Speermint Working Group                                        R. Penno
Internet Draft                                         Juniper Networks
Intended status: Informational                                 D. Malas
Expires: January August 2008                                            Level 3
                                                                S. Khan
                                                              A. Uzelac
                                                        Global Crossing
                                                         August 10, 2007
                                                      February 24, 2008

                      SPEERMINT Peering Architecture

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Copyright Notice

   Copyright (C) The IETF Trust (2007). (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",
   document are to be interpreted as described in RFC-2119[1] RFC 2119[1]

Table of Contents

   1. Introduction...................................................3
   2. Network Context................................................3 Context................................................4
   3. Procedures.....................................................6 Procedures.....................................................5
   4. Reference SPEERMINT Architecture...............................6
   5. Peer Function Examples.........................................8
      5.1. The Location Function (LF) of an Initiating Provider......8
         5.1.1. Target address analysis..............................8
         5.1.2. User ENUM Lookup.....................................9
         5.1.3. Carrier ENUM lookup.................................10
         5.1.4. Routing Table.......................................10
         5.1.5. SIP DNS Resolution..................................10
         5.1.6. SIP Redirect Server.................................11
      5.2. The Location Function (LF) of a Receiving Provider.......11
         5.2.1. Publish ENUM records................................11
         5.2.2. Publish SIP DNS records.............................11
         5.2.3. Subscribe Notify....................................11
      5.3. Signaling Function (SF)..................................11
      5.4. The Signaling Function (SF) of an Initiating Provider....12
         5.4.1. Setup TLS connection................................12
         5.4.2. IPSec...............................................12
         5.4.3. Co-Location.........................................13 Co-Location.........................................12
         5.4.4. Send the SIP request................................13 request................................12
      5.5. The Signaling Function (SF) of an Initiating Provider....14
         5.5.1. Verify TLS connection...............................14
         5.5.2. Receive SIP requests................................14
      5.6. Media Function (MF)......................................15
      5.7. Policy Considerations....................................15
   6. Call Control and Media Control Deployment Options.............16
   7. Address space considerations..................................18 considerations..................................17
   8. Security Considerations.......................................18 Considerations.......................................17
   9. IANA Considerations...........................................18
   10. Acknowledgments..............................................18
   11. References...................................................19
      11.1. Normative References....................................19
      11.2. Informative References..................................20
   Author's Addresses...............................................21
   Intellectual Property Statement..................................21
   Disclaimer of Validity...........................................22

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
   real-time communications (Voice and Multimedia) IP SIP [3] Service provider provider's (SSP) network.

   This architecture allows the interconnection of two service providers SSPs in layer 5
   peering as defined in the SPEERMINT Requirements [13] and
   Terminology [12] documents for the purpose SIP-based voice and
   multimedia traffic. 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]. [12], so the reader should be familiar with all the terms
   defined there.

2. Network Context

   Figure 1 shows an example network context. Two SIP providers SSPs can form a Layer
   5 peer peering over either the public Internet or private Layer 3 Layer3
   networks. In addition, two or more providers may form a SIP (Layer
   5) federation [17] [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 Service Provider SSP across the public Internet

     o  Service Provider  SSP to Service Provider SSP across the public Internet

     o  Enterprise to enterprise across a private Layer 3 network

     o  Enterprise to Service Provider SSP across a private Layer 3 network

     o  Service Provider  SSP to Service Provider SSP across a private Layer 3 network

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

                           |                   |
                           |     Public        |
                           |     Peering Function       |
                           |       or     Function      |
                           |     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   Private   --         +-----------+
                           /     Provider     Network    \
                           |     Private    (Layer 3)    |
                           \     Network                /
      +-----------+         --  (Layer 3)            --          +-----------+
        |Service    |-----------\           /-----------|Service
        |Provider  SSP G    |-----------\           /-----------|   SSP H   |
      |           |            --       --            |Provider H            |           |
      +-----------+               \____/              +-----------+
                           |     Private       |
                           |       SIP         |
                           |     Peering Function       |
                           |       or                   |
                             |Federation Function|

                      Figure 1: SPEERMINT Network Context

3. Procedures

   This document assumes that a call from an a UAC end user in the
   peer peer's network goes through the following steps to
   establish a call to an end
   user a UAS in the receiving peer: peer's network:

     1. The analysis of a target address.

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

     2. the discovery of the receiving peering point address,

     3. the enforcement of authentication and potentially other policy,

     4. the discovery of end user address, the UAS,

     5. the routing of SIP messages,

     6. the session establishment,

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

     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. SSPs.

