) and (i).

   Note that the details of the signaling flow may vary slightly
   depending on the actual approach used for RSVP Proxy. For example, if
   the [L-RSVP] approach was used instead of [RSVP-PROXY], an additional
   PathRequest message would be needed from host to

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                RSVP Aggregation over MPLS TE tunnels       July 2005

   Aggregator/Deaggregator/Proxy in order to trigger the generation of
   the Path message for return direction.

   But regardless of the details of the call flow and of the actual RSVP
   Proxy approach, RSVP proxy may optionally be deployed in combination
   with RSVP Aggregation over MPLS TE Tunnels, in such a way which
   ensures (when used on both the Host-Aggregator and Deaggregator-Host
   sides, and when both end systems support RSVP) that:

      (i)  admission control and resource reservation is performed on
             every segment of the end-to-end path (i.e. between source
             host and Aggregator, over the TE Tunnel between the
             Aggregator and Deaggregator which itself has been subject
             to admission control by MPLS TE, between Deaggregator and
             destination host)

      (ii) this is achieved in both direction

      (iii) RSVP signaling is localized between hosts and
             Aggregator/Deaggregator, which may result in significant
             reduction in reservation establishment delays (and in turn
             in post dial delay in the case where these reservations
             are pre-conditions for voice call establishment),
             particularly in the case where the MPLS TE tunnels span
             long distances with high propagation delays.

8.  Security Considerations

   The security issues inherent to the use of RSVP, RSVP Aggregation and
   MPLS TE apply. Those can be addressed as discussed in [RSVP], [RSVP-
   AGG] and [RSVP-TE].

   In addition, in the case where the Aggregators dynamically resize the
   TE tunnels based on the current level of reservation, there are risks
   that the TE tunnels used for RSVP aggregation hog resources in the
   core which could prevent other TE Tunnels from being established.
   There are also potential risks that such resizing results in
   significant computation and signaling as well as churn on tunnel
   paths. Such risks can be mitigated by configuration options allowing
   control of TE tunnel dynamic resizing (maximum Te tunnel size,
   maximum resizing frequency,...) and/or possibly by the use of TE

9.  IANA Considerations

   This document has no actions for IANA.

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                RSVP Aggregation over MPLS TE tunnels       July 2005

10.  Acknowledgments

   This document builds on the [RSVP-AGGR], [RSVP-TUN] and [LSP-HIER]
   specifications. Also, we would like to thank Tom Phelan, John Drake
   and Arthi Ayyangar for their input into this document.

11.  Normative References

   [RFC2119] S. Bradner, Key words for use in RFCs to Indicate
   Requirement Levels, RFC2119, March 1997.

   [RFC3668] S. Bradner, Intellectual Property Rights in IETF Technology,
   RFC 3668, February 2004.

   [BCP-78], S. Bradner, IETF Rights in Contributions, RFC3978, March

   [INT-SERV] Braden, R., Clark, D. and S. Shenker, Integrated Services
   in the Internet Architecture: an Overview, RFC 1633, June 1994.

   [GUARANTEED] Shenker et al., Specification of Guaranteed Quality of
   Service, RFC2212

   [CONTROLLED] Wroclawski, Specification of the Controlled-Load Network
   Element Service, RFC2211

   [DIFFSERV] Blake et al., An Architecture for Differentiated Services,
   RFC 2475

   [INT-DIFF] A Framework for Integrated Services Operation over
   Diffserv Networks, RFC 2998, November 2000.

   [RSVP-AGGR] Baker et al, Aggregation of RSVP for IPv4 and IPv6
   Reservations, RFC 3175, September 2001.

   [RSVP-TE] Awduche et al, RSVP-TE: Extensions to RSVP for LSP Tunnels,
   RFC 3209, December 2001.

   [DSTE-PROTO] Le Faucheur et al, Protocol extensions for support of
   Diff-Serv-aware MPLS Traffic Engineering, RFC 4124, June 2005.

