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rfc:rfc3175

Network Working Group F. Baker Request for Comments: 3175 C. Iturralde Category: Standards Track F. Le Faucheur

                                                              B. Davie
                                                         Cisco Systems
                                                        September 2001
         Aggregation of RSVP for IPv4 and IPv6 Reservations

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 Internet Society (2001).  All Rights Reserved.

Abstract

 This document describes the use of a single RSVP (Resource
 ReSerVation Protocol) reservation to aggregate other RSVP
 reservations across a transit routing region, in a manner
 conceptually similar to the use of Virtual Paths in an ATM
 (Asynchronous Transfer Mode) network.  It proposes a way to
 dynamically create the aggregate reservation, classify the traffic
 for which the aggregate reservation applies, determine how much
 bandwidth is needed to achieve the requirement, and recover the
 bandwidth when the sub-reservations are no longer required.  It also
 contains recommendations concerning algorithms and policies for
 predictive reservations.

1. Introduction

 A key problem in the design of RSVP version 1 [RSVP] is, as noted in
 its applicability statement, that it lacks facilities for aggregation
 of individual reserved sessions into a common class.  The use of such
 aggregation is recommended in [CSZ], and required for scalability.
 The problem of aggregation may be addressed in a variety of ways.
 For example, it may sometimes be sufficient simply to mark reserved
 traffic with a suitable DSCP (e.g., EF), thus enabling aggregation of
 scheduling and classification state.  It may also be desirable to
 install one or more aggregate reservations from ingress to egress of

Baker, et al. Standards Track [Page 1] RFC 3175 RSVP Reservation Aggregation September 2001

 an "aggregation region" (defined below) where each aggregate
 reservation carries similarly marked packets from a large number of
 flows.  This is to provide high levels of assurance that the end-to-
 end requirements of reserved flows will be met, while at the same
 time enabling reservation state to be aggregated.
 Throughout, we will talk about "Aggregator" and "Deaggregator",
 referring to the routers at the ingress and egress edges of an
 aggregation region.  Exactly how a router determines whether it
 should perform the role of aggregator or deaggregator is described
 below.
 We will refer to the individual reserved sessions (the sessions we
 are attempting to aggregate) as "end-to-end" reservations ("E2E" for
 short), and to their respective Path/Resv messages as E2E Path/Resv
 messages.  We refer to the the larger reservation (that which
 represents many E2E reservations) as an "aggregate" reservation, and
 its respective Path/Resv messages as "aggregate Path/Resv messages".

1.1. Problem Statement: Aggregation Of E2E Reservations

 The problem of many small reservations has been extensively
 discussed, and may be summarized in the observation that each
 reservation requires a non-trivial amount of message exchange,
 computation, and memory resources in each router along the way.  It
 would be nice to reduce this to a more manageable level where the
 load is heaviest and aggregation is possible.
 Aggregation, however, brings its own challenges.  In particular, it
 reduces the level of isolation between individual flows, implying
 that one flow may suffer delay from the bursts of another.
 Synchronization of bursts from different flows may occur.  However,
 there is evidence [CSZ] to suggest that aggregation of flows has no
 negative effect on the mean delay of the flows, and actually leads to
 a reduction of delay in the "tail" of the delay distribution (e.g.,
 99% percentile delay) for the flows.  These benefits of aggregation
 to some extent offset the loss of strict isolation.

1.2. Proposed Solution

 The solution we propose involves the aggregation of several E2E
 reservations that cross an "aggregation region" and share common
 ingress and egress routers into one larger reservation from ingress
 to egress.  We define an "aggregation region" as a contiguous set of
 systems capable of performing RSVP aggregation (as defined following)
 along any possible route through this contiguous set.

Baker, et al. Standards Track [Page 2] RFC 3175 RSVP Reservation Aggregation September 2001

 Communication interfaces fall into two categories with respect to an
 aggregation region; they are "exterior" to an aggregation region, or
 they are "interior" to it.  Routers that have at least one interface
 in the region fall into one of three categories with respect to a
 given RSVP session; they aggregate, they deaggregate, or they are
 between an aggregator and a deaggregator.
 Aggregation depends on being able to hide E2E RSVP messages from
 RSVP-capable routers inside the aggregation region.  To achieve this
 end, the IP Protocol Number in the E2E reservation's Path, PathTear,
 and ResvConf messages is changed from RSVP (46) to RSVP-E2E-IGNORE
 (134) upon entering the aggregation region, and restored to RSVP at
 the deaggregator point.  These messages are ignored (no state is
 stored and the message is forwarded as a normal IP datagram) by each
 router within the aggregation region whenever they are forwarded to
 an interior interface.  Since the deaggregating router perceives the
 previous RSVP hop on such messages to be the aggregating router, Resv
 and other messages do not require this modification; they are unicast
 from RSVP hop to RSVP hop anyway.
 The token buckets (SENDER_TSPECs and FLOWSPECS) of E2E reservations
 are summed into the corresponding information elements in aggregate
 Path and Resv messages.  Aggregate Path messages are sent from the
 aggregator to the deaggregator(s) using RSVP's normal IP Protocol
 Number.  Aggregate Resv messages are sent back from the deaggregator
 to the aggregator, thus establishing an aggregate reservation on
 behalf of the set of E2E flows that use this aggregator and
 deaggregator.
 Such establishment of a smaller number of aggregate reservations on
 behalf of a larger number of E2E reservations yields the
 corresponding reduction in the amount of state to be stored and
 amount of signalling messages exchanged in the aggregation region.
 By using Differentiated Services mechanisms for classification and
 scheduling of traffic supported by aggregate reservations (rather
 than performing per aggregate reservation classification and
 scheduling), the amount of classification and scheduling state in the
 aggregation region is even further reduced.  It is not only
 independent of the number of E2E reservations, it is also independent
 of the number of aggregate reservations in the aggregation region.
 One or more Diff-Serv DSCPs are used to identify traffic covered by
 aggregate reservations and one or more Diff-Serv PHBs are used to
 offer the required forwarding treatment to this traffic.  There may
 be more than one aggregate reservation between the same pair of
 routers, each representing different classes of traffic and each
 using a different DSCP and a different PHB.

Baker, et al. Standards Track [Page 3] RFC 3175 RSVP Reservation Aggregation September 2001

1.3. Definitions

 We define an "aggregation region" as a set of RSVP-capable routers
 for which E2E RSVP messages arriving on an exterior interface of one
 router in the set would traverse one or more interior interfaces (of
 this and possibly of other routers in the set) before finally
 traversing an exterior interface.
 Such an E2E RSVP message is said to have crossed the aggregation
 region.
 We define the "aggregating" router for this E2E flow as the first
 router that processes the E2E Path message as it enters the
 aggregation region (i.e., the one which forwards the message from an
 exterior interface to an interior interface).
 We define the "deaggregating" router for this E2E flow as the last
 router to process the E2E Path as it leaves the aggregation region
 (i.e., the one which forwards the message from an interior interface
 to an exterior interface).
 We define an "interior" router for this E2E flow as any router in the
 aggregation region which receives this message on an interior
 interface and forwards it to another interior interface.  Interior
 routers perform neither aggregation nor deaggregation for this flow.
 Note that by these definitions a single router with a mix of interior
 and exterior interfaces may have the capability to act as an
 aggregator on some E2E flows, a deaggregator on other E2E flows, and
 an interior router on yet other flows.

1.4. Detailed Aspects of Proposed Solution

 A number of issues jump to mind in considering this model.

1.4.1. Traffic Classification Within The Aggregation Region

 One of the reasons that RSVP Version 1 did not identify a way to
 aggregate sessions was that there was not a clear way to classify the
 aggregate.  With the development of the Differentiated Services
 architecture, this is at least partially resolved; traffic of a
 particular class can be marked with a given DSCP and so classified.
 We presume this model.
 We presume that on each link en route, a queue, WDM color, or similar
 management component is set aside for all aggregated traffic of the
 same class, and that sufficient bandwidth is made available to carry

