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                RSVP Extensions for Emergency Services       June 2006



   Internet Draft                                  Francois Le Faucheur
                                                             James Polk
                                                    Cisco Systems, Inc.

                                                           Ken Carlberg
                                                                   G11
   draft-lefaucheur-emergency-rsvp-02.txt
   Expires: December 2006                                     June 2006

                  RSVP Extensions for Emergency Services



Status of this Memo

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Abstract

   An Emergency Telecommunications Service (ETS) requires the ability to
   provide an elevated probability of session establishment to an
   authorized user in times of network congestion (typically, during a
   crisis). When supported over the Internet Protocol suite, this may be
   facilitated through a network layer admission control solution, which
   supports prioritized access to resources (e.g., bandwidth). These
   resources may be explicitly set aside for emergency services, or they
   may be shared with other sessions.



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                RSVP Extensions for Emergency Services       June 2006


   This document specifies RSVP extensions that can be used to support
   such an admission priority capability at the network layer. Note that
   these extensions represent one possible solution component in
   satisfying ETS requirements. Other solution components, or other
   solutions, are outside the scope of this document.


Copyright Notice
      Copyright (C) The Internet Society (2006).


Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


Table of Contents

   1. Introduction...................................................3
   1.1.  Related Work...............................................3
   1.2.  Terminology................................................4
   1.3.  Changes from previous versions.............................4
   1.3.1.  Changes from -01 to -02..................................4
   1.3.2.  Changes from -00 to -01..................................5
   2. Overview of RSVP extensions and Operations.....................5
      2.1. Operations of Admission Priority..........................7
   3. New Policy Elements............................................8
      3.1. Admission Priority Policy Element.........................8
         3.1.1. Admission Priority Merging  10
      3.2. Application-Level Resource Priority Policy Element.......10
         3.2.1. Application-Level Resource Priority Modifying and
         Merging Rules 11
   4. Security Considerations.......................................12
   5. IANA Considerations...........................................12
   6. Acknowledgments...............................................12
   7. Normative References..........................................12
   8. Informative References........................................13
   Appendix A: Examples of Bandwidth Allocation Model for Admission
   Priority.........................................................14
   A.1  Admission Priority with Maximum Allocation Model (MAM)......14
   A.2  Admission Priority with Russian Dolls Model (RDM)...........18
   A.3  Admission Priority with Priority Bypass Model (PBM).........20
   Appendix B: Example Usages of RSVP Extensions....................23
   Authors' Address.................................................25





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1.  Introduction

   [EMERG-RQTS] and [EMERG-TEL] detail requirements for an Emergency
   Telecommunications Service (ETS), which is an umbrella term
   identifying those networks and specific services used to support
   emergency communications. An underlying goal of these documents is to
   present requirements that elevate the probability of session
   establishment from an authorized user in times of network congestion
   (presumably because of a crisis condition). In some extreme cases,
   the requirement for this probability may reach 100%, but that is a
   topic subject to policy and most likely local regulation (the latter
   being outside the scope of this document).

   Solutions to meet this requirement for elevated session establishment
   probability may involve session layer capabilities prioritizing
   access to resources controlled by the session control function. As an
   example, entities involved in session control (such as SIP user
   agents, when SIP is the session control protocol in use) can
   influence their treatment of session establishment requests (such as
   SIP requests). This may include the ability to "queue" call requests
   when those can not be immediately honored (in some cases with the
   notion of "bumping", or "displacement", of less important call
   request from that queue). It may include additional mechanisms such
   as exemption from certain network management controls, and alternate
   routing.

   Solutions to meet the requirement for elevated session establishment
   probability may also take advantage of network layer admission
   control mechanisms supporting admission priority.  Admission priority
   may involves setting aside some network resources (e.g. bandwidth)
   out of the engineered capacity limits for the emergency services only,
   or alternatively may involve allowing the emergency related sessions
   to seize additional resources beyond the engineered capacity limits
   applied to normal calls.

   Note: Below, this document references several examples of IP
   telephony and its use of "calls", which is one form of the term
   "sessions" (Video over IP and Instant Messaging being other examples
   that rely on session establishment). For the sake of simplicity, we
   shall use the widely known term "call" for the remainder of this
   document.

1.1. Related Work

   [EMERG-IMP] is patterned after [ITU.I.225] and describes an example
   of one type of prioritized network layer admission control procedure
   that may be used for emergency services operating over an IP network
   infrastructure. It discusses initial call set up, as well as
   operations after call establishment through maintenance of a


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   continuing call model of the status of all calls. [EMERG-IMP] also
   describes how these network layer admission control procedures can be
   realized using the Resource reSerVation Protocol [RSVP] along with
   its associated protocol suite and extensions, including those for
   policy based admission control ([FW-POLICY], [RSVP-POLICY]), for user
   authentication and authorization ([RSVP-ID]) and for integrity and
   authentication of RSVP messages ([RSVP-CRYPTO-1], [RSVP-CRYPTO-2]).

   Furthermore, [EMERG-IMP] describes how the RSVP Signaled Preemption
   Priority Policy Element specified in [RSVP-PREEMP] can be used to
   enforce the call preemption that may be needed by some emergency
   services.

   In contrast to [EMERG-IMP], this document specifies new RSVP
   extensions to increase the probability of call completion without
   preemption. Engineered capacity techniques in the form of bandwidth
   allocation models are used to satisfy the "admission priority"
   required by an RSVP capable ETS network. In particular this document
   specifies two new RSVP Policy Elements allowing the admission
   priority to be conveyed inside RSVP signaling messages so that RSVP
   nodes can enforce selective bandwidth admission control decision
   based on the call admission priority. Appendix A of this document
   also provides three examples of a bandwidth allocation model, which
   can be used by RSVP-routers to enforce such admission priority on
   every link.

