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Versions: 00 01 02                                                      
MARTINI WG                                                    H. Kaplan
Internet Draft                                              Acme Packet
Intended status: Standards-Track
Expires: April 25, 2011                                October 25, 2010

                           SIP GIN MARTINI with
     Open-plan Local-number Identifier Values for Enterprises (OLIVE)

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 25, 2011.

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   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   The Martini Working Group has defined a mechanism for SIP IP-PBX
   type devices to REGISTER and obtain SIP service for E.164-based
   Address of Records, using the GIN mechanism [draft-gin].  This
   document defines a means for open-plan Local-Numbers to be used with
   Martini-based IP-PBXs.

Table of Contents

   1. Introduction..................................................2
   2. Definitions...................................................3
   3. Background....................................................3
      3.1. The GIN Mechanism........................................3
      3.2. Local-Numbers............................................4
   4. The Solution - an Overview....................................4
   5. Registering for Local-Number AoRs.............................5
   6. SSP Processing of Inbound Non-E.164 Requests..................7
   7. Interaction with Other Mechanisms.............................7
      7.1. Globally Routable User-Agent URIs (GRUU).................7
      7.2. Registration Event Package...............................7
      7.3. Non-Adjacent Contact Registration (Path) and Service Route
   8. Open Issues...................................................8
   9. Examples......................................................8
      9.1. Usage Scenario: Basic Registration case..................9
   10. IANA Considerations.........................................10
   11. Security Considerations.....................................10
   12. Acknowledgements............................................10
   13. Informative References......................................11
   Author's Address.................................................12
   Appendix A - Why Local-Numbers may need processing by SSPs.......12

1. Introduction

   In many deployed SIP Service Provider (SSP) architectures, it is
   common to use REGISTER requests to provide the reachability
   information for IP-PBXs, instead of DNS-based resolution and
   routing.  An IETF-defined mechanism for doing so is being worked on
   in the Martini Working Group, with the GIN mechanism [draft-gin].

   The current GIN mechanism only supports E.164-based AoRs, however in
   actual deployments private-extension or "local" numbers are used for
   hosted and carrier-provided intra-Enterprise calling services.
   These forms of AoRs are not supported by the current GIN mechanism.
   This document defines a means by which they can be supported, in a
   manner consistent with [RFC3261] and [draft-gin].

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2. Definitions

   For brevity's sake, this document uses the word "request" instead of
   "out-of-dialog request", but in all case means out-of-dialog

   AoR: address-of-record, as defined by RFC 3261: a URI by which the
   user is canonically known (e.g., on their business cards, in the
   From header field of their requests, in the To header field of
   REGISTER requests, etc.).

   Open-plan: an open-plan is a dialing-plan which is not constrained
   to be a specific set of numbers all known to the SSP; some specific
   numbers may be known by the SSP, and/or a beginning set of digits
   are known to the SSP and used to route calls to different branches

   Local-Number: an AoR which follows the form of local-number in
   [RFC3966], but may be encoded in a SIP or TEL URI.  The local-number
   contains a 'phone-context' parameter identifying the scope of its

   Implicit Registration: implicitly providing the reachability
   information for something other than the AoR explicitly indicated in
   the Register transaction.

   Reachability Information: a set of URI's identifying the host and
   path of Proxies to reach that host; like any URI, these URI's may
   identify the specific connection transport, IP Address, and port
   information, or they may only identify FQDN's.

   SSP: SIP Service Provider, as defined by [RFC5486].

3. Background

3.1. The GIN Mechanism

   The GIN mechanism, defined in [draft-gin], allows a SIP UA such as
   an IP-PBX to Register a set of E.164 AoRs in "bulk".  Instead of
   creating a separate REGISTER transaction for every E.164 AoR, the
   IP-PBX sends one REGISTER request with a 'bnc' Contact URI parameter
   which indicates the Contact URI needs to be expanded in the
   Registrar's location service database.  The expansion is such that
   each E.164 user number becomes the user portion of the registered
   Contact URI, one for each implicitly registered E.164 number-based

   SIP Request routing to the Registered E.164 AoR then follows normal
   [RFC3261] procedures, replacing the Request URI with the expanded

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   registered Contact URI, and adding any Path information as a Route
   set, etc.

