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Analysis of Existing Quality-of-Service Signaling Protocols
RFC 4094

Network Working Group                                          J. Manner
Request for Comments: 4094                                         X. Fu
Category: Informational                                         May 2005

      Analysis of Existing Quality-of-Service Signaling Protocols

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document reviews some of the existing Quality of Service (QoS)
   signaling protocols for an IP network.  The goal here is to learn
   from them and to avoid common misconceptions.  Further, we need to
   avoid mistakes during the design and implementation of any new
   protocol in this area.

Table of Contents

   1. Introduction ....................................................3
   2. RSVP and RSVP Extensions ........................................4
      2.1. Basic Design ...............................................4
           2.1.1. Signaling Model .....................................4
           2.1.2. Soft State ..........................................5
           2.1.3. Two-Pass Signaling Message Exchanges ................5
           2.1.4. Receiver-Based Resource Reservation .................5
           2.1.5. Separation of QoS Signaling from Routing ............5
      2.2. RSVP Extensions ............................................6
           2.2.1. Simple Tunneling ....................................6
           2.2.2. IPsec Interface .....................................6
           2.2.3. Policy Interface ....................................6
           2.2.4. Refresh Reduction ...................................7
           2.2.5. RSVP over RSVP ......................................8
           2.2.6. IEEE 802-Style LAN Interface ........................8
           2.2.7. ATM Interface .......................................9
           2.2.8. DiffServ Interface ..................................9
           2.2.9. Null Service Type ...................................9
           2.2.10. MPLS Traffic Engineering ..........................10
           2.2.11. GMPLS and RSVP-TE .................................11

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           2.2.12. GMPLS Operation at UNI and E-NNI Reference
                   Points ............................................12
           2.2.13. MPLS and GMPLS Future Extensions ..................12
           2.2.14. ITU-T H.323 Interface .............................13
           2.2.15. 3GPP Interface ....................................13
      2.3. Extensions for New Deployment Scenarios ...................14
      2.4. Conclusion ................................................15
   3. RSVP Transport Mechanism Issues ................................16
      3.1. Messaging Reliability .....................................16
      3.2. Message Packing ...........................................17
      3.3. MTU Problem ...............................................17
      3.4. RSVP-TE vs. Signaling Protocol for RT Applications ........18
      3.5. What Would Be a Better Alternative? .......................18
   4. RSVP Protocol Performance Issues ...............................19
      4.1. Processing Overhead .......................................19
      4.2. Bandwidth Consumption .....................................20
   5. RSVP Security and Mobility .....................................21
      5.1. Security ..................................................21
      5.2. Mobility Support ..........................................22
   6. Other QoS Signaling Proposals ..................................23
      6.1. Tenet and ST-II ...........................................23
      6.2. YESSIR ....................................................24
           6.2.1. Reservation Functionality ..........................24
           6.2.2. Conclusion .........................................25
      6.3. Boomerang .................................................25
           6.3.1. Reservation Functionality ..........................25
           6.3.2. Conclusions ........................................26
      6.4. INSIGNIA ..................................................26
   7. Inter-Domain Signaling .........................................27
      7.1. BGRP ......................................................27
      7.2. SICAP .....................................................27
      7.3. DARIS .....................................................28
   8. Security Considerations ........................................30
   9. Summary ........................................................30
   10. Contributors ..................................................31
   11. Acknowledgements ..............................................31
   12. Appendix A: Comparison of RSVP to the NSIS Requirements .......32
   13. Normative References ..........................................38
   14. Informative References ........................................38

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1.  Introduction

   This document reviews some of the existing QoS signaling protocols
   for an IP network.  The goal here is to learn from them and to avoid
   common misconceptions.  Further, we need to avoid mistakes during the
   design and implementation of any new protocol in this area.

   There have been a number of historic attempts to deliver QoS or
   generic signaling to the Internet.  In the early years, it was
   believed that multicast would be popular for the majority of
   communications; thus, both RSVP and earlier ST-II were designed in a
   way that is multicast-oriented.

   ST-II was developed as a reservation protocol for point-to-multipoint
   communication.  However, since it is sender-initiated, it does not
   scale with the number of receivers in a multicast group.  Its
   processing is fairly complex.  Since every sender needs to set up its
   own reservation, the total amount of reservation states is large.
   RSVP was then designed to provide support for multipoint-to-
   multipoint reservation setup in a more efficient way.  However, its
   complexity, scalability, and ability to meet new requirements have
   been criticized.

   YESSIR (YEt another Sender Session Internet Reservations) [PS98] and
   Boomerang [FNM+99] are examples of protocols designed after RSVP.
   Both were meant to be simpler than RSVP.  YESSIR is an extension to
   RTCP, whereas Boomerang is used with ICMP.

   Previously, a lot of work has been targeted at creating a new
   signaling protocol for resource control.  Istvan Cselenyi suggested
   having a QoSSIG BOF in IETF47, for identifying problems in QoS
   signaling, but failed to get enough support [URL1].  Some people
   argued, "in many ways, RSVP improved upon ST-2, and it did start out
   simpler, but it resulted in a design with complexity and
   scalability", while others thought that "new knowledge and
   requirements" made RSVP insufficient.  Some concluded that there is
   no simpler way to handle the same problem than RSVP.

   Michael Welzl organized a special session "ABR to the Internet" in
   SCI 2001, and gathered some inputs for requesting an "ABR to the
   Internet" BOF in IETF#51, which was intended to introduce explicit
   rate-feedback-related mechanisms for the Internet (e2e, edge2edge).
   This failed because of "missing community interest".

   OPENSIG [URL2] has been involved in the Internet signaling for years.
   Ping Pan initiated a SIGLITE [URL3] BOF mailing list to investigate
   lightweight Internet signaling.  Finally, NSIS BOF was successful,
   and the NSIS WG was formed.

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   The most mature and original protocols are presented in their own
   sections, and other QoS signaling protocols are presented in later
   subsections.  The presented protocols are chosen based on relevance
   to the work within NSIS.  The aim is not to review every existing
   protocol.

2.  RSVP and RSVP Extensions

   RSVP (the Resource Reservation Protocol) [ZDSZ93] [RFC2205] [BEBH96]
   has evolved from ST-II to provide end-to-end QoS signaling services
   for application data streams.  Hosts use RSVP to request a specific
   quality of service (QoS) from the network for particular application
   flows.  Routers use RSVP to deliver QoS requests to all routers along
   the data path.  RSVP also can maintain and refresh states for a
   requested QoS application flow.

   By original design, RSVP fits well into the framework of the
   Integrated Services (IntServ) [RFC2210] [BEBH96] with certain
   modularity and scalability.

   RSVP carries QoS signaling messages through the network, visiting
   each node along the data path.  To make a resource reservation at a
   node, the RSVP module communicates with two local decision modules,
   admission control and policy control.  Admission control determines
   whether the node has sufficient available resources to supply the
   requested QoS.  Policy control provides authorization for the QoS
   request.  If either check fails, the RSVP module returns an error
   notification to the application process that originated the request.
   If both checks succeed, the RSVP module sets parameters in a packet
   classifier and packet scheduler to obtain the desired QoS.

2.1.  Basic Design

   The design of RSVP distinguished itself by a number of fundamental
   ways; particularly, soft state management, two-pass signaling message
   exchanges, receiver-based resource reservation, and separation of QoS
   signaling from routing.

2.1.1.  Signaling Model

   The RSVP signaling model is based on a special handling of multicast.
   The sender of a multicast flow advertises the traffic characteristics
   periodically to the receivers via "Path" messages.  Upon receipt of
   an advertisement, a receiver may generate a "Resv" message to reserve
   resources along the flow path from the sender.  Receiver reservations
   may be heterogeneous.  To accommodate the multipoint-to-multipoint
   multicast applications, RSVP was designed to support a vector of
   reservation attributes called the "style".  A style describes whether

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   all senders of a multicast group share a single reservation and which
   receiver is applied.  The "Scope" object additionally provides the
   explicit list of senders.

2.1.2.  Soft State

   Because the number of receivers in a multicast flow is likely to
   change, and the flow of delivery paths might change during the life
   of an application flow, RSVP takes a soft-state approach in its
   design, creating and removing the protocol states (Path and Resv
   states) in routers and hosts incrementally over time.  RSVP sends
   periodic refresh messages (Path and Resv) to maintain its states and
   to recover from occasional lost messages.  In the absence of refresh
   messages, the RSVP states automatically time out and are deleted.
   States may also be deleted explicitly by PathTear, PathErr with
   Path_State_Removed flag, or ResvTear Message.

2.1.3.  Two-Pass Signaling Message Exchanges

   The receiver in an application flow is responsible for requesting the
   desired QoS from the sender.  To do this, the receiver issues an RSVP
   QoS request on behalf of the local application.  The request
   propagates to all routers in reverse direction of the data paths
   toward the sender.  In this process, RSVP requests might be merged,
   resulting in a protocol that scales well when there are a large
   number of receivers.

2.1.4.  Receiver-Based Resource Reservation

   Receiver-initiation is critical for RSVP to set up multicast sessions
   with a large number of heterogeneous receivers.  A receiver initiates
   a reservation request at a leaf of the multicast distribution tree,
   traveling toward the sender.  Whenever a reservation is found to
   already exist in a node in the distribution tree, the new request
   will be merged with the existing reservation.  This could result in
   fewer signaling operations for the RSVP nodes in the multicast tree
   close to the sender but could introduce a restriction to receiver-
   initiation.

2.1.5.  Separation of QoS Signaling from Routing

   RSVP messages follow normal IP routing.  RSVP is not a routing
   protocol, but rather is designed to operate with current and future
   unicast and multicast routing protocols.  The routing protocols are
   responsible for choosing the routes to use to forward packets, and
   RSVP consults local routing tables to obtain routes.  RSVP is
   responsible only for reservation setup along a data path.

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   A number of messages and objects have been defined for the protocol.
   A detailed description is given in [RFC2205].