   [LSP-HIER] Kompella et al, LSP Hierarchy with Generalized MPLS TE,
   work in progress

12.  Informative References

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                RSVP Aggregation over MPLS TE tunnels       July 2005

   [DIFF-MPLS] Le Faucheur et al, MPLS Support of Diff-Serv, RFC3270,
   May 2002.

   [DSTE-REQ] Le Faucheur et al, Requirements for support of Diff-Serv-
   aware MPLS Traffic Engineering, RFC3564, July 2003.

   [6PE] De Clercq et al, Connecting IPv6 Islands over IPv4 MPLS using
   IPv6 Provider Edge Routers (6PE), work in progress

   [RSVP-IPSEC] Berger et al, RSVP Extensions for IPSEC Data Flows, RFC

   [RSVP-AGG-IPSEC] Le Faucheur et al, Generic Aggregate RSVP
   Reservations, draft-lefaucheur-rsvp-ipsec-01.txt, work in progress

   [RSVP-TUN] Terzis et al., RSVP Operation Over IP Tunnels, RFC 2746,
   January 2000

   [RSVP-PREEMP] Herzog, Signaled Preemption Priority Policy Element,
   RFC 3181

   [L-RSVP] Manner et al., Localized RSVP, draft-manner-lrsvp-04.txt,
   work in progress.

   [RSVP-PROXY] Gai et al., RSVP Proxy, draft-ietf-rsvp-proxy-03.txt
   (expired), work in progress.

   [RSVP-APPID] Bernet et al., Identity Representation for RSVP, RFC

   [AUTOMESH] Vasseur and Leroux, Routing extensions for discovery of
   Multiprotocol (MPLS) Label Switch Router (LSR) Traffic Engineering
   (TE) mesh membership, draft-vasseur-ccamp-automesh-00.txt, work in

   [SIP-RSVP] Camarillo, Integration of Resource Management and Session
   Initiation Protocol (SIP), RFC 3312

13.  Authors Address:

   Francois Le Faucheur
   Cisco Systems, Inc.
   Village d'Entreprise Green Side - Batiment T3
   400, Avenue de Roumanille
   06410 Biot Sophia-Antipolis

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                RSVP Aggregation over MPLS TE tunnels       July 2005

   Michael DiBiasio
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough, MA 01719

   Bruce Davie
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough, MA 01719

   Christou Christou
   Booz Allen Hamilton
   8283 Greensboro Drive
   McLean, VA 22102

   Michael Davenport
   Booz Allen Hamilton
   8283 Greensboro Drive
   McLean, VA 22102

   Jerry Ash
   200 Laurel Avenue
   Middletown, NJ 07748, USA

   Bur Goode
   32 Old Orchard Drive
   Weston, CT 06883

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                RSVP Aggregation over MPLS TE tunnels       July 2005

14.  IPR Statements

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights. Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.
   Please address the information to the IETF at

15.  Disclaimer of Validity

   This document and the information contained herein are provided on an

16.  Copyright Notice

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

Appendix A - Example Usage of RSVP Aggregation over DSTE Tunnels for
VoIP Call Admission Control (CAC)

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                RSVP Aggregation over MPLS TE tunnels       July 2005

   This Appendix presents an example scenario where the mechanisms
   described in this document are used, in combination with other
   mechanisms specified by the IETF, to achieve Call Admission Control
   of Voice over IP (VoIP) traffic over the packet core.

   The information is that Appendix is purely informational and

   Consider the scenario depicted in Figure A1. VoIP Gateways GW1 and
   GW2 are both signaling and media gateways. They are connected to an
   MPLS network via edge routers PE1 and PE2, respectively. In each
   direction, a DSTE tunnel passes from the head-end edge router,
   through core network P routers, to the tail-end edge router. GW1 and
   GW2 are RSVP-enabled. The RSVP reservations established by GW1 and
   GW2 are aggregated by PE1 and PE2 over the DS-TE tunnels. For
   reservations going from GW1 to GW2, PE1 serves as the
   aggregator/head-end and PE2 serves as the de-aggregator/tail-end. For
   reservations going from GW2 to GW2, PE2 serves as the
   aggregator/head-end and PE1 serves as the de-aggregator/tail-end.