Baker, et al. Standards Track [Page 4] RFC 3175 RSVP Reservation Aggregation September 2001

 the traffic that has been assigned to it.  This bandwidth may be
 adjusted based on the total amount of aggregated reservation traffic
 assigned to the same class.
 There are numerous options for exactly which Diff-serv PHBs might be
 used for different classes of traffic as it crosses the aggregation
 region.  This is the "service mapping" problem described in
 [RFC2998], and is applicable to situations broader than those
 described in this document.  Arguments can be made for using either
 EF or one or more AF PHBs for aggregated traffic.  For example, since
 controlled load requires non-TSpec-conformant (policed) traffic to be
 forwarded as best effort traffic rather than dropped, it may be
 appropriate to use an AF class for controlled load, using the higher
 drop preference for non-conformant packets.
 In conventional (unaggregated) RSVP operation, a session is
 identified by a destination address and optionally a protocol port.
 Since data belonging to an aggregated reservation is identified by a
 DSCP, the session is defined by the destination address and DSCP.
 For those cases where two DSCPs are used (for conformant and non-
 conformant packets, as noted above), the session is identified by the
 DSCP of conformant packets.  In general we will talk about mapping
 aggregated traffic onto a DSCP (even if a second DSCP may be used for
 non-conformant traffic).
 Whichever PHB or PHBs are used to carry aggregated reservations, care
 needs to be take in an environment where provisioned Diff-Serv and
 aggregated RSVP are used in the same network, to ensure that the
 total admitted load for a single PHB does not exceed the link
 capacity allocated to that PHB.  One solution to this is to reserve
 one PHB (or more) strictly for the aggregated reservation traffic
 (e.g., AF1 Class) while using other PHBs for provisioned Diff-Serv
 (e.g., AF2, AF3 and AF4 Classes).
 Inside the aggregation region, some RSVP reservation state is
 maintained per aggregate reservation, while classification and
 scheduling state (e.g., DSCPs used for classifying traffic) is
 maintained on a per aggregate reservation class basis (rather than
 per aggregate reservation).  For example, if Guaranteed Service
 reservations are mapped to the EF DSCP throughout the aggregation
 region, there may be a reservation for each aggregator/deaggregator
 pair in each router, but only the EF DSCP needs to be inspected at
 each interior interface, and only a single queue is used for all EF
 traffic.

Baker, et al. Standards Track [Page 5] RFC 3175 RSVP Reservation Aggregation September 2001

1.4.2. Deaggregator Determination

 The first question is "How do we determine the
 Aggregator/Deaggregator pair that are responsible for aggregating a
 particular E2E flow through the aggregation region?"
 Determination of the aggregator is trivial: we know that an E2E flow
 has arrived at an aggregator when its Path message arrives at a
 router on an exterior interface and must be forwarded on an interior
 interface.
 Determination of the deaggregator is more involved.  If an SPF
 routing protocol, such as OSPF or IS-IS, is in use, and if it has
 been extended to advertise information on Deaggregation roles, it can
 tell us the set of routers from which the deaggregator will be
 chosen.  In principle, if the aggregator and deaggregator are in the
 same area, then the identity of the deaggregator could be determined
 from the link state database.  However, this approach would not work
 in multi-area environments or for distance vector protocols.
 One method for Deaggregator determination is manual configuration.
 With this method the network operator would configure the Aggregator
 and the Deaggregator with the necessary information.
 Another method allows automatic Deaggregator determination and
 corresponding Aggregator notification.  When the E2E RSVP Path
 message transits from an interior interface to an exterior interface,
 the deaggregating router must advise the aggregating router of the
 correlation between itself and the flow.  This has the nice attribute
 of not being specific to the routing protocol.  It also has the
 property of automatically adjusting to route changes.  For instance,
 if because of a topology change, another Deaggregator is now on the
 shortest path, this method will automatically identify the new
 Deaggregator and swap to it.

1.4.3. Mapping E2E Reservations Onto Aggregate Reservations

 As discussed above, there may be multiple Aggregate Reservations
 between the same Aggregator/Deaggregator pair.  The rules for mapping
 E2E reservations onto aggregate reservations are policy decisions
 which depend on the network environment and network administrator's
 objectives.  Such a policy is outside the scope of this specification
 and we simply assume that such a policy is defined by the network
 administrator.  We also assume that such a policy is somehow
 accessible to the Aggregators/Deaggregators but the details of how
 this policy is made accessible to Aggregators/Deaggregators (Local
 Configuration, COPS, LDAP, etc.) is outside the scope of this
 specification.

Baker, et al. Standards Track [Page 6] RFC 3175 RSVP Reservation Aggregation September 2001

 An example of very simple policy would be that all the E2E
 reservations are mapped onto a single Aggregate Reservation (i.e.,
 single DSCP) between a given pair of Aggregator/Deaggregator.
 Another example of policy, which takes into account the Int-Serv
 service type requested by the receiver (and signalled in the E2E
 Resv), would be where Guaranteed Service E2E reservations are mapped
 onto one DSCP in the aggregation region and where Controlled Load E2E
 reservations are mapped onto another DSCP.
 A third example of policy would be one where the mapping of E2E
 reservations onto Aggregate Reservations take into account Policy
 Objects (such as information authenticating the end user) which may
 be included by the sender in the E2E path and/or by the receiver in
 the E2E Resv.
 Regardless of the actual policy, a range of options are conceivable
 for where the decision to map an E2E reservation onto an aggregate
 reservation is taken and how this decision is communicated between
 Aggregator and Deaggregator.  Both Aggregator and Deaggregator could
 be assumed to make such a decision independently.  However, this
 would either require definition of additional procedures to solve
 inconsistent mapping decisions (i.e., Aggregator and Deaggregator
 decide to map a given E2E reservation onto different Aggregate
 Reservations) or would result in possible undetected misbehavior in
 the case of inconsistent decisions.
 For simplicity and reliability, we assign the responsibility of the
 mapping decision entirely to the Deaggregator.  The Aggregator is
 notified of the selected mapping by the Deaggregator and follows this
 decision.  The Deaggregator was chosen rather than the Aggregator
 because the Deaggregator is the first to have access to all the
 information required to make such a decision (in particular receipt
 of the E2E Resv which indicates the requested Int-Serv service type
 and includes information signalled by the receiver).  This allows
 faster operations such as set-up or size adjustment of an Aggregate
 Reservation in a number of situations resulting in faster E2E
 reservation establishment.

1.4.4. Size of Aggregate Reservations

 A range of options exist for determining the size of the aggregate
 reservation, presenting a tradeoff between simplicity and
 scalability.  Simplistically, the size of the aggregate reservation
 needs to be greater than or equal to the sum of the bandwidth of the
 E2E reservations it aggregates, and its burst capacity must be
 greater than or equal to the sum of their burst capacities.  However,
 if followed religiously, this leads us to change the bandwidth of the

Baker, et al. Standards Track [Page 7] RFC 3175 RSVP Reservation Aggregation September 2001

 aggregate reservation each time an underlying E2E reservation
 changes, which loses one of the key benefits of aggregation, the
 reduction of message processing cost in the aggregation region.
 We assume, therefore, that there is some policy, not defined in this
 specification (although sample policies are suggested which have the
 necessary characteristics).  This policy maintains the amount of
 bandwidth required on a given aggregate reservation by taking account
 of the sum of the bandwidths of its underlying E2E reservations,
 while endeavoring to change it infrequently.  This may require some
 level of trend analysis.  If there is a significant probability that
 in the next interval of time the current aggregate reservation will
 be exhausted, the router must predict the necessary bandwidth and
 request it.  If the router has a significant amount of bandwidth
 reserved but has very little probability of using it, the policy may
 be to predict the amount of bandwidth required and release the
 excess.
 This policy is likely to benefit from introduction of some hysteresis
 (i.e., ensure that the trigger condition for aggregate reservation
 size increase is sufficiently different from the trigger condition
 for aggregate reservation size decrease) to avoid oscillation in
 stable conditions.
 Clearly, the definition and operation of such policies are as much
 business issues as they are technical, and are out of the scope of
 this document.

1.4.5. E2E Path ADSPEC update

 As described above, E2E RSVP messages are hidden from the Interior
 routers inside the aggregation region.  Consequently, the ADSPECs of
 E2E Path messages are not updated as they travel through the
 aggregation region.  Therefore, the Deaggregator for a flow is
 responsible for updating the ADSPEC in the corresponding E2E Path to
 reflect the impact of the aggregation region on the QoS that may be
 achieved end-to-end.  The Deaggregator should update the ADSPEC of
 the E2E Path as accurately as possible.
 Since Aggregate Path messages are processed inside the aggregation
 region, their ADSPEC is updated by Interior routers to reflect the
 impact of the aggregation region on the QoS that may be achieved
 within the interior region.  Consequently, the Deaggregator should
 make use of the information included in the ADSPEC from an Aggregate
 Path where available.  The Deaggregator may elect to wait until such
 information is available before forwarding the E2E Path in order to
 accurately update its ADSPEC.