2.2.  RSVP Extensions

   RSVP [RFC2205] was originally designed to support real-time
   applications over the Internet.  Over the past several years, the
   demand for multicast-capable real-time teleconferencing, which many
   people had envisioned to be one of the key Internet applications that
   could benefit from network-wide deployment of RSVP, has never
   materialized.  Instead, RSVP-TE [RFC3209], a RSVP extension for
   traffic engineering, has been widely deployed by a large number of
   network providers to support MPLS applications.

   There are a large number of protocol extensions based on RSVP.  Some
   provide additional features, such as security and scalability, to the
   original protocol.  Some introduce additional interfaces to other
   services, such as DiffServ.  And some simply define new applications,
   such as MPLS and GMPLS, that are completely irrelevant from
   protocol's original intent.

   In this section, we list only IETF-based RFCs and a limited set of
   other organizations' specifications.  Informational RFCs (e.g.,
   RFC2998 [RFC2998]) and work-in-progress I-Ds (e.g., proxy) are not
   covered here.

2.2.1.  Simple Tunneling

   [RFC2746] describes an IP tunneling enhancement mechanism that allows
   RSVP to make reservations across all IP-in-IP tunnels, basically by
   recursively applying RSVP over the tunnel portion of the path.

2.2.2.  IPsec Interface

   RSVP can support IPsec on a per-address, per-protocol basis instead
   of on a per flow basis.  [RFC2207] extends RSVP by using the IPsec
   Security Parameter Index (SPI) in place of the UDP/TCP-like ports.
   This introduces a new FILTER_SPEC object, which contains the IPsec
   SPI, and a new SESSION object.

2.2.3.  Policy Interface

   [RFC2750] specifies the format of POLICY_DATA objects and RSVP's
   handling of policy events.  It introduces objects that are
   interpreted only by policy-aware nodes (PEPs) that interact with
   policy decision points (PDPs).  Nodes that are unable to interpret
   the POLICY_DATA objects are called policy-ignorant nodes (PINs).  The

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   content of the POLICY_DATA object itself is protected only between
   PEPs and therefore provides end-to-middle or middle-to-middle
   security.

   [RFC2749] specifies the usage of COPS policy services in RSVP
   environments.  [RFC3181] specifies a preemption priority policy
   element (PREEMPTION_PRI) for use by RSVP POLICY_DATA Object.
   [RFC3520] describes how authorization provided by a separate protocol
   (such as SIP) can be reused with the help of an authorization token
   within RSVP.  The token might therefore contain either the authorized
   information itself (e.g., QoS parameters) or a reference to those
   values.  The token might be unprotected (which is strongly
   discouraged) or protected based on symmetric or asymmetric
   cryptography.  Moreover, the document describes how to provide the
   host with encoded session authorization information as a POLICY_DATA
   object.

2.2.4.  Refresh Reduction

   [RFC2961] describes mechanisms to reduce processing overhead
   requirements of refresh messages, eliminate the state synchronization
   latency incurred when an RSVP message is lost, and refresh state
   without the transmission of whole refresh messages.  It defines the
   following objects: MESSAGE_ID, MESSAGE_ID_ACK, MESSAGE_ID_NACK,
   MESSAGE_ID LIST, MESSAGE_ID SRC_LIST, and MESSAGE_ID MCAST_LIST
   objects.  Three new RSVP message types are defined:

   1) Bundle messages consist of a bundle header followed by a body
      consisting one or more standard RSVP messages.  Bundle messages
      help in scaling RSVP to reduce processing overhead and bandwidth
      consumption.

   2) ACK messages carry one or more MESSAGE_ID_ACK or MESSAGE_ID_NACK
      objects.  ACK messages are sent between neighboring RSVP nodes to
      detect message loss and to support reliable RSVP message delivery
      on a per-hop basis.

   3) Srefresh messages carry one or more MESSAGE_ID LIST, MESSAGE_ID
      SRC_LIST, and MESSAGE_ID MCAST_LIST objects.  They correspond to
      Path and Resv messages that establish the states.  Srefresh
      messages are used to refresh RSVP states without transmitting
      standard Path or Resv messages.

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2.2.5.  RSVP over RSVP

   [RFC3175] allows installation of one or more aggregated reservations
   in an aggregation region; thus, the number of individual RSVP
   sessions can be reduced.  The protocol type is swapped from RSVP to
   RSVP-E2E-IGNORE in E2E (standard) Path, PathTear, and ResvConf
   messages when they enter the aggregation region, and is swapped back
   when they leave.  In addition to a new PathErr code
   (NEW_AGGREGATE_NEEDED), three new objects are introduced:

   1) SESSION object, which contains two values: the IP Address of the
      aggregate session destination, and the Differentiated Services
      Code Point (DSCP) that it will use on the E2E data the reservation
      contains.

   2) SENDER_TEMPLATE object, which identifies the aggregating router
      for the aggregate reservation.

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

   From the perspective of RSVP signaling and the handling of data
   packets in the aggregation region, these cases are equivalent to that
   of aggregating E2E RSVP reservations.  The only difference is that
   E2E RSVP signaling does not take place and cannot therefore be used
   as a trigger, so some additional knowledge is required for setting up
   the aggregate reservation.

2.2.6.  IEEE 802-Style LAN Interface

   [RFC2814] introduces an RSVP LAN_NHOP address object that keeps track
   of the next L3 hop as the PATH message traverses an L2 domain between
   two L3 entities (RSVP PHOP and NHOP nodes).  Both layer-2 and layer-3
   addresses are included in the LAN_NHOP; the RSVP_HOP_L2 object is
   used to include the Layer-2 address (L2ADDR) of the previous hop,
   complementing the L3 address information included in the RSVP_HOP
   object (RSVP_HOP_L3 address).

   To provide sufficient information for debugging or resource
   management, RSVP diagnostic messages (DREQ and DREP) are defined in
   [RFC2745] to collect and report RSVP state information along the path
   from a receiver to a specific sender.

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2.2.7.  ATM Interface

   [RFC2379] and [RFC2380] define RSVP over ATM implementation
   guidelines and requirements to interwork with the ATM (Forum) UNI
   3.x/4.0.  [RFC2380] states that the RSVP (control) messages and RSVP
   associated data packets must not be sent on the same virtual circuits
   (VCs), and that an explicit release of RSVP associated QoS VCs must
   be performed once the VC for forwarding RSVP control messages
   terminates.  Although a separate control VC is also possible for
   forwarding RSVP control messages, [RFC2379] recommends creating a
   best-effort short-cut first (if one does not exist), which can allow
   setting up RSVP-triggered VCs to use the best-effort end-point.  (A
   short-cut is a point-to-point VC where the two end-points are located
   in different IP subnets.)  For data flows, the subnet senders must
   establish all QoS VCs, and the RSVP-enabled subnet receiver must be
   able to accept incoming QoS VCs.  RSVP must request that the
   configurable inactivity timers of VCs be set to "infinite".  If it is
   too complex to do this at the VC receiver, RSVP over ATM
   implementations are required not to use an inactivity timer to clear
   any received connections.  For dynamic QoS, the replacement of VC
   should be done gracefully.

2.2.8.  DiffServ Interface

   RFC2996 [RFC2996] introduces a DCLASS Object to carry Differentiated
   Services Code Points (DSCPs) in RSVP message objects.  If the network
   element determines that the RSVP request is admissible to the
   DiffServ network, one or more DSCPs corresponding to the behavior
   aggregate are determined, and will be carried by the DCLASS Object
   added to the RESV message upstream toward the RSVP sender.

2.2.9.  Null Service Type

   For some applications, service parameters are specified by the
   network, not by the application; e.g., enterprise resource planning
   (ERP) applications.  The Null Service [RFC2997] allows applications
   to identify themselves to network QoS policy agents using RSVP
   signaling, but does not require them to specify resource
   requirements.  QoS policy agents in the network respond by applying
   QoS policies appropriate for the application (as determined by the
   network administrator).  The RSVP sender offers the new service type,
   'Null Service Type', in the ADSPEC that is included with the PATH
   message.  A new TSPEC corresponding to the new service type is added
   to the SENDER_TSPEC.  In addition, the RSVP sender will typically
   include with the PATH message policy objects identifying the user,
   application and sub-flow, which will be used for network nodes to
   manage the correspondent traffic flow.

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2.2.10.  MPLS Traffic Engineering

   RSVP-TE [RFC3209] specifies the core extensions to RSVP for
   establishing constraint-based explicitly routed LSPs in MPLS networks
   using RSVP as a signaling protocol.  RSVP-TE is intended for use by
   label switching routers (as well as hosts) to establish and maintain
   LSP-tunnels and to reserve network resources for such LSP-tunnels.

   RFC3209 defines a new Hello message (for rapid node failure
   detection).

   RFC3209 also defines new C-Types (LSP_TUNNEL_IPv4 and
   LSP_TUNNEL_IPv6) for the SESSION, SENDER_TEMPLATE, and FILTER_SPEC
   objects.  Here, a session is the association of LSPs that support the
   LSP-tunnel.  The traffic on an LSP can be classified as the set of
   packets that are assigned the same MPLS label value at the
   originating node of an LSP-tunnel.

   The following 5 new objects are also defined:

   1) EXPLICIT_ROUTE object (ERO), which is incorporated into RSVP Path
      messages, encapsulating a concatenation of hops that constitutes
      the explicitly routed path.  Using this object, the paths taken by
      label-switched RSVP-MPLS flows can be pre-determined independently
      of conventional IP routing.

   2) LABEL_REQUEST object.  To establish an LSP tunnel, the sender can
      create a Path message with a LABEL_REQUEST object.  A node that
      sends a LABEL_REQUEST object MUST be ready to accept and correctly
      process a LABEL object in the corresponding Resv messages.

   3) LABEL object.  Each node that receives a Resv message containing a
      LABEL object uses that label for outgoing traffic associated with
      this LSP tunnel.

   4) SESSION_ATTRIBUTE object, which can be added to Path messages to
      aid in session identification and diagnostics.  Additional control
      information, such as setup and holding priorities, resource
      affinities, and local-protection, are also included in this
      object.

   5) RECORD_ROUTE object (RRO).  The RECORD_ROUTE object may appear in
      both Path and Resv messages.  It is used to collect detailed path
      information and is useful for loop detection and for diagnostics.

