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SPEERMING Working Group                                   A. Uzelac, Ed.
Internet-Draft                                           Global Crossing
Intended status: Informational                               Y. Lee, Ed.
Expires: February 27, 2009                                 Comcast Cable
                                                         August 26, 2008


                       VoIP SIP Peering Use Cases
           draft-ietf-speermint-voip-consolidated-usecases-10

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   This Internet-Draft will expire on February 27, 2009.

Abstract

   This document depicts many common Voice over IP (VoIP) use cases for
   Session Initiation Protocol (SIP) Peering.  These use cases are
   categorized into static and on-demand, and then further sub-
   categorized into direct and indirect.  These use cases are not an
   exhaustive set, but rather the most common use cases deployed today.
   In describing use cases, the intent is descriptive, not prescriptive.








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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3

   3.  Reference Architecture . . . . . . . . . . . . . . . . . . . .  3

   4.  Contexts of Use Cases  . . . . . . . . . . . . . . . . . . . .  4

   5.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     5.1.  Static Peering Use Cases . . . . . . . . . . . . . . . . .  5
     5.2.  Static Direct Peering Use Case . . . . . . . . . . . . . .  5
       5.2.1.  Administrative characteristics . . . . . . . . . . . . 10
       5.2.2.  Options and Nuances  . . . . . . . . . . . . . . . . . 10
     5.3.  Static Direct Peering Use Case - Assisted LUF and LRF  . . 11
       5.3.1.  Administrative Characteristics . . . . . . . . . . . . 12
       5.3.2.  Options and Nuances  . . . . . . . . . . . . . . . . . 13
     5.4.  Static Indirect Peering Use Case - Assisted LUF and LRF  . 13
       5.4.1.  Administrative characteristics . . . . . . . . . . . . 19
       5.4.2.  Options and Nuances  . . . . . . . . . . . . . . . . . 19
     5.5.  Static Indirect Peering Use Case . . . . . . . . . . . . . 20
       5.5.1.  Administrative characteristics . . . . . . . . . . . . 20
       5.5.2.  Options and Nuances  . . . . . . . . . . . . . . . . . 21
     5.6.  On-demand Peering Use Cases  . . . . . . . . . . . . . . . 21
       5.6.1.  Administrative characteristics . . . . . . . . . . . . 21
       5.6.2.  Options and Nuances  . . . . . . . . . . . . . . . . . 21

   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 22

   7.  Security and Privacy Considerations  . . . . . . . . . . . . . 22

   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22

   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 22
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 23

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
   Intellectual Property and Copyright Statements . . . . . . . . . . 26











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1.  Introduction

   This document attempts to capture Voice over IP (VoIP) use cases for
   Session Initiation Protocol (SIP) [RFC3261] based peering.  These use
   cases will assist in identifying requirements and future works for
   VoIP Peering using SIP.

   Only use cases related to VoIP are considered in this document.
   Other real-time SIP communications use cases, like Instant Messaging
   (IM) and presence are out of scope for this document.  In describing
   use cases, the intent is descriptive, not prescriptive.

   The use cases contained in this document attempts to be as
   comprehensive as possible, but should not be considered the exclusive
   set of use cases.


2.  Terminology

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

   This document also uses terms defined in
   [I-D.ietf-speermint-terminology].  Please refer to it for
   definitions.


3.  Reference Architecture

   The diagram below provides the reader with a context for the VoIP use
   cases in this document.  Terms such as SSP, LUF, LRF, SBE and DBE are
   defined in [I-D.ietf-speermint-terminology].

   Originating SSP (O-SSP) is the SSP originating a request.
   Terminating SSP (T-SSP) is the SSP terminating the request
   originating from O-SSP.  Assisted LUF and LRF Provider offers LUF and
   LRF services to O-SSP.  Indirect SSP (I-SSP) is the SSP providing
   indirect peering service(s) to O-SSP to connect to T-SSP.












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    +--------------------+------------------------+--------------------+
    |  Originating SSP   |  Assisted LUF and LRF  |  Terminating SSP   |
    |     Domain         |    Provider Domain     |      Domain        |
    |                    |                        |                    |
    |  +-----+  +-----+  |    +------+ +------+   |  +-----+  +-----+  |
    |  |O-LUF|  |O-LRF|  |    |A-LUF | | A-LRF|   |  |T-LUF|  |T-LRF|  |
    |  +-----+  +-----+  |    +------+ +------+   |  +-----+  +-----+  |
    |                    |                        |                    |
    | +-------+ +-----+  +------------------------+  +-----+ +-------+ |
    | |O-Proxy| |O-SBE|  |  Indirect SSP Domain   |  |T-SBE| |T-Proxy| |
    | +-------+ +-----+  |                        |  +-----+ +-------+ |
    |                    |    +-----+  +-----+    |                    |
    |    +---+  +-----+  |    |O-SBE|  |O-DBE|    |  +-----+  +---+    |
    |    |UAC|  |O-DBE|  |    +-----+  +-----+    |  |T-DBE|  |UAS|    |
    |    +---+  +-----+  |                        |  +-----+  +---+    |
    |                    |                        |                    |
    +--------------------+------------------------+--------------------+

                             General Overview

                                 Figure 1

   Note that in Figure 1 - some elements defined are optional in many
   use cases.