Baker, et al. Standards Track [Page 8] RFC 3175 RSVP Reservation Aggregation September 2001

 To maximize the information made available to the Deaggregator,
 whenever the Aggregator signals an Aggregate Path,  the Aggregator
 should include an ADSPEC with fragments for all service types
 supported in the aggregation region (even if the Aggregate Path
 corresponds to an Aggregate Reservation that only supports a subset
 of those service types).  Providing this information to the
 Deaggregator for every possible service type facilitates accurate and
 timely update of the E2E ADSPEC by the Deaggregator.
 Depending on the environment and on the policy for mapping E2E
 reservations onto Aggregate Reservations, to accurately update the
 E2E Path ADSPEC, the Deaggregator may for example:
  1. update all the E2E Path ADSPEC segments (Default General

Parameters Fragment, Guaranteed Service Fragment, Controlled-Load

    Service Fragment) based on the ADSPEC of a single Aggregate Path,
    or
  1. update the E2E Path ADSPEC by taking into account the ADSPEC from

multiple Aggregate Path messages (e.g.,. update the Default

    General Parameters Fragment using the "worst" value for each
    parameter across all the Aggregate Paths' ADSPECs, update the
    Guaranteed Service Fragment using the Guaranteed Service Fragment
    from the ADSPEC of the Aggregate Path for the reservation used for
    Guaranteed Services).
 By taking into account the information contained in the ADSPEC of
 Aggregate Path(s) as mentioned above, the Deaggregator should be able
 to accurately update the E2E Path ADSPEC in most situations.
 However, we note that there may be particular situations where the
 E2E Path ADSPEC update cannot be made entirely accurately by the
 Deaggregator.  This is most likely to happen when the path taken
 across the aggregation region depends on the service requested in the
 E2E Resv, which is yet to arrive.  Such a situation could arise if,
 for example:
  1. The service mapping policy for the aggregation region is such that

E2E reservations requesting Guaranteed Service are mapped to a

    different PHB that those requesting Controlled Load service.
  1. Diff-Serv aware routing is used in the aggregation region, so that

packets with different DSCPs follow different paths (sending them

    over different MPLS label switched paths, for example).
 As a result, the ADSPEC for the aggregate reservation that supports
 guaranteed service may differ from the ADSPEC for the aggregate
 reservation that supports controlled load.

Baker, et al. Standards Track [Page 9] RFC 3175 RSVP Reservation Aggregation September 2001

 Assume that the sender sends an E2E Path with an ADSPEC containing
 segments for both Guaranteed Services and Controlled Load.  Then, at
 the time of updating the E2E ADSPEC, the Deaggregator does not know
 which service type will actually be requested by the receiver and
 therefore cannot know which PHB will be used to transport this E2E
 flow and, in turn, cannot pick the right parameter values to factor
 in when updating the Default General Parameters Fragment.  As
 mentioned above, in this particular case, a conservative approach
 would be to always take into account the worst value for every
 parameter.  Regardless of whether this conservative approach is
 followed or some simpler approach such as taking into account one of
 the two Aggregate Path ADSPEC, the E2E Path ADSPEC will be inaccurate
 (over-optimistic or over-pessimistic) for at least one service type
 actually requested by the destination.
 Recognizing that entirely accurate update of E2E Path ADSPEC may not
 be possible in all situations, we recommend that a conservative
 approach be taken in such situations (over-pessimistic rather than
 over-optimistic) and that the E2E Path ADSPEC be corrected as soon as
 possible.  In the example described above, this would mean that as
 soon as the Deaggregator receives the E2E Resv from the receiver, the
 Deaggregator should generate another E2E Path with an accurately
 updated ADSPEC based on the knowledge of which aggregate reservation
 will actually carry the E2E flow.

1.4.6. Intra-domain Routes

 RSVP directly handles route changes, in that reservations follow the
 routes that their data follow.  This follows from the property that
 Path messages contain the same IP source and destination address as
 the data flow for which a reservation is to be established.  However,
 since we are now making aggregate reservations by sending a Path
 message from an aggregating to a deaggregating router, the reserved
 (E2E) data packets no longer carry the same IP addresses as the
 relevant (aggregate) Path message.  The issue becomes one of making
 sure that data packets for reserved flows follow the same path as the
 Path message that established Path state for the aggregate
 reservation.  Several approaches are viable.
 First, the data may be tunneled from aggregator to deaggregator,
 using technologies such as IP-in-IP tunnels, GRE tunnels, MPLS
 label-switched paths, and so on.  These each have particular
 advantages, especially MPLS, which allows traffic engineering.  They
 each also have some cost in link overhead and configuration
 complexity.

Baker, et al. Standards Track [Page 10] RFC 3175 RSVP Reservation Aggregation September 2001

 If data is not tunneled, then we are depending on a characteristic of
 IP best metric routing , which is that if the route from A to Z
 includes the path from H to L, and the best metric route was chosen
 all along the way, then the best metric route was chosen from H to L.
 Therefore, an aggregate path message which crosses a given aggregator
 and deaggregator will of necessity use the best path between them.
 If this is a single path, the problem is solved.  If it is a multi-
 path route, and the paths are of equal cost, then we are forced to
 determine, perhaps by measurement, what proportion of the traffic for
 a given E2E reservation is passing along each of the paths, and
 assure ourselves of sufficient bandwidth for the present use.  A
 simple, though wasteful, way of doing this is to reserve the total
 capacity of the aggregate route down each path.
 For this reason, we believe it is advantageous to use one of the
 above-mentioned tunneling mechanisms in cases where multiple equal-
 cost paths may exist.

1.4.7. Inter-domain Routes

 The case of inter-domain routes differs somewhat from the intra-
 domain case just described.  Specifically, best-path considerations
 do not apply, as routing is by a combination of routing policy and
 shortest AS path rather than simple best metric.
 In the case of inter-domain routes, data traffic belonging to
 different E2E sessions (but the same aggregate session) may not enter
 an aggregation region via the same aggregator interface, and/or may
 not leave via the same deaggregator interface.  It is possible that
 we could identify this occurrence in some central system which sees
 the reservation information for both of the apparent sessions, but it
 is not clear that we could determine a priori how much traffic went
 one way or the other apart from measurement.
 We simply note that this problem can occur and needs to be allowed
 for in the implementation.  We recommend that each such E2E
 reservation be summed into its appropriate aggregate reservation,
 even though this involves over-reservation.

1.4.8. Reservations for Multicast Sessions

 Aggregating reservations for multicast sessions is significantly more
 complex than for unicast sessions.  The first challenge is to
 construct a multicast tree for distribution of the aggregate Path
 messages which follows the same path as will be followed by the data
 packets for which the aggregate reservation is to be made.  This is
 complicated by the fact that the path taken by a data packet may

Baker, et al. Standards Track [Page 11] RFC 3175 RSVP Reservation Aggregation September 2001

 depend on many factors such as its source address, the choice of
 shared trees or source-specific trees, and the location of a
 rendezvous point for the tree.
 Once the problem of distributing aggregate Path messages is solved,
 there are considerable problems in determining the correct amount of
 resources to reserve at each link along the multicast tree.  Because
 of the amount of heterogeneity that may exist in an aggregate
 multicast reservation, it appears that it would be necessary to
 retain information about individual E2E reservations within the
 aggregation region to allocate resources correctly.  Thus, we may end
 up with a complex set of procedures for forming aggregate
 reservations that do not actually reduce the amount of stored state
 significantly for multicast sessions.
 As noted above, there are several aspects to RSVP state, and our
 approach for unicast aggregates all forms of state:  classification,
 scheduling, and reservation state.  One possible approach to
 multicast is to focus only on aggregation of classification and
 scheduling state, which are arguably the most important because of
 their impact on the forwarding path.  That approach is the one
 described in the current draft.

1.4.9. Multi-level Aggregation

 Ideally, an aggregation scheme should be able to accommodate
 recursive aggregation, with aggregate reservations being themselves
 aggregated.  Multi-level aggregation can be accomplished using the
 procedures described here and a simple extension to the protocol
 number swapping process.
 We can consider E2E RSVP reservations to be at aggregation level 0.
 When we aggregate these reservations, we produce reservations at
 aggregation level 1.  In general, level n reservations may be
 aggregated to form reservations at level n+1.
 When an aggregating router receives an E2E Path, it swaps the
 protocol number from RSVP to RSVP-E2E-IGNORE.  In addition, it should
 write the aggregation level (1, in this case) in the 2 byte field
 that is present (and currently unused) in the router alert option.
 In general, a router which aggregates reservations at level n to
 create reservations at level n+1 will write the number n+1 in the
 router alert field.  A router which deaggregates level n+1
 reservations will examine all messages with IP protocol number RSVP-
 E2E-IGNORE but will process the message and swap the protocol number
 back to RSVP only in the case where the router alert field carries
 the number n+1.  For any other value, the message is forwarded
 unchanged.  Interior routers ignore all messages with IP protocol

Baker, et al. Standards Track [Page 12] RFC 3175 RSVP Reservation Aggregation September 2001

 number RSVP-E2E-IGNORE.  Note that only a few bits of the 2 byte
 field in the option would be needed, given the likely number of
 levels of aggregation.
 For IPv6, certain values of the router alert "value" field are
 reserved.  This specification requires IANA assignment of a small
 number of consecutive values for the purpose of recording the
 aggregation level.