3.2. Local-Numbers

   The Local-Number syntax for TEL URIs is defined in [RFC3966], such
   that a local-number is a set of digits, possibly with an extension
   or isdn-subaddress parameter, and scoped to the domain name or
   global-number-digits in its phone-context.  In theory, a SIP UA can
   target its request to a Local-Number using the [RFC3966] syntax in a
   TEL URI or SIP URI, and have the request delivered to the UA or IP-
   PBX identified by the user digits for the given phone-context, which
   may subsequently route the request to the specific extension or

   In practice it's not that simple.  Most branch-office IP-PBXs do not
   use the Local-Number syntax for their targets, and do not recognize
   such syntax if they receive it in the Request URI.  Often the SSP
   adds the phone-context to received requests from the IP-PBX, and
   removes it when sending to the IP-PBX.  The reasons for this
   include: (a) the IP-PBX is wholly within the context and thus has no
   knowledge of, nor concern that there cold be, other contexts; (b)
   the IP-PBX may not actually know all the numbers in the private
   number plan, only its local ones; and (c) historically it has not
   been necessary for them to add such explicit indicators for things
   to work, and thus the status-quo is difficult to change.

   Furthermore, Local-Numbers are difficult because they are doubly-
   scoped: once at the URI level by the domain name, and internally by
   the phone-context URI user parameter.  The authoritative system for
   the Local-Number user portion (the system(s) which knows what they
   are and how to process them) is not necessarily identified by the
   URI's domain name, but rather may be identified by the phone-
   context's value.  In other words, the SSP may not know about all
   possible Local-Number numbers, and even a given IP-PBX may not know
   them all for its Enterprise; the knowledge may be distributed.  This
   presents difficulties for certain GIN functions such as reg-event,
   and is why this document refers to GIN support for Local-Numbers as
   being for "open-plan" scenarios.

4. The Solution - an Overview

   The general concept proposed in this document is to logically apply
   GIN for the complete set of Local-Number "AoRs" of the Registered-to
   domain, as if they were individually Registered.  The GIN-based
   REGISTER request would cause the Registrar to logically populate the
   set of AoR-to-Contact bindings, as it did before.

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   The Contact URI user portion would also be "expanded", using the
   same user portion as that of the implicitly registered AoRs: namely
   a Local-Number format.  The Local-Number username is "normalized" in
   the same manner as [draft-gin].

   Note that the list of Local-Number AoRs associated with a PBX is a
   matter of local provisioning at the SSP and at the PBX, as it was in
   [draft-gin].  The mechanism defined in this document does not
   provide any means to detect or recover from provisioning mismatches
   (although the registration event package can be used as a
   standardized means for auditing such AoRs).

   No new option-tag is required, because this document's mechanism
   does not require any changes in GIN [draft-gin] registration nor in
   subsequent [RFC3261] routing behavior in the IP-PBX, nor in any
   proxies along the path.  The routing follows the [RFC3261]
   Registered AoR-contact resolution model, which is a basic function
   of SIP.

   The only SIP devices affected by this document's mechanism is the
   SSP's Registrar, which needs to update the appropriate AoR entries,
   and any proxy/ies of the SSP which perform route resolution by
   looking up the contents of the (logical) location-service database.
   Since such proxies may not even be in the path of the REGISTER
   request, an option-tag will not help.  And since the Registrar and
   Proxies in question are all under control of the same administrative
   entity (the SSP), it is reasonable to expect them all to support
   this document's mechanism, if any do.

5. Registering for Local-Number AoRs

   This document's mechanism relies on the GIN [draft-gin] Registration
   mechanism.  The IP-PBX Registers into the SSP, using a REGISTER
   request with the "gin" option-tag in the Require and Proxy-Require
   header fields, and a Contact URI containing the "bnc" URI parameter
   and no user portion.  After the PBX is authenticated, the registrar
   updates its location service so that each of the Local-Number AoRs
   associated with the PBX creates a unique AOR to Contact mapping.

   In practice, however, the SSP domain may not have specific knowledge
   of any or all user names within a given phone-context's scope.  In
   fact, the Local-Number TEL URI parameters (which are URI user
   parameters in SIP URIs) may only have meaning to the ultimate target
   of the request, or some entity which is authoritative for the phone-
   context's user names.  Those parameters cannot be removed by the SSP
   if it does not actually process the user portions of the Local-
   Number. (i.e., if it does not have the dial-plan, etc.)

