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RFC 4804 - Aggregation of Resource ReSerVation Protocol (RSVP) R


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Network Working Group                                F. Le Faucheur, Ed.
Request for Comments: 4804                           Cisco Systems, Inc.
Category: Standards Track                                  February 2007

          Aggregation of Resource ReSerVation Protocol (RSVP)
                Reservations over MPLS TE/DS-TE Tunnels

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   RFC 3175 specifies aggregation of Resource ReSerVation Protocol
   (RSVP) end-to-end reservations over aggregate RSVP reservations.
   This document specifies 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 aggregate 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.

Table of Contents

   1. Introduction ....................................................3
   2. Specification of Requirements ...................................7
   3. Definitions .....................................................7
   4. Operations of RSVP Aggregation over TE with
      Pre-established Tunnels .........................................8
      4.1. Reference Model ............................................9
      4.2. Receipt of E2E Path Message by the Aggregator ..............9
      4.3. Handling of E2E Path Message by Transit LSRs ..............11
      4.4. Receipt of E2E Path Message by the Deaggregator ...........11
      4.5. Handling of E2E Resv Message by the Deaggregator ..........12
      4.6. Handling of E2E Resv Message by the Aggregator ............12
      4.7. Forwarding of E2E Traffic by the Aggregator ...............14
      4.8. Removal of E2E Reservations ...............................14
      4.9. Removal of the TE Tunnel ..................................14
      4.10. Example Signaling Flow ...................................15
   5. IPv4 and IPv6 Applicability ....................................16
   6. E2E Reservations Applicability .................................16
   7. Example Deployment Scenarios ...................................16
      7.1. Voice and Video Reservations Scenario .....................16
      7.2. PSTN/3G Voice Trunking Scenario ...........................17
   8. Security Considerations ........................................18
   9. Acknowledgments ................................................20
   10. Normative References ..........................................20
   11. Informative References ........................................21
   Appendix A - Optional Use of RSVP Proxy on RSVP Aggregator ........23
   Appendix B - Example Usage of RSVP Aggregation over DSTE Tunnels
                for VoIP Call Admission Control (CAC) ................25

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 that can be used by
   applications to request resources from the network.  The network
   responds by explicitly 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],
   [CONTROLLED]).

   The Differentiated Services (DiffServ) architecture ([DIFFSERV]) was
   then developed to support the 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 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 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 RSVP aware.  When it is RSVP aware, several mechanisms
   may be used to support dynamic provisioning and topology-aware
   admission control, including aggregate RSVP reservations, per-flow
   RSVP, or a bandwidth broker.  The advantage of using aggregate RSVP
   reservations is that it offers dynamic, topology-aware admission
   control over the Diffserv region without per-flow reservations and
   the associated level of RSVP signaling in the Diffserv core.  In
   turn, this allows dynamic, topology-aware admission control of flows
   requiring QoS reservations over the Diffserv core even when the total
   number of such flows carried over the Diffserv core is extremely
   large.

   [RSVP-AGG] and [RSVP-GEN-AGG] describe in detail how to perform such
   aggregation of end-to-end RSVP reservations over aggregate RSVP
   reservations in a Diffserv cloud.  They establish an architecture

   where multiple end-to-end RSVP reservations sharing the same ingress
   router (Aggregator) and 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 marking.

   [MPLS-TE] describes how MPLS Traffic Engineering (TE) tunnels can be
   used to carry arbitrary aggregates of traffic for the purposes of
   traffic engineering.  [RSVP-TE] specifies how such MPLS TE tunnels
   can be established using RSVP-TE signaling.  MPLS TE uses
   Constraint-Based Routing to compute the path for a TE tunnel.  Then,
   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
   Diffserv-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 Intermediate System to
   Intermediate System (IS-IS) 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-AGG] and [RSVP-GEN-AGG]:

      - A TE tunnel is subject to Admission Control and thus is
        effectively an aggregate bandwidth reservation.

      - In the data plane, packet scheduling relies exclusively on
        Diffserv classification and PHBs.

      - Both TE tunnels and aggregate RSVP reservations are controlled
        by "intelligent" devices on the edge of the "aggregation core"
        (Head-end and Tail-end in the case of TE tunnels; Aggregator and
        Deaggregator in the case of aggregate 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
        tunnels).

