Speermint Working Group                                        R. Penno
Internet Draft                                         Juniper Networks
Intended status: Informational                                 D. Malas
Expires: September 2008 May 2009                                             CableLabs
                                                                S. Khan
                                                              A. Uzelac
                                                        Global Crossing
                                                              M. Hammer
                                                          Cisco Systems
                                                            May 2,
                                                       November 3, 2008

                      SPEERMINT Peering Architecture

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Copyright Notice

   Copyright (C) The IETF Trust (2008).


   This document defines the SPEERMINT peering architecture, its
   functional components and peering interface functions. It also
   describes the steps taken to establish a session between two peering
   domains in the context of the functions defined.

Conventions used in this document

   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 RFC-2119[1]

Table of Contents

   1. Introduction...................................................3
   2. Network Context................................................3
   3. Procedures.....................................................6
   4. Reference SPEERMINT Architecture...............................6
   5. Recommended SSP Procedures.....................................8
      5.1. Originating SSP Procedures................................8
         5.1.1. The Look-Up Function (LUF)...........................8
   Target address analysis.........................8
   User ENUM Lookup................................9
   Infrastructure ENUM lookup......................9
         5.1.2. Location Routing Function (LRF).....................10
   Routing Table..................................10
   SIP DNS Resolution.............................10
   SIP Redirect Server............................11
         5.1.3. The Signaling Function (SF).........................11
   Establishing a Trusted Relationship............11
   Sending the SIP request........................12
      5.2. Terminating SSP Procedures...............................12
         5.2.1. The Location Function (LF)..........................12
   Publish ENUM records...........................12
   Publish SIP DNS records........................13
   Subscribe Notify...............................13
         5.2.2. Signaling Function (SF).............................13
   Receive SIP requests...........................13
      5.3. Target SSP Procedures....................................14
         5.3.1. Signaling Function (SF).............................14
   Receive SIP requests...........................14
      5.4. Media Function (MF)......................................14
      5.5. Policy Considerations....................................14
   6. Call Control and Media Control Deployment Options.............15
   7. Address space considerations..................................17
   8. Security Considerations.......................................17
   9. IANA Considerations...........................................17
   10. Acknowledgments..............................................17
   11. References...................................................18
      11.1. Normative References....................................18
      11.2. Informative References..................................19
   Author's Addresses...............................................20
   Intellectual Property Statement..................................20
   Disclaimer of Validity...........................................21

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), it's functional
   components, and peering interface functions from the perspective of
   a SIP Service provider's (SSP) network.

   This architecture allows the interconnection of two SSPs in layer 5
   peering as defined in the SPEERMINT Requirements [13] and
   Terminology [12] documents.

   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], so the reader should be familiar with all the terms
   defined there.

2. Network Context

   Figure 1 shows an example network context. Two SSPs can form a Layer
   5 peering over either the public Internet or private Layer3
   networks. In addition, two or more providers may form a SIP (Layer
   5) federation [13] 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 SSP across the public Internet
     o  SSP to SSP across the public Internet

     o  Enterprise to enterprise across a private Layer 3 network

     o  Enterprise to SSP across a private Layer 3 network

     o  SSP to SSP across a private Layer 3 network

   The members of a federation may jointly use a set of functions such
   as location function, signaling function, media function, ENUM
   database or SIP Registrar, SIP proxies, and/or functions that
   synthesize various SIP and non-SIP based applications. Similarly,
   two SSPs may jointly use a set of functions. The functions can be
   either public or private.

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

                      Figure 1: SPEERMINT Network Context

3. Procedures

   This document assumes that in order for call to be establish from a
   UAC end user in the initiating peer's network to a UAS in the
   receiving peer's network the following steps are taken:

     1. The analysis of the target address.

          . If the target address represents an intra-SSP resource, the
             behavior is out-of-scope with respect to this draft.

     2. the determination of the target SSP,

     3. the determination of the SF next-hop in the target SSP,

     4. the enforcement of authentication and potentially other

     5. the determination of the UAS,

     6. the session establishment,

     7. the transfer of media which could include voice, video, text
        and others,

     8. and the session termination.

   The originating SSP would likely perform steps 1-4, and the
   terminating SSP would likely perform steps 4-5.

   In the case the target SSP is different from the terminating SSP it
   would repeat steps 1-4. This is reflected in Figure 2 that shows the
   target SSP with its own peering functions.

