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

                       SPEERMINT Peering Architecture
                   draft-ietf-speermint-architecture-07
                     draft-ietf-speermint-architecture-08

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Abstract

   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 Architecture...............................4
   4. Procedures of Interdomain SSP Session Establishment............6
   5. Recommended SSP Procedures.....................................8 Procedures.....................................7
      5.1. Originating SSP Procedures................................8 Procedures................................7
         5.1.1. The Look-Up Function (LUF)...........................8 (LUF)...........................7
            5.1.1.1. Target address analysis.........................8 analysis.........................7
            5.1.1.2. End User ENUM Lookup................................9 Lookup............................8
            5.1.1.3. Infrastructure ENUM lookup......................9 lookup......................8
         5.1.2. Location Routing Function (LRF).....................10 (LRF)......................8
            5.1.2.1. Routing Table..................................10
            5.1.2.2. SIP DNS Resolution.............................10 Resolution..............................8
            5.1.2.2. Routing Table...................................9
            5.1.2.3. SIP Redirect Server............................11 Server.............................9
         5.1.3. The Signaling Function (SF).........................11 (SF)..........................9
            5.1.3.1. Establishing a Trusted Relationship............11 Relationship.............9
            5.1.3.2. Sending the SIP request........................12 request........................10
      5.2. Terminating SSP Procedures...............................12 Procedures...............................10
         5.2.1. The Location Function (LF)..........................12 (LF)..........................10
            5.2.1.1. Publish ENUM records...........................12 records...........................10
            5.2.1.2. Publish SIP DNS records........................13 records........................11
            5.2.1.3. Subscribe Notify...............................13 Notify...............................11
         5.2.2. Signaling Function (SF).............................13 (SF).............................11
            5.2.2.1. TLS............................................13 TLS............................................11
            5.2.2.2. Receive SIP requests...........................13 requests...........................11
      5.3. Target SSP Procedures....................................14 Procedures....................................12
         5.3.1. Signaling Function (SF).............................14 (SF).............................12
            5.3.1.1. TLS............................................14 TLS............................................12
            5.3.1.2. Receive SIP requests...........................14 requests...........................12
      5.4. Media Function (MF)......................................14 (MF)......................................12
      5.5. Policy Considerations....................................14 Considerations....................................12
   6. Call Control and Media Control Deployment Options.............15 Options.............13
   7. Address space considerations..................................17 considerations..................................14
   8. Security Considerations.......................................17 Considerations.......................................15
   9. IANA Considerations...........................................17 Considerations...........................................15
   10. Acknowledgments..............................................17 Acknowledgments..............................................15
   11. References...................................................18 References...................................................16
      11.1. Normative References....................................18 References....................................16
      11.2. Informative References..................................19 References..................................17
   Author's Addresses...............................................20
   Intellectual Property Statement..................................20
   Disclaimer of Validity...........................................21 Addresses...............................................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), it's architecture, its 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] [14] and Terminology [12] [13] 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],
   [13], 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 this document, the SIP
   providers directly peer key words "MUST", "MUST NOT", "REQUIRED",   "SHALL",
   "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are
   to each other or through Layer 3 transit
   network be interpreted as per use case of [16].

   Note that described in [RFC2119].

2. Network Context

   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        |
                           |

                           +-------------------+
                           |                   |
                           |     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
        policies,

     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 following 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 routed.

   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.

   The Signaling Function (SF): Purpose is to perform (SF) provides 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).

   The Media Function (MF): Purpose is to perform (MF) provides media related function functions such as media transcoding
   transcoding, topology hiding and media security implementation between two SIP providers.
   SSPs.

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

5. Recommended SSP

4. Procedures of Interdomain SSP Session Establishment

   This section describes the functions in more detail and provides
   some recommendations on the role they would play document assumes that in order for a SIP call in session to be established from a
   Layer 5 peering scenario.

   Some of UA
   in the information originating SSP's network to an UA in the chapter is Target SSP's network the
   following steps are taken:

     1. analyze the target address.

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

     2. determine the target SSP (LUF)

     3. determine the SF next-hop in the target SSP (LRF)

     4. enforce authentication and potentially other policies

     5. determine of the UA

     6. establish the session,

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

     8. terminate the session (BYE)

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

   In the case the target SSP changes, then steps 1-4 would be repeated. This is
   reflected in Figure 2 that shows the target SSP with its own peering functions.

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 section 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]. Data.

5.1.1.1. Target address analysis

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

   If the target address does not represent a resource inside the
   initiating originating
   SSP's administrative domain or federation of domains, the
   initiating originating 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
   originating SSP follows the procedures in [8].  If the highest priority
   supported URI scheme is sip: or sips:, sips: the
   initiating peer originating SSP 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 originating SSP skips to SIP DNS
   resolution in Section 5.1.2.2. 5.1.2.1.

   If the target address corresponds to a specific E.164 address, the
   peer SSP 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 SSP has an E.164 address, it can use ENUM.

5.1.1.2. End User ENUM Lookup

   If an external E.164 address is the target, the initiating peer originating SSP consults the
   public "User ENUM" rooted at e164.arpa, according to the procedures described
   in RFC 3761.  The peer SSP must query for the "E2U+sip" enumservice as described in
   RFC 3764 [11], but MAY check for other enumservices.  The initiating peer originating SSP MAY
   consult a cache or alternate representation of the ENUM data rather than actual
   DNS queries.  Also, the peer SSP may skip actual DNS queries if the
   initiating peer originating SSP
   is sure that the target address country code is not represented in e164.arpa.
   If a sip: or sips: URI is chosen the peer SSP skips to Section 5.1.6.