4.  Contexts of Use Cases

   Use cases are sorted into two general groups: Static and On-demand
   Peering [I-D.ietf-speermint-terminology].  Each group can be further
   sub-divided into Direct Peering and Indirect Peering
   [I-D.ietf-speermint-terminology].  Although there may be some overlap
   among the use cases in these categories, there are different
   requirements between the scenarios.  Each use-case must specify a
   basic set of required operations to be performed by each member when
   peering.

   These can include:

   o  Peer Discovery - Peer discovery via a Look-Up Function (LUF) to
      determine the Session Establishment Data (SED) of the request.  In
      VoIP use cases, a request normally contains a phone number.  The
      O-SSP will input the phone number to the LUF and the LUF will
      normally return a SIP URI [RFC3261] which contains a domain name.

   o  Next Hop Routing Determination - Resolving the SED information is
      necessary to route the request to the T-SSP.  The LRF is used for
      this determination.  The O-SSP may also use the standard procedure



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      defined in [RFC3263] to discover the next hop.

   o  Call setup - SSPs that are interconnecting to one another may also
      define specifics on what SIP features need to be used when
      contacting the next hop in order to a) reach the next hop at all
      and b) to prove that the sender is a legitimate peering partner.

      Examples: hard-code transport (TCP/UDP/TLS), non-standard port
      number, specific source IP address (e.g. in a private Layer-3
      network), which TLS client certificate [RFC3546] to use, and other
      authentication schemes.

   o  Call reception - This step serves to ensure that the type of
      relationship (static or on-demand, indirect or direct) is
      understood and acceptable.  For example, the receiving SBE needs
      to determine whether the INVITE it received really came from a
      trusted member possibly via an access control list entry.



5.  Use Cases

   Please note there are intra-domain message flows within the use cases
   to serve as supporting background information.  Only inter-domain
   communications are germane to Speermint.

5.1.  Static Peering Use Cases

   Static Peering [I-D.ietf-speermint-terminology] describes the use
   case when two SSPs form a peering relationship with some form of
   association established prior to the exchange of traffic.  Pre-
   association is a prerequisite to static peering.  Static peering is
   used in cases when two peers want a consistent and tightly controlled
   approach to peering.  In this scenario, a number of variables, such
   as an identification method (remote proxy IP address) and QoS
   parameters, can be defined upfront and known by each SSP prior to
   peering.

5.2.  Static Direct Peering Use Case

   This is the simplest form of a peering use case.  Two SSPs negotiate
   and agree to establish a SIP peering relationship.  The peer
   connection is statically configured and is direct between the
   connected SSPs.  The peers may exchange interconnection parameters
   such as DSCP [RFC2474] policies, the maximum number of requests per
   second and proxy location prior to establishing the interconnection.
   Typically, the T-SSP only accepts traffic originating directly from
   the trusted peer.



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         +--------------------+             +---------------------+
         |        O-SSP       |             |        T-SSP        |
         |       +-----+      |             |       +-----+       |
         |       |O-LUF|      |             |       |T-LUF|       |
         |       |O-LRF|      |             |      /|T-LRF|       |
         |      /+-----+\     |             |     / +-----+       |
         |    (2)     (4,5,6) |             |    /                |
         |    /           \   |             |   /(8,9)            |
         |+-------+     +-----+             +-----+      +-------+|
         ||O-Proxy|-(3)-|O-SBE+-----(7)-----+T-SBE|-(10)-|T-Proxy||
         |+-------+     +-----+             +-----+      +-------+|
         |    |               |             |                |    |
         |   (1)              |             |               (11)  |
         |    |               |             |                |    |
         | +-----+      +-----+             +-----+       +-----+ |
         | | UAC +======|O-DBE+=====(12)====+T-DBE|=======+ UAS | |
         | +-----+      +-----+             +-----+       +-----+ |
         +--------------------+             +---------------------+
              example.com                         example.net


                      Static Direct Peering Use Case

                                 Figure 2

   The following is a high-level depiction of the use case:

   1.   UAC initiates a call via SIP INVITE to O-Proxy.  O-Proxy is the
        home proxy for UAC.

         INVITE sip:+19175550100@example.com;user=phone SIP/2.0
         Via: SIP/2.0/TCP client.example.com:5060
           ;branch=z9hG4bK74bf9
         Max-Forwards: 10
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=12345
         To: Bob <sip+19175550100@example.com;user=phone>
         Call-ID: abcde@client.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@client.example.com;user=phone
           ;transport=tcp>

        Note that UAC inserted its Fully Qualified Domain Name (FQDN) in
        the VIA and CONTACT headers.  This example assumes that UAC has
        its own FQDN.  In the deployment where UAC does not have its own
        FQDN, UAC may insert IP address into the headers.





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   2.   UAC only knows UAS's TN but not UAS's domain.  It appends its
        own domain to generate the SIP URI in Request-URI and To header.
        O-Proxy checks the Request-URI's domain and discovers that the
        UAS's domain is internal but the TN is unknown to O-Proxy.  So,
        O-Proxy queries LUF for SED information from a routing database.
        In this example, the LUF is an ENUM [RFC3761] database.  The
        ENUM entry looks similar to this:

          $ORIGIN 0.0.1.0.5.5.5.7.1.9.1.e164.arpa.
          IN NAPTR (
            10
            100
            "u"
            "E2U+SIP"
            "!^.*$!sip:+19175550100@example.net!"
            . )

        This SED data can be provisioned by O-SSP or populated by the
        T-SSP.