4. Reference SPEERMINT Architecture

   Figure 2 depicts the SPEERMINT architecture and logical functions
   that form the peering between two SSPs.

                                | DNS, |
                    +---------->| Db,  |<---------+
                    |           | etc  |          |
                    |           +------+          |
                    |                             |
              ------|--------              -------|-------
             /      v        \            /       v       \
            |    +--LUF-+     |          |     +--LUF-+    |
            |    |      |     |          |     |      |    |
            |    |      |     |          |     |      |    |
            |    |      |     |          |     |      |    |
            |    +------+     |          |     +------+    |
            |                 |          |                 |
            |    +--LRF-+     |          |     +--LRF-+    |
            |    |      |     |          |     |      |    |
            |    |      |     |          |     |      |    |
            |    |      |     |          |     |      |    |
            |    +------+     |          |     +------+    |
            |                 |          |                 |
            |                 |          |                 |
            |             +---SF--+  +---SF--+             |
            |             |       |  |       |             |
            |             |  SBE  |  |  SBE  |             |
            | Originating |       |  |       |  Target     |
            |             +---SF--+  +---SF--+             |
            |    SSP          |          |       SSP       |
            |             +---MF--+  +---MF--+             |
            |             |       |  |       |             |
            |             |  DBE  |  |  DBE  |             |
            |             |       |  |       |             |
            |             +---MF--+  +---MF--+             |
             \               /            \               /
              ---------------              ---------------
                Figure 2: Reference SPEERMINT Architecture

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

   The Look-Up Function (LUF) provides a mechanism for determining for
   a given request the target domain to which the request should be

   The Location Routing Function (LRF) determines for the target domain
   of a given request the location of the SF in that domain and
   optionally develops other Session Establishment Data (SED) required
   to route the request to that domain.

   Signaling Function (SF): Purpose is to perform SIP call routing, 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).

   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 independently.

5. Recommended SSP Procedures

   This section describes the functions in more detail and provides
   some recommendations 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] and is put
   here for continuity purposes.

5.1. Originating SSP Procedures

5.1.1. The Look-Up Function (LUF)

   Purpose is to determine the SF of the target domain of a given
   request and optionally develop Session Establishment Data (SED)
   [12]. Target address analysis

   When the initiating SSP receives a request to communicate, it
   analyzes the target URI to determine whether the call needs to be
   terminated internally or externally to its network. The analysis
   method is internal to the SSP; thus, outside the scope of SPEERMINT.
   Note that the SSP is free to consult any manner of private data
   sources to make this determination.

   If the target address does not represent a resource inside the
   initiating SSP's administrative domain or federation of domains, the
   initiating SSP resolves the call routing data by using the Location
   Routing Function (LRF).

   For example, 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 5.1.3.
   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

   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. 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 5.1.6.

   If an im: or pres: URI is retrieved 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. Infrastructure 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 , otherwise the peer continues processing according to the
   next section.

5.1.2. Location Routing Function (LRF)

   The LRF of an Initiating SSP analyzes target address and discovers
   the next hop signaling function (SF) in a peering relationship. The
   resource to determine the SF of the target domain might be provided
   by a third-party as in the assisted-peering case. 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 it.  Note that
   the initiating peer may still forward the call to another SSP for
   PSTN gateway termination by prior arrangement using the routing

   If so, the initiating peer may rewrite the Request-URI to address
   the gateway resource in the target SSP's domain and may forward the
   request on to that SSP using the procedures described in the
   remainder of these steps.

   Alternatively to Request-URI re-writing, the initiating peer may
   populate the Route header with the address of the gateway resource
   in the target SSP's domain and forward the request on to that SSP
   using the procedures described in the remainder of these steps, but
   applied to the Route header. SIP DNS Resolution

   Once a sip: or sips: in an external domain is selected as the
   target, the initiating peer may apply local policy to decide whether
   forwarding requests to the target domain is acceptable.  If so, the
   initiating peer uses the procedures in RFC 3263 [4] Section 4 to
   determine how to contact the receiving peer.  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.

   When communicating with another SSP, entities compliant to this
   document should select a TLS-protected transport for communication
   from the initiating peer to the receiving peer if available.  Note
   that this is a single-hop requirement. SIP Redirect Server

   A SIP Redirect Server may help in resolving the current address of
   the next-hop SF in the target domain.

