Speermint Working Group                                 R.Penno (Editor)
Internet Draft                                          Juniper Networks
Expires: March 2007                                   September 18, 2006

                      SPEERMINT Peering Architecture

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   This Internet-Draft will expire on November 2006.


   This document defines the SPEERMINT peering architecture, its
   functional components and peering interface functions.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [1]

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Table of Contents

   1. Introduction...................................................2
   2. Network Context................................................3
   3. Procedures.....................................................5
   4. Reference SPEERMINT Architecture...............................5
   5. Peer Function Examples.........................................7
      5.1. The Location Function (LF) of an Initiating Provider......7
         5.1.1. Target address analysis..............................7
         5.1.2. User ENUM Lookup.....................................8
         5.1.3. Carrier ENUM lookup..................................8
         5.1.4. Routing Table........................................8
         5.1.5. SIP DNS Resolution...................................8
         5.1.6. SIP Redirect Server..................................9
      5.2. The Location Function (LF) of a Receiving Provider........9
         5.2.1. Publish ENUM records.................................9
         5.2.2. Publish SIP DNS records..............................9
      5.3. Policy Function (PF)......................................9
         5.3.1. TLS.................................................11
         5.3.2. IPSec...............................................11
         5.3.3. Subscribe Notify....................................11
      5.4. Signaling Function (SF)..................................11
      5.5. Media Function (MF)......................................12
   6. Call Control and Media Control Deployment Options.............12
   7. Security Considerations.......................................13
   8. IANA Considerations...........................................14
   9. Acknowledgments...............................................14
   Author's Addresses...............................................15
   10. References...................................................15
      10.1. Normative References....................................15
      10.2. Informative References..................................16
   Intellectual Property Statement..................................17
   Disclaimer of Validity...........................................18
   Copyright Statement..............................................18

1. Introduction

   The objective of this document is to define a reference peering
   architecture in the context of Session PEERing for Multimedia
   INTerconnect (SPEERMINT). In this process, we define the peering
   reference architecture (reference, for short), its functional
   components, and peering interface functions from the perspective of a
   real-time communications (Voice and Multimedia) IP Service provider

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   This architecture allows the interconnection of two service providers
   in layer 5 peering as defined in the SPEERMINT Requirements [13] and
   Terminology [12] documents for the purpose SIP-based voice and
   multimedia traffic.

   Layer 3 peering is outside the scope of this document. Hence, the
   figures in this document do not show routers so that the focus is on
   Layer 5 protocol aspects.

   This document uses terminology defined in the SPEERMINT Terminology
   document [12].

2. Network Context

   Figure 1 shows an example network context. Two SIP providers can form
   a Layer 5 peer over either the public Internet or private Layer 3
   networks. In addition, two or more providers may form a SIP (Layer 5)
   federation [17] on either the public Internet or private Layer 3
   networks. This document does not make any assumption whether the SIP
   providers directly peer to each other or through Layer 3 transit
   network as per use case of [16].

   Note that Figure 1 allows for the following potential SPEERMINT
   peering scenarios:

   o  Enterprise to Enterprise across the public Internet

   o  Enterprise to Service Provider across the public Internet

   o  Service Provider to Service Provider across the public Internet

   o  Enterprise to enterprise across a private Layer 3 network

   o  Enterprise to Service Provider across a private Layer 3 network

   o  Service Provider to Service Provider across a private Layer 3

   The members of a federation may jointly use a set of functions such
   as location peering function, application function, subscriber
   database function, SIP proxies, and/or functions that synthesize
   various SIP and non-SIP based applications. Similarly, two providers
   may jointly use a set of peering functions. The federation functions
   or the peering functions can be either public or private.