   To determine whether there is sufficient bandwidth in the MPLS core
   to complete a connection, the originating and destination GWs each
   send for each connection a Resource Reservation Protocol (RSVP)
   bandwidth request to the network PE router to which it is connected.
   The bandwidth request takes into account VoIP header compression,
   where applicable. As part of its Aggregator role, the PE router
   effectively performs admission control of the bandwidth request
   generated by the GW onto the resources of the corresponding DS-TE

   In this example, in addition to behaving as Aggregator/Deaggregator,
   PE1 and PE2 behave as RSVP proxy. So when a PE receives a Path
   message from a GW, it does not propagate the Path message any further.
   Rather, the PE performs admission control of the bandwidth signaled
   in the Path message over the DSTE tunnel towards the destination.
   Assuming there is enough bandwidth available on that tunnel, the PE
   adjusts its book-keeping of remaining available bandwidth on the
   tunnel and generates a Resv message back towards the GW to confirm
   resources have been reserved over the DSTE tunnel.

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                RSVP Aggregation over MPLS TE tunnels       July 2005

                                ,-.     ,-.
                          _.---'   `---'   `-+
                      ,-''   +------------+  :
                     (       |            |   `.
                      \     ,'    CCA     `.    :
                       \  ,' |            | `.  ;
                        ;'   +------------+   `._
                      ,'+                     ; `.
                    ,' -+   Application Layer'    `.
               SIP,'     `---+       |    ;         `.SIP
                ,'            `------+---'            `.
              ,'                                        `.
            ,'                                            `.
          ,'                  ,-.        ,-.                `.
        ,'                ,--+   `--+--'-   --'\              `._
     +-`--+_____+------+  {   +----+   +----+   `. +------+_____+----+
     |GW1 | RSVP|      |______| P  |___| P  |______|      | RSVP|GW2 |
     |    |-----| PE1  |  {   +----+   +----+    /+| PE2  |-----|    |
     |    |     |      |==========================>|      |     |    |
     +-:--+ RTP |      |<==========================|      | RTP +-:--+
      _|..__    +------+  {     DSTE Tunnels    ;  +------+ __----|--.
    _,'    \-|          ./                    -'._          /         |
    | Access  \         /        +----+           \,        |_ Access |
    | Network   |       \_       | P  |             |       /  Network |
    |          /          `|     +----+            /        |         '
    `--.  ,.__,|           |    IP/MPLS Network   /         '---'- ----'
       '`'  ''             ' .._,,'`.__   _/ '---'                |
        |                             '`'''                       |
        C1                                                        C2

      Figure A1.  Integration of SIP Resource Management, DSTE
                  and RSVP  Aggregation

   [SIP-RSVP] discusses how network quality of service can be made a
   precondition for establishment of sessions initiated by the Session
   Initiation Protocol (SIP). These preconditions require that the
   participant reserve network resources before continuing with the
   session. The reservation of network resources are performed through a
   signaling protocol such as RSVP.

   Our example environment relies of [SIP-RSVP] to synchronize RSVP
   bandwidth reservations with SIP. For example, the RSVP bandwidth
   requests may be integrated into the call setup flow as follows (See
   call setup flow diagram in Figure A2):

      - Caller C1 initiates a call by sending a SIP INVITE to VoIP
        gateway GW1, which passes the INVITE along to the call control

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                RSVP Aggregation over MPLS TE tunnels       July 2005

        agent (CCA).  The INVITE message may contain a list of codecs
        that the calling phone can support.

      - VoIP gateway GW2, chooses a compatible codec from the list and
        responds with a SIP message 183 Session Progress.

      - When GW1 receives the SIP response message and learns the codec
        to be used, it knows how much bandwidth is required for the

      - GW1 sends an RSVP Path message to PE1, requesting bandwidth for
        the call.

      - GW2 also sends an RSVP Path message to PE2.

      - Assuming that the tunnel (from left to right) has sufficient
        bandwidth, PE1 responds to GW1 with a Resv message

      - Again assuming the tunnel (from right to left) has sufficient
        bandwidth, PE2 responds to GW2 with a Resv message

      - GW2 sends a SIP 200 OK message to GW1.