1.2. Terminology

   This document assumes the terminology defined in [FW-POLICY]. For
   convenience, the definition of a few key terms is repeated here:

   - Policy Decision Point (PDP): The point where policy decisions are
   made.

   - Local Policy Decision Point (LPDP): PDP local to the network
   element

   - Policy Enforcement Point (PEP): The point where the policy
   decisions are actually enforced.

   - Policy Ignorant Node (PIN): A network element that does not
   explicitly support policy control using the mechanisms defined in
   [FW-POLICY].


1.3. Changes from previous versions

1.3.1.  Changes from -01 to -02



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   The most significant changes are:

      o modified the Introduction to add additional clarity and to
      place related work in a better context to the extensions proposed
      in this draft

      o Moved bandwidth allocation models to an appendix

      o Allowed multiple Application-Level Resource Priority inside
      ALRP Policy Element

      o Added a 2nd appendix providing examples of RSVP extensions
      usage


1.3.2.  Changes from -00 to -01

   The most significant changes were:

      o adding a second RSVP Policy Element that contains the
      application-level resource priority requirements (for example as
      communicated in the SIP Resource-Priority Header) for scenarios
      where priority calls transits through multiple administrative
      domains.

      o adding description of a third bandwidth allocation model
      example: the Priority Bypass Model

      o adding discussion on policies for mapping the various bandwidth
      allocation model over the engineered capacity limits.


2.  Overview of RSVP extensions and Operations

   Let us consider the case where a call requiring ETS type service is
   to be established, and more specifically that the preference to be
   granted to this call is in terms of network layer "admission
   priority" (as opposed to preference granted through preemption of
   existing calls). By "admission priority" we mean allowing that
   priority call to seize network layer resources from the engineered
   capacity that have been set-aside and not made available to normal
   calls, or alternatively by allowing that call to seize additional
   resources beyond the engineered capacity limits applied to normal
   calls.

   As described in [EMERG-IMP], the session establishment can be
   conditioned to resource-based and policy-based network layer
   admission control achieved via RSVP signaling. In the case where the



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   session control protocol is SIP, the use of RSVP-based admission
   control by SIP is specified in [SIP-RESOURCE].

   Devices involved in the session establishment are expected to be
   aware of the application-level priority requirements of emergency
   calls. Again considering the case where the session control protocol
   is SIP, the SIP user agents can be made aware of the resource
   priority requirements in the case of an emergency call using the
   Resource-Priority Header mechanism specified in [SIP-PRIORITY]. The
   end-devices involved in the upper-layer session establishment simply
   need to copy the application-level resource priority requirements
   (e.g. as communicated in SIP Resource-Priority Header) inside the new
   RSVP Application-Level Resource-Priority Policy Element defined in
   this document.

   Conveying the application-level resource priority requirements inside
   the RSVP message allows this application level requirement to be
   mapped/remapped into a different RSVP "admission priority" at every
   administrative domain boundary based on the policy applicable in that
   domain. In a typical model (see [FW-POLICY]) where PDPs control PEPs
   at the periphery of the policy domain (e.g., in border routers), PDPs
   would interpret the RSVP Application-Level Resource-Priority Policy
   Element and map the requirement of the emergency session into an RSVP
   "admission priority" level. Then, PDPs would convey this information
   inside the new Admission Priority Policy Element defined in this
   document. This way, the RSVP admission priority can be communicated
   to downstream PEPs (ie RSVP Routers) of the same policy domain, which
   have LPDPs but no controlling PDP. In turn, this means the necessary
   RSVP Admission priority can be enforced at every RSVP hop, including
   all the (many) hops which do not have any understanding of
   Application-Level Resource-Priority semantics.

   As an example of operation across multiple administrative domains, a
   first domain might decide to provide network layer admission priority
   to calls of a given Application Level Resource Priority and map it
   into a high RSVP admission control priority inside the Admission
   Priority Policy Element; while a second domain may decide to not
   provide admission priority to calls of this same Application Level
   Resource Priority  and hence map it into a low RSVP admission control
   priority.

   As another example of operation across multiple administrative
   domains, we can consider the case where the resource priority header
   enumerates several namespaces, as explicitly allowed by [SIP-
   PRIORITY], for support of scenarios where calls traverse multiple
   administrative domains using different namespace. In that case, the
   relevant namespace can be used at each domain boundary to map into an
   RSVP Admission priority for that domain. It is not expected that the
   RSVP Application-Level Resource-Priority Header Policy Element would


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   be taken into account at RSVP-hops within a given administrative
   domain. It is expected to be used at administrative domain boundaries
   only in order to set/reset the RSVP Admission Priority Policy Element.

   The existence of pre-established inter-domain policy agreements or
   Service Level Agreements may avoid the need to take real-time action
   at administrative domain boundaries for mapping/remapping of
   admission priorities.

   Mapping/remapping by PDPs may also be applied to boundaries between
   various signaling protocols, such as those advanced by the NSIS
   working group.

   As can be observed, the framework described above for
   mapping/remapping application level resource priority requirements
   into an RSVP admission priority can also be used for
   mapping/remapping application level resource priority requirements
   into an RSVP preemption priority (when preemption is indeed needed).
   In that case, when processing the RSVP Application-Level Resource-
   Priority Policy Element, the PDPs at boundaries between
   administrative domains (or between various QoS signaling protocols)
   can map it into an RSVP "preemption priority" information. This
   Preemption priority information comprises a setup preemption level
   and a defending preemption priority level. This preemption priority
   information can then be encoded inside the Preemption Priority Policy
   Element of [RSVP-PREEMP] and thus, can be taken into account at every
   RSVP-enabled network hop as discussed [EMERG-IMP]. Appendix B
   provides examples of various hypothetical policies for emergency call
   handling, some of them involving admission priority, some of them
   involving both admission priority and preemption priority. Appendix B
   also identifies how the Application-Level Resource Priority need to
   be mapped into RSVP policy elements by the PDPs to realize these
   policies.