   This document provides a detailed specification for performing
   aggregation of end-to-end RSVP reservations over MPLS TE tunnels
   (which act as aggregate reservations in the core).  This document
   builds on the RSVP Aggregation procedures defined in [RSVP-AGG] and
   [RSVP-GEN-AGG], and only changes those where necessary to operate
   over TE tunnels.  With [RSVP-AGG] and [RSVP-GEN-AGG], 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-AGG] and [RSVP-GEN-AGG] 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
   ways:

      - This document describes operation over MPLS tunnels, whereas RFC
        2746 describes operation with IP 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
        document.

      - This document builds on the fact that there is exactly one
        aggregate reservation per MPLS-TE tunnel, whereas RFC 2746
        permits a model where one reservation is established on the
        tunnel path for each end-to-end flow.

      - We have assumed in the current document 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.

      - There may be several MPLS-TE tunnels that share common Head-end
        and Tail-end routers, with the 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 document does have many similarities with RFC
   2746.  MPLS-TE tunnels are "type 2 tunnels" in the nomenclature of
   RFC 2746:

      "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-AGG] and [RSVP-GEN-AGG] with the benefits of
   MPLS, including the following:

      - Applications can benefit from dynamic, topology-aware,
        resource-based admission control 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 over-engineered links and RSVP
        need not be processed on the corresponding router hops).

      - The core scalability is not affected (relative to the
        traditional MPLS TE deployment model) since the core remains
        unaware of end-to-end RSVP reservations and only has to maintain
        aggregate TE tunnels since the datapath classification and
        scheduling in the core relies purely on the Diffserv mechanism
        (or more precisely the 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-AGG] and [RSVP-GEN-AGG], covers aggregation
   of unicast sessions.  Aggregation of multicast sessions is for
   further study.

2.  Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].

3.  Definitions

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

   Aggregator       This is the process in (or associated with) 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 Head-end.

   Deaggregator     This is the process in (or associated with) 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 Tail-end

   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

                    (ii)  corresponding Resv messages are initiated
                          downstream of the Deaggregator and terminated
                          upstream of the Aggregator, and

                    (iii) this RSVP reservation is 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 5 and 6 for more details
                    on the types of E2E RSVP reservations.  As per
                    regular RSVP operations, E2E RSVP reservations are
                    unidirectional.

   Head-end         This is the Label Switch Router responsible for
                    establishing, maintaining, and tearing down a given
                    TE tunnel.

   Tail-end         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 Tail-end.

4.  Operations of RSVP Aggregation over TE with Pre-established Tunnels

   [RSVP-AGG] and [RSVP-GEN-AGG] support operations both in the case
   where aggregate RSVP reservations are pre-established and where
   Aggregators and Deaggregators have to dynamically discover each other
   and dynamically establish the necessary aggregate RSVP reservations.

   Similarly, RSVP Aggregation over TE tunnels could operate both in the
   case where the TE tunnels are pre-established and 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].  The routing
   aspects discussed in Section 3 of [LSP-HIER] are not relevant here
   because those aim at allowing the constraint based routing of end-
   to-end TE LSPs to take into account the (aggregate) TE tunnels.  In
   the present document, the end-to-end RSVP reservations to be
   aggregated over the TE tunnels rely on regular SPF routing.  However,
   as already mentioned in [LSP-HIER], we note that a TE tunnel may be
   advertised into IS-IS or OSPF, to be used in normal SPF by nodes
   upstream of the Aggregator.  This would affect SPF routing and thus
   routing of end-to-end RSVP reservations.  The control of aggregation
   boundaries discussed in Section 6 of [LSP-HIER] is also not relevant
   here.  This uses information exchanged in GMPLS protocols to
   dynamically discover the aggregation boundary.  In this document, TE
   tunnels are pre-established, so that the aggregation boundary can be
   easily inferred.  The signaling aspects discussed in Section 6.2 of

   [LSP-HIER] apply to the establishment/termination of the aggregate TE
   tunnels when this is triggered by GMPLS mechanisms (e.g., as a result
   of an end-to-end TE LSP establishment request received at the
   aggregation boundary).  As this document assumes pre-established
   tunnels, those aspects are not relevant here.  The signaling aspects
   discussed in Section 6.1 of [LSP-HIER] relate to the
   establishment/maintenance of the end-to-end TE LSPs over the
   aggregate TE tunnel.  This document describes how to use the same
   procedures as those specified in Section 6.1 of [LSP-HIER], but for
   the establishment of end-to-end RSVP reservations (instead of end-
   to-end TE LSPs) over the TE tunnels.  This is covered further in
   Section 4 of the present document.