   3.   O-Proxy examines the SED and discover the domain is external.
        Given the O-Proxy's internal routing policy, O-Proxy decides to
        use O-SBE to reach T-SBE.  O-Proxy routes the INVITE request to
        O-SBE and adds a Route header which contains O-SBE.

         INVITE sip:+19175550100@example.net;user=phone SIP/2.0
         Via: SIP/2.0/TCP o-proxy.example.com:5060
           ;branch=z9hG4bKye8ad
         Via: SIP/2.0/TCP client.example.com:5060
           ;branch=z9hG4bK74bf9;received=192.0.1.1
         Max-Forwards: 9
         Route: <sip:o-sbe1.example.com;lr>
         Record-Route: <sip:o-proxy.example.com;lr>
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=12345
         To: Bob s<ip+19175550100@example.com;user=phone>
         Call-ID: abcde@client.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@client.example.com;user=phone
           ;transport=tcp>

   4.   O-SBE receives the requests and pops the top entry of the Route
        header which contains "o-sbe1.exapmle.com".  O-SBE examines the
        Request-URI and does a LRF for "example.net".  In this example,
        the LRF is a NAPTR DNS query [RFC3403] of the domain name.
        O-SBE receives a NAPTR response form LRF.  The response looks
        similar to this:




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          IN NAPTR (
            50
            50
            "S"
            "SIP+D2T"
            ""
            _sip._tcp.t-sbe.example.net. )

          IN NAPTR (
            90
            50
            "S"
            "SIP+D2U"
            ""
            _sip._udp.t-sbe.example.net. )

   5.   Given the lower order for TCP in the NAPTR response, O-SBE
        decides to use TCP as transport protocol, so it sends a SRV DNS
        query for the SRV record [RFC2782] for "_sip._tcp.t-
        sbe.example.net".

        ;;     priority  weight   port  target
        IN SRV 0         2        5060  t-sbe1.example.net.
        IN SRV 0         1        5060  t-sbe2.example.net.

   6.   Given the higher weight for "t-sbe1.example.net", O-SBE sends an
        A record DNS query for "t-sbe1.example.net." to get the A
        record:

          ;; DNS ANSWER
          t-sbe1.example.net.   IN A   192.2.0.100
          t-sbe1.example.net.   IN A   192.2.0.101

   7.   O-SBE sends the INVITE to T-SBE.  O-SBE is the egress point to
        the O-SSP domain, so it should ensure subsequent mid-dialog
        requests traverse via itself.  If O-SBE chooses to act as Back-
        to-Back User Agent (B2BUA) [RFC3261], it will terminate the call
        and generate a new back-to-back INVITE request.  If O-SBC
        chooses to act as proxy, it should record-route to stay in the
        call path.  In this example, O-SBE is a B2BUA.











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         INVITE sip:+19175550100@example.net;user=phone SIP/2.0
         Via: SIP/2.0/TCP o-sbe1.example.com:5060
           ;branch= z9hG4bK2d4zzz;
         Max-Forwards: 10
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=54321
         To: Bob <sip:+19175550100@example.net;user=phone>
         Call-ID: abcde-osbe1@o-sbe1.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@o-sbe1.example.com;user=phone
           ;transport=tcp>

        Note that O-SBE may re-write the Request-URI with the target
        domain in the SIP URI.  Some proxy implementations will only
        accept the request if the Request-URI contains their own
        domains.

   8.   T-SBE determines called party home proxy and directs call to
        called party.  T-SBE may use ENUM or other internal mechanism to
        locate the home proxy.  If T-SSP uses ENUM, this internal ENUM
        entry is different from the external ENUM entry populated for
        O-SSP.  In this example, the internal ENUM query returns the
        UAS's home proxy.

         $ORIGIN 0.0.1.0.5.5.5.7.1.9.1.e164.arpa.
         IN NAPTR (
           10
           100
           "u"
           "E2U+SIP"
           "!^.*$!sip:+19175550100@t-proxy.example.net!"
           . )

   9.   T-SBE receives the NAPTR record and query DNS for the A record
        of domain "t-proxy.example.net.".  The DNS returns an A record:

          ;; DNS ANSWER
          t-proxy.example.net.   IN A   192.2.1.2

   10.  T-SBE is a B2BUA, so it generates a new INVITE and sends it to
        UAS's home proxy:










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         INVITE sip:bob@t-proxy.example.net;user=phone SIP/2.0
         Via: SIP/2.0/TCP t-sbe1.example.net:5060
           ;branch= z9hG4bK28uyyy;
         Max-Forwards: 10
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=54321
         To: Bob <sip:+19175550100@t-proxy.example.net;user=phone>
         Call-ID: abcde-tsbe1@t-sbe1.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@t-sbe1.example.net;user=phone
           ;transport=tcp>

   11.  Finally, UAS's home proxy forwards the INVITE request to UAS.

         INVITE sip:+19175550100@server.example.net;user=phone SIP/2.0
         Via: SIP/2.0/TCP t-proxy.example.net:5060
           ;branch= z9hG4bK28u111;
         Via: SIP/2.0/TCP t-sbe1.example.net:5060
           ;branch= z9hG4bK28uyyy; received=192.2.0.100
         Max-Forwards: 9
         Record-Route: <sip:t-proxy.example.net:5060;lr>,
           <sip:t-sbe1.example.net:5060;lr>
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=54321
         To: Bob <sip:+19175550100@t-proxy.example.net;user=phone>
         Call-ID: abcde-tsbe1@t-sbe1.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@t-sbe1.example.net;user=phone
           ;transport=tcp>

   12.  RTP is established between UAC and UAS.  Note that the media
        passes through O-DBE and T-DBE in the .  This is optional.