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                          |     Public        |
                          | Peering Function  |
                          |       or          |
                          |     Public        |
                          |Federation Function|
     +-----------+              /     \              +-----------+
     |Enterprise |            --       --            |Enterprise |
     |Provider A |-----------/           \-----------|Provider B |
     +-----------+         --             --         +-----------+
                          /      Public     \
                          |     Internet    |
                          \     (Layer 3)   /
     +-----------+         --             --         +-----------+
     |Service    |-----------\           /-----------|Service    |
     |Provider C |            --       --            |Provider D |
     +-----------+              \_____/              +-----------+
                                   | Layer 3 Peering
                                   | Point (out of scope)
     +-----------+              /     \              +-----------+
     |Enterprise |            --       --            |Enterprise |
     |Provider E |-----------/           \-----------|Provider F |
     +-----------+         --   Service   --         +-----------+
                          /     Provider    \
                          |     Private     |
                          \     Network     /
     +-----------+         --  (Layer 3)  --         +-----------+
     |Service    |-----------\           /-----------|Service    |
     |Provider G |            --       --            |Provider H |
     +-----------+               \____/              +-----------+
                          |     Private       |
                          | Peering Function  |
                          |       or          |
                          |Federation Function|

                     Figure 1: SPEERMINT Network Context

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3. Procedures

   This document assumes that a call from an end user in the initiating
   peer goes through the following steps to establish a call to an end
   user in the receiving peer:

         1. The analysis of a target address.

             a. If the target address represents an intra-VSP resource,
                we go directly to step 4.

         2. the discovery of the receiving peering point address,

         3. the enforcement of authentication and other policy,

         4. the discovery of end user address,

         5. the routing of SIP messages,

         6. the session establishment,

         7. the transfer of media,

         8. and the session termination.

4. Reference SPEERMINT Architecture

   Figure 2 depicts the SPEERMINT architecture and logical functions
   that form the peering between two SIP service providers I and R,
   where I is the Initiating peer and R is the Receiving peer.

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                                  | DNS, |
                                  | Db,  |
                                  | etc  |
                       -------    +------+    -------
                      /       \     |  |     /       \
                     |         LF---+  +---LF         |
                     |         |            |         |
                     |         PF----------PF         |
                     |         |            |         |
                     |   SIP   SF----------SF   SIP   |
                     | Service |            | Service |
                     |Provider MF----------MF Provider|
                     |    I    |            |    R    |
                     |         |            |         |
                     |         |            |         |
                      \       /              \       /
                       -------                -------

                Figure 2: Reference SPEERMINT Architecture

   The procedures presented in Chapter 3 are implemented by a set of
   peering functions:

   o  Location Function (LF): Purpose is to develop call routing data
      (CRD) by discovering the Signaling Function (SF), Policy Function
      (PF), and end user's reachable host (IP address and port).

   o  Policy Function (PF): Purpose is to perform authentication and to
      exchange policy parameters to be used by the SF. The data acquired
      through the policy function can provide input to the LF, SF or MF
      functions. Therefore the policy function can happen multiple times
      (through multiple methods) during the procedures used to establish
      a call.

   o  Signaling Function (SF): Purpose is to perform routing of SIP
      messages, to optionally perform termination and re-initiation of
      call, to optionally implement security and policies on SIP
      messages, and to assist in discovery/exchange of parameters to be
      used by the Media Function (MF).

   o  Media Function (MF): Purpose is to perform media related function
      such as media transcoding and media security implementation
      between two SIP providers.

   The intention of defining these functions is to provide a framework
   for design segmentation and allow each one to evolve separately.

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5. Peer Function Examples

   This section describes the peering functions in more detail and
   provides some examples on the role they would play in a SIP call in a
   Layer 5 peering scenario.

   Some of the information in the chapter is taken from [14].

5.1. The Location Function (LF) of an Initiating Provider

   Purpose is to develop call routing data (CRD) [12] by discovering
   the Signaling Function (SF), Policy Function (PF), and end user's
   reachable host (IP address and host). The LF of an Initiating
   provider analyzes target address and discovers the next hop
   signaling function (SF) in a peering relationship using DNS, SIP
   Redirect Server, or a functional equivalent database.