   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.

4.1.  Reference Model

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

4.2.  Receipt of E2E Path Message by the Aggregator

   The first event is the arrival of the E2E Path message at the
   Aggregator.  The Aggregator MUST follow traditional RSVP procedures
   for the processing of this E2E path message augmented with the
   extensions documented in this section.

   The Aggregator MUST first attempt 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 setup 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 toward 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
   identifies two DS-TE tunnels toward 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
   toward 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 the information
   available in the MPLS TE topology database, on the current TE tunnel
   path, on information collected via RSVP-TE signaling, or a
   combination thereof.  Updating the ADSPEC allows receivers that take
   into account the information collected in the ADSPEC within the
   network (such as delay and bandwidth estimates) to make more informed
   reservation decisions.

   The Aggregator MUST then forward the E2E Path message to the
   Deaggregator (which is the Tail-end of the selected TE tunnel).  In
   accordance with [LSP-HIER], the Aggregator MUST send the E2E Path
   message with an IF_ID RSVP_HOP object instead of an RSVP_HOP object.
   The data interface identification MUST identify the TE tunnel.

   To send the E2E Path message, the Aggregator MUST address it directly
   to the Deaggregator by setting the destination address in the IP
   Header of the E2E Path message to the Deaggregator address.  The
   Router Alert is not set in the E2E Path message.

   Optionally, the Aggregator MAY also encapsulate the E2E Path message
   in an IP tunnel or in the TE tunnel itself.

   Regardless of the encapsulation method, the Router Alert is not set.
   Thus, the E2E Path message will not be visible to routers along the
   path from the Aggregator to the Deaggregator.  Therefore, in contrast
   to the procedures of [RSVP-AGG] and [RSVP-GEN-AGG], the IP Protocol
   number does not need to be modified to "RSVP-E2E-IGNORE"; it MUST be
   left as is (indicating "RSVP") by the Aggregator.

   In some environments, the Aggregator and Deaggregator MAY also act as
   IPsec Security Gateways in order to provide IPsec protection to E2E
   traffic when it transits between the Aggregator and the Deaggregator.
   In that case, to transmit the E2E Path message to the Deaggregator,
   the Aggregator MUST send the E2E Path message into the relevant IPsec
   tunnel terminating on the Deaggregator.

   E2E PathTear and ResvConf messages MUST be forwarded by the
   Aggregator to the Deaggregator exactly like Path messages.

4.3.  Handling of E2E Path Message by Transit LSRs

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

4.4.  Receipt of E2E Path Message by the Deaggregator

   Upon 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 is not to be made
   because of the presence of the IF_ID RSVP HOP object.

   The Deaggregator MAY support the option to perform the following
   checks (defined in [LSP-HIER]) by the receiver Y of the IF_ID
   RSVP_HOP object:

   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, i.e., 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.

   The information necessary to perform these checks may not always be
   available to the Deaggregator.  Hence, the Deaggregator MUST support
   operations in such environments where the checks cannot be made.

   The Deaggregator MUST forward the E2E Path downstream toward the
   receiver.  In doing so, the Deaggregator sets the destination address
   in the IP header of the E2E Path message to the IP address found in
   the destination address field of the Session object.  The
   Deaggregator also sets the Router Alert.

   An E2E PathErr sent by the Deaggregator in response to the E2E Path
   message (which contains an IF_ID RSVP_HOP object) SHOULD contain an
   IF_ID RSVP_HOP object.

4.5.  Handling of E2E Resv Message by the Deaggregator

   As per regular RSVP operations, after receipt of the E2E Path, the
   receiver generates an E2E Resv message which travels upstream hop-
   by-hop towards the sender.