2.1.  Operations of Admission Priority

   The RSVP Admission Priority policy element defined in this document
   allows admission bandwidth to be allocated preferentially to an
   authorized priority service. Multiple models of bandwidth allocation
   MAY be used to that end.

   A number of bandwidth allocation models have been defined in the IETF
   for allocation of bandwidth across different classes of traffic
   trunks in the context of Diffserv-aware MPLS Traffic Engineering.
   Those include the Maximum Allocation Model (MAM) defined in [DSTE-
   MAM] and the Russian Dolls Model (RDM) specified in [DSTE-RDM]. These
   same models MAY however be applied for allocation of bandwidth across
   different levels of admission priority as defined in this document.


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   Appendix A provides an illustration of how these bandwidth allocation
   models can be applied for such purposes and introduces an additional
   bandwidth allocation model that we term the Priority Bypass Model
   (PBM). It is important to note that the models described and
   illustrated in Appendix A are only informative and do not represent a
   recommended course of action.

3.  New Policy Elements

   The Framework document for policy-based admission control [FW-POLICY]
   describes the various components that participate in policy decision
   making (i.e., PDP, PEP and LPDP).

   As described in section 2 of the present document, the Application-
   Level Resource Priority Policy Element and the Admission Priority
   Policy Element serve different roles in this framework:

      - the Application-Level Resource Priority Policy Element conveys
        application level information and is processed by PDPs

      - the emphasis of Admission Priority Policy Element is to be
        simple, stateless, and light-weight such that it can be
        processed internally within a node's LPDP. It can then be
        enforced internally within a node's PEP. It is set by PDPs
        based on processing of the Application-Level Resource Priority
        Policy Element.


   [RSVP-POLICY] defines extensions for supporting generic policy based
   admission control in RSVP. These extensions include the standard
   format of POLICY_DATA objects and a description of RSVP handling of
   policy events.

   The POLICY_DATA object contains one or more of Policy Elements, each
   representing a different (and perhaps orthogonal) policy. As an
   example, [RSVP-PREEMP] specifies the Preemption Priority Policy
   Element.

   This document defines two new Policy Elements called:
      - the Admission Priority Policy Element
      - the Application-Level Resource Priority Policy Element

3.1.  Admission Priority Policy Element

   The format of the Admission Priority policy element is as follows:

         +-------------+-------------+-------------+-------------+
         |     Length                | P-Type = ADMISSION_PRI    |
         +-------------+-------------+-------------+-------------+


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         | Flags       | M. Strategy | Error Code  | Reserved    |
         +-------------+-------------+-------------+-------------+
         | Rvd    | Pri|            Reserved                     |
         +---------------------------+---------------------------+


   Length: 16 bits
      Always 12. The overall length of the policy element, in bytes.

   P-Type: 16 bits
       ADMISSION_PRI  = To be allocated by IANA
      (see "IANA Considerations" section)

  Flags: Reserved (MUST be set to zero on transmit and ignored on
       receive)

   Merge Strategy: 8 bit (only applicable to multicast flows)
       1    Take priority of highest QoS
       2    Take highest priority
       3    Force Error on heterogeneous merge

   Error code: 8 bits (only applicable to multicast flows)
       0  NO_ERROR        Value used for regular ADMISSION_PRI elements
       2  HETEROGENEOUS   This element encountered heterogeneous merge

   Reserved: 8 bits
       Always 0.

   Reserved: 5 bits
       Always 0.

   Pri. (Admission Priority): 3 bits (unsigned)
       The admission control priority of the flow, in terms of access
       to network bandwidth in order to provide higher probability of
       call completion to selected flows. Lower values represent higher
       Priority. 0 represents the highest priority.

       Bandwidth allocation models such as those described in Appendix
       A are to be used by the RSVP router to achieve such increased
       probability of call completion. The admission priority value
       effectively indicates which bandwidth constraint(s) of the
       bandwidth constraint model in use is(are) applicable to
       admission of this RSVP reservation.

   Reserved: 16 bits
       Always 0.





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   Note that the Admission Priority Policy Element does NOT indicate
   that this RSVP reservation is to preempt any other RSVP reservation.
   If a priority session justifies both admission priority and
   preemption priority, the corresponding RSVP reservation needs to
   carry both an Admission Priority Policy Element and a Preemption
   Priority Policy Element. The Admission Priority and Preemption
   Priority are handled by LPDPs and PEPs as orthogonal and independent
   mechanisms.

3.1.1.
       Admission Priority Merging

   This section discusses alternatives for dealing with RSVP admission
   priority in case of merging of reservations. As merging is only
   applicable to multicast, this section also only applies to multicast
   sessions.

   The rules for merging Admission Priority Policy Elements are the same
   as those defined in [RSVP-PREEMP] for merging Preemption Priority
   Policy Elements. In particular, the following merging strategies are
   supported:
      - Take priority of highest QoS
      - Take highest priority
      - Force Error on heterogeneous merge.
   The only difference with [RSVP-PREEMP] is that this document does not
   recommend any merge strategies for Admission Priority while [RSVP-
   PREEMP] recommends the first of these merge strategies for Preemption
   Priority.

   Note that with the Admission Priority, "Take Highest Priority"
   translates into "take the lowest numerical value", while with the
   Preemption Priority it translates into "take the highest numerical
   value".

3.2.  Application-Level Resource Priority Policy Element

   The format of the Application-Level Resource Priority policy element
   is as follows:

         +-------------+-------------+-------------+-------------+
         | Length                    | P-Type = APP_RESOURCE_PRI |
         +-------------+-------------+-------------+-------------+
         //     ALRP List                                        //
         +---------------------------+---------------------------+


   Length: The length of the policy element (including the Length and P-
          Type) is in number of octets (MUST be a multiple of 4) and
          indicates the end of the ALRP list.