1.4.10. Reliability Issues

 There are a variety of issues that arise in the context of
 aggregation that would benefit from some form of explicit
 acknowledgment mechanism for RSVP messages.  For example, it is
 possible to configure a set of routers such that an E2E Path of
 protocol type RSVP-E2E-IGNORE would be effectively "black-holed", if
 it never reached a router which was appropriately configured to act
 as a deaggregator.  It could then travel all the way to its
 destination where it would probably be ignored due to its non-
 standard protocol number.  This situation is not easy to detect.  The
 aggregator can be sure this problem has not occurred if an aggregate
 PathErr message is received from the deaggregator (as described in
 detail below).  It can also be sure there is no problem if an E2E
 Resv is received.  However, the fact that neither of these events has
 happened may only mean that no receiver wishes to reserve resources
 for this session, or that an RSVP message loss occurred, or it may
 mean that the Path was black-holed.  However, if a neighbor-to-
 neighbor acknowledgment mechanism existed, the aggregator would
 expect to receive an acknowledgment of the E2E Path from the
 deaggregator, and would interpret the lack of a response as an
 indication that a problem of configuration existed.  It could then
 refrain from aggregating this particular session.  We note that such
 a reliability mechanism has been proposed for RSVP in [RFC291] and
 propose that it be used here.

1.4.11. Message Integrity and Node Authentication

 [RSVP] defines a hop-by-hop authentication and integrity check.  The
 present specification allows use of this check on Aggregate RSVP
 messages and also preserves this check on E2E RSVP messages for E2E
 RSVP messages.
 Outside the Aggregation Region, any E2E RSVP message may contain an
 INTEGRITY object using a keyed cryptographic digest technique which
 assumes that RSVP neighbors share a secret.  Because E2E RSVP
 messages are not processed by routers in the Aggregation Region, the
 Aggregator and Deaggregator appear as logical RSVP neighbors of each
 other.  The Deaggregator is the Aggregator's Next Hop for E2E RSVP

Baker, et al. Standards Track [Page 13] RFC 3175 RSVP Reservation Aggregation September 2001

 messages while the Aggregator is the Deaggregator's Previous Hop.
 Consequently, INTEGRITY objects which may appear in E2E RSVP messages
 traversing the Aggregation Region are exchanged directly between the
 Aggregator and Deaggregator in a manner which is entirely transparent
 to the Interior routers.  Thus, hop-by-hop integrity checking for E2E
 messages over the Aggregation Region requires that the Aggregator and
 Deaggregator share a secret.  Techniques for establishing that secret
 are described in [INTEGRITY].
 Inside the Aggregation Region, any Aggregate RSVP message may contain
 an INTEGRITY object which assumes that the corresponding RSVP
 neighbors inside the Aggregation Region (e.g., Aggregator and
 Interior Router, two Interior Routers, Interior Router and
 Deaggregator) share a secret.

1.4.12. Aggregated reservations without E2E reservations

 Up to this point we have assumed that the aggregate reservation is
 established as a result of the establishment of E2E reservations from
 outside the aggregation region.  It should be clear that alternative
 triggers are possible.  As discussed in [RFC2998], an aggregate RSVP
 reservation can be used to manage bandwidth in a diff-serv cloud even
 if RSVP is not used end-to-end.
 The simplest example of an alternative configuration is the static
 configuration of an aggregated reservation for a certain amount for
 traffic from an ingress (aggregator) router to an egress (de-
 aggregator) router.  This would have to be configured in at least the
 system originating the aggregate PATH message (the aggregator).  The
 deaggregator could detect that the PATH message is directed to it,
 and could be configured to "turn around" such messages, i.e., it
 responds with a RESV back to the aggregator.  Alternatively,
 configuration of the aggregate reservation could be performed at both
 the aggregator and the deaggregator.  As before, an aggregate
 reservation is associated with a DSCP for the traffic that will use
 the reserved capacity.
 In the absence of E2E microflow reservations, the aggregator can use
 a variety of policies to set the DSCP of packets passing into the
 aggregation region, thus determining whether they gain access to the
 resources reserved by the aggregate reservation.  These policies are
 a matter of local configuration, as usual for a device at the edge of
 a diffserv cloud.

Baker, et al. Standards Track [Page 14] RFC 3175 RSVP Reservation Aggregation September 2001

 Note that the "aggregator" could even be a device such as a PSTN
 gateway which makes an aggregate reservation for the set of calls to
 another PSTN gateway (the deaggregator) across an intervening diff-
 serv region.  In this case the reservation may be established in
 response to call signalling.
 From the perspective of RSVP signalling and the handling of data
 packets in the aggregation region, these cases are equivalent to the
 case of aggregating E2E RSVP reservations.  The only difference is
 that E2E RSVP signalling does not take place and cannot therefore be
 used as a trigger, so some additional knowledge is required in
 setting up the aggregate reservation.

2. Elements of Procedure

 To implement aggregation, we define a number of elements of
 procedure.

2.1. Receipt of E2E Path Message By Aggregating Router

 The very first event is the arrival of the E2E Path message at an
 exterior interface of an aggregator.  Standard RSVP procedures [RSVP]
 are followed for this, including onto what set of interfaces the
 message should be forwarded.  These interfaces comprise zero or more
 exterior interfaces and zero or more interior interfaces.  (If the
 number of interior interfaces is zero, the router is not acting as an
 aggregator for this E2E flow.)
 Service on exterior interfaces is handled as defined in [RSVP].
 Service on interior interfaces is complicated by the fact that the
 message needs to be included in some aggregate reservation, but at
 this point it is not known which one, because the deaggregator is not
 known.  Therefore, the E2E Path message is forwarded on the interior
 interface(s) using the IP Protocol number RSVP-E2E-IGNORE, but in
 every other respect identically to the way it would be sent by an
 RSVP router that was not performing aggregation.

2.2. Handling Of E2E Path Message By Interior Routers

 At this point, the E2E Path message traverses zero or more interior
 routers.  Interior routers receive the E2E Path message on an
 interior interface and forward it on another interior interface.  The
 Router Alert IP Option alerts interior routers to check internally,
 but they find that the IP Protocol is RSVP-E2E-IGNORE and the next
 hop interface is interior.  As such, they simply forward it as a
 normal IP datagram.

Baker, et al. Standards Track [Page 15] RFC 3175 RSVP Reservation Aggregation September 2001

2.3. Receipt of E2E Path Message By Deaggregating Router

 The E2E Path message finally arrives at a deaggregating router, which
 receives it on an interior interface and forwards it on an exterior
 interface.  Again, the Router Alert IP Option alerts it to intercept
 the message, but this time the IP Protocol is RSVP-E2E-IGNORE and the
 next hop interface is an exterior interface.
 Before forwarding the E2E Path towards the receiver, the Deaggregator
 should update its ADSPEC.  This update is to reflect the impact of
 the aggregation region onto the QoS to be achieved E2E by the flow.
 Such information can be collected by the ADSPEC of Aggregate Path
 messages travelling from the Aggregator to the Deaggregator.  Thus,
 to enable correct updating of the ADSPEC, a deaggregating router may
 wait as described below for the arrival of an aggregate Path before
 forwarding the E2E Path.
 When receiving the E2E Path, depending on the policy for mapping E2E
 reservation onto Aggregate Reservations, the Deaggregator may or may
 not be in a position to decide which DSCP the E2E flow for the
 processed E2E Path is going to be mapped onto, as described above.
 If the Deaggregator is in a position to know the mapping at this
 point, then the Deaggregator first checks that there is an Aggregate
 Path in place for the corresponding DSCP.  If so, then the
 Deaggregator uses the ADSPEC of this Aggregate Path to update the
 ADSPEC of the E2E Path and then forwards the E2E Path towards the
 receiver.  If not, then the Deaggregator requests establishment of
 the corresponding Aggregate Path by sending an E2E PathErr message
 with an error code of NEW-AGGREGATE-NEEDED and the desired DSCP
 encoded in the DCLASS Object.  The Deaggregator may also at the same
 time request establishment of an aggregate reservation for other
 DSCPs.  When receiving the Aggregate Path for the desired DSCP, the
 Deaggregator then uses the ADSPEC of this Aggregate Path to update
 the ADSPEC of the E2E Path.
 If the Deaggregator is not in a position to know the mapping at this
 point, then the Deaggregator uses the information contained in the
 ADSPEC of one Aggregate Path or of multiple Aggregate Paths to update
 the E2E Path ADSPEC.  Similarly, if one or more of the necessary
 Aggregate Paths is not yet established, the Deaggregator requests
 establishment of the corresponding Aggregate Path by sending an E2E
 PathErr message with an error code of NEW-AGGREGATE-NEEDED and the
 desired DSCP encoded in the respective DCLASS Object.  When receiving
 the Aggregate Path for the desired DSCP, the Deaggregator then uses
 the ADSPEC of this Aggregate Path to update the ADSPEC of the E2E
 Path.

Baker, et al. Standards Track [Page 16] RFC 3175 RSVP Reservation Aggregation September 2001

 Generating a E2E PathErr message with an error code of NEW-
 AGGREGATE-NEEDED should not result in any Path state being removed,
 but should result in the aggregating router initiating the necessary
 aggregate Path message, as described in the following section.
 The deaggregating router changes the E2E Path message's IP Protocol
 from RSVP-E2E-IGNORE to RSVP and forwards the E2E Path message
 towards its intended destination.