5.2.1.  Administrative characteristics

   The static direct peering use case is typically implemented in a
   scenario where there is a strong degree of trust between the two
   administrative domains.  Both administrative domains typically sign a
   peering agreement which state clearly the policies and terms.

5.2.2.  Options and Nuances

   In Figure 2.  O-SSP and T-SSP peer via SBEs.  Normally, the operator
   will deploy the SBE at the edge of its administrative domain.  The
   signalling traffic will pass between two networks through the SBEs.
   The operator has many reasons to deploy a SBE.  For example, either
   proxy and UA may use [RFC1918] addresses that are not routable in the
   target network.  The SBE can perform a NAT function.  Also, the SBE



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   eases the operation cost for deploying or removing Layer-5 network
   elements.  Consider the deployment architecture where multiple
   proxies connect to a single SBE.  An operator can add or remove a
   proxy without coordinating with the peer operator.  The peer operator
   "sees" only the SBE.  As long as the SBE is maintained in the path,
   the peer operator does not need to be notified.

   When an operator deploys SBEs, the operator is required to advertise
   the SBE to the peer LRF so that the peer operator can locate the SBE
   and route the traffic to the SBE accordingly.

   SBE deployment is a decision within an administrative domain.  Either
   administrative domain or both administrative domains can decide to
   deploy SBE(s).  To the peer network, most important is to identify
   the next-hop address.  Whether next-hop is a proxy or SBE, the peer
   network will not see any difference.

5.3.  Static Direct Peering Use Case - Assisted LUF and LRF

   This use case shares many properties with the static direct use case.
   There must exist a pre-association between the O-SSP and T-SSP.  The
   difference is O-SSP will use the Assisted LUF/LRF Provider for LUF
   and LRF.  In other words, LUF/LRF provider stores the SED to reach
   T-SSP and provides to O-SSP when O-SSP queries it.



























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                            +-----------------+
                            |LUF/LRF Provider |
                            |                 |
                            |     +-------+   |
                            |   +-+ A-LUF |   |
                            |  /  | A-LRF |   |
       +--------------------+ /  ++-------+   +---------------------+
       |       O-SSP        |/  /             |         T-SSP       |
       |       +------------/(4,5,6)          |        +-----+      |
       |      /             | /               |        |T-LUF|      |
       |    (2)           +-+/                |      +-|T-LRF|      |
       |    /            /  |                 |     /  +-----+      |
       |   /            /   |                 |    /(8,9)           |
       |+-------+     +-----+                 +-----+      +-------+|
       ||O-Proxy|-(3)-|O-SBE+-------(7)-------+T-SBE|-(10)-|T-Proxy||
       |+-------+     +-----+                 +-----+      +-------+|
       |    |               |                 |                |    |
       |   (1)              |                 |              (11)   |
       |    |               |                 |                |    |
       | +-----+      +-----+                 +-----+       +-----+ |
       | | UAC +======|O-DBE+=======(12)======+T-DBE+=======+ UAS | |
       | +-----+      +-----+                 +-----+       +-----+ |
       +--------------------+                 +---------------------+
             example.com                            example.net


              Static Direct Peering with Assisted LUF and LRF

                                 Figure 3

   The call flow looks almost identical to Static Direct Peering Use
   Case except Step 2,4,5 and 6 which happen in LUF/LRF provider
   remotely instead of happening in O-SSP domain.

   Similar to Static Direct Peering Use case, O-DBE and T-DBE in the
   Figure 3 are optional.

5.3.1.  Administrative Characteristics

   The LUF/LRF provider provides the LUF and LRF services for the O-SSP.
   As such , LUF/LRF provider, O-SSP and T-SSP form a trusted
   administrative domain.  To reach T-SSP, O-SSP must still require pre-
   arranged assignments for the peer relationship with T-SSP.  Layer-5
   policy is maintained in the O-SSP and T-SSP domains, and LUF/LRF
   provider may not aware any Layer-5 policy between O-SSP and T-SSP.

   A LUF/LRF provider can serve multiple administrative domains.  The
   LUF/LRF provider typically does not share SED from one administrative



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   domain to another administrative domain without appropriate
   permission granted.

5.3.2.  Options and Nuances

   LRF/LRF provider can use multiple methods to provide SED to O-SSP.
   Most commonly used are ENUM query and SIP Redirect.  O-SSP should
   negotiate with LUF/LRF provider which query method it will use prior
   to sending query to LUF/LRF provider.

   T-SSP needs to populate its users' SED to LUF/LRF provider.
   Currently, this procedure is non-standardized and labor intensive.
   IETF is working on this problem and trying to standardize this
   procedure for ENUM.  [I-D.ietf-drinks-cons-rqts] lists the problem
   statements.