5.1.3. The 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 signaling function performs the routing of SIP messages. The
   optional termination and re-initiation of calls are performed by the
   signaling path border element (SBE).

   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

   The SF 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 the network to pass Layer 3 related policies [10] Establishing a Trusted Relationship

   Depending on the security needs and trust relationship between SSPs,
   different security mechanism can be used to establish SIP calls.
   These are discussed in the following subsections. TLS connection

   Once a transport, port, and address are found, the initiating SSP
   will open or find a reusable TLS connection to the peer. The
   procedures to authenticate the SSP's target domain is specified in
   [24] IPSec

   In certain deployments, the use of IPSec between the signaling
   functions of the originating and terminating domains can be used as
   a security mechanism instead of TLS. Co-Location

   In this scenario, the SFs are co-located in a physically secure
   location and/or are members of a segregated network. In this case
   messages between the originating and terminating SSPs would be sent
   as clear text. Sending the SIP request

   Once a trust relationship between the peers is established, the
   initiating peer sends the request. TLS

   If the trust relationship was established through TLS, the
   initiating peer can optionally verify and assert the sender's
   identity using the SIP Identity mechanism.

   In addition, new requests should contain a valid Identity and
   Identity-Info header as described in [12].  The Identity-Info header
   must present a domain name that is represented in the certificate
   provided when establishing the TLS connection over which the request
   is sent.  The initiating peer should include an Identity header on
   in-dialog requests as well if the From header field value matches an
   identity the initiating peer is willing to assert.

5.2. Terminating SSP Procedures

5.2.1. The Location Function (LF) Publish ENUM records

   The receiving peer should publish "E2U+SIP" and "E2U+pstn" records
   with sip: or sips: URIs wherever a public carrier ENUM root is
   available. In the event that a public root is not available, a
   publishing to a common ENUM registry with the originating peer will

   This assumes that the receiving peer wants to peer by default. When
   the receiving peer does not want to accept traffic from specific
   initiating peers, it may still reject requests on a call-by-call
   basis. Publish SIP DNS records

   To receive peer requests, the receiving peer must ensure that it
   publishes appropriate NAPTR, SRV, and address (A and/or AAAA)
   records in the LF relevant to the originating peer's SF. Subscribe Notify

   A policy notification function may also be optionally implemented by
   dynamic subscribe, notify, and exchange of policy information and
   feature information among SSPs [21].

5.2.2. Signaling Function (SF) TLS

   When the receiving peer receives a TLS client hello, it responds
   with its certificate.  The target SSP certificate should be valid
   and rooted in a well-known certificate authority. The procedures to
   authenticate the SSP's originating domain are specified in [24].

   The terminating SF verifies that the Identity header is valid,
   corresponds to the message, corresponds to the Identity-Info header,
   and that the domain in the From header corresponds to one of the
   domains in the TLS client certificate. Receive SIP requests

   Once a trust relationship is established, the receiving peer is
   prepared to receive incoming SIP requests.  For new requests (dialog
   forming or not) the receiving peer verifies if the target (request-
   URI) is a domain that for which it is responsible. For these
   requests, there should be no remaining Route header field values.
   For in-dialog requests, the receiving peer can verify that it
   corresponds to the top-most Route header field value.

   The receiving peer may reject incoming requests due to local policy.
   When a request is rejected because the initiating peer is not
   authorized to peer, the receiving peer should respond with a 403
   response with the reason phrase "Unsupported Peer".

5.3. Target SSP Procedures

5.3.1. Signaling Function (SF) TLS

   When the receiving peer receives a TLS client hello, it responds
   with its certificate.  The target SSP certificate should be valid
   and rooted in a well-known certificate authority. The procedures to
   authenticate the SSP's originating domain are specified in [24].

   If the requests should contain a valid Identity and Identity-Info
   header as described in [12] the target SF verifies that the Identity
   header is valid, corresponds to the message, corresponds to the
   Identity-Info header, and that the domain in the From header
   corresponds to one of the domains in the TLS client certificate. Receive SIP requests

   The procedures of the SF of the target SSP are the same as the ones
   described in section with the addition that it might
   establish a connection to another target SSP, and in this case use
   the procedures recommended to an originating SSP (section 5.1).