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   Section 5 of [RFC3270] further specifies the extensions to RSVP to
   establish LSPs supporting DiffServ in MPLS networks, introducing a
   new DIFFSERV Object (applicable in the Path messages), and using
   pre-configured or signaled "EXP<-->PHB mapping" (e.g., [RFC3270]).

   RSVP-TE provides a way to indicate an unnumbered link in its Explicit
   Route and Record Route Objects through [RFC3477].  This specifies the
   following extensions:

   - An Unnumbered Interface ID Subobject, which is a subobject of the
     Explicit Route Object (ERO) used to specify unnumbered links.

   - An LSP_TUNNEL_INTERFACE_ID Object, to allow the adjacent LSR to
     form or use an identifier for an unnumbered Forwarding Adjacency.

   - A new subobject of the Record Route Object, used to record that the
     LSP path traversed an unnumbered link.

2.2.11.  GMPLS and RSVP-TE

   GMPLS RSVP-TE [RFC3473] is an extension of RSVP-TE.  It enables the
   provisioning of data-paths within networks supporting a variety of
   switching types including packet and cell switching networks, layer
   two networks, TDM networks, and photonic networks.

   It defines the new Notify message (for general event notification),
   which may contain notifications being sent, with respect to each
   listed LSP, both upstream and downstream.  Notify messages can be
   used for expedited notification of failures and other events to nodes
   responsible for restoring failed LSPs.  A Notify message is sent
   without the router alert option.

   A number of new RSVP-TE (sub)objects are defined in GMPLS RSVP-TE for
   general uses of MPLS:

   - a Generalized Label Request Object;

   - a Generalized Label Object;

   - a Suggested Label Object;

   - a Label Set Object (to restrict label choice);

   - an Upstream_Label object (to support bidirectional LSPs);

   - a Label ERO subobject;

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   - IF_ID RSVP_HOP objects (IPv4 & IPv6; to identify interfaces in
     out-of-band signaling or in bundled links);

   - IF_ID ERROR_SPEC objects (IPv4 & IPv6; to identify interfaces in
     out-of-band signaling or in bundled links);

   - an Acceptable Label Set object (to support negotiation of label
     values in particular for bidirectional LSPs)

   - a Notify Request object (may be inserted in a Path or Resv message
     to indicate where a notification of LSP failure is to be sent)

   - a Restart_Cap Object (used on Hello messages to identify recovery
     capabilities)

   - an Admin Status Object (to notify each node along the path of the
     status of the LSP, and to control that state).

2.2.12.  GMPLS Operation at UNI and E-NNI Reference Points

   The ITU-T defines network reference points that separate
   administrative or operational parts of the network.  The reference
   points are designated as:

   - User to Network Interfaces (UNIs) if they lie between the user or
     user network and the core network, or

   - External Network to Network Interfaces (E-NNIs) if they lie between
     peer networks, network domains, or subnetworks.

   GMPLS is applicable to the UNI and E-NNI without further
   modification, and no new messages, objects, or C-Types are required.
   See [OVERLAY].

2.2.13.  MPLS and GMPLS Future Extensions

   At the time of writing, MPLS and GMPLS are being extended by the MPLS
   and CCAMP Working Groups to support additional sophisticated
   functions.  This will inevitably lead to the introduction of new
   C-Types for existing objects, and to the requirement for new objects
   (CNums).  It is possible that new messages will also be introduced.

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   Some of the key features and functions being introduced include the
   following:

   - Protection and restoration.  Features will be developed to provide
      - end-to-end protection
      - segment protection
      - various protection schemes (1+1, 1:1, 1:n)
      - support of extra traffic on backup LSPs
   - Diverse path establishment for protection and load sharing.
   - Establishment of point-to-multipoint paths.
   - Inter-area and inter-AS path establishment with
      - explicit path control
      - bandwidth reservation
      - path diversity
   - Support for the requirements of Automatic Switched Optical Network
     (ASON) signaling as defined by the ITU-T, including call and
     connection separation.
   - Crankback during LSP setup.

2.2.14.  ITU-T H.323 Interface

   ITU-T H.323 ([H.323]) recommends the IntServ resource reservation
   procedure using RSVP.  The information as to whether an endpoint
   supports RSVP should be conveyed during the H.245 [H.245] capability
   exchange phase, by setting appropriate qOSMode fields.  If both
   endpoints are RSVP-capable, when opening an H.245 logical channel, a
   receiver port ID should be conveyed to the sender by the
   openLogicalChannelAck message.  Only after that can a "Path - Resv -
   ResvConf" process take place.  The timer of waiting for ResvConf
   message will be set by the endpoint.  If this timer expires or RSVP
   reservation fails at any point during an H.323 call, the action is up
   to the vendor.  Once a ResvConf message is sent or received, the
   endpoints should stop reservation timers and resume with the H.323
   call procedures.  Only explicit release of reservations are supported
   in [H.323].  Before sending a closeLogicalChannel message for a
   stream, a sender should send a PathTear message if an RSVP session
   has been previous created for that stream.  After receiving a
   closeLogicalChannel, a receiver should send a ResvTear similarly.
   Only the FF style is supported, even for point-to-multipoint calls.

2.2.15.  3GPP Interface

   Third Generation Partnership Project (3GPP) TS 23.207
   ([3GPP-TS23207]) specifies the QoS signaling procedure with policy
   control within the Universal Mobile Telecommunications System (UMTS)
   end-to-end QoS architecture.  When using RSVP, the signaling source
   and/or destination are the User Equipments (UEs, devices that allow
   users access to network services) that locate in the Mobile

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   Originating (MO) side and the Mobile Terminating (MT) side.  An RSVP
   signaling process can either trigger or be triggered by the (COPS)
   PDP Context establishment/modification process.  The operation of
   refreshing states is not specified in [3GPP-TS23207].  If a
   bidirectional reservation is needed, the RSVP signaling exchange must
   be performed twice between the end-points.  The authorization token
   and flow identifier(s) in a policy data object should be included in
   the RSVP messages sent by the UE, if the token is available in the
   UE.  When both RSVP and Service-based Local Policy are used, the
   Gateway GPRS Support Node (GGSN, the access point of the network)
   should use the policy information to decide whether to accept and
   forward Path/Resv messages.

2.3.  Extensions for New Deployment Scenarios

   As a well-acknowledged protocol in the Internet, RSVP is expected
   more and more to provide a more generic service for various signaling
   applications.  However, RSVP messages were designed in a way to
   support end-to-end QoS signaling optimally.  To meet the increasing
   demand that a signaling protocol also operate in host-to-edge and
   edge-to-edge ways, and that it serve for some other signaling
   purposes in addition to end-to-end QoS signaling, RSVP needs to be
   made more flexible and applicable for more generic signaling.

   RSVP proxies [BEGD02] extend RSVP by originating or receiving the
   RSVP message on behalf of the end node(s), so that applications may
   still benefit from reservations that are not truly end-to-end.
   However, there are certainly scenarios where an application would
   want to explicitly convey its non-QoS purposed (as well as QoS) data
   from a host into the network, or from an ingress node to an egress
   node of an administrative domain.  It must do so without burdening
   the network with excess messaging overhead.  Typical examples are an
   end host desiring a firewall service from its provider's network and
   MPLS label setup within an MPLS domain.

   RSVP requires support from network routers and user space
   applications.  Domains not supporting RSVP are traversed
   transparently.  Unfortunately, like other IP options, RSVP messages
   implemented by way of IP alert option may be dropped by some routers
   [FJ02].  Although applications need to be built with RSVP libraries,
   one article presents a mechanism that would allow any host to benefit
   from RSVP mechanisms without applications' awareness [MHS02].

   A somewhat similar deployment benefit can be gained from the
   Localized RSVP (LRSVP) [JR03] [MSK+04].  The documents present the
   concept of local RSVP-based reservation that alone can be used to
   trigger reservation within an access network.  In those cases, an
   end-host may request QoS from its own access network without the

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   cooperation of a correspondent node outside the access network.  This
   would be especially helpful when the correspondent node is unaware of
   RSVP.  A proxy node responds to the messages sent by the end host and
   enables both upstream and downstream reservations.  Furthermore, the
   scheme allows for faster reservation repairs following a handover by
   triggering the proxy to assist in an RSVP local repair.

   Still, in end-hosts that are low in processing power and
   functionality, having an RSVP daemon run and take care of the
   signaling may introduce unnecessary overhead.  One article [Kars01]
   proposes to create a remote API so that the daemon would in fact run
   on the end-host's default router and the end-host application would
   send its requests to that daemon.

   Another potential problem lies in the limited size of signaled data
   due to the limitation of message size.  An RSVP message must fit
   entirely into a single non-fragmented IP datagram.  Bundle messages
   [RFC2961] can aggregate multiple RSVP messages within a single PDU,
   but they still only occupy one IP datagram (i.e., approximately 64K).
   If it exceeds the MTU, the datagram is fragmented by IP and
   reassembled at the recipient node.

2.4.  Conclusion

   A good signaling protocol should be transparent to the applications.
   RSVP has proven to be a very well designed protocol.  However, it has
   a number of fundamental protocol design issues that require more
   careful re-evaluation.

   The design of RSVP was originally targeted at multicast applications.
   The result has been that the message processing within nodes is
   somewhat heavy, mainly due to flow merging.  Still, merging rules
   should not appear in the specification as they are QoS-specific.

   RSVP has a comprehensive set of filtering styles, including
   Wildcard-Filter (WF), Fixed-Filter (FF), and Shared-Explicit (SE),
   and is not tied to certain QoS objects.  (RSVP is not tied to IntServ
   Guaranteed Service/Controlled Load (GS/CL) specifications.)  Objects
   were designed to be modular, but Xspecs (TSPEC, etc.) are more or
   less QoS-specific and should be more generalized; there is no clear
   layering/separation between the signaled data and signaling protocol.

   RSVP uses a soft state mechanism to maintain states and allows each
   node to define its own refresh timer.  The protocol is also
   independent of underlying routing protocols.  Still, in mobile
   networks the movement of the mobile nodes may not properly trigger a
   reservation refresh for the new path, and therefore a mobile node may
   be left without a reservation up to the length of the refresh timer.