                                | DNS, |
                    +---------->| Db,  |---------+  |<---------+
                    |           | etc  |          |
                    |           +------+          |
                    |                             |
               ---------------              ---------------
              ------|--------              -------|-------
             /      v        \            /       v       \
            |    +--LUF-+     |          |     +--LUF-+    |
            |    |      |     |          |     +------+     |      |     +------+    |
            |    | DNS,      |     |          |     | DNS,      |    |
            |    | Db,      |     |          |     | Db,  |    |
             |     | etc  |    |          |     | etc      |    |
            |    +------+     |          |     +------+    |
            |       |         |          |        |        |
            |       |         |             +---SF--+  +---SF--+             |          |        |        |
            |       v         |          |        v        |
            |  SBE  |  |  SBE    +--LRF-+     |          |     +--LRF-+    | Originating
            |    |      |     | Terminating          |     |             +---SF--+  +---SF--+      |    |    Domain
            |    |       Domain      |     |             +---MF--+  +---MF--+          |     |      SSP      |    |
            |    |    SSP      |     |          |  DBE     |      |  DBE    |
            |    +------+     |          |     +------+    |
            |      \          |          |          /      |             +---MF--+  +---MF--+
            |       `.        |          |         /       |
            |         \       |           +----LF---+  +----LF---+          |       .'        |     +-LF--|----+
            |          `. +---SF--+  +---SF--+  /          |    +----|--LS-+
            |            \|       |  |       | /           |
            |             |  SBE  |  |  SBE  |             |
            | Originating | SM       |  | LS       |  Target     | LS
            |             +---SF--+  +---SF--+             |  SM
            |    SSP          |          |       SSP       |
            |             +---MF--+  +---MF--+             |
            |             |       |  |       |             |
            |             |     +----|----+  +----|----+  DBE  |  |  DBE  |     +----------+|          |+----------+             |
            |             |       |  |       |             |
            |             +---MF--+  +---MF--+             |
             \               /            \               /
              ---------------              ---------------
                Figure 2: Reference SPEERMINT Architecture

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

   o  Location

   The Look-Up Function (LF): Purpose is (LUF) provides a mechanism for determining for
   a given request the target domain to develop Session
      Establishment Data (SED) by discovering which the Signaling request should be

   The Location Routing Function
     (SF) and (LRF) determines for the end user's reachable host (IP address target domain
   of a given request the location of the SF in that domain and port).
   optionally develops other SED required to route the request to that

   Location Function (LF): The
      location function Location functions is distributed across composed of the Location Server (LS)
   LUF and Session Manager (SM).

   o LRF functions

   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). The signaling function is located within the
      Signaling Path Border Element (SBE)


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

   The media function is located within
      the Data Path Border Element (DBE).

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

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]. [14] and is put
   here for continuity purposes.

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

   Purpose is to determine the SF of the target domain of a given
   request and optionally develop Session Establishment Data (SED) [12] by
   discovering the Signaling Function (SF), and end user's reachable
   host (IP address and host).
   [12]. The LF of an Initiating provider SSP analyzes target address and
   discovers the next hop signaling function (SF) in a peering
   relationship using DNS, SIP Redirect Server, or the Look-Up Function. The resource to determine
   the SF of the target domain might be provided by a
   functional equivalent database. third-party as in
   the assisted-peering case.

5.1.1. Target address analysis
   When the initiating provider SSP receives a request to communicate, the
   initiating provider it
   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; SSP; thus, outside the scope of SPEERMINT.
   Note that the peer 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 peer's SSP's administrative domain or federation of domains, the
   initiating provider SSP 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.

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 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
   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. it.  Note that
   the initiating peer MAY still sends forward the call to another provider SSP for
   PSTN gateway termination by prior arrangement using a the routing

   If so, the initiating peer rewrites the Request-URI to address the
   gateway resource in the target provider's SSP's domain and MAY forward the
   request on to that provider SSP 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 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 [6] [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 a public external peer, entities compliant
   to this document MUST only select a TLS-protected transport for
   communication from the initiating peer to the receiving peer.  Note
   that this is a single-hop requirement.  Either peer MAY insist on
   using a sips: URI which asserts that each hop is TLS-protected, but
   this document does not require protection over each hop.

5.1.6. SIP Redirect Server

   A SIP Redirect Server may help in resolving the 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 When the receiving peer does not want to accept
   traffic from specific initiating peers, it MAY still reject requests
   on a case-by-case call-by-call 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 LF relevant SIP server. to the peer's SF.

5.2.3. Subscribe Notify


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

5.3. 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 perform the routing of SIP messages are performed by SIP proxies. messages. The
   optional termination and re-initiation of calls are performed by
   B2BUA. 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 signaling function 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 layer to pass Layer 3 related policies [10]

5.4. The Signaling Function (SF) of an Initiating Provider

5.4.1. Setup TLS connection

   Once a transport, port, and address are found, the initiating peer SSP
   will open or find a reusable TLS connection to the peer.  The
   initiating provider MUST verify the server certificate which that SHOULD
   be rooted in a well-known certificate authority.  The initiating
   provider SSP
   MUST be prepared to provide a TLS client certificate upon request
   during the TLS handshake.  The client certificate MUST contain a DNS
   or URI choice type in the subjectAltName 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 well-known certificate

   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.

5.4.2. 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.

5.4.3. Co-Location

   In this scenario the signaling functions 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 domains SSPs would be sent as clear text.