   Upon receipt of the E2E Resv, the Deaggregator MUST follow
   traditional 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
   traditional RSVP Resv procedures), the E2E Resv message is hidden
   from the routers between the Deaggregator and the Aggregator which,
   therefore, handle the E2E Resv message as a regular IP packet.

   If the Aggregator and Deaggregator are also acting as IPsec Security
   Gateways, the Deaggregator MUST send the E2E Resv message into the
   relevant IPsec tunnel terminating on the Aggregator.

4.6.  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 MUST first perform
   the final mapping onto the final TE tunnel (if the previous mapping
   was only a tentative one).

   If the tunnel did not change during the final mapping, the Aggregator
   continues the processing of the E2E Resv as described in the four
   following paragraphs.

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

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

   As noted in [RSVP-AGG], 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
   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 it.  That is, the
   reservation is not installed and a ResvError is sent back toward the
   receiver.

   If the tunnel did change during the final mapping, the Aggregator
   MUST first resend to the Deaggregator an E2E Path message with the
   IF_ID RSVP_HOP data interface identification identifying the final TE
   tunnel.  If needed, the ADSPEC information in this E2E Path message
   SHOULD be updated.  Then the Aggregator MUST

      - either drop the E2E Resv message

      - or proceed with the processing of the E2E Resv in the same
        manner as in the case where the tunnel did not change (described
        above).

   In the former case, admission control over the final TE tunnel (and
   forwarding of E2E Resv message upstream toward the sender) would only
   occur when the Aggregator received the subsequent E2E Resv message
   (that will be sent by the Deaggregator in response to the resent E2E
   Path).  In the latter case, admission control over the final tunnel
   is carried out immediately by the Aggregator, and if successful the
   E2E Resv message is generated upstream toward the sender.

   Upon receipt of an E2E ResvConf from the Aggregator, the Deaggregator
   MUST forward the E2E ResvConf downstream toward the receiver.  In
   doing so, the Deaggregator sets the destination address in the IP
   header of the E2E ResvConf message to the IP address found in the
   RESV_CONFIRM object of the corresponding Resv.  The Deaggregator also
   sets the Router Alert.

4.7.  Forwarding of E2E Traffic by the Aggregator

   When the Aggregator receives a data packet belonging to an E2E
   reservations currently mapped over a given TE tunnel, the Aggregator
   MUST encapsulate the packet into that TE tunnel.

   If the Aggregator and Deaggregator are also acting as IPsec Security
   Gateways, the Aggregator MUST also encapsulate the data packet into
   the relevant IPsec tunnel terminating on the Deaggregator before
   transmission into the MPLS TE tunnel.

4.8.  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 MUST update its local view of the
   resources available on the corresponding TE tunnel accordingly.

4.9.  Removal of the 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 a suitable tunnel does not exist.  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 refreshed.

4.10.  Example Signaling Flow

               Aggregator                      Deaggregator

                  (*)
                             RSVP-TE Path
                       =========================>

                             RSVP-TE Resv
                       <=========================
                 (**)

   E2E Path
     -------------->
                  (1)
                             E2E Path
                    ------------------------------->
                                                   (2)
                                                       E2E Path
                                                       ----------->

                                                           E2E Resv
                                                       <-----------
                                                    (3)
                             E2E Resv
                     <-----------------------------
                  (4)
         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 toward the receiver

     (3)  Deaggregator forwards the E2E Resv to the Aggregator

     (4)  Aggregator selects final TE tunnel, checks that there is
          sufficient bandwidth on TE tunnel, and forwards E2E Resv to
          PHOP.  If final tunnel is different from tunnel tentatively
          selected, the Aggregator re-sends an E2E Path with an updated
          IF_ID RSVP_HOP and possibly an updated ADSPEC.

5.  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
           tunnels.

      (2)  Aggregation of E2E IPv6 RSVP reservations over IPv6 TE
           tunnels.

      (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.

6.  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] or [RSVP-GEN-AGG] where the
           set of flows is characterized by the <source address,
           destination address, DSCP>

      (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
           [RSVP-IPSEC].

7.  Example Deployment Scenarios

7.1.  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 a very
   high number of hosts.  In the example illustrated below, hosts
   generate E2E 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 calls.