5.4.  Static Indirect Peering Use Case - Assisted LUF and LRF

   The difference between Static Direct Use Case and Static Indirect Use
   Case lies within the Layer-5 relationship of which O-SSP and T-SSP
   maintain.  In the Indirect use case, the O-SSP and T-SSP do not have
   direct Layer-5 connectivity.  They require one or multiple Indirect
   Domains to assist routing the SIP messages and possibly the
   associated media.

   In this use case, O-SSP and T-SSP want to form a peer relationship.
   For some reason, O-SSP and T-SSP do not have direct Layer-5
   connectivity.  The reasons may vary, for example business demands
   and/or domain policy controls.  Due to this indirect relationship the
   signalling will traverse from O-SSP to one or multiple I-SSP(s) to
   reach T-SSP.

   In addition, O-SSP decides to use a LUF/LRF provider.  This LUF/LRF
   provider stores the SED pre-populated by T-SSP.  One important
   motivation to use the LUR/LRF provider is that T-SSP only needs to
   populate its SED once to the provider.  Any O-SSP who wants to query
   T-SSP's SED can use this LUF/LRF provider.  Current practice has
   shown that it is rather difficult for T-SSP to populate its SED to
   every O-SSP who likes to reach the T-SSP's subscribers.  This is
   especially true in Enterprise environment.

   Note that LUF/LRF provider and I-SSP can be the same provider or
   different providers.








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                            +------------------+
                            | LUF/LRF Provider |
                            |       I-SSP      |
                            |      +-------+   |
                            |   ---+ A-LUF |   |
                            |  /   | A-LRF |   |
       +--------------------+ /    +-------+   +---------------------+
       |       O-SSP        |/     /           |         T-SSP       |
       |      +-------------/     /            |        +-----+      |
       |     /              |(4,5,6)           |        |T-LUF|      |
       |    /               |   /              |   +----+T-LRF|      |
       |  (2)             + +---               |  /     +-----+      |
       |  /              /  |                  | /(9,10)             |
       |+-------+     +-----+     +-----+      +-----+      +-------+|
       ||O-Proxy|-(3)-|O-SBE+-(7)-+I-SBE+-(8)--+T-SBE+-(11)-|T-Proxy||
       |+-------+     +-----+     +-----+      +-----+      +-------+|
       |    |               |                  |                |    |
       |   (1)              |                  |               (12)  |
       |    |               |                  |                |    |
       | +-----+      +-----+     +-----+      +-----+       +-----+ |
       | | UAC +=(13)=|O-DBE+=====+I-DBE+======+T-DBE+=======+ UAS | |
       | +-----+      +-----+     +-----+      +-----+       +-----+ |
       +-------------------------------------------------------------+
            example.com          example.org         example.net


      Indirect Peering via LUR/LRF provider and I-SSP (SIP and media)

                                 Figure 4

   The following is a high-level depiction of the use case:

   1.   UAC initiates a call via SIP INVITE to O-Proxy.  O-Proxy is the
        home proxy for UAC.

         INVITE sip:+19175550100@example.com;user=phone SIP/2.0
         Via: SIP/2.0/TCP client.example.com:5060
           ;branch=z9hG4bK74bf9
         Max-Forwards: 10
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=12345
         To: Bob <sip+19175550100@example.com;user=phone>
         Call-ID: abcde@client.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@client.example.com;user=phone
           ;transport=tcp>





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   2.   UAC only knows UAS's TN but not UAS's domain.  It appends its
        domain to generate the SIP URI in Request-URI and To header.
        O-Proxy checks the Request-URI's domain and discovers that the
        UAS's domain is internal but the TN is unknown to O-Proxy.  So,
        O-Proxy queries LUF for SED information from a routing database.
        In this example, the LUF is an ENUM database.  The ENUM entry
        looks similar to this:

          $ORIGIN 0.0.1.0.5.5.5.7.1.9.1.e164.arpa.
          IN NAPTR (
            10
            100
            "u"
            "E2U+SIP"
            "!^.*$!sip:+19175550100@example.org!"
            . )

        Note that the response shows the next-hop is the SBE in Indirect
        SSP.

        Alternatively, O-SSP may have a pre-association with I-SSP.  As
        such, O-SSP will forward all requests of which it contains an
        external domain or the TN is unknown to O-SSP to I-SSP.  O-SSP
        will rely on I-SSP to determine T-SSP and route the request
        correctly.  In this setup, O-SSP can skip Steps 2,4,5 and 6 and
        forward the request to I-SBE.  This setup is commonly used in
        Enterprise use cases.

   3.   Given the O-Proxy's internal routing policy, O-Proxy decides to
        use O-SBE to reach I-SBE.  O-Proxy routes the INVITE request to
        O-SBE and adds a Route header which contains O-SBE.