5.1.1. Target address analysis

   When the initiating provider receives a request to communicate, the
   initiating provider analyzes the target state data to determine
   whether the call needs to be terminated internal or external to its
   network. The analysis method is internal to the provider's policy;
   thus, outside the scope of SPEERMINT. Note that the peer is free to
   consult any manner of private data sources to make this

   If the target address does not represent a resource inside the
   initiating peer's administrative domain or federation of domains, the
   initiating provider resolves the call routing data by using the
   Location Function (LF). Examples of the LF are the functions of ENUM,
   Routing Table, SIP DNS, and SIP Redirect Server.

   If the request to communicate is for an im: or pres: URI type, the
   initiating peer follows the procedures in [8].  If the highest
   priority supported URI scheme is sip: or sips:, the initiating peer
   skips to SIP DNS resolution in Section 5.1.5. Likewise, if the target
   address is already a sip: or sips: URI in an external domain, the
   initiating peer skips to SIP DNS resolution in Section 5.1.5.

   If the target address corresponds to a specific E.164 address, the
   peer may need to perform some form of number plan mapping according
   to local policy.  For example, in the United States, a dial string
   beginning "011 44" could be converted to "+44", or in the United
   Kingdom "00 1" could be converted to "+1".  Once the peer has an
   E.164 address, it can use ENUM.

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5.1.2. User ENUM Lookup

   If an external E.164 address is the target, the initiating peer
   consults the public "User ENUM" rooted at e164.arpa, according to the
   procedures described in RFC 3761.  The peer MUST query for the
   "E2U+sip" enumservice as described in RFC 3764 [11], but MAY check
   for other enumservices.  The initiating peer MAY consult a cache or
   alternate representation of the ENUM data rather than actual DNS
   queries.  Also, the peer MAY skip actual DNS queries if the
   initiating peer is sure that the target address country code is not
   represented in e164.arpa.  If a sip: or sips: URI is chosen the peer
   skips to Section 5.1.5.

   If an im: or pres: URI is chosen for based on an "E2U+im" [10] or
   "E2U+pres" [9] enumserver, the peer follows the procedures for
   resolving these URIs to URIs for specific protocols such a SIP or
   XMPP as described in the previous section.

5.1.3. Carrier ENUM lookup

   Next the initiating peer checks for a carrier-of-record in a carrier
   ENUM domain according to the procedures described in [12].  As in the
   previous step, the peer MAY consult a cache or alternate
   representation of the ENUM data in lieu of actual DNS queries.  The
   peer first checks for records for the "E2U+sip" enumservice, then for
   the "E2U+pstn" enumservice as defined in [21].  If a terminal record
   is found with a sip: or sips: URI, the peer skips to Section 5.1.5,
   otherwise the peer continues processing according to the next

5.1.4. Routing Table

   If there is no user ENUM records and the initiating peer cannot
   discover the carrier-of-record or if the initiating peer cannot reach
   the carrier-of-record via SIP peering, the initiating peer still
   needs to deliver the call to the PSTN or reject the call.  Note that
   the initiating peer MAY still sends the call to another provider for
   PSTN gateway termination by prior arrangement using a routing table.
   If so, the initiating peer rewrites the Request-URI to address the
   gateway resource in the target provider's domain and MAY forward the
   request on to that provider using the procedures described in the
   remainder of these steps.

5.1.5. SIP DNS Resolution

   Once a sip: or sips: in an external domain is selected as the target,
   the initiating peer uses the procedures described in [4] Section 4.

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   To summarize the RFC 3263 procedure: unless these are explicitly
   encoded in the target URI, a transport is chosen using NAPTR records,
   a port is chosen using SRV records, and an address is chosen using A
   or AAAA records.  Note that these are queries of records in the
   global DNS.

   It is worth mentioning that the PF can override the default RFC 3263
   procedure. That may be based on learned routes (via SUBSCRIBE), or
   federation announcements.