   If an im: or pres: URI is retrieved chosen for based on an "E2U+im" [10] [8] or "E2U+pres" [9]
   enumserver, the peer SSP follows the procedures for resolving these URIs to URIs for
   specific protocols such a SIP or XMPP as described in the previous section.

5.1.1.3. Infrastructure ENUM lookup

   Next the initiating peer checks

   An originating SSP may check for a carrier-of-record in a carrier an Infrastructure ENUM
   domain according to the procedures described in [12].  As in the previous step,
   the peer SSP may consult a cache or alternate representation of the ENUM data in
   lieu of actual DNS queries.  The
   peer SSP 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 SSP skips to Section
   5.1.2.2.
   5.1.2.1. , otherwise the peer SSP continues processing according to the next
   section.

5.1.2. Location Routing Function (LRF)

   The LRF of an Initiating Originating SSP analyzes target address and target domain
   identified by the LUF, 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.

5.1.2.1. Routing Table

   If there SIP DNS Resolution

   Once a sip: or sips: in an external domain 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
   table.

   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.

5.1.2.2. SIP DNS Resolution

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

5.1.2.2. Routing Table

   If there are no End User ENUM records and the Originating SSP cannot discover
   the carrier-of-record or if the Originating SSP cannot reach the carrier-of-
   record via SIP peering, the Originating SSP may deliver the call to the PSTN or
   reject it.  Note that this is a single-hop requirement. the originating SSP may forward the call to another SSP
   for PSTN gateway termination by prior arrangement using the routing table.

   If so, the originating SSP rewrites 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.

5.1.2.3. SIP Redirect Server

   A SIP Redirect Server may help using 3XX SIP Redirect is another option in resolving the current address of
   the
   next-hop SF in of 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 messages as well
   as 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 may be performed by the signaling path border element
   Session 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 encryption.

   The SF of a SBE 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]

5.1.3.1. Establishing a Trusted Relationship

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

5.1.3.1.1. TLS connection

   Once a transport, port, and address are found, the initiating originating 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]

5.1.3.1.2. 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.

5.1.3.1.3. 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.

5.1.3.2. Sending the SIP request

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

5.1.3.2.1. TLS

   If the trust relationship was established through TLS, the
   initiating peer originating SSP can
   optionally verify and assert the sender's senders 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 originating SSP should include
   an Identity header on in-dialog requests as well if the From header field value
   matches an identity the initiating peer originating SSP is willing to assert.

5.1.3.1.3. 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.

5.1.3.1.4. 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.

5.1.3.2. Sending the SIP request

   Once a trust relationship between the peers is established, the originating SSP
   sends the request.

5.2. Terminating SSP Procedures

5.2.1. The Location Function (LF)

5.2.1.1. Publish ENUM records

   The receiving peer SSP should publish "E2U+SIP" participate by publishing "E2U+sip" and "E2U+pstn"
   records with sip: or sips: URIs wherever a public carrier Infrastructure 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
   suffice.  This assumes that the receiving peer SSP wants to peer by default. When
   the receiving peer SSP does not want to accept traffic from specific
   initiating peers, originating
   SSPs, it may still reject requests on a call-by-call basis.

5.2.1.2. Publish SIP DNS records

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

5.2.1.3. Subscribe Notify

   A policy notification

   Policies 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)

5.2.2.1. TLS

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

   The terminating SF of the Target SSP 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.

5.2.2.2. Receive SIP requests

   Once a trust relationship is established, the receiving peer Target SSP is prepared to receive
   incoming SIP requests.  For new requests (dialog forming or not) the receiving peer
   SSP verifies if the target (request-
   URI) (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 SSP can verify that it
   corresponds to the top-most Route header field value.

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

5.3. Target SSP Procedures

5.3.1. Signaling Function (SF)

5.3.1.1. TLS

   When the receiving peer SSP receives a TLS client hello, it responds with its
   certificate.  The target SSP Target SSP's 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] [24] 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.

5.3.1.2. Receive SIP requests

   The procedures of the SF of the target SSP are the same as the ones described
   in section 5.2.2.2 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 SS (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 SSPs.

   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 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

   These policies that may can be peer-dependent SSP dependent or peer-independent.  That is, independent, creating the session-dependent and session-independent policies may by
   further sub-divided and modified by additional controls that depend
   on which peer following
   peering policy definition:

     o SSP Independent or federation with which communications is being
   established. Dependent
        Session dependent                                         Session
        independent

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 network.

   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)|~~~~| |<~~~| (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 one-element solves
   all peering issues. Disadvantage examples of this architecture are single point
   of failure, bottleneck, and complex scalability.

   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 SSP 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 significant portion of this draft is taken from [14] with
   permission from the author R. Mahy. The other important contributor
   is Otmar Lendl. Special thanks to Jim McEachern for detailed comments and
feedback.

11. References

10.1.

11.1. 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.

11.2. Informative References

   [13]  Malas, D., "SPEERMINT Terminology", draft-ietf-speermint-
         terminology-16 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 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
         2006
   [24]  Gurbani, V., Lawrence, S., and B. Laboratories, "Domain Certificates in
         the Session Initiation Protocol (SIP)", draft-
         ietf-sip-domain-certs-00 draft-ietf-sip-domain-certs-00
         (work in progress), November 2007.

Author's Addresses

   Adam Uzelac
   Global Crossing
   Rochester, NY - USA
   Email: adam.uzelac@globalcrossing.com

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

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

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

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

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

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