      - GW1 sends a SIP UPDATE message to GW2.

      - Upon receiving the UPDATE, GW2 sends the INVITE to the
        destination phone, which responds with SIP message 180 RINGING.

      - When (and if) the called party answers, the destination phone
        responds with another SIP 200 OK which completes the connection
        and tells the calling party that there is now reserved
        bandwidth in both directions so that conversation can begin.

      - RTP media streams in both directions pass through the DSTE
        tunnels as they traverse the MPLS network.

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                RSVP Aggregation over MPLS TE tunnels       July 2005

    IP-Phone/                                                  IP-Phone/
     TA-C1      GW1     PE1         CCA          PE2      GW2      TA-C2
     |     INVITE|(SDP1) |  INVITE   |   INVITE   |        |           |
     |---------->|-------|---------->|------------|------->|           |
     |        100|TRYING |           |            |        |           |
     |<----------|-------|-----------|            |        |           |
     |        183|(SDP2) |           |            |        |           |
     |<----------|-------|-----------|------------|--------|           |
     |           | PATH  |           |            |  PATH  |           |
     |           |------>|           |            |<-------|           |
     |           | RESV  |           |            |  RESV  |           |
     |           |<------|           |            |------->|           |
     |           |       |     UPDATE|(SDP3)      |        |           |
     |           |-------|-----------|------------|------->|           |
     |           |       |     200 OK|(SDP4)      |        |           |
     |           |<------|-----------|------------|--------|  INVITE   |
     |           |       |           |            |        |---------->|
     |180 RINGING|       |        180|RINGING     |        |180 RINGING|
     | 200 OK    |    200|OK         |         200|OK      |  200 OK   |
     |           |       |           |            |        |           |
     |           |       |       DSTE|TUNNEL      |        |           |
     |        RTP|MEDIA  |-----------|------------|        |           |
     |           |       |-----------|------------|        |           |
     |           |       |           |            |        |           |
     |           |       |-----------|------------|        |           |
     |           |       |-----------|------------|        |           |
                                 DSTE TUNNEL

           Figure A2. VoIP QoS CAC using SIP with Preconditions

   Through the collaboration between SIP resource management, RSVP
   signaling, RSVP Aggregation and DS-TE as described above, we see
      a) the PE and GW collaborate to determine whether there is enough
   bandwidth on the tunnel between the calling and called GWs to
   accommodate the connection,
      b) the corresponding accept/reject decision is communicated to the
   GWs on a connection-by-connection basis, and
      c) the PE can optimize network resources by dynamically adjusting
   the bandwidth of each tunnel according to the load over that tunnel.
   For example, if a tunnel is operating near capacity, the network may
   dynamically adjust the tunnel size within a set of parameters.

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                RSVP Aggregation over MPLS TE tunnels       July 2005

   We note that admission Control of voice calls over the core network
   capacity is achieved in a hierarchical manner whereby:
      - DSTE tunnels are subject to CAC over the resources of the MPLS
        TE core
      - Voice calls are subject to CAC over the DSTE tunnel bandwidth
   This hierarchy is a key element in the scalability of this CAC
   solution for voice calls over an MPLS Core.

   It is also possible for the GWs to use aggregate RSVP reservations
   themselves instead of per-call RSVP reservations. For example,
   instead of setting one reservation for each call GW1 has in place
   towards GW2, GW1 may establish one (or a small number of) aggregate
   reservations as defined in [RSVP-AGGR] which is used for all (or a
   subset of all) the calls towards GW2. This effectively provides an
   additional level of hierarchy whereby:
         DSTE tunnels are subject to CAC over the resources of the MPLS
        TE core
      - Aggregate RSVP reservations from GW to GW are subject to CAC
        over the DSTE tunnels (as per the "RSVP Aggregation over TE
        Tunnels" procedures defined in this document)
      - Voice calls are subject to CAC by the GW over the aggregate
        reservation towards the appropriate destination GW.
   This pushes even further the scalability limits of this voice CAC

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