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                RSVP Extensions for Emergency Services       June 2006


   P-Type: 16 bits
       APP_RESOURCE_PRI  = To be allocated by IANA
      (see "IANA Considerations" section)

   ARLP:

         +---------------------------+---------------------------+
         |     ALRP Namespace        |ALRP Priority| Reserved    |
         +---------------------------+---------------------------+

       ALRP Namespace (Application-Level Resource Priority Namespace):
           16 bits (unsigned)
           Contains the namespace of the application-level resource
           priority. This is encoded as a numerical value which
           represents the position of the namespace in the "Resource-
           Priority Namespace" IANA registry, starting with 0. Creation
           of this registry has been requested to IANA in [SIP-
           PRIORITY].
           For example, as "dsn", "drsn", "q735", "ets" and "wps" are
           currently the first, second, third, fourth and fifth
           namespaces defined in the "Resource-Priority Namespace"
           registry, those are respectively encoded as value 0, 1, 2, 3
           and 4.

       ALRP Priority: (Application-Level Resource Priority Priority):
          8 bits (unsigned)
           Contains the priority value within the namespace of the
           application-level resource priority. This is encoded as a
           numerical value which represents the priority defined in the
           "Resource-Priority Namespace" IANA registry for the
           considered namespace, starting from 0 for the highest
           priority and increasing as priority decreases.
           For example, as "flash-override", "flash", "immediate",
           "priority" and "routine" are the priorities in decreasing
           order of priority registered for the "dsn" namespace, those
           are respectively encoded as value 0, 1, 2, 3 and 4.

   Reserved: 16 bits
       Always 0.


3.2.1.
      Application-Level Resource Priority Modifying and Merging Rules

   When POLICY_DATA objects are protected by integrity, LPDPs should not
   attempt to modify them. They MUST be forwarded as-is to ensure their
   security envelope is not invalidated.

   In case of multicast, when POLICY_DATA objects are not protected by
   integrity, LPDPs MAY merge incoming Application-Level Resource


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   Priority elements to reduce their size and number. When they do merge
   those, LPDPs MUST do so according to the following rule:

       The ALRP List in the outgoing APP_RESOURCE_PRI element MUST list
       all the ALRPs appearing in the ALRP List of an incoming
       APP_RESOURCE_PR element. A given ALRP MUST NOT appear more than
       once. In other words, the outgoing ALRP List is the reunion of
       the incoming ARLP Lists that are merged.

   As merging is only applicable to Multicast, this rule only applies to
   Multicast sessions.


4.  Security Considerations

   The integrity of ADMISSION_PRI and APP_RESOURCE_PRI is guaranteed, as
   any other policy element, by the encapsulation into a Policy Data
   object [RSVP-POLICY]. The two optional security mechanisms discussed
   in section 6 of [RSVP-POLICY] can be used to protect the
   ADMISSION_PRI and APP_RESOURCE_PRI policy elements.


5.  IANA Considerations

   As specified in [POLICY-RSVP], Standard RSVP Policy Elements (P-type
   values) are to be assigned by IANA as per "IETF Consensus" following
   the policies outlined in [IANA-CONSIDERATIONS].

   IANA needs to allocate two P-Types from the Standard RSVP Policy
   Element range:
           - one P-Type to the Admission Priority Policy Element
           - one P-Type to the Application-Level Resource Priority
             Policy Element


6.  Acknowledgments

   We would like to thank An Nguyen for his encouragement to address
   this topic and ongoing comments. Also, this document borrows heavily
   from some of the work of S. Herzog on Preemption Priority Policy
   Element [RSVP-PREEMP]. Dave Oran and Janet Gunn provided useful input
   into this document.


7.  Normative References

   [EMERG-RQTS]  Carlberg, K. and R. Atkinson, "General Requirements for
   Emergency Telecommunication Service (ETS)", RFC 3689, February 2004.



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                RSVP Extensions for Emergency Services       June 2006


   [EMERG-TEL]  Carlberg, K. and R. Atkinson, "IP Telephony Requirements
   for Emergency Telecommunication Service (ETS)", RFC 3690, February
   2004.

   [RSVP] Braden, R., ed., et al., "Resource ReSerVation Protocol
   (RSVP)- Functional Specification", RFC 2205, September 1997.

   [FW-POLICY]  Yavatkar, R., Pendarakis, D., and R. Guerin, "A
   Framework for Policy-based Admission Control", RFC 2753, January 2000.

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

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

   [DSTE-MAM] Le Faucheur & Lai, "Maximum Allocation Bandwidth
   Constraints Model for Diffserv-aware MPLS Traffic Engineering", RFC
   4125, June 2005.

   [DSTE-RDM] Le Faucheur et al, Russian Dolls Bandwidth Constraints
   Model for Diffserv-aware MPLS Traffic Engineering, RFC 4127, June
   2005

   [SIP-PRIORITY] H. Schulzrinne & J. Polk. Communications Resource
   Priority for the Session Initiation Protocol (SIP), RFC4412, February
   2006.


8.  Informative References

   [EMERG-IMP] F. Baker & J. Polk, "Implementing an Emergency
   Telecommunications Service for Real Time Services in the Internet
   Protocol Suite", RFC 4542, May 2006.

   [ITU.I.225] ITU, "Multi-Level Precedence and Preemption Service, ITU,
   Recommendation, I.255.3, July, 1990.

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

   [RSVP-CRYPTO-1]  Baker, F., Lindell, B., and M. Talwar, "RSVP
   Cryptographic Authentication", RFC 2747, January 2000.

   [RSVP-CRYPTO-2]  Braden, R. and L. Zhang, "RSVP Cryptographic
   Authentication -- Updated Message Type Value", RFC 3097, April 2001.