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   Furthermore, RSVP does not work properly with changing end-point
   identifiers; that is, if one of the IP addresses of a mobile node
   changes, the filters may not be able to identify the flow that had a
   reservation.

   From the security point of view, RSVP does provide the basic building
   blocks for deploying the protocol in various environments to protect
   its messages from forgery and modification.  Hop-by-hop protection is
   provided.  However, the current RSVP security mechanism does not
   provide non-repudiation and protection against message deletion; the
   two-way peer authentication and key management procedures are still
   missing.

   Finally, since the publication of the RSVP standard, tens of
   extensions have emerged that allow for much wider deployment than
   RSVP was originally designed for -- for instance, the Subnet
   Bandwidth Manager, the NULL service type, aggregation, operation over
   tunneling, and MPLS, as well as diagnostic messages.

   Domains not supporting RSVP are traversed transparently by default.
   Unfortunately, like other IP options, RSVP messages implemented by
   way of IP alert option may be dropped by some routers.  Also, the
   maximal size of RSVP message is limited.

   The transport mechanisms, performance, security, and mobility issues
   are detailed in the following sections.

3.  RSVP Transport Mechanism Issues

3.1.  Messaging Reliability

   RSVP messages are defined as a new IP protocol (that is, a new ptype
   in the IP header).  RSVP Path messages must be delivered end-to-end.
   For the transit routers to intercept the Path messages, a new IP
   Router Alert option [RFC2113] was introduced.  This design is simple
   to implement and efficient to run.  As shown from the experiments in
   [PS00], with minor kernel changes IP option processing introduces
   very little overhead on a Free BSD box.

   However, RSVP does not have a good message delivery mechanism.  If a
   message is lost on the wire, the next re-transmit cycle by the
   network would be one soft-state refresh interval later.  By default,
   a soft-state refresh interval is 30 seconds.

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   To overcome this problem, [PS97] introduced a staged refresh timer
   mechanism, which has been defined as a RSVP extension in [RFC2961].
   The staged refresh timer mechanism retransmits RSVP messages until
   the receiving node acknowledges.  It can address the reliability
   problem in RSVP.

   However, during the mechanism's implementation, a lot of effort had
   to be spent on per-session timer maintenance, message retransmission
   (e.g., avoid message bursts), and message sequencing.  In addition,
   we have to make an effort to try to separate the transport functions
   from protocol processing.  For example, if a protocol extension
   requires a natural RSVP session time-out (such as RSVP-TE one-to-one
   fast-reroute [FAST-REROUTE]), we have to turn off the staged refresh
   timers.

3.2.  Message Packing

   According to RSVP [RFC2205], each RSVP message can only contain
   information for one session.  In a network that has a reasonably
   large number of RSVP sessions, this constraint imposes a heavy
   processing burden on the routers.  Many router OSes are based on
   UNIX.  [PS00] showed that the UNIX socket I/O processing is not very
   sensitive to packet size.  In fact, processing small packets takes
   almost as much CPU overhead as processing large ones.  However,
   processing too many individual messages can easily cause congestion
   at socket I/O interfaces.

   To overcome this problem, RFC2961 introduced the message bundling
   mechanism.  The bundling mechanism packs multiple RSVP messages
   between two adjacent nodes into a single packet.  In one deployed
   router platform, the bundling mechanism has improved the number of
   RSVP sessions that a router can handle from 2,000 to over 7,000.

3.3.  MTU Problem

   RSVP does not support message fragmentation and reassembly at
   protocol level.  If the size of a RSVP message is larger than the
   link MTU, the message will be fragmented.  The routers simply cannot
   detect and process RSVP message fragments.

   There is no solution for the MTU problem.  Fortunately, at places
   where RSVP-TE has been used, either the amount of per-session RSVP
   data is never too large, or the link MTU is adjustable; PPP and Frame
   Relay can always increase or decrease the MTU sizes.  For example, on
   some routers, a Frame Relay interface can support a link MTU size up
   to 9600 bytes.  Currently, the RSVP MTU problem is not a realistic
   concern in MPLS networks.

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   However, when and if RSVP is used for end-user applications, for
   which network security is an essential and critical concern, it is
   possible that the size of RSVP messages can be larger than the link
   MTU.  Note that end-users will most likely have to deal with a small
   1500-byte Ethernet MTU.

3.4.  RSVP-TE vs. Signaling Protocol for RT Applications

   RSVP-TE works in an environment that is different from what the
   original RSVP has been designed for: in MPLS networks, the RSVP
   sessions that are used to support Label-Switched Paths (LSPs) do not
   change frequently.

   In fact, the network operators typically set up the MPLS LSPs so that
   they cannot switch too quickly.  For example, the operators often
   regulate the Constraint-based Shortest Path First (CSPF) computation
   interval to prevent or delay a large volume of user traffic from
   shifting from one session to another during LSP path optimization.
   (CSPF is a routing algorithm that operates from the network edge to
   compute the "most" optimal routes for the LSPs.)  As a result, RSVP-
   TE does not have to handle a large amount of "triggered" (new or
   modified)  messages.  Most of the messages are refresh messages,
   which can be handled by the mechanisms introduced in RFC2961.  In
   particular, in the Summary Refresh extension [RFC2961], each RSVP
   refresh message can be represented as a 4-byte ID.  The routers can
   simply exchange the IDs to refresh RSVP sessions.  With the full
   implementation of RFC2961, MPLS routers do not have any RSVP scaling
   issue.  On one deployed router platform, it can support over 50,000
   RSVP sessions in a stable backbone network.

   On the other hand, in many of the new applications for which a
   signaling protocol is required, the user session duration can be
   relatively short.  The dynamics of adding/dropping user sessions
   could introduce a large number of "triggered" messages in the
   network.  This can clearly introduce a substantial amount of
   processing overhead to the routers.  This is one area where a new
   signaling protocol may be needed to reduce the processing complexity
   in the resource reservation process.

3.5.  What Would Be a Better Alternative?

   A good signaling protocol should be transparent to the applications.
   On the other hand, the design of a signaling protocol must take the
   intended and potential applications into consideration.

   With the addition of RFC2961, RSVP-TE is sufficient to support its
   intended application, MPLS, within the backbone.  There is no
   significant transport-layer problem that needs to be solved.

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   In the last several years, a number of new applications have emerged
   that are proposed to need IP signaling, beyond the traditional ones
   associated with quality of service and resource allocation.  On-path
   firewall control/NAT traversal (synergistic with the midcom design of
   [RFC3303]) is one of these.  There are far-out applications such as
   depositing active network code in network devices.  Next-generation
   signaling protocols dealing with novel applications, with network
   security requirements, and with the MTU problems described above,
   will prevent the re-use of the existing RSVP transport mechanism.

   If a new transport protocol is needed, the protocol must be able to
   handle the following:

   - reliable messaging;

   - message packing;

   - the MTU problem;

   - small triggered message volume.

4.  RSVP Protocol Performance Issues

4.1.  Processing Overhead

   By "processing overhead" we mean the amount of processing required to
   handle messages belonging to a reservation session.  This is the
   processing required in addition to the processing needed for routing
   an (ordinary) IP packet.  The processing overhead of RSVP originates
   from two major issues:

   1) Complexity of the protocol elements.  First, RSVP itself is per-
      flow based; thus the number of states is proportional to RSVP
      session number.  Path and Resv states have to be maintained in
      each RSVP router for each session (and Path state also has to
      record the reverse route for the correspondent Resv message).
      Second, being receiver-initiated, RSVP optimizes various merging
      operations for multicast reservations while the Resv message is
      processed.  To handle multicast, other mechanisms such as
      reservation styles, scope object, and blockade state, are also
      required to be presented in the basic protocol.  This not only
      adds sources of failures and errors, but also complicates the
      state machine [Fu02].  Third, the same RSVP signaling messages are
      used not only for maintaining the state, but also for dealing with
      recovery of signaling message loss and discovery of route change.
      Thus, although protocol elements that represent the actual data
      (e.g., QoS parameters) specification are separated from signaling
      elements, the processing overhead needed for all RSVP messages is

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      not marginal.  Finally, the possible variations of the order and
      existence of objects increases the complexity of message parsing
      and internal message and state representation.

   2) Implementation-specific Overhead.  There are two ways to send and
      receive RSVP messages: either as "raw" IP datagrams with protocol
      number 46, or as encapsulated UDP datagrams, which increase the
      efficiency of RSVP processing.  Typical RSVP implementations are
      user-space daemons interacting with the kernel; thus, state
      management, message sending, and reception would affect the
      efficiency of the protocol processing.  For example, in the recent
      version of the implementation described in [KSS01], the relative
      execution costs for the message sending/reception system calls
      "sendto", "select", and "recvmsg" were 14-16%, 6-7%, 9-10%,
      individually, of the total execution cost.  [KSS01] also found
      that state (memory) management can use up to 17-18% of the total
      execution cost, but it is possible to decrease that cost to 6-7%,
      if appropriate action is taken to replace the standard memory
      management with dedicated memory management for state information.
      RSVP/routing, RSVP/policy control, and RSVP/traffic control
      interfaces can also pose different overhead depending on
      implementation.  For example, the RSVP/routing overhead has been
      measured to be approximately 11-12% of the total execution cost
      [KSS01].

4.2.  Bandwidth Consumption

   By "bandwidth consumption" we mean the amount of bandwidth used
   during the lifetime of a session: to set up a reservation session, to
   keep the session alive, and finally to close it.

   RSVP messages are sent either to trigger a new reservation or to
   refresh an existing reservation.  In standard RSVP, Path/Resv
   messages are used for triggering and refreshing/recovering
   reservations, identically, which results in an increased size of
   refresh messages.  The hop-by-hop refreshment may reduce the
   bandwidth consumption for RSVP, but could result in more sources of
   error/failure events.  [RFC2961] presents a way to bundle standard
   RSVP messages and reduces the refreshment redundancy by Srefresh
   message.