         INVITE sip:+19175550100@example.org;user=phone SIP/2.0
         Via: SIP/2.0/TCP o-proxy.example.com:5060
           ;branch=z9hG4bKye8ad
         Via: SIP/2.0/TCP client.example.com:5060
           ;branch=z9hG4bK74bf9;received=192.0.1.1
         Max-Forwards: 9
         Route: <sip:o-sbe1.example.com;lr>
         Record-Route: <sip:o-proxy.example.com;lr>
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=12345
         To: Bob <sip+19175550100@example.net;user=phone>
         Call-ID: abcde@client.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@client.example.com;user=phone
           ;transport=tcp>




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   4.   O-SBE receives the requests and pops the top entry of the Route
        header which contains "sip:o-sbe1.example.com".  O-SBE examines
        the Request-URI and does a LRF for "example.org".  In this
        example, the LRF is a NAPTR DNS query of the domain.  O-SBE
        receives a response similar to this:

          IN NAPTR (
            50
            50
            "S"
            "SIP+D2T"
            ""
            _sip._tcp.i-sbe.example.org. )

          IN NAPTR (
            90
            50
            "S"
            "SIP+D2U"
            ""
            _sip._udp.i-sbe.example.org. )

   5.   Given the lower order for TCP in the NAPTR response, O-SBE
        decides to use TCP for transport protocol, so it sends a SRV DNS
        query for the SRV record for "_sip._tcp.i-sbe.example.org.".

        ;;     priority  weight   port  target
        IN SRV 0         2        5060  i-sbe1.example.org.
        IN SRV 0         1        5060  i-sbe2.example.org.

   6.   Given the higher weight for "i-sbe1.example.org", O-SBE sends a
        DNS query for A record of "i-sbe1.example.org." to get the A
        record:

          ;; DNS ANSWER
          i-sbe1.example.org.   IN A   192.3.0.100
          i-sbe1.example.org.   IN A   192.3.0.101

   7.   O-SBE sends the INVITE to I-SBE.  O-SBE is the entry point to
        the O-SSP domain, so it should ensure subsequent mid-dialog
        requests traverse via itself.  If O-SBE chooses to act as B2BUA,
        it will terminate the call and generate a new back-to-back
        INVITE request.  If O-SBC chooses to act as proxy, it should
        record-route to stay in the call path.  In this example, O-SBE
        is a B2BUA.






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         INVITE sip:+19175550100@example.org;user=phone SIP/2.0
         Via: SIP/2.0/TCP o-sbe1.example.com:5060
           ;branch= z9hG4bK2d4zzz;
         Max-Forwards: 10
         Route:  <sip:i-sbe1.example.org;lr>
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=54321
         To: Bob <sip:+19175550100@example.net;user=phone>
         Call-ID: abcde-osbe1@o-sbe1.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@o-sbe1.example.com;user=phone
           transport=tcp>

   8.   I-SBE receives the request and queries its internal routing
        database on the TN.  It determines the target belongs to T-SSP.
        Since I-SBE is a B2BUA, I-SBE generates a new INVITE request to
        T-SSP.

         INVITE sip:+19175550100@.example.net;user=phone SIP/2.0
         Via: SIP/2.0/TCP i-sbe1.example.org:5060
           ;branch= z9hG4bK2d4777;
         Max-Forwards: 10
         Route: <sip:t-sbe1.example.net;lr>
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=54321
         To: Bob <sip:+19175550100@example.net;user=phone>
         Call-ID: abcde-isbe1@i-sbe1.example.org
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@i-sbe1.example.org;user=phone
           transport=tcp>

        Note that if I-SSP wants the media to traverse through the
        I-DBE, I-SBE must modify the SDP in the Offer to point to its
        DBE.

   9.   T-SBE determines called party home proxy and directs call to
        called party.  T-SBE may use ENUM or other internal mechanism to
        locate the home proxy.  If T-SSP uses ENUM, this internal ENUM
        entry is different from the external ENUM entry populated for
        O-SSP.  In this example, the internal ENUM query returns the
        UAS's home proxy.










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         $ORIGIN 0.0.1.0.5.5.5.7.1.9.1.e164.arpa.
         IN NAPTR (
           10
           100
           "u"
           "E2U+SIP"
           "!^.*$!sip:+19175550100@t-proxy.example.net!"
           . )

        Note that this step is optional.  If T-SBE has other ways to
        locate the UAS home proxy, T-SBE can skip this step and send the
        request to the UAS's home proxy.  We show this step to
        illustrate one of the many possible ways to locate UAS's home
        proxy.

   10.  T-SBE receives the NAPTR record and query DNS for the A record
        of "t-proxy.example.net".  The DNS returns an A record:

          ;; DNS ANSWER
          t-proxy.example.net.   IN A   192.2.1.2

   11.  T-SBE sends the INVITE to UAS's home proxy:

         INVITE sip:+19175550100@t-proxy.example.net;user=phone SIP/2.0
         Via: SIP/2.0/TCP t-sbe1.example.net:5060
           ;branch= z9hG4bK28uyyy;
         Max-Forwards: 10
         Record-Route: <sip:t-sbe1.example.net:5060;lr>
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=54321
         To: Bob <sip:+19175550100@example.net;user=phone>
         Call-ID: abcde-tsbe1@t-sbe1.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@t-sbe1.example.com;user=phone
           transport=tcp>