5.1.6. SIP Redirect Server

   A SIP Redirect Server may help in resolving current address of a
   mobile target address.

5.2. The Location Function (LF) of a Receiving Provider

5.2.1. Publish ENUM records

   The receiving peer SHOULD participate by publishing "E2U+sip" and
   "E2U+pstn" records with sip: or sips: URIs wherever a public carrier
   ENUM root is available.  This assumes that the receiving peer wants
   to peer by default.  Even when the receiving peer does not want to
   accept traffic from specific initiating peers, it MAY still reject
   requests on a case-by-case basis.

5.2.2. Publish SIP DNS records

   To receive peer requests, the receiving peer MUST insure that it
   publishes appropriate NAPTR, SRV, and address (A and/or AAAA) records
   in the global DNS that resolve an appropriate transport, port, and
   address to a relevant SIP server.

5.3. Policy Function (PF)

   The purpose of policy function is to perform authentication and to
   exchange peering policy capabilities to be used by the signaling
   function. The policy function can happen multiple times (through
   multiple methods) during the procedures used to establish a call and
   the data acquired as a result can provide input to the LF, SF or MF

   Policy data can come through DNS NAPTR resolution as shown in [18]
   and/or a SIP peering event package [22].

   The policy capabilities should be specified through well defined XML
   schemas. These policies define the capabilities of each peer and its

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   devices used for peering. For example, the following capabilities
   could be exchanged through the policy function:

   o  Adjacency (Next hop network attributes)

       o If there are many adjacent proxies to use, the choice could be
          based on:

            . Location of the proxy

            . Maximum number of calls per second (CPS)

            . Maximum number of established calls

            . Maximum allowed bandwidth (KBS)

   o  Path Discovery (Domains that are NOT adjacent)

       o What are the paths to the destination domain that can:

            . Guarantee quality

            . Participate in Guarantee's for Trust

            . Are these paths available?

   o  Adjacency and Path Congestion detection/avoidance

     o  Inflow Traffic Restriction (not call-by-call)

       o For maintenance actions

       o For congestion management

     o  How can a carrier prevent upstream networks from submitting
        calls for certain destinations in overload

   The authentication policy function can be implemented by TLS (as
   described in (5.3.1), IPSec or any other method that meet the
   security needs to a specific deployment.

   Editor's Note: This section will be updated based on the progress on
   the SPEERMINT policy document.

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5.3.1. TLS

   Once a transport, port, and address are found, the initiating peer
   will open or find a reusable TLS connection to the peer.  The
   initiating provider should verify the server certificate which should
   be rooted in a well-known certificate authority.  The initiating
   provider should be prepared to provide a TLS client certificate upon
   request during the TLS handshake.  The client certificate should
   contain a DNS or URI choice type in the subject AltName which
   corresponds to the domain asserted in the host production of the From
   header URI.  The certificate should be valid and rooted in a well-
   known certificate authority. Note that the client certificate MAY
   contain a list of entries in the subjectAltName, only one of which
   has to match the domain in the From header URI.

   When the receiving peer receives a TLS client hello, it responds with
   its certificate.  The receiving peer certificate SHOULD be valid and
   rooted in a well-known certificate authority.  The receiving peer
   should request and verify the client certificate during the TLS

5.3.2. IPSec

       Editor's Note: will be described later.

5.3.3. Subscribe Notify

   Policy function may also be optionally implemented by dynamic
   subscribe, notify, and exchange of policy information and feature
   information among providers [22].

5.4. Signaling Function (SF)

   The purpose of signaling function is to perform routing of SIP
   messages, to optionally perform termination and re-initiation of a
   call, to optionally implement security and policies on SIP messages,
   and to assist in discovery/exchange of parameters to be used by the
   Media Function (MF).