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   Thus, the following formula represents the bandwidth consumption in
   bytes for an RSVP session lasting n seconds:

      F(n) = (bP + bR) + ((n/Ri) * (bP + bR)) + bPt

      bP:  IP payload size of Path message
      bR:  IP payload size of Resv message
      bPt: IP payload size of Path Tear message
      Ri:  refresh interval

   For example, for a simple Controlled Load reservation without
   security and identification requirements (where bP is 172 bytes, bR
   is 92, bPt is 44 bytes, and Ri is 30 seconds), the bandwidth
   consumption would be as follows:

      F(n) = (172 + 92) + ((n/30) * (172 + 92)) + 44

           = 308 + (264n/30) bytes

5.  RSVP Security and Mobility

5.1.  Security

   To allow a process on a system to securely identify the owner and the
   application of the communicating process (e.g., user id) and to
   convey this information in RSVP messages (PATH or RESV) in a secure
   manner, [RFC3182] specifies the encoding of identities as RSVP
   POLICY_DATA Object.  However, to provide ironclad security
   protection, cryptographic authentication combined with authorization
   has to be provided.  Such a functionality is typically offered by
   authentication and key exchange protocols.  Solely including a user
   identifier is insufficient.

   To provide hop-by-hop integrity and authentication of RSVP messages,
   an RSVP message may contain an INTEGRITY object ([RFC2747]) using a
   keyed message digest.  Since intermediate routers need to modify and
   process the content of the signaling message, a hop-by-hop security
   architecture based on a chain-of-trust is used.  However, with the
   different usage of RSVP as described throughout this document and
   with new requirements, a re-evaluation of the original assumptions
   might be necessary.

   RFC2747 provides protection against forgery and message modification.
   However, this does not provide non-repudiation or protect against
   message deletion.  In the current RSVP security scheme, the two-way
   peer authentication and key management procedures are still missing.

   The security issues have been well analyzed in [Tsch03].

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5.2.  Mobility Support

   Two issues raise concern when a mobile node (MN) uses RSVP: the flow
   identifier and reservation refresh.  When an MN changes locations, it
   may need to change one of its assigned IP addresses.  An MN may have
   an IP address by which it is reachable by nodes outside the access
   network, and an IP address used to support local mobility management.
   Depending on the mobility management mechanism, a handover may force
   a change in any of these addresses.  As a consequence, the filters
   associated with a reservation may not identify the flow anymore, and
   the resource reservation is ineffective until a refresh with a new
   set of filters is initialized.

   The second issue relates to following the movement of a mobile node.
   RFC2205 defines that Path messages can perform a local repair of
   reservation paths.  When the route between the communicating end
   hosts changes, a Path message will set the state of the reservation
   on the new route, and a subsequent Resv message will make the
   resource reservation.  Therefore, by sending a Resv message a host
   cannot alone update the reservation, and thus it cannot perform a
   local repair before a Path message has passed.  Also, in order to
   provide fast adaptation to routing changes without the overhead of
   short refresh periods, the local routing protocol module can notify
   the RSVP process of route changes for particular destinations.  The
   RSVP process should use this information to trigger a quick refresh
   of state for these destinations, using the new route (Section 3.6,
   [RFC2205]).  However, not all local mobility protocols affect routing
   directly in routers (not even Mobile IP), and thus mobility may not
   be noticed at RSVP routers.  Therefore, it may take a relatively long
   time before a reservation is refreshed following a handover.

   There have been several designs for extensions to RSVP to allow for
   more seamless mobility.  One solution is presented in [MSK+04], in
   which one section discusses the coupling of RSVP and the mobility
   management mechanisms and proposes small extensions to RSVP to handle
   the handover event better, among other things.  The extension allows
   the mobile host to request a Path for the downstream reservation when
   a handover has happened.

   Another example is Mobile RSVP (MRSVP) [TBA01], which is an extension
   to standard RSVP.  It is based on advance reservations, where
   neighboring access points keep resources reserved for mobile nodes
   moving to their coverage area.  When a mobile node requests
   resources, the neighboring access points are checked, too, and a
   passive reservation is done around the mobile nodes' current
   location.

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   The problem with the various "advance reservation" schemes is that
   they require topological information of the access network and,
   usually, advance knowledge of the handover event.  Furthermore, the
   way the resources reserved in advance are used in the neighboring
   service areas is an open issue.  A good overview of these different
   schemes can be found in [MA01].

   The interactions of RSVP and Mobile IP have been well documented in
   [Thom02].

6.  Other QoS Signaling Proposals

6.1.  Tenet and ST-II

   Tenet and ST-II are two original QoS signaling protocols for the
   Internet.

   In the original Tenet architecture [BFM+96], the receiver sends a
   reservation request toward the source.  Each network node along the
   way makes the reservation.  Once the request arrives at the source,
   the source sends another Relax message back toward to the receiver,
   and has the option to modify the previous reservation at each node.

   ST-II [RFC1819] basically works in the following way: a sender
   originates a Connect message to a set of receivers.  Each
   intermediate node determines the next hop subnets, and makes
   reservations on the links going to these next hops.  Upon receiving a
   Connect indication, a receiver must send back either an Accept or a
   Refuse message to the sender.  In the case of an Accept, the receiver
   may further reduce the resource request by updating the returned flow
   specifications.

   ST-II consists of two protocols: ST for the data transport and the
   Stream Control Message Protocol (SCMP) for all control functions.
   ST is simple and contains only a single PDU format, which is designed
   for fast and efficient data forwarding in order to achieve low
   communication delays.  SCMP packets are transferred within ST
   packets.

   ST-II has no built-in soft states; thus, it requires that the network
   be responsible for correctness.  It is sender-initiated, and the
   overhead for ST-II to handle group membership dynamics is higher than
   that for RSVP [MESZ94].  ST-II does not provide security, but
   [RFC1819] describes some objects related to charging.

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6.2.  YESSIR

   YESSIR (YEt another Sender Session Internet Reservations) [PS98] is a
   resource reservation protocol that seeks to simplify the process of
   establishing reserved flows while preserving many unique features
   introduced in RSVP.  Simplicity is measured in terms of control
   message processing, data packet processing, and user-level
   flexibility.  Features such as robustness, advertising network
   service availability, and resource sharing among multiple senders are
   also supported in the proposal.

   The proposed mechanism generates reservation requests by senders to
   reduce the processing overhead.  It is built as an extension to the
   Real-Time Transport Control Protocol (RTCP), taking advantage of
   Real-Time Protocol (RTP).  YESSIR also introduces a concept called
   partial reservation, in which, for certain types of applications, the
   reservation requests can be passed to the next hop, even though there
   are not enough resources on a local node.  The local node can rely on
   optimized retries to complete the reservations.

6.2.1.  Reservation Functionality

   YESSIR [PS98] was designed for one-way, sender-initiated end-to-end
   resource reservation.  It also uses soft state to maintain states.
   It supports resource query (similar to RSVP diagnosis message),
   advertising (similar to RSVP ADSPEC), shared reservation, partial
   reservations, and flow merging.

   To support multicast, YESSIR simplifies the reservation styles to
   individual and shared reservation styles.  Individual reservations
   are made separately for each sender, whereas shared reservations
   allocate resources that can be used by all senders in an RTP session.
   Although RSVP supports shared reservation (SE and WF styles) from the
   receiver's direction, YESSIR handles the shared reservation style
   from the sender's direction; thus, new receivers can re-use the
   existing reservation of the previous sender.

   It has been shown that the YESSIR one-pass reservation model has
   better performance and lower processing cost than a regular two-way
   signaling protocol, such as RSVP [PS98].  The bandwidth consumption
   of YESSIR is somewhat lower than that of, for example, RSVP, because
   it does not require additional IP and transport headers.  Bandwidth
   consumption is limited to the extension header size.

   YESSIR does not have any particular support for mobility, and the
   security of YESSIR relies on RTP/RTCP security measures.

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6.2.2.  Conclusion

   YESSIR requires support in applications since it is an integral part
   of RTCP.  Similarly, it requires network routers to inspect RTCP
   packets to identify reservation requests and refreshes.  Routers
   unaware of YESSIR forward the RTCP packets transparently.

6.3.  Boomerang

   Boomerang [FNM+99] is a another resource reservation protocol for IP
   networks.  The protocol has only one message type and a single
   signaling loop for reservation setup and teardown, and it has no
   requirements on the far end node.  Instead, it concentrates the
   intelligence in the Initiating Node (IN).

   In addition, the Boomerang protocol allows for sender- or receiver-
   oriented reservations and resource query.  Flows are identified with
   the common 5-tuple, and the QoS can be specified by various means;
   e.g., service class and bit rate.  In the initial implementation,
   Boomerang messages are transported in ICMP ECHO/REPLY messages.

6.3.1.  Reservation Functionality

   Boomerang can only be used for unicast sessions; no support for
   multicast exists.  The requested QoS can be specified with various
   methods, and both ends of a communication session can make a
   reservation for their transmitted flow.

   The authors of Boomerang show in [FNS02] that the processing of the
   protocol is considerably lower than that of the ISI RSVP daemon
   implementation.  However, this is mainly due to the limited
   functionality provided by the protocol compared to that provided by
   RSVP.

   Boomerang messages are quite short and consume a relatively low
   amount of link bandwidth.  This is due to the limited functionality
   of the protocol; for example, no security-specific information or
   policy-based interaction is provided.  Being sender oriented, the
   bandwidth consumption mostly affects the downstream direction, from
   the sender to the receiver.

   As Boomerang is sender oriented, there is no need to store backward
   information.  This reduces the signaling required.  The rest of the
   issues that were identified with RSVP apply with Boomerang.  No
   security mechanism is specified for Boomerang.

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   The Boomerang protocol has deployment issues similar to those of any
   host-network-host protocol.  It requires an implementation at both
   communicating nodes and in routers.  Boomerang-unaware routers should
   be able to forward Boomerang messages transparently.  Still,
   firewalls often drop ICMP packets, making the protocol useless.

6.3.2.  Conclusions

   Boomerang seems to be a very lightweight protocol and efficient in
   its own scenarios.  However, the apparent low processing overhead and
   bandwidth consumption results from the limited functionality.  No
   support for multicast or any security features are present, which
   allows for a different functionality than RSVP, which the authors
   like to compare Boomerang to.