   These reservations are aggregated over MPLS DS-TE tunnels over the
   packet core.  The mapping policy defined by the user may be 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.

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

   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

7.2.  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 toward another given remote
   Trunk VoIP Gateway (with resizing of this aggregate reservation in a
   step function depending on the 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:

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

   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

8.  Security Considerations

   In the environments concerned by this document, RSVP messages are
   used to control resource reservations for E2E flows outside the MPLS
   region as well as to control resource reservations for MPLS TE
   tunnels inside the MPLS region.  To ensure the integrity of the
   associated reservation and admission control mechanisms, the
   mechanisms defined in [RSVP-CRYPTO1] and [RSVP-CRYPTO2] can be used.
   The mechanisms protect the integrity of RSVP messages hop-by-hop and
   provide node authentication, thereby protecting against corruption
   and spoofing of RSVP messages.  These hop-by-hop integrity mechanisms
   can naturally be used to protect the RSVP messages used for E2E
   reservations outside the MPLS region, to protect RSVP messages used
   for MPLS TE tunnels inside the MPLS region, or for both.  These hop-
   by-hop RSVP integrity mechanisms can also be used to protect RSVP
   messages used for E2E reservations when those transit through the
   MPLS region.  This is because the Aggregator and Deaggregator behave
   as RSVP neighbors from the viewpoint of the E2E flows (even if they
   are not necessarily IP neighbors nor RSVP-TE neighbors).  In that
   case, the Aggregator and Deaggregator need to use a pre-shared
   secret.

   As discussed in Section 6 of [RSVP-TE], filtering of traffic
   associated with an MPLS TE tunnel can only be done on the basis of an
   MPLS label, instead of the 5-tuple of conventional RSVP reservation
   as per [RSVP].  Thus, as explained in [RSVP-TE], an administrator may
   wish to limit the domain over which TE tunnels (which are used for
   aggregation of RSVP E2E reservations as per this specification) can
   be established.  See Section 6 of [RSVP-TE] for a description of how

   filtering of RSVP messages associated with MPLS TE tunnels can be
   deployed to that end.

   This document is based in part on [RSVP-AGG], which specifies
   aggregation of RSVP reservations.  Section 5 of [RSVP-AGG] raises the
   point that because many E2E flows may share an aggregate reservation,
   if the security of an aggregate reservation is compromised, there is
   a multiplying effect in the sense that it can in turn compromise the
   security of many E2E reservations whose quality of service depends on
   the aggregate reservation.  This concern applies also to RSVP
   Aggregation over TE tunnels as specified in the present document.
   However, the integrity of MPLS TE tunnels operation can be protected
   using the mechanisms discussed in the previous paragraphs.  Also,
   while [RSVP-AGG] specifies RSVP Aggregation over dynamically
   established aggregate reservations, the present document restricts
   itself to RSVP Aggregation over pre-established TE tunnels.  This
   further reduces the security risks.

   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, etc.), and/or possibly by the use of TE preemption.

   Section 5 of [RSVP-AGG] also discusses a security issue specific to
   RSVP aggregation related to the necessary modification of the IP
   Protocol number in RSVP E2E Path messages that traverses the
   aggregation region.  This security issue does not apply to the
   present document since aggregation of RSVP reservation over TE
   tunnels does not use this approach of changing the protocol number in
   RSVP messages.

   Section 7 of [LSP-HIER] discusses security considerations stemming
   from the fact that the implicit assumption of a binding between data
   interface and the interface over which a control message is sent is
   no longer valid.  These security considerations are equally
   applicable to the present document.

   If the Aggregator and Deaggregator are also acting as IPsec Security
   Gateways, the Security Considerations of [SEC-ARCH] apply.

9.  Acknowledgments

   This document builds on the [RSVP-AGG], [RSVP-TUN], and [LSP-HIER]
   specifications.  We would like to thank Tom Phelan, John Drake, Arthi
   Ayyangar, Fred Baker, Subha Dhesikan, Kwok-Ho Chan, Carol Iturralde,
   and James Gibson for their input into this document.

10.  Normative References

   [CONTROLLED]   Wroclawski, J., "Specification of the Controlled-Load
                  Network Element Service", RFC 2211, September 1997.