2.4. Initiation of New Aggregate Path Message By Aggregating Router

 The aggregating Router is responsible for generating a new Aggregate
 Path for a DSCP when receiving a E2E PathErr message with the error
 code NEW-AGGREGATE-NEEDED from the deaggregator.  The DSCP value to
 include in the Aggregate Path Session is found in the DCLASS Object
 of the received E2E PathErr message.  The identity of the
 deaggregator itself is found in the ERROR SPECIFICATION of the E2E
 PathErr message.  The destination address of the aggregate Path
 message is the address of the deaggregating router, and the message
 is sent with IP protocol number RSVP.
 Existing RSVP procedures specify that the size of a reservation
 established for a flow is set to the minimum of the Path SENDER_TSPEC
 and the Resv FLOW_SPEC.  Consequently, the size of an Aggregate
 Reservation cannot be larger than the SENDER_TSPEC included in the
 Aggregate Path by the Aggregator.  To ensure that Aggregate
 Reservations can be sized by the Deaggregator without undesired
 limitations, the Aggregating router should always attempt to include
 in the Aggregate Path a SENDER_TSPEC which is at least as large as
 the size that would actually be required as determined by the
 Deaggregator.  One method to achieve this is to use a SENDER_TSPEC
 which is obviously larger than the highest load of E2E reservations
 that may be supported onto this network.  Another method is for the
 Aggregator to keep track of which flows are mapped onto a DSCP and
 always add their E2E Path SENDER_TSPEC into the Aggregate Path
 SENDER_TSPEC (and possibly also add some additional bandwidth in
 anticipation of future E2E reservations).
 The aggregating router is notified of the mapping from an E2E flow to
 a DSCP in two ways.  First, when the aggregating router receives a
 E2E PathErr with error code NEW-AGGREGATE-NEEDED, the Aggregator is
 notified that the corresponding E2E flow is (at least temporarily)
 mapped onto a given DSCP.  Secondly, when the aggregating router
 receives an E2E Resv containing a DCLASS Object (as described further
 below), the Aggregating Router is notified that the corresponding E2E
 flow is mapped onto a given DSCP.

Baker, et al. Standards Track [Page 17] RFC 3175 RSVP Reservation Aggregation September 2001

2.5. Handling of E2E Resv Message by Deaggregating Router

 Having sent the E2E Path message on toward the destination, the
 deaggregator must now expect to receive an E2E Resv for the session.
 On receipt, its responsibility is to ensure that there is sufficient
 bandwidth reserved within the aggregation region to support the new
 E2E reservation, and if there is, then to forward the E2E Resv to the
 aggregating router.
 The Deaggregating router first makes the final decision of which
 Aggregate Reservation (and thus which DSCP) this E2E reservation is
 to be mapped onto.  This decision is made according to the policy
 selected by the network administrator as described above.
 If this final mapping decision is such that the Deaggregator can now
 make a more accurate update of the E2E Path ADSPEC than done when
 forwarding the initial E2E Path, the Deaggregator should do so and
 generate a new E2E Path immediately in order to provide the accurate
 ADSPEC information to the receiver as soon as possible.  Otherwise,
 normal Refresh procedures should be followed for the E2E Path.
 If no Aggregate Reservation currently exists from the corresponding
 aggregating router with the corresponding DSCP, the Deaggregating
 router will establish a new Aggregate Reservation as described in the
 next section.
 If the corresponding Aggregate Reservation exists but has
 insufficient bandwidth reserved to accommodate the new E2E
 reservation (in addition to all the existing E2E reservations
 currently mapped onto it), it should follow the normal RSVP
 procedures [RSVP] for a reservation being placed with insufficient
 bandwidth to support the reservation.  It may also first attempt to
 increase the aggregate reservation that is supplying bandwidth by
 increasing the size of the FLOW_SPEC that it includes in the
 aggregate Resv that it sends upstream.  As discussed in the previous
 section, the Aggregating Router should ensure that the SENDER_TSPEC
 it includes in the Aggregate Path is always in excess of the
 FLOW_SPEC that may be requested in the Aggregate Resv by the
 Deaggregator, so that the Deaggregator is not unnecessarily prevented
 from effectively increasing the Aggregate Reservation bandwidth as
 required.
 When sufficient bandwidth is available on the corresponding aggregate
 reservation, the Deaggregating Router may simply send the E2E Resv
 message with IP Protocol RSVP to the aggregating router.  This
 message should include the DCLASS object to indicate which DSCP the
 aggregator must use for this E2E flow.  The deaggregator will also

Baker, et al. Standards Track [Page 18] RFC 3175 RSVP Reservation Aggregation September 2001

 add the token bucket from the E2E Resv FLOWSPEC object into its
 internal understanding of how much of the Aggregate reservation is in
 use.
 As discussed above, in order to minimize the occurrence of situations
 where insufficient bandwidth is reserved on the corresponding
 Aggregate Reservation at the time of processing an E2E Resv, and in
 turn to avoid the delay associated with the increase of this
 aggregate bandwidth, the Deaggregator MAY anticipate the current
 demand and increase the Aggregate Reservations size ahead of actual
 requirements by E2E reservations.

2.6. Initiation of New Aggregate Resv Message By Deaggregating Router

 Upon receiving an E2E Resv message on an exterior interface, and
 having determined the appropriate DSCP for the session according to
 the mapping policy, the Deaggregator looks for the corresponding path
 state for a session with the chosen DSCP.  If aggregate Path state
 exists, but no aggregate Resv state exists, the Deaggregator creates
 a new aggregate Resv.
 If no aggregate Path state exists for the appropriate DSCP, this may
 be because the Deaggregator could not decide earlier the final
 mapping for this E2E flow and elected to not establish Aggregate Path
 state for all DSCPs.  In that case, the Deaggregator should request
 establishment of the corresponding Aggregate Path by sending a E2E
 PathErr with error code of NEW-AGGREGATE-NEEDED and with a DCLASS
 containing the required DSCP.  This will trigger the Aggregator to
 establish the corresponding Aggregate Path.  Once the Deaggregator
 has determined that the aggregate Path state is established, it
 creates a new Aggregate Resv.
 The FLOW_SPEC of the new Aggregate Resv is set to a value not smaller
 than the requirement of the E2E reservation it is supporting.  The
 Aggregate Resv is sent toward the aggregator (i.e., to the previous
 hop), using the AGGREGATED-RSVP session and filter specifications
 defined below.  Since the DSCP is in the SESSION object, no DCLASS
 object is necessary.  The message should be reliably delivered using
 the mechanisms in [RFC2961] or, alternatively, the CONFIRM object may
 be used, to assure that the aggregate Resv does indeed arrive and is
 granted.  This enables the deaggregator to determine that the
 requested bandwidth is available to allocate to the E2E flows it
 supports.
 In order to minimize the occurrence of situations where no
 corresponding Aggregate Reservation is established at the time of
 processing an E2E Resv, and in turn to avoid the delay associated
 with the creation of this aggregate reservation, the Deaggregator MAY

Baker, et al. Standards Track [Page 19] RFC 3175 RSVP Reservation Aggregation September 2001

 anticipate the current demand and create the Aggregate Reservation
 before receiving E2E Resv messages requiring bandwidth on those
 aggregate reservations.

2.7. Handling of Aggregate Resv Message by Interior Routers

 The aggregate Resv message is handled in essentially the same way as
 defined in [RSVP].  The Session object contains the address of the
 deaggregating router (or the group address for the session in the
 case of multicast) and the DSCP that has been chosen for the session.
 The Filterspec object identifies the aggregating router.  These
 routers perform admission control and resource allocation as usual
 and send the aggregate Resv on towards the aggregator.

2.8. Handling of E2E Resv Message by Aggregating Router

 The receipt of the E2E Resv message with a DCLASS Object is the final
 confirmation to the aggregating router of the mapping of the E2E
 reservation onto an Aggregate Reservation.  Under normal
 circumstances, this is the only way it will be informed of this
 association.  It should now forward the E2E Resv to its previous hop,
 following normal RSVP processing rules [RSVP].

2.9. Removal of E2E Reservation

 E2E reservations are removed in the usual way via PathTear, ResvTear,
 timeout, or as the result of an error condition.  When they are
 removed, their FLOWSPEC information must also be removed from the
 allocated portion of the aggregate reservation.  This same bandwidth
 may be re-used for other traffic in the near future.  When E2E Path
 messages are removed, their SENDER_TSPEC information must also be
 removed from the aggregate Path.

2.10. Removal of Aggregate Reservation

 Should an aggregate reservation go away (presumably due to a
 configuration  change, route change, or policy event), the E2E
 reservations it supports are no longer active.  They must be treated
 accordingly.