5.4.4. Send the SIP request

   Once a TLS connection between the peers is established, the
   initiating peer sends the request.  When sending some requests, the
   initiating peer MUST verify and assert the senders identity using
   the SIP Identity mechanism.

   The domain name in the URI of the From: header MUST be a domain
   which was present in the certificate presented provided when establishing the
   TLS connection for this request, even if the user part has an
   anonymous value.  If the From header contains the user URI parameter
   with the value of "phone", the user part of the From header URI MUST
   be a complete and valid tel: URI [9] telephone-subscriber
   production, and SHOULD be a global-number.  For example, the
   following are all
   acceptable, acceptable and the first three are encouraged:

      From: "John Doe" <john.doe@example.net> john.doe@example.net

      From: "+12125551212" <+12125551212@example.net;user=phone>

      From: "Anonymous" <anonymous@example.net>

      From: <4092;phone-context=+12125554000@example.net;user=phone>

      From: "5551212" <5551212@example.net>

      The following are not acceptable:

      From: "2125551212" <2125551212@example.net;user=phone>

      From: "Anonymous" <anonymous@anonymous.invalid>

   In addition, for new dialog-forming requests and non-dialog-forming
   requests, the request MUST contain a valid Identity and
   Identity-Info header as described in [12].  The Identity-Info header
   must present a domain name which that is represented in the certificate presented
   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.

   The initiating peer MAY include any SIP option-tags in Supported,
   Require, or Proxy-Require headers according to procedures in
   standards-track SIP extensions.  Note however that the initiating
   peer MUST be prepared to fallback to baseline SIP functionality as
   defined by the mandatory-to-implement features of RFC 3261, RFC 3263,
   3263,and RFC 3264 [7], except that peers implementing this
   specification MUST implement SIP over TLS using the sip: URI scheme,
   the SIP Identity header, and RFC 4320 [10] non-INVITE transaction

5.5. The Signaling Function (SF) of an Initiating Target Provider

5.5.1. Verify TLS connection

   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 MUST request and verify the client certificate during
   the TLS handshake.

   Once the initiating peer has been authenticated, the receiving peer
   can authorize communication from this peer based on the domain name
   of the peer and the root of its certificate.  This allows two
   authorization models to be used, together or separately.  In the
   domain-based model, the receiving peer can allow communication from
   peers with some trusted administrative domains which that use general-
   purpose certificate authorities, without explicitly permitting all
   domains with certificates rooted in the same authority.  It also
   allows a certificate authority (CA) based model where every domain
   with a valid certificate rooted in some list of CAs is automatically

5.5.2. Receive SIP requests

   Once a TLS connection is established, the receiving peer is prepared
   to receive incoming SIP requests.  For new dialog-forming requests
   and out-of-dialog requests, (dialog forming
   or not) the receiving peer verifies that the target (request-URI) is
   a domain which that for which it is responsible.
   (For For these requests, there
   should be no remaining Route header field
   values.) values. Next the receiving
   verifies that the Identity header is valid, corresponds to the
   message, and 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.

   For in-dialog requests, the receiving peer can verify that it
   corresponds to the top-most Route header field value.  The peer also
   validates any Identity header if present.

   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".

5.6. Media Function (MF)


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

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

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

5.7. Policy Considerations

   In the context of the SPEERMINT working group when two Layer 5
   devices (e.g., SIP Proxies) SSPs peer,
   there is MAY be a need desire to exchange peering policy information. 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.

   These policies can be Peer dependent or independent, creating the
   following peering policy tree definition:

     o  Peer Independent
        Session dependent
        Session independent
     o  Peer Dependent
        Session dependent
        Session independent

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
   must flow through the same physical and geographic nodes elements as the
   call signaling, SIP
   dialogs and sessions.

   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 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)|~~~~| 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, bottle neck, bottleneck, and complex

   In a decomposed model, SF and MF are implemented in separate peering
   logical elements. Signaling functions SFs are implemented in a proxy and
   media functions 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 peering proxies. Generally, a vertical protocol
   associates the relationship between a SF and a MF. This architecture
   reduces the potential of a single point of failure. This architecture, 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 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 that same address space.  If they are
   not, then a network address translation (NAT) or similar 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 significant portion of this draft is taken from [14] with
   permission from the author R. Mahy. The other important contributor
   is Otmar Lendl.

11. References

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.

11.2. Informative References

   [13]  Meyer,  Malas, D., "SPEERMINT Terminology", draft-ietf-speermint-
         terminology-16 (work in progress), Junly 2007. February 2008.

   [14]  Mule, J-F., "SPEERMINT Requirements for SIP-based VoIP
         Interconnection", draft-ietf-speermint-requirements-02.txt,
         July draft-ietf-speermint-requirements-03.txt,
         November 2007.

   [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]  Lee, Y., "Session Peering Use Case for Cable", draft-lee-
         speermint-use-case-cable-01.txt, June, 2006.

   [18]  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.

   [21] RFC 5028

   [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-01 (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

Author's Addresses

   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
   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

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