   The routing of SIP messages are performed by SIP proxies. The
   optional termination and re-initiation of calls are performed by

   Optionally, a SF may perform additional functions such as Session
   Admission Control, SIP Denial of Service protection, SIP Topology
   Hiding, SIP header normalization, and SIP security, privacy and

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   The signaling function can also process SDP payloads for media
   information such as media type, bandwidth, and type of codec; then,
   communicate this information to the media function. Signaling
   function may optionally communicate with network layer to pass Layer
   3 related policies [10]

5.5. Media Function (MF)

   Examples of the media function is to transform voice payload from one
   coding (e.g., G.711) to another (e.g., EvRC), media relaying, media
   security, privacy, and encryption.

   Editor's Note: This section will be further updated.

6. Call Control and Media Control Deployment Options

   The peering functions can either be deployed along the following two
   dimensions depending upon how the signaling function and the media
   function along with IP functions are implemented:

   Composed or Decomposed:  Addresses the question whether the media
   paths must flow through the same physical and geographic nodes as the
   call signaling,

   Centralized or Distributed:  Addresses the question whether the
   logical and physical peering points are in one geographical location
   or distributed to multiple physical locations on the service provider

   In a composed model, SF and MF functions are implemented in one
   peering logical element.

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                  Provider A                        Provider B
                  ----------   .               .   ----------
                 /          \  .               .  /          \
                |            | .       _       . |            |
                |       +----+ .     /   \_    . +----+       |
                |       | SF |<-----/     \------| SF |       |
                |       +-+--+ .   /Transit\   . |    |       |
                |         | |  .  /   IP    \  . |    |       |
                |       +-+--+ .  \ Provider|  . |    |       |
                |       | MF |<~~~~\(Option)|~~~~| MF |       |
                |       +----+ .    \      /   . +----+       |
                |            | .     \__ _/    . |            |
                 \_________ /  .               .  \________ _/
                  ----------                       ----------

             --- Signal (SIP)
             ~~~ Bearer (RTP/IP)
             ... Scope of peering

                 Figure 3: Decomposed v. Collapsed Peering

   The advantage of a collapsed peering architecture is that one-element
   solves all peering issues. Disadvantage examples of this architecture
   are single point failure, bottle neck, and complex scalability.

   In a decomposed model, SF and MF are implemented in separate peering
   logical elements. Signaling functions are implemented in a proxy and
   media functions are implemented in another logical element.  The
   scaling of signaling versus scaling of media may differ between
   applications.  Decomposing allows each to follow a separate migration

   This model allows the implementation of M:N model where one SF is
   associated with multiple peering MF and one peering MF is associated
   with multiple peering proxies. Generally, a vertical protocol
   associates the relationship between a SF and a MF. This architecture
   reduces the potential of single point failure. This architecture,
   allows separation of the policy decision point and the policy
   enforcement point. An example of disadvantages is the scaling
   complexity because of the M:N relationship and latency due to the
   vertical control messages between entities.

7. Security Considerations

   In all cases, cryptographic-based security should be maintained as an
   optional requirement between peering providers conditioned on the

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   presence or absence of underlying physical security of peer
   connections, e.g. within the same secure physical building.

   In order to maintain a consistent approach, unique and specialized
   security requirements common for the majority of peering
   relationships, should be standardized within the IETF.  These
   standardized methods may enable capabilities such as dynamic peering
   relationships across publicly maintained interconnections.

   TODO:  Address RFC-3552 BCP items.

8. IANA Considerations

   There are no IANA considerations at this time.

9. Acknowledgments

   The working group thanks Sohel Khan for his initial architecture
   draft that helped to initiate work on this draft.

   A significant portion of this draft is taken from [14] with
   permission from the author R. Mahy. The other important contributor
   is Otmar Lendl.