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                RSVP Extensions for Emergency Services       June 2006


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


Appendix A: Examples of Bandwidth Allocation Model for Admission
Priority

   Sections A.1 and A.2 respectively illustrate how the Maximum
   Allocation Model [DSTE-MAM] and the Russian Dolls Model (RDM) [DSTE-
   RDM] can be used for support of admission priority. Section A.3
   illustrates how a simple "Priority Bypass Model" can also be used for
   support of admission priority.

   For simplicity, operations with only a single "priority" level
   (beyond non-priority) are illustrated here; However, the reader will
   appreciate that operations with multiple priority levels can easily
   be supported with these models.

   In all the charts below:
      x represents a non-priority session
      o represents a priority session

 A.1  Admission Priority with Maximum Allocation Model (MAM)

   This section illustrates operations of admission priority when a
   Maximum Allocation Model (MAM) is used for bandwidth allocation
   across non-priority traffic and priority traffic. A property of the
   Maximum Allocation Model is that priority traffic can not use more
   than the bandwidth made available to priority traffic (even if the
   non-priority traffic is not using all of the bandwidth available for
   it).


                -----------------------
           ^  ^  ^  |              |  ^
           .  .  .  |              |  .
    Total  .  .  .  |              |  .   Bandwidth
          (1)(2)(3) |              |  .   Available
    Engi-  .  .  .  |              |  .   for non-priority use
   neered  .or.or.  |              |  .
           .  .  .  |              |  .
   Capacity.  .  .  |              |  .
           v  .  .  |              |  v
              .  .  |--------------| ---
              v  .  |              |  ^
                 .  |              |  .   Bandwidth available for
                 v  |              |  v   priority use
                -------------------------


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                RSVP Extensions for Emergency Services       June 2006



           Chart 1. MAM Bandwidth Allocation

   Chart 1 shows a link within a routed network conforming to this
   document. On this link are two amounts of bandwidth available to two
   types of traffic: non-priority and priority.
   If the non-priority traffic load reaches the maximum bandwidth
   available for non-priority, no additional non-priority sessions can
   be accepted even if the bandwidth reserved for priority traffic is
   not currently fully utilized.

   With the Maximum Allocation Model, in the case where the priority
   load reaches the maximum bandwidth reserved for priority calls, no
   additional priority sessions can be accepted.

   As illustrated in Chart 1, an operator may map the MAM model onto the
   Engineered Capacity limits according to different policies. At one
   extreme, where the proportion of priority traffic is reliably known
   to be fairly small at all times and where there may be some safety
   margin factored in the engineered capacity limits, the operator may
   decide to configure the bandwidth available for non-priority use to
   the full engineered capacity limits; effectively allowing the
   priority traffic to ride within the safety margin of this engineered
   capacity. This policy can be seen as an economically attractive
   approach as all of the engineered capacity is made available to non-
   priority calls. This policy illustrated as (1) in Chart 1. As an
   example, if the engineered capacity limit on a given link is X, the
   operator may configure the bandwidth available to non-priority
   traffic to X, and the bandwidth available to priority traffic to 5%
   of X.

   At the other extreme, where the proportion of priority traffic may be
   significant at times and the engineered capacity limits are very
   tight, the operator may decide to configure the bandwidth available
   to non-priority traffic and the bandwidth available to priority
   traffic such that their sum is equal to the engineered capacity
   limits. This guarantees that the total load across non-priority and
   priority traffic is always below the engineered capacity and, in turn,
   guarantees there will never be any QoS degradation. However, this
   policy is less attractive economically as it prevents non-priority
   calls from using the full engineered capacity, even when there is no
   or little priority load, which is the majority of time. This policy
   illustrated as (3) in Chart 1. As an example, if the engineered
   capacity limit on a given link is X, the operator may configure the
   bandwidth available to non-priority traffic to 95% of X, and the
   bandwidth available to priority traffic to 5% of X.

   Of course, an operator may also strike a balance anywhere in between
   these two approaches. This policy illustrated as (2) in Chart 1.


Le Faucheur, et al.                                          [Page 15]


                RSVP Extensions for Emergency Services       June 2006



   Chart 2 shows some of the non-priority capacity of this link being
   used.

                -----------------------
           ^  ^  ^  |              |  ^
           .  .  .  |              |  .
    Total  .  .  .  |              |  .   Bandwidth
           .  .  .  |              |  .   Available
    Engi-  .  .  .  |              |  .   for non-priority use
   neered  .or.or.  |xxxxxxxxxxxxxx|  .
           .  .  .  |xxxxxxxxxxxxxx|  .
   Capacity.  .  .  |xxxxxxxxxxxxxx|  .
           v  .  .  |xxxxxxxxxxxxxx|  v
              .  .  |--------------| ---
              v  .  |              |  ^
                 .  |              |  .   Bandwidth available for
                 v  |              |  v   priority use
                -------------------------
           Chart 2. Partial load of non-priority calls


   Chart 3 shows the same amount of non-priority load being used at this
   link, and a small amount of priority bandwidth being used.

                -----------------------
           ^  ^  ^  |              |  ^
           .  .  .  |              |  .
    Total  .  .  .  |              |  .   Bandwidth
           .  .  .  |              |  .   Available
    Engi-  .  .  .  |              |  .   for non-priority use
   neered  .or.or.  |xxxxxxxxxxxxxx|  .
           .  .  .  |xxxxxxxxxxxxxx|  .
   Capacity.  .  .  |xxxxxxxxxxxxxx|  .
           v  .  .  |xxxxxxxxxxxxxx|  v
              .  .  |--------------| ---
              v  .  |              |  ^
                 .  |              |  .   Bandwidth available for
                 v  |oooooooooooooo|  v   priority use
                -------------------------

           Chart 3. Partial load of non-priority calls
                    & partial load of priority calls


   Chart 4 shows the case where non-priority load equates or exceeds the
   maximum bandwidth available to non-priority traffic. Note that
   additional non-priority sessions would be rejected even if the
   bandwidth reserved for priority sessions is not fully utilized.