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

   [DSTE-PROTO]   Le Faucheur, F., "Protocol Extensions for Support of
                  Diffserv-aware MPLS Traffic Engineering", RFC 4124,
                  June 2005.

   [GUARANTEED]   Shenker, S., Partridge, C., and R. Guerin,
                  "Specification of Guaranteed Quality of Service", RFC
                  2212, September 1997.

   [INT-DIFF]     Bernet, Y., Ford, P., Yavatkar, R., Baker, F., Zhang,
                  L., Speer, M., Braden, R., Davie, B., Wroclawski, J.,
                  and E. Felstaine, "A Framework for Integrated Services
                  Operation over Diffserv Networks", RFC 2998, November
                  2000.

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

   [KEYWORDS]     Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

   [LSP-HIER]     Kompella, K. and Y. Rekhter, "Label Switched Paths
                  (LSP) Hierarchy with Generalized Multi-Protocol Label
                  Switching (GMPLS) Traffic Engineering (TE)", RFC 4206,
                  October 2005.

   [MPLS-TE]      Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and
                  J. McManus, "Requirements for Traffic Engineering Over
                  MPLS", RFC 2702, September 1999.

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

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

   [RSVP-CRYPTO1] Baker, F., Lindell, B., and M. Talwar, "RSVP
                  Cryptographic Authentication", RFC 2747, January 2000.

   [RSVP-CRYPTO2] Braden, R. and L. Zhang, "RSVP Cryptographic
                  Authentication -- Updated Message Type Value", RFC
                  3097, April 2001.

   [RSVP-TE]      Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
                  V., and G. Swallow, "RSVP-TE: Extensions to RSVP for
                  LSP Tunnels", RFC 3209, December 2001.

   [SEC-ARCH]     Kent, S. and K. Seo, "Security Architecture for the
                  Internet Protocol", RFC 4301, December 2005.

11.  Informative References

   [6PE]          De Clercq, J., Ooms, D., Prevost, S., and F. Le
                  Faucheur, "Connecting IPv6 Islands over IPv4 MPLS
                  using IPv6 Provider Edge Routers (6PE)", RFC 4798,
                  February 2007.

   [AUTOMESH]     Vasseur and Leroux, "Routing extensions for discovery
                  of Multiprotocol (MPLS) Label Switch Router (LSR)
                  Traffic Engineering (TE) mesh membership", Work in
                  Progress.

   [DIFF-MPLS]    Le Faucheur, F., Wu, L., Davie, B., Davari, S.,
                  Vaananen, P., Krishnan, R., Cheval, P., and J.
                  Heinanen, "Multi-Protocol Label Switching (MPLS)
                  Support of Differentiated Services", RFC 3270, May
                  2002.

   [DSTE-REQ]     Le Faucheur, F. and W. Lai, "Requirements for Support
                  of Differentiated Services-aware MPLS Traffic
                  Engineering", RFC 3564, July 2003.

   [L-RSVP]       Manner, et al., Localized RSVP for Controlling RSVP
                  Proxies, Work in Progress.

   [RSVP-APPID]   Yadav, S., Yavatkar, R., Pabbati, R., Ford, P., Moore,
                  T., Herzog, S., and R. Hess, "Identity Representation
                  for RSVP", RFC 3182, October 2001.

   [RSVP-GEN-AGG] Le Faucheur, R., Davie, B., Bose, P., Martin, L.,
                  Christou, C., Davenport, M., and A. Hamilton, "Generic
                  Aggregate Resource ReSerVation Protocol (RSVP)
                  Reservations", Work in Progress, January 2007.

   [RSVP-IPSEC]   Berger, L. and T. O'Malley, "RSVP Extensions for IPSEC
                  Data Flows", RFC 2207, September 1997.

   [RSVP-PREEMP]  Herzog, S., "Signaled Preemption Priority Policy
                  Element", RFC 3181, October 2001.

   [RSVP-PROXY1]  Gai, et al., RSVP Proxy, Work in Progress.

   [RSVP-PROXY2]  Le Faucheur, et al., RSVP Proxy Approaches, Work in
                  Progress.