2.11. Handling of Data On Reserved E2E Flow by Aggregating Router

 Prior to establishment that a given E2E flow is part of a given
 aggregate, the flow's data should be treated as traffic without a
 reservation by whatever policies prevail for such.  Generally, this
 will mean being given the same forwarding behavior as best effort
 traffic.  However, upon establishing that the flow belongs to a given
 aggregate, the aggregating router is responsible for marking any

Baker, et al. Standards Track [Page 20] RFC 3175 RSVP Reservation Aggregation September 2001

 related traffic with the correct DSCP and forwarding it in the manner
 appropriate to traffic on that reservation.  This may imply
 forwarding it to a given IP next hop, or piping it down a given link
 layer circuit, tunnel, or MPLS label switched path.
 The aggregator is responsible for performing per-reservation policing
 on the E2E flows that it is aggregating.  The aggregator performs
 metering of traffic belonging to each reservation to assess
 compliance to the token bucket for the corresponding E2E reservation.
 Packets which are assessed in compliance are forwarded as mentioned
 above.  Packets which are assessed out of compliance must be either
 dropped, reshaped or marked to a different DSCP.  The detailed
 policing behavior is an aspect of the service mapping described in
 [RFC2998].

2.12. Procedures for Multicast Sessions

 Because of the difficulties of aggregating multicast sessions
 described above, we focus on the aggregation of scheduling and
 classification state in the multicast case.  The main difference
 between the multicast and unicast cases is that rather than sending
 an aggregate Path message to the unicast address of a single
 deaggregating router, in the multicast case we send the "aggregate"
 Path message to the same group address as the E2E session.  This
 ensures that the aggregate Path message follows the same route as the
 E2E Path.  This difference between unicast and multicast is reflected
 in the Session objects defined below.  A consequence of this approach
 is that we continue to have reservation state per multicast session
 inside the aggregation region.
 A further challenge arises in multicast sessions with heterogeneous
 receivers.  Consider an interior router which must forward packets
 for a multicast session on two interfaces, but has only received a
 reservation request on one of those interfaces.  It receives packets
 marked with the DSCP chosen for the aggregate reservation.  When
 sending them out the interface which has no installed reservation, it
 has the following options:
 a) remark those packets to best effort before sending them out the
    interface;
 b) send the packets out the interface with the DSCP chosen for the
    aggregate reservation.
 The first approach suffers from the drawback that it requires nMF
 classification at an interior router in order to recognize the flows
 whose packets must be demoted.  The second approach requires over-
 reservation of resources on the interface on which no reservation was

Baker, et al. Standards Track [Page 21] RFC 3175 RSVP Reservation Aggregation September 2001

 received.  In the absence of such over-reservation, the packets sent
 with the "wrong" DSCP would be able to degrade the service
 experienced by packets using that DSCP legitimately.
 To make MF classification acceptable in an interior router, it may be
 possible to treat the case of heterogeneous flows as an exception.
 That is, an interior router only needs to be able to recognize those
 individual microflows that have heterogeneous resource needs on the
 outbound interfaces of this router.

3. Protocol Elements

3.1. IP Protocol RSVP-E2E-IGNORE

 This specification requires the assignment of a protocol type RSVP-
 E2E-IGNORE, whose number is at this point 134.  This is used only on
 E2E messages which require a router alert (Path, PathTear, and
 ResvConf), and signifies that the message must be treated one way
 when destined to an interior interface, and another way when destined
 to an exterior interface.  The protocol type is swapped by the
 Aggregator from RSVP to RSVP-E2E-IGNORE in E2E Path, PathTear, and
 ResvConf messages when they enter the Aggregation Region.  The
 protocol type is swapped back by the Deaggregator from RSVP-E2E-
 IGNORE to RSVP in such E2E messages when they exit the Aggregation
 Region.

3.2. Path Error Code

 A PathErr code NEW-AGGREGATE-NEEDED is required.  This value does not
 signify that a fatal error has occurred, but that an action is
 required of the aggregating router to avoid an error condition in the
 near future.

3.3. SESSION Object

 The SESSION object contains two values: the IP Address of the
 aggregate session destination, and the DSCP that it will use on the
 E2E data the reservation contains.  For unicast sessions, the session
 destination address is the address of the deaggregating router.  For
 multicast sessions, the session destination is the multicast address
 of the E2E session (or sessions) being aggregated.  The inclusion of
 the DSCP in the session allows for multiple sessions toward the same
 address to be distinguished by their DSCP and queued separately.  It
 also provides the means for aggregating scheduling and classification
 state.  In the case where a session uses a pair of PHBs (e.g., AF11
 and AF12), the DSCP used should represent the numerically smallest
 PHB (e.g., AF11).  This follows the same naming convention described
 in [BRIM].

Baker, et al. Standards Track [Page 22] RFC 3175 RSVP Reservation Aggregation September 2001

 Session types are defined for IPv4 and IPv6 addresses.
 o  IP4 SESSION object: Class = SESSION,
    C-Type = RSVP-AGGREGATE-IP4
      +-------------+-------------+-------------+-------------+
      |              IPv4 Session Address (4 bytes)           |
      +-------------+-------------+-------------+-------------+
      | /////////// |    Flags    |  /////////  |     DSCP    |
      +-------------+-------------+-------------+-------------+
 o  IP6 SESSION object: Class = SESSION,
    C-Type = RSVP-AGGREGATE-IP6
      +-------------+-------------+-------------+-------------+
      |                                                       |
      +                                                       +
      |                                                       |
      +              IPv6 Session Address (16 bytes)          +
      |                                                       |
      +                                                       +
      |                                                       |
      +-------------+-------------+-------------+-------------+
      | /////////// |    Flags    |  /////////  |     DSCP    |
      +-------------+-------------+-------------+-------------+

3.4. SENDER_TEMPLATE Object

 The SENDER_TEMPLATE object identifies the aggregating router for the
 aggregate reservation.
 o  IP4 SENDER_TEMPLATE object: Class = SENDER_TEMPLATE,
    C-Type = RSVP-AGGREGATE-IP4
      +-------------+-------------+-------------+-------------+
      |                IPv4 Aggregator Address (4 bytes)      |
      +-------------+-------------+-------------+-------------+

Baker, et al. Standards Track [Page 23] RFC 3175 RSVP Reservation Aggregation September 2001

 o  IP6 SENDER_TEMPLATE object: Class = SENDER_TEMPLATE,
    C-Type = RSVP-AGGREGATE-IP6
      +-------------+-------------+-------------+-------------+
      |                                                       |
      +                                                       +
      |                                                       |
      +           IPv6 Aggregator Address (16 bytes)          +
      |                                                       |
      +                                                       +
      |                                                       |
      +-------------+-------------+-------------+-------------+

3.5. FILTER_SPEC Object

 The FILTER_SPEC object identifies the aggregating router for the
 aggregate reservation, and is syntactically identical to the
 SENDER_TEMPLATE object.

4. Policies and Algorithms For Predictive Management Of Blocks Of

  Bandwidth
 The exact policies used in determining how much bandwidth should be
 allocated to an aggregate reservation at any given time are beyond
 the scope of this document, and may be proprietary to the service
 provider in question.  However, here we explore some of the issues
 and suggest approaches.
 In short, the ideal condition is that the aggregate reservation
 always has enough resources to allocate to any E2E reservation that
 requires its support, and never takes too much.  Simply stated, but
 more difficult to achieve.  Factors that come into account include
 significant times in the diurnal cycle: one may find that a large
 number of people start placing calls at 8:00 AM, even though the hour
 from 7:00 to 8:00 is dead calm.  They also include recent history: if
 more people have been  placing calls recently than have been
 finishing them, a prediction of the necessary bandwidth a few moments
 hence may call for more bandwidth than is currently allocated.
 Likewise, at the end of a busy period, we may find that the trend
 calls for declining reservation amounts.
 We recommend a policy something along this line.  At any given time,
 one should expect that the amount of bandwidth required for the
 aggregate reservation is the larger of the following:
 (a) a requirement known a priori, such as from history of the diurnal
     cycle at a particular week day and time of day, and

Baker, et al. Standards Track [Page 24] RFC 3175 RSVP Reservation Aggregation September 2001

 (b) the trend line over recent history, with 90 or 99% statistical
     confidence.
 We further expect that changes to that aggregate reservation would be
 made no more often than every few minutes, and ideally perhaps on
 larger granularity such as fifteen minute intervals or hourly.  The
 finer the granularity, the greater the level of signaling required,
 while the coarser the granularity, the greater the chance for error,
 and the need to recover from that error.
 In general, we expect that the aggregate reservation will not ever
 add up to exactly the sum of the reservations it supports, but rather
 will be an integer multiple of some block reservation size, which
 exceeds that value.