Le Faucheur, et al.                                          [Page 16]


                RSVP Extensions for Emergency Services       June 2006



                -----------------------
           ^  ^  ^  |xxxxxxxxxxxxxx|  ^
           .  .  .  |xxxxxxxxxxxxxx|  .
    Total  .  .  .  |xxxxxxxxxxxxxx|  .   Bandwidth
           .  .  .  |xxxxxxxxxxxxxx|  .   Available
    Engi-  .  .  .  |xxxxxxxxxxxxxx|  .   for non-priority use
   neered  .or.or.  |xxxxxxxxxxxxxx|  .
           .  .  .  |xxxxxxxxxxxxxx|  .
   Capacity.  .  .  |xxxxxxxxxxxxxx|  .
           v  .  .  |xxxxxxxxxxxxxx|  v
              .  .  |--------------| ---
              v  .  |              |  ^
                 .  |              |  .   Bandwidth available for
                 v  |oooooooooooooo|  v   priority use
                -------------------------
           Chart 4. Full non-priority load
                    & partial load of priority calls


   Chart 5 shows the case where the priority traffic equates or exceeds
   the bandwidth reserved for such priority traffic.

   In that case additional priority sessions could not be accepted. Note
   that this does not mean that such calls are dropped altogether: they
   may be handled by mechanisms, which are beyond the scope of this
   particular document (such as establishment through preemption of
   existing non-priority sessions, or such as queuing of new priority
   session requests until capacity becomes available again for priority
   traffic).

                -----------------------
           ^  ^  ^  |xxxxxxxxxxxxxx|  ^
           .  .  .  |xxxxxxxxxxxxxx|  .
    Total  .  .  .  |xxxxxxxxxxxxxx|  .   Bandwidth
           .  .  .  |xxxxxxxxxxxxxx|  .   Available
    Engi-  .  .  .  |xxxxxxxxxxxxxx|  .   for non-priority use
   neered  .or.or.  |xxxxxxxxxxxxxx|  .
           .  .  .  |xxxxxxxxxxxxxx|  .
   Capacity.  .  .  |              |  .
           v  .  .  |              |  v
              .  .  |--------------| ---
              v  .  |oooooooooooooo|  ^
                 .  |oooooooooooooo|  .   Bandwidth available for
                 v  |oooooooooooooo|  v   priority use
                -------------------------

           Chart 5. Partial non-priority load & Full priority load



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A.2  Admission Priority with Russian Dolls Model (RDM)

   This section illustrates operations of admission priority when a
   Russian Dolls Model (RDM) is used for bandwidth allocation across
   non-priority traffic and priority traffic. A property of the Russian
   Dolls Model is that priority traffic can use the bandwidth which is
   not currently used by non-priority traffic.

   As with the MAM model, an operator may map the RDM model onto the
   Engineered Capacity limits according to different policies. The
   operator may decide to configure the bandwidth available for non-
   priority use to the full engineered capacity limits; As an example,
   if the engineered capacity limit on a given link is X, the operator
   may configure the bandwidth available to non-priority traffic to X,
   and the bandwidth available to non-priority and priority traffic to
   105% of X.

   Alternatively, the operator may decide to configure the bandwidth
   available to non-priority and priority traffic to the engineered
   capacity limits; As an example, if the engineered capacity limit on a
   given link is X, the operator may configure the bandwidth available
   to non-priority traffic to 95% of X, and the bandwidth available to
   non-priority and priority traffic to X.

   Finally, the operator may decide to strike a balance in between. The
   considerations presented for these policies in the previous section
   in the MAM context are equally applicable to RDM.

   Chart 6 shows the case where only some of the bandwidth available to
   non-priority traffic is being used and a small amount of priority
   traffic is in place. In that situation both new non-priority sessions
   and new priority sessions would be accepted.

               --------------------------------------
               |xxxxxxxxxxxxxx|  .                 ^
               |xxxxxxxxxxxxxx|  . Bandwidth       .
               |xxxxxxxxxxxxxx|  . Available for   .
               |xxxxxxxxxxxxxx|  . non-priority    .
               |xxxxxxxxxxxxxx|  . use             .
               |xxxxxxxxxxxxxx|  .                 . Bandwidth
               |              |  .                 . available for
               |              |  v                 . non-priority
               |--------------| ---                . and priority
               |              |                    . use
               |              |                    .
               |oooooooooooooo|                    v
               ---------------------------------------



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           Chart 6. Partial non-priority load & Partial Aggregate load


   Chart 7 shows the case where all of the bandwidth available to non-
   priority traffic is being used and a small amount of priority traffic
   is in place. In that situation new priority sessions would be
   accepted but new non-priority sessions would be rejected.

               --------------------------------------
               |xxxxxxxxxxxxxx|  .                 ^
               |xxxxxxxxxxxxxx|  . Bandwidth       .
               |xxxxxxxxxxxxxx|  . Available for   .
               |xxxxxxxxxxxxxx|  . non-priority    .
               |xxxxxxxxxxxxxx|  . use             .
               |xxxxxxxxxxxxxx|  .                 . Bandwidth
               |xxxxxxxxxxxxxx|  .                 . available for
               |xxxxxxxxxxxxxx|  v                 . non-priority
               |--------------| ---                . and priority
               |              |                    . use
               |              |                    .
               |oooooooooooooo|                    v
               ---------------------------------------

           Chart 7. Full non-priority load & Partial Aggregate load


   Chart 8 shows the case where only some of the bandwidth available to
   non-priority traffic is being used and a heavy load of priority
   traffic is in place. In that situation both new non-priority sessions
   and new priority sessions would be accepted.
   Note that, as illustrated in Chart 7, priority calls use some of the
   bandwidth currently not used by non-priority traffic.