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Author's Addresses

   Mike Hammer
   Cisco Systems
   13615 Dulles Technology Drive
   Herndon, VA 20171
   Email: mhammer@cisco.com

   Sohel Khan, Ph.D.
   Technology Strategist
   6220 Sprint Parkway
   Overland Park, KS 66251
   Email: Sohel.Q.Khan@sprint.com

   Daryl Malas
   Level 3 Communications LLC
   1025 Eldorado Blvd.
   Broomfield, CO 80021
   EMail: daryl.malas@level3.com

   Reinaldo Penno (Editor)
   Juniper Networks
   1194 N Mathilda Avenue
   Sunnyvale, CA
   Email: rpenno@juniper.net

   Adam Uzelac
   Global Crossing
   1120 Pittsford Victor Road
   PITTSFORD, NY 14534
   Email: adam.uzelac@globalcrossing.com

10. References

10.1. Normative References

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

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   [2]   Mealling, M. and R. Daniel, "The Naming Authority Pointer
         (NAPTR) DNS Resource Record", RFC 2915, September 2000.

   [3]   Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
         Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
         Session Initiation Protocol", RFC 3261, June 2002.

   [4]   Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
         (SIP): Locating SIP Servers", RFC 3263, June 2002.

   [5]   Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and
         T. Wright, "Transport Layer Security (TLS) Extensions", RFC
         3546, June 2003.

   [6]   Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
         "RTP: A Transport Protocol for Real-Time Applications", STD 64,
         RFC 3550, July 2003.

   [7]   Peterson, J., Liu, H., Yu, J., and B. Campbell, "Using E.164
         numbers with the Session Initiation Protocol (SIP)", RFC 3824,
         June 2004.

   [8]   Peterson, J., "Address Resolution for Instant Messaging and
         Presence",RFC 3861, August 2004.

   [9]   Peterson, J., "Telephone Number Mapping (ENUM) Service
         Registration for Presence Services", RFC 3953, January 2005.

   [10]  ETSI TS 102 333: " Telecommunications and Internet converged
         Services and Protocols for Advanced Networking (TISPAN); Gate
         control protocol".

   [11]  Peterson, J., "enumservice registration for Session Initiation
         Protocol (SIP) Addresses-of-Record", RFC 3764, April 2004.

10.2. Informative References

   [12]  Meyer, D., "SPEERMINT Terminology", draft-ietf-speermint-
         terminology-04 (work in progress), May 2006.

   [13]  Mule, J-F., "SPEERMINT Requirements for SIP-based VoIP
         Interconnection", draft-ietf-speermint-requirements-00.txt,
         June 2006.

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   [14]  Mahy, R., "A Minimalist Approach to Direct Peering", draft-
         mahy-speermint-direct-peering-00.txt, June 19, 2006.

   [15]  Penno, R., et al., "SPEERMINT Routing Architecture Message
         Flows", draft-ietf-speermint-flows-00.txt", August 2006.

   [16]  Lee, Y., "Session Peering Use Case for Cable", draft-lee-
         speermint-use-case-cable-00.txt, June, 2006.

   [17]  Houri, A., et al., "RTC Provisioning Requirements", draft-
         houri-speermint-rtc-provisioning-reqs-00.txt, June, 2006.

   [18]  Habler, M., et al., "A Federation based VOIP Peering
         Architecture", draft-lendl-speermint-federations-03.txt,
         September 2006.

   [19]  Mahy, R., "A Telephone Number Mapping (ENUM) Service
         Registration for Instant Messaging (IM) Services", draft-ietf-
         enum-im-service-00 (work in progress), March 2006.

   [20]  Haberler, M. and R. Stastny, "Combined User and Carrier ENUM in
         the e164.arpa tree", draft-haberler-carrier-enum-02 (work in
         progress), March 2006.

   [21]  Livingood, J. and R. Shockey, "IANA Registration for an
         Enumservice Containing PSTN Signaling Information", draft-ietf-
         enum-pstn-04 (work in progress), May 2006.

   [22]  Penno, R., Malas D., and Melampy, P., "A Session Initiation
         Protocol (SIP) Event package for Peering", draft-penno-sipping-
         peering-package-00 (work in progress), September 2006.

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Internet-Draft    draft-ietf-speermint-architecture-00   September 2006

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