5. Security Considerations

 Numerous security issues pertain to this document; for example, the
 loss of an aggregate reservation to an aggressor causes many calls to
 operate unreserved, and the reservation of a great excess of
 bandwidth may result in a denial of service.  However, these issues
 are not confined to this extension: RSVP itself has them.  We believe
 that the security mechanisms in RSVP address these issues as well.
 One security issue specific to RSVP aggregation involves the
 modification of the IP protocol number in RSVP Path messages that
 traverse an aggregation region.  If that field were maliciously
 modified in a Path message, it would cause the message to be ignored
 by all subsequent devices on its path, preventing reservations from
 being made.  It could even be possible to correct the value before it
 reached the receiver, making it difficult to detect the attack.  In
 theory, it might also be possible for a node to modify the IP
 protocol number for non-RSVP messages as well, thus interfering with
 the operation of other protocols.
 One way to mitigate the risks of malicious modification of the IP
 protocol number is to use an IPSEC authentication header, which would
 ensure that malicious modification of the IP header is detected.
 This is a desirable approach but imposes some administrative burden
 in the form of key management for authentication purposes.
 It is RECOMMENDED that implementations of this specification only
 support modification of the IP protocol number for RSVP Path,
 PathTear, and ResvConf messages.  That is, a general facility for
 modification of the IP protocol number SHOULD NOT be made available.

Baker, et al. Standards Track [Page 25] RFC 3175 RSVP Reservation Aggregation September 2001

 Network operators deploying routers with RSVP aggregation capability
 should be aware of the risks of inappropriate modification of the IP
 protocol number and should take appropriate steps (physical security,
 password protection, etc.) to reduce the risk that a router could be
 configured by an attacker to perform malicious modification of the
 protocol number.

6. IANA Considerations

 Section 1.2 proposes a new protocol type, RSVP-E2E-IGNORE, which is
 used to identify a message that routers in the network core will see;
 further processing of such messages may or may not be required,
 depending on the egress interface type, as described in Section 1.2.
 The IANA assigned IP protocol number 134, in accordance with
 [RFC2780], meeting the Standards Track publication criterion.
 Section 1.4.9 describes the manner in which the Router Alert is used
 in the context of this specification, which is essentially a simple
 counter of the depth of nesting of aggregation.  The IPv4 Router
 Alert [RFC2113] has the option simply to ask the router to look at
 the protocol type of the intercepted datagram and decide what to do
 with it; the parameter is additional information to that decision.
 The IPv6 Router Alert [RFC2711] turns the parameter into an option
 sub-type.  As a result, the IPv6 router alert option may not be used
 algorithmically in the context of the protocol in question.  The IANA
 assigned a block of 32 values (3-35, "Aggregated Reservation Nesting
 Level") which we may map to nesting depths 0..31, hoping that 32
 levels is enough.
 Section 3.2 discusses a new, required path error code.  The IANA has
 assigned RSVP Parameters Error Code 26 to NEW-AGGREGATE-NEEDED.
 Sections 3.3, 3.4, and 3.5 describe extensions to three object
 classes: Session, Filter Specification, and Sender Template.  The
 IANA has assigned two new common C-Types to be specified for the
 aggregator's address.  RSVP-AGGREGATE-IP4 is C-Type 9 and RSVP-
 AGGREGATE-IP6 is C-Type 10.  In adding these C-types to IANA RSVP
 Class Names, Class Numbers and Class Types registry, the same
 numbering for them is used in all three Classes, as is done for IPv4
 and IPv6 address tuples in [RSVP].

Baker, et al. Standards Track [Page 26] RFC 3175 RSVP Reservation Aggregation September 2001

7. Acknowledgments

 The authors acknowledge that published documents and discussion with
 several people, notably John Wroclawski, Steve Berson, and Andreas
 Terzis materially contributed to this document.  The design is
 influenced by the RSVP tunnels document [TERZIS].

Baker, et al. Standards Track [Page 27] RFC 3175 RSVP Reservation Aggregation September 2001

APPENDIX 1: Example Signalling Flow For First E2E Flow

 This Appendix does not provide additional specification.  It only
 illustrates the specification detailed above through a possible flow
 of RSVP signalling messages involved in the successful establishment
 of a unicast E2E reservation which is the first between a given pair
 of Aggregator/Deaggregator.
         Aggregator                              Deaggregator
  E2E Path
 ---------------->
              (1)
                         E2E Path
                   ------------------------------->
                                                      (2)
                    E2E PathErr(New-agg-needed, DCLASS=x)
                   <-------------------------------
                    E2E PathErr(New-agg-needed, DCLASS=y)
                   <-------------------------------
              (3)
                         AggPath(DSCP=x)
                   ------------------------------->
                         AggPath(DSCP=y)
                   ------------------------------->
                                                      (4)
                                                         E2E Path
                                                         ----------->
                                                      (5)
                         AggResv (DSCP=x)
                   <-------------------------------
                         AggResv (DSCP=y)
                   <-------------------------------
             (6)
                         AggResvConfirm (DSCP=x)
                   ------------------------------>
                         AggResvConfirm (DSCP=y)
                   ------------------------------>
                                                      (7)
                                                         E2E Resv
                                                         <----------
                                                      (8)
                         E2E Resv (DCLASS=x)
                   <-----------------------------
             (9)
     E2E Resv
 <---------------

Baker, et al. Standards Track [Page 28] RFC 3175 RSVP Reservation Aggregation September 2001

 (1)  Aggregator forwards E2E Path into aggregation region after
      modifying its IP Protocol Number to RSVP-E2E-IGNORE
 (2)  Let's assume no Aggregate Path exists.  To be able to accurately
      update the ADSPEC of the E2E Path, the Deaggregator needs the
      ADSPEC of Aggregate PATH.  In this example the Deaggregator
      elects to instruct the Aggregator to set up Aggregate Path
      states for the two supported DSCPs by sending a New-Agg-Needed
      PathErr code for each DSCP.
 (3)  The Aggregator follows the request from the Deaggregator and
      signals an Aggregate Path for both DSCPs.
 (4)  The Deaggregator takes into account the information contained in
      the ADSPEC from both Aggregate Path and updates the E2E Path
      ADSPEC accordingly.  The Deaggregator also modifies the E2E Path
      IP Protocol Number to RSVP before forwarding it.
 (5)  In this example, the Deaggregator elects to immediately proceed
      with establishment of Aggregate Reservations for both DSCPs.  In
      effect, the Deaggregator can be seen as anticipating the actual
      demand of E2E reservations so that resources are available on
      Aggregate Reservations when the E2E Resv requests arrive in
      order to speed up establishment of E2E reservations.  Assume
      also that the Deaggregator includes the optional Resv Confirm
      Request in these Aggregate Resv.
 (6)  The Aggregator merely complies with the received ResvConfirm
      Request and returns the corresponding Aggregate ResvConfirm.
 (7)  The Deaggregator has explicit confirmation that both Aggregate
      Resv are established.
 (8)  On receipt of the E2E Resv, the Deaggregator applies the mapping
      policy defined by the network administrator to map the E2E Resv
      onto an Aggregate Reservation.  Let's assume that this policy is
      such that the E2E reservation is to be mapped onto the Aggregate
      Reservation with DSCP=x.  The Deaggregator knows that an
      Aggregate Reservation is in place for the corresponding DSCP
      since (7).  The Deaggregator performs admission control of the
      E2E Resv onto the Aggregate Resv for DSCP=x.  Assuming that the
      Aggregate Resv for DSCP=x had been established with sufficient
      bandwidth to support the E2E Resv, the Deaggregator adjusts its
      counter tracking the unused bandwidth on the Aggregate
      Reservation and forwards the E2E Resv to the Aggregator
      including a DCLASS object conveying the selected mapping onto
      DSCP=x.

Baker, et al. Standards Track [Page 29] RFC 3175 RSVP Reservation Aggregation September 2001

 (9)  The Aggregator records the mapping of the E2E Resv onto DSCP=x.
      The Aggregator removes the DCLASS object and forwards the E2E
      Resv towards the sender.