6.4.  INSIGNIA

   INSIGNIA [LGZC00] is proposed as a very simple signaling mechanism
   for supporting QoS in mobile ad-hoc networks.  It avoids the need for
   separate signaling by carrying the QoS signaling data along with the
   normal data in IP packets using IP packet header options.  This
   approach, known as "in-band signaling", is proposed as more suitable
   in the rapidly changing environment of mobile networks since the
   signaled QoS information is not tied to a particular path.  It also
   allows the flows to be rapidly established and, thus, is suitable for
   short-lived and dynamic flows.

   INSIGNIA aims to minimize signaling by reducing the number of
   parameters that are provided to the network.  It assumes that real-
   time flows may tolerate some loss, but are very delay sensitive so
   that the only QoS information needed is the required minimum and
   maximum bandwidth.

   The INSIGNIA protocol operates at the network layer and assumes that
   link status sensing and access schemes are provided by lower-layer
   entities.  The usefulness of the scheme depends on the MAC layers,
   but this is undefined, so INSIGNIA can run over any MAC layer.  The
   protocol requires that each router maintains per-flow state.

   The INSIGNIA system implicitly supports mobility.  A near-minimal
   amount of information is exchanged with the network.  To achieve
   this, INSIGNIA makes many assumptions about the nature of traffic
   that a source will send.  This may also simplify admission control
   and buffer allocation.  The system basically assumes that "real-time"
   will be defined as a maximum delay, and the user can simply request
   real-time service for a particular quantity of traffic.

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   After handover, data that was transmitted to the old base station can
   be forwarded to the new base station, so no data loss should occur.
   However, there is no way to differentiate between re-routed and new
   traffic, so priority cannot be given to handover traffic, for
   example.

   INSIGNIA, however, (completely) lacks a security framework and does
   not investigate how to secure signaled QoS data in an ad-hoc network,
   where relatively weak trust or even no trust exists between the
   participating nodes.  Therefore, authorization and charging
   especially might be a challenge.  The security protection of in-band
   signaling is costly since the data delivery itself experiences
   increased latency if security processing is done hop-by-hop.  Because
   the QoS signaling information is encoded into the flow label and
   end-to-end addressing is used, it is very difficult to provide
   security other than IPsec in tunnel mode.

7.  Inter-Domain Signaling

   This section gives a short overview of protocols designed for inter-
   domain signaling.

7.1.  BGRP

   Border Gateway Reservation Protocol (BGRP) [BGRP] is a signaling
   protocol for inter-domain aggregated resource reservation for unicast
   traffic.  BGRP builds a sink tree for each of the stub domains.  Each
   sink tree aggregates bandwidth reservations from all data sources in
   the network.  BGRP maintains these aggregated reservations using soft
   state and relies on Differentiated Services for data forwarding.

   In terms of message processing load, BGRP scales state storage and
   bandwidth.  Because backbone routers only maintain the sink tree
   information, the total number of reservations at each router scales
   linearly with the number of Internet domains.

7.2.  SICAP

   SICAP (Shared-segment Inter-domain Control Aggregation protocol)
   [SGV03] is an inter-domain signaling solution that performs shared-
   segment aggregation [SGV02] on the Autonomous System (AS) level in
   order to reduce state required at Boundary Routers (BRs).  SICAP
   performs aggregation based on path segments that different
   reservations share.  Thus, reservations may be merged into aggregates
   that do not necessarily extend all the way to the reservation's
   destination.  The motivation for creating "shorter" aggregates is
   that, on one hand, their ability to accommodate future requests more
   easily, and, on the other hand, the minimization of aggregates

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   created and consequently, the reduction of state required to manage
   established reservations.  However, in contrast to the sink-tree
   approach (used by BGRP [BGRP]), the shared-segment approach
   introduces intermediate de-aggregation locations.  These are ASes
   where aggregates may experience "re-aggregation".  At these
   locations, routers that perform aggregation (AS egress routers) have
   to keep track of the mapping between reservations and aggregates.
   One possible way to do this is to keep each reservation identifier
   and the corresponding resources stored at each aggregator.  However,
   this solution incurs a high state penalty.  SICAP avoids this state
   penalty by keeping track of the mapping between aggregates and
   reservations at the level of destination domains rather than
   explicitly map individual reservations to aggregates.  In other
   words, SICAP maintains, per aggregate, a list of the destination
   prefixes advertised by the destination AS an aggregate provides
   access to.

   Pan et al. show that BGRP scales well in terms of control state,
   message processing, and bandwidth efficiency, when compared to RSVP
   without aggregation.  However, partially given that BGRP was the
   first approach to explore the issue of inter-domain control
   aggregation in detail, they did not provide a comparison with other
   aggregation protocols.

   SICAP and BGRP messaging sequences are similar, and consequently,
   these protocols attain the same signaling load.  This load is exactly
   the same as that attained by proposals that do not perform
   aggregation, given that SICAP and BGRP exchange messages per
   individual reservation.  In terms of bandwidth, both protocols
   provision aggregates with the exact bandwidth required by their
   merged reservations.  Therefore, the major difference between SICAP
   and BGRP is state maintained at BRs, which is significantly reduced
   by SICAP.  We consider this to be of importance not so much for
   offering a better-performing alternative to BGRP, but for quantifying
   the performance improvements that might still be available in the
   research field of control path aggregation.  Finally, to deal with
   the possible problem of the signaling load, SICAP uses an over-
   reservation mechanism [SGV03b], whose design took into consideration
   a possible support for BGRP.

7.3.  DARIS

   Dynamic Aggregation of Reservations for Internet Services (DARIS)
   [Bless02] [Bless04] defines an inter-domain aggregation scheme for
   resource reservations.  Basically, it aggregates reservations along
   Autonomous System (AS) paths (or parts thereof).  A set of
   reservations whose data paths share a common sequence of ASes are
   integrated into a joint reservation aggregate along that shared sub-

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   path.  All entities within the aggregate, except for aggregate
   starting and end point, can remove state information of the included
   individual reservations, thereby saving states.  They just need to
   hold the necessary information about the encompassing aggregate.
   Moreover, these intermediate ASes are no longer involved in signaling
   that is related to the aggregated reservations.  If more aggregate
   resources are reserved than were actually required, the capacity of
   the aggregate does not need to be adapted with every new or released
   reservation (thereby reducing the number of message exchanges).

   An aggregate between two ASes is created as soon as a threshold k is
   exceeded that describes the active number of unidirectional
   reservations between them.  It is, however, possible to apply
   different aggregation triggers.  Furthermore, DARIS allows aggregates
   to be nested hierarchically.  Therefore, the existence of shorter
   aggregates does not prevent the creation of longer (and thus more
   efficient) aggregates, and vice versa.  An evaluation of recent BGP
   routing information in [Bless02] showed that 92% of all end-to-end
   paths contain at least four ASes.  Consequently, an aggregate from
   edge AS to edge AS can span four or more ASes, thus saving states and
   signaling message processing in at least two ASes.

   There is, however, a small chance that a reservation cannot be
   included in a new aggregate, because it was already aggregated
   elsewhere.  This so-called "aggregation conflict" is caused by the
   prior removal of state information related to individual reservations
   within intermediate ASes of the encompassing aggregate.  This may
   also bring difficulties if reservations or aggregates are re-routed
   between ASes.  One must be careful when considering how to define
   sophisticated adaptation techniques for these special cases, because
   they seem to become very complex.

   The signaling protocol DMSP (Domain Manager Signaling Protocol)
   supports aggregation by special extensions that reduce the
   reservation setup time for more than one round-trip time in some
   cases (e.g., if an aggregate's capacity must be increased before a
   new reservation can be included).  Details can be found in [Bless02].

   The DARIS concept was evaluated by using a simulation with a topology
   that was derived from real BGP routing table information and
   comprised more than 5500 ASes.  In comparison to a non-aggregated
   scenario, the number of saved states lay in the range of one to two
   orders of magnitude, and similar results were obtained with respect
   to the number of signaling messages.  Though [Bless02] describes
   DARIS in the context of distributed Domain Management entities
   (similar to a bandwidth broker), it can be applied in a router-based

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   resource management environment, too.  This will achieve a higher
   degree of distribution, which is beneficial for large ASes, which are
   highly interconnected.

   A general issue with aggregation is that it is not the aggregating
   and de-aggregating ASes that profit from their initiated aggregates,
   but all intermediate ASes within an aggregate.  Therefore, some
   incentive for aggregate creation has to be given.  This may lead to
   novel cost models that have to be developed for aggregation concepts
   in the future.

8.  Security Considerations

   This document does not present new technology or protocols.  Thus,
   there are no explicit security issues.  Still, individual protocols
   include different levels of security issues and those are highlighted
   in the relevant sections and references.

9.  Summary

   Supporting flow-based soft state reservations has been proven useful.
   Still, there have been different ways to improve the performance,
   including refresh reduction and aggregation.  However, some of the
   main concerns with these signaling protocols are the complexity of
   the protocol, which affects implementations and processing overhead,
   and the security of the signaling.  Especially, a proper scheme to
   handle authentication and authorization of QoS resource requests and
   a framework for providing signaling message security seem to be
   missing from most protocols.  RSVP has a mechanism to protect
   signaling messages based on manually distributed keys and concepts
   for authorization, but they seem to be insufficient for a dynamic and
   mobile environment.  [Tsch03] provides more details on security
   properties provided by RSVP.  Moreover, secure and efficient
   signaling to and from mobile nodes has been one of the critical
   challenges not fully met by existing protocols.

   Moving QoS signaling protocols into a generic messenger can provide
   much adoption.  It is expected that the development of future
   protocols should learn from the lessons of existing ones.
   Nevertheless, the tradeoffs between the expected functionality,
   protocol complexity/performance would still be taken into account.
   For example, RSVP uses the two-way signaling mechanism, whereas
   YESSIR employs only one-pass signaling.  Both can be shown to out-
   perform the other in specific carefully chosen signaling scenarios.