               --------------------------------------
               |xxxxxxxxxxxxxx|  .                 ^
               |xxxxxxxxxxxxxx|  . Bandwidth       .
               |xxxxxxxxxxxxxx|  . Available for   .
               |xxxxxxxxxxxxxx|  . non-priority    .
               |xxxxxxxxxxxxxx|  . use             .
               |              |  .                 . Bandwidth
               |              |  .                 . available for
               |oooooooooooooo|  v                 . non-priority
               |--------------| ---                . and priority
               |oooooooooooooo|                    . use
               |oooooooooooooo|                    .
               |oooooooooooooo|                    v
               ---------------------------------------



Le Faucheur, et al.                                          [Page 19]


                RSVP Extensions for Emergency Services       June 2006


           Chart 8. Partial non-priority load & Heavy Aggregate load


   Chart 9 shows the case where all of the bandwidth available to non-
   priority traffic is being used and all of the remaining available
   bandwidth is used by priority traffic. In that situation new non-
   priority sessions would be rejected. In that situation new priority
   sessions could not be accepted right away. Those priority sessions
   may be handled by mechanisms, which are beyond the scope of this
   particular document (such as established through preemption of
   existing non-priority sessions, or such as queuing of new priority
   session requests until capacity becomes available again for priority
   traffic).

               --------------------------------------
               |xxxxxxxxxxxxxx|  .                 ^
               |xxxxxxxxxxxxxx|  . Bandwidth       .
               |xxxxxxxxxxxxxx|  . Available for   .
               |xxxxxxxxxxxxxx|  . non-priority    .
               |xxxxxxxxxxxxxx|  . use             .
               |xxxxxxxxxxxxxx|  .                 . Bandwidth
               |xxxxxxxxxxxxxx|  .                 . available for
               |xxxxxxxxxxxxxx|  v                 . non-priority
               |--------------| ---                . and priority
               |oooooooooooooo|                    . use
               |oooooooooooooo|                    .
               |oooooooooooooo|                    v
               ---------------------------------------

           Chart 9. Full non-priority load & Full Aggregate load


 A.3  Admission Priority with Priority Bypass Model (PBM)

   This section illustrates operations of admission priority when a
   simple Priority Bypass Model (PBM) is used for bandwidth allocation
   across non-priority traffic and priority traffic. With the Priority
   Bypass Model, non-priority traffic is subject to resource based
   admission control while priority traffic simply bypasses the resource
   based admission control. In other words:
      - when a non-priority call arrives, this call is subject to
   bandwidth admission control and is accepted if the current total load
   (aggregate over non-priority and priority traffic) is below the
   engineered/allocated bandwidth.
      - when a priority call arrives, this call is admitted regardless
   of the current load.

   A property of this model is that a priority call is never rejected.



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   The rationale for this simple scheme is that, in practice in some
   networks:
      - the volume of priority calls is very low for the vast majority
        of time, so it may not be economical to completely set aside
        bandwidth for priority calls and preclude the utilization of
        this bandwidth by normal calls in normal situations
      - even in emergency periods where priority calls are more heavily
        used, those always still represent a fairly small proportion of
        the overall load which can be absorbed within the safety margin
        of the engineered capacity limits. Thus, even if they are
        admitted beyond the engineered bandwidth threshold, they are
        unlikely to result in noticeable QoS degradation.

   As with the MAM and RDM model, an operator may map the Priority
   Bypass model onto the Engineered Capacity limits according to
   different policies. The operator may decide to configure the
   bandwidth limit for admission of non-priority traffic to the full
   engineered capacity limits; As an example, if the engineered capacity
   limit on a given link is X, the operator may configure the bandwidth
   limit for non-priority traffic to X. Alternatively, the operator may
   decide to configure the bandwidth limit for non-priority traffic to
   below the engineered capacity limits (so that the sum of the non-
   priority and priority traffic stays below the engineered capacity);
   As an example, if the engineered capacity limit on a given link is X,
   the operator may configure the bandwidth limit for non-priority
   traffic to 95% of X. Finally, the operator may decide to strike a
   balance in between. The considerations presented for these policies
   in the previous sections in the MAM and RDM contexts are equally
   applicable to the Priority Bypass Model.

   Chart 10 shows illustrates the bandwidth allocation with the Priority
   Bypass Model.

                -----------------------
           ^     ^  |              |  ^
           .     .  |              |  .
    Total  .     .  |              |  .   Bandwidth Limit
          (1)   (2) |              |  .   (on non-priority + priority)
    Engi-  .     .  |              |  .   for admission
   neered  . or  .  |              |  .   of non-priority traffic
           .     .  |              |  .
   Capacity.     .  |              |  .
           v     .  |              |  v
                 .  |--------------| ---
                 .  |              |
                 v  |              |
                    |              |



Le Faucheur, et al.                                          [Page 21]


                RSVP Extensions for Emergency Services       June 2006


           Chart 10. Priority Bypass Model Bandwidth Allocation

   Chart 11 shows some of the non-priority capacity of this link being
   used. In this situation, both new non-priority and new priority calls
   would be accepted.

                -----------------------
           ^     ^  |xxxxxxxxxxxxxx|  ^
           .     .  |xxxxxxxxxxxxxx|  .
    Total  .     .  |xxxxxxxxxxxxxx|  .   Bandwidth Limit
          (1)   (2) |xxxxxxxxxxxxxx|  .   (on non-priority + priority)
    Engi-  .     .  |              |  .   for admission
   neered  . or  .  |              |  .   of non-priority traffic
           .     .  |              |  .
   Capacity.     .  |              |  .
           v     .  |              |  v
                 .  |--------------| ---
                 .  |              |
                 v  |              |
                    |              |

           Chart 11. Partial load of non-priority calls


   Chart 12 shows the same amount of non-priority load being used at
   this link, and a small amount of priority bandwidth being used. In
   this situation, both new non-priority and new priority calls would be
   accepted.