APPENDIX 2: Example Signalling Flow For Subsequent E2E Flow Without

          Reservation Resizing
 This Appendix does not provide additional specification.  It only
 illustrates the specification detailed above through a possible flow
 of RSVP signalling messages involved in the successful establishment
 of a unicast E2E reservation which follows other E2E reservations
 between a given pair of Aggregator/Deaggregator.  This flow could be
 imagined as following the flow of messages illustrated in Appendix 1.
         Aggregator                              Deaggregator
  E2E Path
 ---------------->
              (10)
                         E2E Path
                     ------------------------------->
                                                    (11)
                                                       E2E Path
                                                       ----------->
                                                        E2E Resv
                                                       <-----------
                                                    (12)
                         E2E Resv (DCLASS=x)
                   <-----------------------------
               (13)
     E2E Resv
 <---------------
 (10) Aggregator forwards E2E Path into aggregation region after
      modifying its IP Protocol Number to RSVP-E2E-IGNORE
 (11) Because previous E2E reservations have been established, let's
      assume that Aggregate Path exists for all supported DSCPs.  The
      Deaggregator takes into account the information contained in the
      ADSPEC from the Aggregate Paths and updates the E2E Path ADSPEC
      accordingly.  The Deaggregator also modifies the E2E Path IP
      Protocol Number to RSVP before forwarding it.
 (12) On receipt of the E2E Resv, the Deaggregator applies the mapping
      policy defined by the network administrator to map the E2E Resv
      onto an Aggregate Reservation.  Let's assume that this policy is
      such that the E2E reservation is to be mapped onto the Aggregate
      Reservation with DSCP=x.  Because previous E2E reservations have

Baker, et al. Standards Track [Page 30] RFC 3175 RSVP Reservation Aggregation September 2001

      been established, let's assume that an Aggregate Reservation is
      in place for DSCP=x.  The Deaggregator performs admission
      control of the E2E Resv onto the Aggregate Resv for DSCP=x.
      Assuming that the Aggregate Resv for DSCP=x has sufficient
      unused bandwidth to support the new E2E Resv, the Deaggregator
      then adjusts its counter tracking the unused bandwidth on the
      Aggregate Reservation and forwards the E2E Resv to the
      Aggregator including a DCLASS object conveying the selected
      mapping onto DSCP=x.
 (13) The Aggregator records the mapping of the E2E Resv onto DSCP=x.
      The Aggregator removes the DCLASS object and forwards the E2E
      Resv towards the sender.

APPENDIX 3: Example Signalling Flow For Subsequent E2E Flow With

          Reservation Resizing
 This Appendix does not provide additional specification.  It only
 illustrates the specification detailed above through a possible flow
 of RSVP signalling messages involved in the successful establishment
 of a unicast E2E reservation which follows other E2E reservations
 between a given pair of Aggregator/Deaggregator.  This flow could be
 imagined as following the flow of messages illustrated in Appendix 2.

Baker, et al. Standards Track [Page 31] RFC 3175 RSVP Reservation Aggregation September 2001

               Aggregator                        Deaggregator
  E2E Path
 ---------------->
                  (14)
                         E2E Path
                     ------------------------------->
                                                     (15)
                                                         E2E Path
                                                         ----------->
                                                         E2E Resv
                                                         <-----------
                                                     (16)
                      AggResv (DSCP=x, increased Bw)
                     <-------------------------------
                 (17)
                     AggResvConfirm (DSCP=x, increased Bw)
                     ------------------------------>
                                                     (18)
                        E2E Resv (DCLASS=x)
                     <-----------------------------
                 (19)
     E2E Resv
 <---------------
 (14) Aggregator forwards E2E Path into aggregation region after
      modifying its IP Protocol Number to RSVP-E2E-IGNORE
 (15) Because previous E2E reservations have been established, let's
      assume that Aggregate Path exists for all supported DSCPs.  The
      Deaggregator takes into account the information contained in the
      ADSPEC from the Aggregate Paths and updates the E2E Path ADSPEC
      accordingly.  The Deaggregator also modifies the E2E Path IP
      Protocol Number to RSVP before forwarding it.
 (16) On receipt of the E2E Resv, the Deaggregator applies the mapping
      policy defined by the network administrator to map the E2E Resv
      onto an Aggregate Reservation.  Let's assume that this policy is
      such that the E2E reservation is to be mapped onto the Aggregate
      Reservation with DSCP=x.  Because previous E2E reservations have
      been established, let's assume that an Aggregate Reservation is
      in place for DSCP=x.  The Deaggregator performs admission
      control of the E2E Resv onto the Agg Resv for DSCP=x.  Let's
      assume that the Aggregate Resv for DSCP=x does NOT have
      sufficient unused bandwidth to support the new E2E Resv.  The

Baker, et al. Standards Track [Page 32] RFC 3175 RSVP Reservation Aggregation September 2001

      Deaggregator then attempts to increase the Aggregate Reservation
      bandwidth for DSCP=x by sending a new Aggregate Resv with an
      increased bandwidth sufficient to accommodate all the E2E
      reservations already mapped onto that Aggregate reservation plus
      the new E2E reservation plus possibly some additional spare
      bandwidth in anticipation of additional E2E reservations to
      come.  Assume also that the Deaggregator includes the optional
      Resv Confirm Request in these Aggregate Resv.
 (17) The Aggregator merely complies with the received ResvConfirm
      Request and returns the corresponding Aggregate ResvConfirm.
 (18) The Deaggregator has explicit confirmation that the Aggregate
      Resv has been successfully increased.  The Deaggregator performs
      again admission control of the E2E Resv onto the increased
      Aggregate Reservation for DSCP=x.  Assuming that the increased
      Aggregate Reservation for DSCP=x now has sufficient unused
      bandwidth and resources to support the new E2E Resv, the
      Deaggregator then adjusts its counter tracking the unused
      bandwidth on the Aggregate Reservation and forwards the E2E Resv
      to the Aggregator including a DCLASS object conveying the
      selected mapping onto DSCP=x.
 (19) The Aggregator records the mapping of the E2E Resv onto DSCP=x.
      The Aggregator removes the DCLASS object and forwards the E2E
      Resv towards the sender.

References

 [CSZ]        Clark, D., S. Shenker, and L. Zhang, "Supporting Real-
              Time Applications in an Integrated Services Packet
              Network:  Architecture and Mechanism," in Proc.
              SIGCOMM'92, September 1992.
 [IP]         Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.
 [HOSTREQ]    Braden, R., "Requirements for Internet hosts -
              communication layers", STD 3, RFC 1122, October 1989.
 [DSFIELD]    Nichols, K., Blake, S., Baker, F. and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474, December
              1998.
 [PRINCIPLES] Carpenter, B., "Architectural Principles of the
              Internet", RFC 1958, June 1996.

Baker, et al. Standards Track [Page 33] RFC 3175 RSVP Reservation Aggregation September 2001

 [ASSURED]    Heinanen, J, Baker, F., Weiss, W. and J. Wroclawski,
              "Assured Forwarding PHB Group", RFC 2597, June 1999.
 [BROKER]     Jacobson, V., Nichols K. and L. Zhang, "A Two-bit
              Differentiated Services Architecture for the Internet",
              RFC 2638, June 1999.
 [BRIM]       Brim, S., Carpenter, B. and F. LeFaucheur, "Per Hop
              Behavior Identification Codes", RFC 2836, May 2000.
 [RSVP]       Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
              Jamin, "Resource Reservation Protocol (RSVP) Version 1
              Functional Specification", RFC 2205, September 1997.
 [TERZIS]     Terzis, A., Krawczyk, J., Wroclawski, J. and L. Zhang,
              "RSVP Operation Over IP Tunnels", RFC 2746, January
              2000.
 [DCLASS]     Bernet, Y., "Format of the RSVP DCLASS Object", RFC
              2996, November 2000.
 [INTEGRITY]  Baker, F., Lindell, B. and M. Talwar, "RSVP
              Cryptographic Authentication", RFC 2747, January 2000.
 [RFC2998]    Bernet Y., Ford, P., Yavatkar, R., Baker, F., Zhang, L.,
              Speer, M., Braden, R., Davie, B., Wroclawski, J. and E.
              Felstaine, "Integrated Services Operation Over Diffserv
              Networks", RFC 2998, November 2000.
 [RFC2961]    Berger, L., Gan, D., Swallow, G., Pan, P. and F.
              Tommasi, "RSVP Refresh Reduction Extensions", RFC 2961,
              April 2001.
 [RFC2780]    Bradner, S. and V. Paxson, "IANA Allocation Guidelines
              For Values In the Internet Protocol and Related
              Headers", RFC 2780, March 2000.
 [RFC2711]    Partridge, C. and A. Jackson, "IPv6 Router Alert
              Option", RFC 2711, October 1999.
 [RFC2113]    Katz, D. "IP Router Alert Option", RFC 2113, February
              1997.

Baker, et al. Standards Track [Page 34] RFC 3175 RSVP Reservation Aggregation September 2001

Authors' Addresses

 Fred Baker
 Cisco Systems
 1121 Via Del Rey
 Santa Barbara, CA, 93117  USA
 Phone: (408) 526-4257
 EMail: fred@cisco.com
 Carol Iturralde
 Cisco Systems
 250 Apollo Drive
 Chelmsford MA, 01824 USA
 Phone: 978-244-8532
 EMail: cei@cisco.com
 Francois Le Faucheur
 Cisco Systems
 Domaine Green Side
 400, Avenue de Roumanille
 06410 Biot - Sophia Antipolis
 France
 Phone: +33.4.97.23.26.19
 EMail: flefauch@cisco.com
 Bruce Davie
 Cisco Systems
 250 Apollo Drive
 Chelmsford MA,01824 USA
 Phone: 978-244-8921
 EMail: bdavie@cisco.com

Baker, et al. Standards Track [Page 35] RFC 3175 RSVP Reservation Aggregation September 2001

Full Copyright Statement

 Copyright (C) The Internet Society (2001).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
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 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
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 This document and the information contained herein is provided on an
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 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Baker, et al. Standards Track [Page 36]

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