   12.  Finally, UAS's home proxy forwards the INVITE request to UAS.














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         INVITE sip:+19175550100@server.example.net;user=phone SIP/2.0
         Via: SIP/2.0/TCP t-proxy.example.net:5060
           ;branch= z9hG4bK28u111;
         Via: SIP/2.0/TCP t-sbe1.example.net:5060
           ;branch= z9hG4bK28uyyy; received=192.2.0.100
         Max-Forwards: 9
         Record-Route: <sip:t-proxy.example.net:5060;lr>,
           <sip:t-sbe1.example.net:5060;lr>
         From: Alice <sip:+14085550101@example.com;user=phone>
           ;tag=54321
         To: Bob <sip:+19175550100@example.net;user=phone>
         Call-ID: abcde-tsbe1@t-sbe1.example.com
         CSeq: 1 INVITE
         Contact: <sip:+19175550100@t-sbe1.example.com;user=phone
           transport=tcp>

   13.  RTP is established between UAC and UAS.

5.4.1.  Administrative characteristics

   This use case looks very similar to Static Direct Peering with
   Assisted LUF and LRF.  The major difference is O-SSP and T-SSP do not
   have direct Layer-5 connectivity.  Instead, O-SSP connects to T-SSP
   indirectly via I-SSP.

   O-SSP employs this use case when it uses different I-SSP to reach
   different T-SSPs.  Typically, LUF/LRF provider serves multiple O-SSP.
   Two O-SSP may use different I-SSP to reach the same T-SSP.  For
   example, O-SSP1 may use I-SSP1 to reach T-SSP, but O-SSP2 may use
   I-SSP2 to reach T-SSP.  In other words, given the O-SSP and T-SSP
   pair as input, LUF/LRF provider will return the SED of I-SSP that is
   trusted by O-SSP to forward the request to T-SSP.

   There are two levels of trust relationship.  First trust relationship
   between O-SSP and LUF/LRF provider.  LUF/LRF provider provides LUF
   and LRF for O-SSP.  Once O-SSP queries for the SED, LUF/LRF provider
   is out of the picture.  Second trust relationship is between O-SSP
   and I-SSP.  I-SSP provides Layer-5 connectivity to assist O-SSP to
   reach T-SSP.  O-SSP and I-SSP have a pre-association for policy
   before peering happens.  Although Figure 4 shows a single provider to
   provide both LUR/LRF and I-SSP, O-SSP can choose two different
   providers.

5.4.2.  Options and Nuances

   Similar to the Static Direct Peering Use Case, O-SSP and T-SSP may
   deploy SBE and DBE for NAT traversal, security, transcoding, etc.
   I-SSP can also deploy SBE and DBE for similar reasons. (as depicted



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   in Figure 4)

5.5.  Static Indirect Peering Use Case

   This use case O-SSP uses its internal LUF/LRF.  One of the reasons of
   using internal LUF/LRF is to control the routing database.  By
   controlling the database, O-SSP can apply different routing rules and
   policies to different T-SSPs.  For example, O-SSP can use I-SSP1 and
   Policy-1 to reach T-SSP1, and use I-SSP2 and Policy-2 to reach
   T-SSP2.  Note that there could be multiple I-SSPs and multiple SIP
   routes to reach the same T-SSP; this is out of scope of speermint and
   has become a focus in the drinks working group.

      +--------------------+-------------------+---------------------+
      |       O-SSP        |       I-SSP       |         T-SSP       |
      |      +-----+       |                   |        +-----+      |
      |     -+O-LUF|       |                   |        |T-LUF|      |
      |    / |O-LRF+\      |                   |   +----+T-LRF|      |
      |   /  +-----+ \     |                   |  /     +-----+      |
      |  /(2)         \(4,5,6)                 | /(9,10)             |
      |+-------+     +-----+      +-----+      +-----+      +-------+|
      ||O-Proxy|-(3)-|O-SBE+--(7)-+I-SBE+-(8)--+T-SBE+-(11)-|T-Proxy||
      |+-------+     +-----+      +-----+      +-----+      +-------+|
      |    |               |                   |                |    |
      |   (1)              |                   |               (12)  |
      |    |               |                   |                |    |
      | +-----+      +-----+      +-----+      +-----+       +-----+ |
      | | UAC +=(13)=+O-DBE+======+I-DBE+======+T-DBE+=======+ UAS | |
      | +-----+      +-----+      +-----+      +-----+       +-----+ |
      +--------------------------------------------------------------+
           example.com          example.org          example.net


                Indirect Peering via I-SSP (SIP and media)

                                 Figure 5

5.5.1.  Administrative characteristics

   The Static Indirect Use Case is implemented in cases where no direct
   interconnection exists between originating and terminating domains
   due to either business or physical constraints.

   O-SSP <---> I-SSP = Relationship O-I

   In the O-I relationship, typical policies, features or functions that
   deem this relationship necessary are number portability, Ubiquity of
   termination options, security certificate management and masquerading



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   of originating VoIP network gear.

   T-SSP <---> I-SSP = Relationship T-I

   In the T-I relationship, typical policies, features or functions
   observed consist of codec "scrubbing", anonymizing, and transcoding.
   I-SSP must record-route and stay in the signalling path.  T-SSP will
   not accept message directly sent from O-SSP.

5.5.2.  Options and Nuances

   In Figure 5, we show I-DBE.  One scenario the I-DBE can be used is
   when O-SSP and T-SSP do not have a common codec.  To involve I-DBE,
   I-SSP should know the list of codec supported by O-SSP and T-SSP.
   When I-SBE receives the INVITE, it will make a decision to invoke the
   I-DBE.  Another scenario an I-DBE will be used is if O-SSP uses SRTP
   [RFC3711] for media and T-SSP does not support SRTP, I-DBE can be
   used.