   [RSVP-TUN]     Terzis, A., Krawczyk, J., Wroclawski, J., and L.
                  Zhang, "RSVP Operation Over IP Tunnels", RFC 2746,
                  January 2000.

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

Appendix A - Optional Use of RSVP Proxy on RSVP Aggregator

   A number of approaches ([RSVP-PROXY1],[RSVP-PROXY2], [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.

   The information in this Appendix is purely informational and
   illustrative.

   As discussed in [RSVP-PROXY1]:

   "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
   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:

   |----|       |--------------|  |------|   |--------------|     |----|
   |    |       | Aggregator/  |  | MPLS |   | Aggregator/  |     |    |
   |Host|       | Deaggregator/|  | cloud|   | Deaggregator/|     |Host|
   |    |       | RSVP Proxy   |  |      |   | RSVP Proxy   |     |    |
   |----|       |--------------|  |------|   |--------------|     |----|

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

     Path                                                      Path
    ------------> (1)-\                          /-(i)  <----------
           Resv       |                         |        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) happen independently of each other.

   (2)(ii)  : Aggregator/Deaggregator/Proxy generates the Resv message
             toward 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
             toward 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-PROXY1], an
   additional PathRequest message would be needed from host to
   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 that

   ensures (when used on both the Host-Aggregator and Deaggregator-Host
   sides, and when both end systems support RSVP):

      (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 that itself has been subject to
            admission control by MPLS TE, between Deaggregator and
            destination host).

      (ii)  this is achieved in both directions.

      (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.

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

   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
   (CAC) of Voice over IP (VoIP) traffic over the packet core.

   The information in this Appendix is purely informational and
   illustrative.

   Consider the scenario depicted in Figure B1.  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 Deaggregator/Tail-end.  For
   reservations going from GW2 to GW2, PE2 serves as the
   Aggregator/Head-end and PE1 serves as the Deaggregator/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.
   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 tunnel.

   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 toward the
   destination.  Assuming there is enough bandwidth available on that
   tunnel, the PE adjusts its bookkeeping of remaining available
   bandwidth on the tunnel and generates a Resv message back toward the
   GW to confirm resources have been reserved over the DSTE tunnel.

                               ,-.     ,-.
                         _.---'   `---'   `-+
                     ,-''   +------------+  :
                    (       |            |   `.
                     \     ,'    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 B1.  Integration of SIP Resource Management and
                   RSVP Aggregation over MPLS TE Tunnels

   [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.

   Through the collaboration between SIP resource management, RSVP
   signaling, RSVP Aggregation and DS-TE as described above, we see
   that:

      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 at near
         capacity, the network may dynamically adjust the tunnel size
         within a set of parameters.

   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 Admission Control 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
   toward GW2, GW1 may establish one (or a small number of) aggregate
   reservations as defined in [RSVP-AGG] or [RSVP-GEN-AGG], which is
   used for all (or a subset of all) the calls toward GW2.  This
   effectively provides an additional level of hierarchy whereby:

      - DSTE tunnels are subject to Admission Control over the resources
        of the MPLS TE core

      - Aggregate RSVP reservations (for the calls from one GW to
        another GW) are subject to Admission Control 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 toward the appropriate destination GW.

   This pushes even further the scalability limits of this voice CAC
   architecture.

Contributing Authors

   This document was the collective work of several authors.  The text
   and content were contributed by the editor and the co-authors listed
   below.

   Michael DiBiasio
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough, MA 01719
   USA
   EMail: dibiasio@cisco.com

   Bruce Davie
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough, MA 01719
   USA
   EMail: bdavie@cisco.com

   Christou Christou
   Booz Allen Hamilton
   8283 Greensboro Drive
   McLean, VA 22102
   USA
   EMail: christou_chris@bah.com

   Michael Davenport
   Booz Allen Hamilton
   8283 Greensboro Drive
   McLean, VA 22102
   USA
   EMail: davenport_michael@bah.com

   Jerry Ash
   AT&T
   200 Laurel Avenue
   Middletown, NJ 07748
   USA
   EMail: gash@att.com

   Bur Goode
   AT&T
   32 Old Orchard Drive
   Weston, CT 06883
   USA
   EMail: bgoode@att.com

Editor's Address

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

   EMail: flefauch@cisco.com

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