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10.  Contributors

   This document is part of the work done in the NSIS Working Group.
   The document was initially written by Jukka Manner and Xiaoming Fu.
   Since the first version, Martin Karsten has provided text about the
   processing overhead of RSVP, and Hannes Tschofenig has provided text
   about various security issues in the protocols.  Henning Schulzrinne
   and Ping Pan have provided more information on RSVP transportation
   after the second revision.  Kireeti Kompella and Adrian Farrel
   provided a review and updates to the discussion on RSVP-TE and GMPLS.

11.  Acknowledgements

   We would like to acknowledge Bob Braden and Vlora Rexhepi for their
   useful comments.

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12.  Appendix A: Comparison of RSVP to the NSIS Requirements

   This section provides a comparison of RSVP to the requirements
   identified as part of the work in NSIS [RFC3726].  The numbering
   follows the division in the requirements document.

   5.1.  Architecture and Design Goals

      5.1.1.  NSIS SHOULD Provide Availability Information on Request

        RSVP itself does not support query-type of operations.  However,
        the RSVP diagnosis messages extension [RFC2745] provides a means
        to query resource availability.

      5.1.2.  NSIS MUST Be Designed Modularly

        RSVP was designed to be modular by way of TLV objects, however
        it is regarded being lack of sufficient extensibility in various
        kind of signalling applications.

      5.1.3.  NSIS MUST Decouple Protocol and Information

        RSVP is decoupled from the IntServ QoS specifications.  Still,
        the concept of sessions in RSVP are somewhat coupled to the
        information it carries.

      5.1.4.  NSIS MUST Support Independence of Signaling and Network
              Control Paradigm

        The IntServ information carried by RSVP does not tie the QoS
        provisioning mechanisms.

      5.1.5.  NSIS SHOULD Be Able To Carry Opaque Objects

        RSVP supports this.

   5.2.  Signaling Flows

      5.2.1.  The Placement of NSIS Initiator, Forwarder, and Responder
              Anywhere in the Network MUST Be Allowed

        Standard RSVP works only end-to-end, although the RSVP proxy
        [BEGD02] and the Localized RSVP [MSK+04] have relaxed this
        assumption.  RSVP relies on receiver-initiation way to perform
        QoS reservations.

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      5.2.2.  NSIS MUST support Path-Coupled and MAY Support Path-
              Decoupled Signaling

        Standard RSVP is path-coupled, but the Subnet Bandwidth
        Manager (SBM) work makes RSVP somewhat path-decoupled.

      5.2.3.  Concealment of Topology and Technology Information SHOULD
              Be Possible

        RSVP itself does not provide such capability.

      5.2.4.  Transparent Signaling through Networks SHOULD Be Possible

        RSVP messages are intercepted and evaluated in each RSVP router,
        and thus they may not cross certain RSVP-routers unnoticed.
        Still, the message processing rules allow unknown RSVP messages
        to be forwarded unharmed.

   5.3.  Messaging

      5.3.1.  Explicit Erasure of State MUST Be Possible

        Supported by the PathTear and ResvTear messages.

      5.3.2.  Automatic Release of State After Failure MUST Be Possible

        On error reservation states are torn down with PathTear
        messages.

      5.3.3.  NSIS SHOULD Allow for Sending Notifications Upstream

        There are two notifications in RSVP, confirm of a reservation
        set-up and tear down of reservation states as a result of
        errors.

      5.3.4.  Establishment and Refusal To Set Up State MUST Be Notified

        PathErr and ResvErr messages provide refusal to set up state in
        RSVP.

      5.3.5.  NSIS MUST Allow for Local Information Exchange

        RSVP NULL service type [RFC2997] provides such a feature.

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   5.4.  Control Information

      5.4.1.  Mutability Information on Parameters SHOULD Be Possible

        Rspec and Adspec are mutable; Tspec is (generally) end-to-end
        not mutable.

      5.4.2.  It SHOULD Be Possible To Add and Remove Local Domain
              Information

        RSVP aggregation [RFC3175] and NULL service type [RFC2997] can
        provide such a feature.

      5.4.3.  State MUST Be Addressed Independent of Flow Identification

        RSVP states are tied to the flows, thus this requirement is not
        met.

      5.4.4.  Modification of Already Established State SHOULD Be
              Seamless

        Modifications of a reservation is possible with RSVP.

      5.4.5.  Grouping of Signaling for Several Micro-Flows MAY Be
              Provided

        Aggregated RSVP and RFC2961 allow this.

   5.5.  Performance

      5.5.1.  Scalability

        RSVP scales linearly to the number of reservation states.

      5.5.2.  NSIS SHOULD Allow for Low Latency in Setup

        Setting up an RSVP reservation takes one round-trip time and the
        processing times are each RSVP router.

      5.5.3.  NSIS MUST Allow for Low Bandwidth Consumption for the
              Signaling Protocol

        The initial reservations messages can not be compressed, but the
        refresh interval can be adjusted to consume less bandwidth, at
        the expense of possible inefficient resource usage.

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      5.5.4.  NSIS SHOULD Allow To Constrain Load on Devices

        See discussions on RSVP performance (section 4).

      5.5.5.  NSIS SHOULD Target the Highest Possible Network
              Utilization

        This depends on the IntServ service types, Controlled Load can
        provide better overall utilization than Guaranteed Service.

   5.6.  Flexibility

      5.6.1.  Flow Aggregation

        Aggregated RSVP and RFC2961 allow this.

      5.6.2.  Flexibility in the Placement of the NSIS
              Initiator/Responder

        RSVP allows receiver as initiator of reservations.

      5.6.3.  Flexibility in the Initiation of State Change

        RSVP receivers can initiate the state change during its
        refreshment.

      5.6.4.  SHOULD Support Network-Initiated State Change

        As RSVP supports hop-by-hop refreshment, this is made possible.

      5.6.5.  Uni / Bi-Directional State Setup

        RSVP is only uni-directional.

   5.7.  Security

      5.7.1.  Authentication of Signaling Requests

        Authentication is available in RSVP.

      5.7.2.  Request Authorization

        Authorization with a PDP is possible in RSVP.

      5.7.3.  Integrity Protection

        The INTEGRITY Object is available in RSVP.

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      5.7.4.  Replay Protection

        The INTEGRITY Object to replay protect the content of the
        signaling messages between two RSVP nodes.

      5.7.5.  Hop-By-Hop Security

        The RSVP security model works only hop-by-hop.

      5.7.6.  Identity Confidentiality and Network Topology Hiding

        The INTEGRITY Object can be used for this purpose.

      5.7.7.  Denial-Of-Service Attacks

        Challenging with RSVP.

      5.7.8.  Confidentiality of Signaling Messages

        Not supported by RSVP.

      5.7.9. Ownership of State

        Challenging with RSVP.

   5.8.  Mobility

      5.8.1.  Allow Efficient Service Re-Establishment After Handover

        Works for upstream but may not be achieved for the downstream
        if mobility is not noticed at the cross-over router.

   5.9.  Interworking with Other Protocols and Techniques

      5.9.1.  MUST Interwork with IP Tunneling

        RFC 2746 discusses these issues.

      5.9.2.  MUST NOT Constrain either to IPv4 or IPv6

        RSVP supports both IP versions.

      5.9.3.  MUST Be Independent from Charging Model

        RSVP does not discuss this.

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      5.9.4.  SHOULD Provide Hooks for AAA Protocols

        COPS and RSVP work together.

      5.9.5.  SHOULD Work with Seamless Handoff Protocols

        Not supported by RSVP.  Still, [RFC2205] suggests that route
        changes should be indicated to the local RSVP daemon, which can
        then initiate state refresh.

      5.9.6.  MUST Work with Traditional Routing

        RSVP expects traditional routing.

   5.10.  Operational

      5.10.1.  Ability to Assign Transport Quality to Signaling Messages

        This is a network design issue, but is possible with DiffServ.

      5.10.2.  Graceful Fail Over

        RSVP supports this.

      5.10.3.  Graceful Handling of NSIS Entity Problems

        RSVP itself does not supports this.

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13.  Normative References

   [RFC3726]      Brunner, M., "Requirements for Signaling Protocols",
                  RFC 3726, April 2004.

14.  Informative References

   [3GPP-TS23207] 3GPP TS 23.207 V5.6.0, End-to-end Quality of Service
                  (QoS) Concept and Architecture, Release 5, December
                  2002.

   [BEBH96]       Braden, R., Estrin, D., Berson, S., Herzog, and D.
                  Zappala, "The Design of the RSVP Protocol", ISI Final
                  Technical Report, July 1996.

   [BEGD02]       Y. Bernet, N. Elfassy, S. Gai, and D. Dutt, "RSVP
                  Proxy", Work in Progress, March 2002.

   [BFM+96]       A. Banerjea, D. Ferrari, B. Mah, M. Moran, D. Verma,
                  and H.  Zhang, "The Tenet Real-Time Protocol Suite:
                  Design, Implementation, and Experiences", IEEE/ACM
                  Transactions on Networking, Volume 4, Issue 1,
                  February 1996, pp. 1-10.

   [BGRP]         P. Pan, E, Hahne, and H. Schulzrinne, "BGRP: A Tree-
                  Based Aggregation Protocol for Inter-domain
                  Reservations", Journal of Communications and Networks,
                  Vol. 2, No. 2, June 2000, pp. 157-167.

   [Bless02]      R. Bless, "Dynamic Aggregation of Reservations for
                  Internet Services", Proceedings of the Tenth
                  International Conference on Telecommunication Systems
                  - Modeling and Analysis (ICTSM 10), Vol. 1, pp. 26-38,
                  October 3-6 2002, Monterey, California, available at
                  http://www.tm.uka.de/doc/2003/ictsm-daris-journal-
                  crc-web.pdf.

   [Bless04]      R. Bless, "Towards Scalable Management of QoS-based
                  End-to- End Services" (PDF), Proceedings of NOMS 2004
                  (IEEE/IFIP 2004 Network Operations and Management
                  Symposium), April 2004, Seoul, Korea.

   [FAST-REROUTE] P. Pan, G. Swallow, and A. Atlas, "Fast Reroute
                  Extensions to RSVP-TE for LSP Tunnels", Work in
                  Progress, January 2004.