5.6.  On-demand Peering Use Cases

   On-demand Peering [I-D.ietf-speermint-terminology] describes two SSPs
   form the peering relationship without a pre-arranged agreement.

   The basis of this use case is built on the fact that there is no pre-
   established relationship between the O-SSP and the T-SSP.  The O-SSP
   and T-SSP did not share any information prior to the dialog
   initiation request.  When the O-Proxy invokes the LUF and LRF on the
   Request-URI, the terminating user information must be publicly
   available.  Besides, when the O-Proxy routes the request to the
   T-Proxy, the T-Proxy must accept the request without any pre-
   association with O-SSP.

5.6.1.  Administrative characteristics

   The On-demand Direct Peering Use Case is typically implemented in a
   scenario where the T-SSP allows any O-SSP to reach its serving
   subscribers.  T-SSP administrative domain does not require any pre-
   arranged agreement to accept the call.  T-SSP makes its subscribers
   information available in public.  This model mimics the Internet
   email model.  Sender does not need an pre-arranged agreement to send
   email to the receiver.

5.6.2.  Options and Nuances

   Similar to Static Direct Peering Use Case, O-SSP and T-SSP can decide
   to deploy SBE.  T-SSP is open to the public, T-SSP is considered to
   be in higher security risk than static model because there is no



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   trusted relationship between O-SSP and T-SSP.  T-SSP should protect
   itself from any attack launch by untrusted O-SSP.


6.  Acknowledgments

   This document is a consolidation of many early individual drafts
   (Please refer to the Section Informative References).  Michael
   Haberler, Mike Mammer, Otmar Lendl, Rohan Mahy, David Schwartz, Eli
   Katz and Jeremy Barkan are the authors of the early individual
   drafts.  Besides, Jason Livingood, Daryl Malas, David Meyer, Hadriel
   kaplan, John Elwell, Reinaldo Penno, Sohel Khan, James McEachern, Jon
   Peterson, Alexander Mayrhofer, and Jean-Francois Mule made many
   valuable comments to this document.


7.  Security and Privacy Considerations

   This document introduces no new security considerations.  However, it
   is important to note that session interconnect, as described in this
   document, has a wide variety of security issues that should be
   considered in documents addressing both protocol and use case
   analyzes.  [I-D.niccolini-speermint-voipthreats] discuss the
   different security threats related to VoIP peering.


8.  IANA Considerations

   This document creates no new requirements on IANA namespaces
   [RFC2434].


9.  References

9.1.  Normative References

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

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.




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   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [RFC3261]  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.

   [RFC3263]  Rosenberg, J. and H. Schulzrinne, "Session Initiation
              Protocol (SIP): Locating SIP Servers", RFC 3263,
              June 2002.

   [RFC3403]  Mealling, M., "Dynamic Delegation Discovery System (DDDS)
              Part Three: The Domain Name System (DNS) Database",
              RFC 3403, October 2002.

   [RFC3761]  Faltstrom, P. and M. Mealling, "The E.164 to Uniform
              Resource Identifiers (URI) Dynamic Delegation Discovery
              System (DDDS) Application (ENUM)", RFC 3761, April 2004.

9.2.  Informative References

   [I-D.ietf-drinks-cons-rqts]
              Schwartz, D., Mahy, R., Duric, A., and E. Lewis,
              "Consolidated Provisioning Problem Statement",
              draft-ietf-drinks-cons-rqts-00 (work in progress),
              July 2008.

   [I-D.lee-speermint-use-case-cable]
              Lee, Y., "Session Peering Use Case for Cable",
              draft-lee-speermint-use-case-cable-01 (work in progress),
              September 2006.

   [I-D.lendl-speermint-federations]
              Lendl, O., "A Federation based VoIP Peering Architecture",
              draft-lendl-speermint-federations-03 (work in progress),
              September 2006.

   [I-D.mahy-speermint-direct-peering]
              Mahy, R., "A Minimalist Approach to Direct Peering",
              draft-mahy-speermint-direct-peering-02 (work in progress),
              July 2007.




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   [I-D.niccolini-speermint-voipthreats]
              Niccolini, S., Chen, E., and J. Seedorf, "SPEERMINT
              Security Threats and Suggested Countermeasures",
              draft-niccolini-speermint-voipthreats-04 (work in
              progress), July 2008.

   [I-D.schwartz-speermint-use-cases-federations]
              Schwartz, D., "Session Peering Use Cases for Federations",
              draft-schwartz-speermint-use-cases-federations-00 (work in
              progress), November 2006.

   [I-D.uzelac-speermint-use-cases]
              Uzelac, A., "SIP Peering Use Case for VSPs",
              draft-uzelac-speermint-use-cases-00 (work in progress),
              October 2006.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              December 1998.

   [RFC3546]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 3546, June 2003.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.


Authors' Addresses

   Adam Uzelac (editor)
   Global Crossing
   U.S.A.

   Phone:
   Email: adam.uzelac@globalcrossing.com
   URI:   http://www.globalcrossing.com












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   Yiu L.Lee (editor)
   Comcast Cable
   U.S.A.

   Phone:
   Email: yiu_lee@cable.comcast.com
   URI:   http://www.comcast.com












































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