5.4. Media Function (MF)

   The purpose of the MF is to perform media related functions such as
   media transcoding and media security implementation between two

   An Example of this is to transform a voice payload from one codec
   (e.g., G.711) to another (e.g., EvRC).  Additionally, the MF may
   perform media relaying, media security, privacy, and encryption.

5.5. Policy Considerations

   In the context of the SPEERMINT working group when two SSPs peer,
   there MAY be a desire to exchange peering policy information
   dynamically. There are specifications in progress in the SIPPING
   working group to define policy exchange between an UA and a domain
   [23] and providing profile data to SIP user agents [24] These
   considerations borrow from both.

   Following the terminology introduced in [12], this package uses the
   terms Peering Session-Independent and Session-Specific policies in
   the following context.

     o  Peering Session-Independent policies include Diffserv Marking,
        Policing, Session Admission Control, and domain reachabilities,
        amongst others. The time period between Peering Session-
        Independent policy changes is much greater than the time it
        takes to establish a call.

     o  Peering Session-Specific polices includes supported
        connection/call rate, total number of connections/calls
        available, current utilization, amongst others. Peering
        Session-specific policies can change within the time it takes
        to establish a call.

   Likewise, but orthogonal to session dependency, an SSP may have
   policies that may be peer-dependent or peer-independent.  That is,
   the session-dependent and session-independent policies may by
   further sub-divided and modified by additional controls that depend
   on which peer SSP or federation with which communications is being

6. Call Control and Media Control Deployment Options

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

   Composed or Decomposed:  Addresses the question whether the media
   must flow through the same physical and geographic elements as SIP
   dialogs and sessions.

   Centralized or Distributed:  Addresses the question whether the
   logical and physical interconnections are in one geographical
   location or distributed to multiple physical locations on the SSP's

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

             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 of failure, bottleneck, and complex

   In a decomposed model, SF and MF are implemented in separate peering
   logical elements. SFs are implemented in a proxy and MFs 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 path.

   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 SFs. Generally, a vertical protocol associates the
   relationship between a SF and a MF. This architecture reduces the
   potential of a single point of failure. It 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. Address space considerations

   Peering must occur in a common IP address space, which is defined by
   the federation, which may be entirely on the public Internet, or
   some private address space. The origination or termination networks
   may or may not entirely be in the same address space.  If they are
   not, then a network address translation (NAT) or similar function
   may be needed before the signaling or media is presented correctly
   to the federation. The only requirement is that all associated
   entities across the peering interface are reachable.

8. Security Considerations

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

9. IANA Considerations

   There are no IANA considerations at this time.

10. Acknowledgments

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

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


10.1. Normative References

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

   [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
         4366, April 2006.

   [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.

   [12]  Livingood, J. and R. Shockey, "IANA Registration for an
         Enumservice Containing PSTN Signaling Information", RFC 4769,
         November 2006.

10.2. Informative References

   [13]  Malas, D., "SPEERMINT Terminology", draft-ietf-speermint-
         terminology-16 (work in progress), February 2008.

   [14]  Mule, J-F., "SPEERMINT Requirements for SIP-based VoIP
         Interconnection", draft-ietf-speermint-requirements-04.txt,
         February 2008.

   [15]  Mahy, R., "A Minimalist Approach to Direct Peering", draft-
         mahy-speermint-direct-peering-02.txt, July 2007.

   [16]  Penno, R., et al., "SPEERMINT Routing Architecture Message
         Flows", draft-ietf-speermint-flows-02.txt", April 2007.

   [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-03 (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-03 (work
         in progress), March 2006.

   [21]  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.

   [22]  Hollander, D., Bray, T., and A. Layman, "Namespaces in XML",
         W3C REC REC-xml-names-19990114, January 1999.

   [23]  Burger, E (Ed.), "A Mechanism for Content Indirection in
         Session Initiation Protocol (SIP) Messages", RFC 4483, May

   [24]  Gurbani, V., Lawrence, S., and B. Laboratories, "Domain
         Certificates in the Session Initiation Protocol (SIP)", draft-
         ietf-sip-domain-certs-00 (work in progress), November 2007.

Author's Addresses

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

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

   Sohel Khan, Ph.D.
   Comcast Cable Communications
   Email: sohel_khan@cable.comcast.com

   Daryl Malas
   858 Coal Creek Circle
   Louisville, CO 80027
   Email: d.malas@cablelabs.com

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

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