Manner & Fu                  Informational                     [Page 38]
RFC 4094               Analysis of QoS Signaling                May 2005

   [FNM+99]       G. Feher, K. Nemeth, M. Maliosz, I. Cselenyi, J.
                  Bergkvist, D. Ahlard, T. Engborg, "Boomerang A Simple
                  Protocol for Resource Reservation in IP Networks",
                  IEEE RTAS, 1999.

   [FNS02]        G. Feher, K. Nemeth, and I. Cselenyi, "Performance
                  evaluation framework for IP resource reservation
                  signalling". Performance Evaluation 48 (2002), pp.
                  131-156.

   [FJ02]         P. Fransson and A. Jonsson, "The need for an
                  alternative to IPv4-options", in RVK (RadioVetenskap
                  och Kommunikation), Stockholm, Sweden, pp. 162-166,
                  June 2002.

   [Fu02]         X. Fu, C. Kappler, and H. Tschofenig, "Analysis on
                  RSVP Regarding Multicast". Technical Report No. IFI-
                  TB-2002-001, ISSN 1611-1044, Institute for
                  Informatics, University of Goettingen, Oct 2002.

   [H.245]        ITU-T Recommendation H.245, Control Protocol for
                  Multimedia Communication, July 2000.

   [H.323]        ITU-T Recommendation H.323, Packet-based Multimedia
                  Communications Systems, Nov. 2000.

   [JR03]         Jukka Manner, Kimmo Raatikainen, "Localized QoS
                  Management for Multimedia Applications in Wireless
                  Access Networks". IASTED International Conference on
                  Internet and Multimedia Systems and Applications (IMSA
                  2003), August, 2003, pp. 193-200.

   [Kars01]       M. Karsten, "Experimental Extensions to RSVP -- Remote
                  Client and One-Pass Signalling".  IWQoS 2001,
                  Karlsruhe, Germany, June 2001.

   [KSS01]        M. Karsten, Jens Schmitt, Ralf Steinmetz,
                  "Implementation and Evaluation of the KOM RSVP
                  Engine", IEEE Infocom 2001.

   [LGZC00]       S. Lee, A. Gahng-Seop, X. Zhang, A.
                  Campbell,"INSIGNIA: An IP-Based Quality of Service
                  Framework for Mobile Ad Hoc Networks".  Journal of
                  Parallel and Distributed Computing (Academic Press),
                  Special issue on Wireless and Mobile Computing and
                  Communications, Vol. 60, Number 4, April, 2000, pp.
                  374-406.

Manner & Fu                  Informational                     [Page 39]
RFC 4094               Analysis of QoS Signaling                May 2005

   [MA01]         B. Moon, and H. Aghvami, "RSVP Extensions for Real-
                  Time Services in Wireless Mobile Networks".  IEEE
                  Communications Magazine, December 2001, pp. 52-59.

   [MESZ94]       D. Mitzel, D. Estrin, S. Shenker, and L. Zhang, "An
                  Architectural Comparison of ST-II and RSVP", Infocom
                  1994.

   [MHS02]        Y Miao, W. Hwang, and C. Shieh, "A transparent
                  deployment method of RSVP-aware applications on UNIX".
                  Computer Networks, 40 (2002), pp. 45-56.

   [MSK+04]       J. Manner, T. Suihko, M. Kojo, M. Liljeberg, K.
                  Raatikainen, "Localized RSVP", Work in Progress,
                  September 2004.

   [OVERLAY]      G. Swallow, J. Drake, H. Ishimatsu, and Y. Rekhter,
                  "GMPLS UNI: RSVP Support for the Overlay Model", Work
                  in Progress, February 2004.

   [PS97]         P. Pan and H. Schulzrinne, "Staged refresh timers for
                  RSVP", Global Internet, Phoenix, Arizona, November
                  1997.

   [PS98]         P. Pan, and H. Schulzrinne, "YESSIR: A Simple
                  Reservation Mechanism for the Internet". Proceedings
                  of NOSSDAV, Cambridge, UK, July 1998.

   [PS00]         P. Pan, and H. Schulzrinne, "PF_IPOPTION: A kernel
                  extension for IP option packet processing", Technical
                  Memorandum 10009669-02TM, Bell Labs, Lucent
                  Technologies, Murray Hill, NJ, June 2000.

   [RFC1819]      Delgrossi, L. and L. Berger, "Internet Stream Protocol
                  Version 2 (ST2) Protocol Specification - Version
                  ST2+", RFC 1819, August 1995.

   [RFC2113]      Katz, D., "IP Router Alert Option", RFC 2113, February
                  1997.

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

   [RFC2207]      Berger, L. and T. O'Malley, "RSVP Extensions for IPSEC
                  Data Flows", RFC 2207, September 1997.

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

   [RFC2379]      Berger, L., "RSVP over ATM Implementation Guidelines",
                  BCP 24, RFC 2379, August 1998.

   [RFC2380]      Berger, L., "RSVP over ATM Implementation
                  Requirements", RFC 2380, August 1998.

   [RFC2745]      Terzis, A., Braden, B., Vincent, S., and L. Zhang,
                  "RSVP Diagnostic Messages", RFC 2745, January 2000.

   [RFC2746]      Terzis, A., Krawczyk, J., Wroclawski, J., and L.
                  Zhang, "RSVP Operation Over IP Tunnels", RFC 2746,
                  January 2000.

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

   [RFC2749]      Herzog, S., Boyle, J., Cohen, R., Durham, D., Rajan,
                  R., and A. Sastry, "COPS usage for RSVP", RFC 2749,
                  January 2000.

   [RFC2750]      Herzog, S., "RSVP Extensions for Policy Control", RFC
                  2750, January 2000.

   [RFC2814]      Yavatkar, R., Hoffman, D., Bernet, Y., Baker, F., and
                  M. Speer, "SBM (Subnet Bandwidth Manager): A Protocol
                  for RSVP-based Admission Control over IEEE 802-style
                  networks", RFC 2814, May 2000.

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

   [RFC2996]      Bernet, Y., "Format of the RSVP DCLASS Object", RFC
                  2996, November 2000.

   [RFC2997]      Bernet, Y., Smith, A., and B. Davie, "Specification of
                  the Null Service Type", RFC 2997, November 2000.

   [RFC2998]      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.

Manner & Fu                  Informational                     [Page 41]
RFC 4094               Analysis of QoS Signaling                May 2005

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

   [RFC3181]      Herzog, S., "Signaled Preemption Priority Policy
                  Element", RFC 3181, October 2001

   [RFC3182]      Yadav, S., Yavatkar, R., Pabbati, R., Ford, P., Moore,
                  T., Herzog, S., and R. Hess, "Identity Representation
                  for RSVP", RFC 3182, October 2001.

   [RFC3209]      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.

   [RFC3270]      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.

   [RFC3303]      Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A.,
                  and A. Rayhan, "Middlebox communication architecture
                  and framework", RFC 3303, August 2002.

   [RFC3473]      Berger, L., "Generalized Multi-Protocol Label
                  Switching (GMPLS) Signaling Resource ReserVation
                  Protocol-Traffic Engineering (RSVP-TE) Extensions",
                  RFC 3473, January 2003.

   [RFC3477]      Kompella, K. and Y. Rekhter, "Signalling Unnumbered
                  Links in Resource ReSerVation Protocol - Traffic
                  Engineering (RSVP-TE)", RFC 3477, January 2003.

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

   [SGV02]        R. Sofia, R. Guerin, and P. Veiga, "An Investigation
                  of Inter-Domain Control Aggregation Procedures",
                  International Conference on Networking Protocols, ICNP
                  2002, Paris, France, November 2002.

   [SGV03]        R. Sofia, R. Guerin, and P. Veiga. SICAP, a Shared-
                  segment Inter-domain Control Aggregation Protocol.
                  High Performance Switching and Routing, HPSR 2003,
                  Turin, Italy, June 2003.

Manner & Fu                  Informational                     [Page 42]
RFC 4094               Analysis of QoS Signaling                May 2005

   [SGV03b]       R. Sofia, R. Guerin, and P. Veiga. A Study of Over-
                  reservation for Inter-Domain Control Aggregation
                  Protocols. Technical report (short version under
                  submission), University of Pennsylvania, May 2003,
                  available at http://einstein.seas.upenn.edu/mnlab/
                  publications.html.

   [TBA01]        A. Talukdar, B. Badrinath, and A. Acharya, "MRSVP: A
                  Resource Reservation Protocol for an Integrated
                  Services Network with Mobile Hosts", Wireless
                  Networks, vol. 7, no. 1, pp. 5-19, 2001.

   [Thom02]       M. Thomas, "Analysis of Mobile IP and RSVP
                  Interactions", Work in Progress, October 2002.

   [Tsch03]       H. Tschofenig, "RSVP Security Properties", Work in
                  Progress, February 2004.

   [ZDSZ93]       L. Zhang, S. Deering, D. Estrin, and D. Zappala,
                  "RSVP: A New Resource Reservation Protocol", IEEE
                  Network, Volume 7, Pages 8-18, September 1993.

   [URL1]         http://www.atm.tut.fi/list-archive/diffserv/thrd3.html

   [URL2]         OPENSIG http://comet.columbia.edu/opensig/

   [URL3]         SIGLITE http://www1.cs.columbia.edu/~pingpan/projects/
                  siglite.html

Manner & Fu                  Informational                     [Page 43]
RFC 4094               Analysis of QoS Signaling                May 2005

Authors' Addresses

   Jukka Manner
   Department of Computer Science
   University of Helsinki
   P.O. Box 68 (Gustav Hallstrominkatu 2b)
   FIN-00014 HELSINKI
   Finland

   Phone: +358-9-191-51298
   Fax:   +358-9-191-51120
   EMail: jmanner@cs.helsinki.fi

   Xiaoming Fu
   Institute for Informatics
   Georg-August-University of Goettingen
   Lotzestrasse 16-18
   37083 Goettingen
   Germany

   Phone: +49-551-39-14411
   Fax:   +49-551-39-14403
   EMail: fu@cs.uni-goettingen.de

Manner & Fu                  Informational                     [Page 44]
RFC 4094               Analysis of QoS Signaling                May 2005

Full Copyright Statement

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