                -----------------------
           ^     ^  |xxxxxxxxxxxxxx|  ^
           .     .  |xxxxxxxxxxxxxx|  .
    Total  .     .  |xxxxxxxxxxxxxx|  .   Bandwidth Limit
          (1)   (2) |xxxxxxxxxxxxxx|  .   (on non-priority + priority)
    Engi-  .     .  |oooooooooooooo|  .   for admission
   neered  . or  .  |              |  .   of non-priority traffic
           .     .  |              |  .
   Capacity.     .  |              |  .
           v     .  |              |  v
                 .  |--------------| ---
                 .  |              |
                 v  |              |
                    |              |

           Chart 12. Partial load of non-priority calls
                    & partial load of priority calls





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                RSVP Extensions for Emergency Services       June 2006


   Chart 13 shows the case where aggregate non-priority and priority
   load exceeds the bandwidth limit for admission of non-priority
   traffic. In this situation, any new non-priority call is rejected
   while any new priority call is admitted.

                -----------------------
           ^     ^  |xxxxxxxxxxxxxx|  ^
           .     .  |xxxxxxxxxxxxxx|  .
    Total  .     .  |xxxxxxxxxxxxxx|  .   Bandwidth Limit
          (1)   (2) |xxxxxxxxxxxxxx|  .   (on non-priority + priority)
    Engi-  .     .  |oooooooooooooo|  .   for admission
   neered  . or  .  |xxxooxxxooxxxo|  .   of non-priority traffic
           .     .  |xxoxxxxxxoxxxx|  .
   Capacity.     .  |oxxxooooxxxxoo|  .
           v     .  |xxoxxxooxxxxxx|  v
                 .  |--------------| ---
                 .  |oooooooooooooo|
                 v  |              |
                    |              |

           Chart 13. Full non-priority load




Appendix B: Example Usages of RSVP Extensions

   This section provides examples of how RSVP extensions defined in this
   document can be used (in conjunctions with other RSVP functionality
   and SIP functionality) to enforce different hypothetical policies for
   handling Emergency sessions in a given administrative domain. This
   Appendix does not provide additional specification. It is only
   included in this document for illustration purposes. The content of
   this appendix may be moved into a future applicability statement
   document.

   We assume an environment where SIP is used for session control and
   RSVP is used for resource reservation.

   In a mild abuse of language, we refer here to "Call Queueing" as the
   set of "session" layer capabilities that may be implemented by SIP
   user agents to influence their treatment of SIP requests. This may
   include the ability to "queue" call requests when those can not be
   immediately honored (in some cases with the notion of "bumping", or
   "displacement", of less important call request from that queue). It
   may include additional mechanisms such as exemption from certain
   network management controls, and alternate routing.




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   We only mention below the RSVP policy elements that are to be
   enforced by PEPs. It is assumed that these policy elements are set at
   administrative domain boundaries by PDPs. The Admission Priority and
   Preemption Priority RSVP policy elements are set by PDPs as a result
   of processing the Application Level Resource Priority Policy Element
   (which is carried in RSVP messages).

   If one wants to implement an emergency service purely based on Call
   Queueing, one can achieve this by signaling emergency calls:
      * using "Resource-Priority" Header in SIP
      * not using Admission-Priority Policy Element in RSVP
      * not using Preemption Policy Element in RSVP

   If one wants to implement an emergency service based on Call
   Queueing and on "prioritized access to network layer resources", one
   can achieve this by signaling emergency calls:
      * using "Resource-Priority" Header in SIP
      * using Admission-Priority Policy Element in RSVP
      * not using Preemption Policy Element in RSVP
   Emergency calls will not result in preemption of any session.
   Different bandwidth allocation models can be used to offer different
   "prioritized access to network resources". Just as examples, this
   includes strict setting aside of capacity for emergency sessions as
   well as simple bypass of admission limits for emergency sessions.

   If one wants to implement an emergency service based on Call Queueing,
   on "prioritized access to network layer resources", and ensures that
   (say) "Emergency-1" sessions can preempt "Emergency-2" sessions, but
   non-emergency sessions are not affected by preemption, one can do
   that by signaling emergency calls:
      * using "Resource-Priority" Header in SIP
      * using Admission-Priority Policy Element in RSVP
      * using Preemption Policy Element in RSVP with:
            o setup (Emergency-1) > defending (Emergency-2)
            o setup (Emergency-2) <= defending (Emergency-1)
            o setup (Emergency-1) <= defending (Non-Emergency)
            o setup (Emergency-2) <= defending (Non-Emergency)

   If one wants to implement an emergency service based on Call Queueing,
   on "prioritized access to network layer resources", and ensure that
   "emergency" sessions can preempt regular sessions, one could do that
   by signaling emergency calls:
      * using "Resource-Priority" Header in SIP
      * using Admission-Priority Policy Element in RSVP
      * using Preemption Policy Element in RSVP with:
            o setup (Emergency) > defending (Non-Emergency)
            o setup (Non-Emergency) <= defending (Emergency)

   If one wants to implement an emergency service based on Call Queueing,


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                RSVP Extensions for Emergency Services       June 2006


   on "prioritized access to network layer resources", and ensure that
   "emergency" sessions can partially preempt regular sessions (ie
   reduce their reservation size), one could do that by signaling
   emergency calls:
      * using "Resource-Priority" Header in SIP
      * using Admission-Priority Policy Element in RSVP
      * using Preemption in Policy Element RSVP with:
            o setup (Emergency) > defending (Non-Emergency)
            o setup (Non-Emergency) <= defending (Emergency)
      * activate RFC4495 RSVP Bandwidth Reduction mechanisms



Authors' Address


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


   James Polk
   Cisco Systems, Inc.
   2200 East President George Bush Turnpike
   Richardson, Texas  75082
   USA
   Email: jmpolk@cisco.com


   Ken Carlberg
   G11
   123a Versailles Circle
   Towson, MD. 21204
   USA
   email: carlberg@g11.org.uk



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Le Faucheur, et al.                                          [Page 25]


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