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   With regard to this document's mechanism, what this means is that
   such an SSP cannot physically instantiate an AoR in a database for
   every possible Local-Number and cannot physically instantiate an
   expanded Contact URI for every possible Local-Number user name with
   every possible user parameter.  That does not inhibit the mechanism
   from working or being usable, however, because the location-service
   database model is purely an abstract concept.  What's important is
   that the route-resolving Proxy be able to lookup and replace an AoR
   it is authoritative for, to a Registered Contact URI, such that the
   resultant Request URI matches what the IP-PBX expects to receive.

   It is "safe" to do this because the explicitly Registered Contact
   URI of the [draft-gin] REGISTER request had no user portion, and
   thus no possible URI user parameters.  As defined in [draft-gin],
   the Contact URI parameters of the REGISTER are saved and reused, but
   not URI user parameters.

   There are multiple ways of describing the logical AoR instantiation
   and Contact URI expansion rules.  They could be described as
   covering every possible ABNF expansion, such that every possible
   user and parameter logically exists in the location-service database
   (but obviously not physically exists).  Or it could be described as
   only the phone-context value itself being an "AoR" entry and Contact
   URI expansion, with a policy to allow any and all user names and
   parameters to be copied instead of replaced by the Contact URI.

   This remains an open issue for discussion, as discussed in section

   Regardless, for an implicitly Registered SIP AoR with a URI user
   portion matching the syntax outlined for "local-number" TEL URIs in
   [RFC3966]: the Contact is expanded following the other AoR models,
   EXCEPT that all URI user parameters are also included.  For example,
   if the logically provisioned "AoR" from the previous examples were:
   "sip:12345;ext=678;phone-context=+1212555@ssp.example.com", it would
   logically get an automatically generated Contact value of
   and if the AoR were "sip:12345;ext=678;phone-
   context=ssp.example.com@ssp.example.com", the resultant Contact
   value would be <sip:12345;ext=678;phone-

   Note that in practice it is not uncommon to receive a SIP URI which
   does not strictly comply with the formatting rules of [RFC3966], but
   is processed as if it were, based on local policies.  That is legal,
   of course, but from a logical perspective the SIP URI is actually
   retargeted or transformed into the syntactically valid form
   following [RFC3966], and that form MUST be the one used for routing,
   Contact URI expansions, etc.  Likewise, if the URI were a TEL URI,

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   it MUST be logically transformed into a SIP URI of the SSP's domain
   as defined in section 19.1.6 of [RFC3261], with an appropriate
   phone-context, before executing the rules.

   As in [draft-gin], aside from the "bnc" parameter, all URI
   parameters present in the Contact URI in the REGISTER message MUST
   be copied to the Contact value stored in the location service.

   Note that the location service database, and any entry model
   described here, is purely an abstract concept used by [RFC3261],
   [draft-gin], and this document; an actual implementation may do
   whatever it likes internally, so long as the external behavior
   follows the model.  For example, if an SSP does not maintain any
   specific knowledge of the Local Number dial-plan, but simply
   performs prefix or default routing for an Enterprise's private
   extensions, the SSP could just route based on the E.164 phone-
   context field value without having a separate physical "AoR"
   database entry for each local number of that context.

6. SSP Processing of Inbound Non-E.164 Requests

   The SSP Proxy/Registrar (or equivalent entity) performs traditional
   Proxy/Registrar behavior, based on the logical mapping described in
   Section 5 and [draft-gin].

7. Interaction with Other Mechanisms

   The following sections describe the means by which this mechanism
   interacts with relevant REGISTER-related extensions currently
   defined by the IETF.

   Currently, the descriptions are somewhat informal, and omit some
   details for the sake of brevity.  If the MARTINI working group
   expresses interest in furthering the mechanism described by this
   document, they will be fleshed out with more detail and formality.

7.1. Globally Routable User-Agent URIs (GRUU)

   The GRUU mechanism for this document's mechanism works exactly the
   same way as defined in [draft-gin].  The GIN GRUU mechanism has no
   dependency on the AoR being an E.164.

7.2. Registration Event Package

   The Registration Event Packet behavior for this document's mechanism
   works exactly the same way as defined in [draft-gin].  The [draft-
   gin] reg-event model has no dependency on the AoR being an E.164.

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   There is, however, an issue for Local-Numbers, if the SSP does not
   actually know the full list of Local-Number user names in the given
   phone-context scope.  In such a case, it is TBD for how to handle

   This remains an open issue for discussion, as discussed in section

7.3. Non-Adjacent Contact Registration (Path) and Service Route

   The Path and Service-Route behavior and considerations for this
   document's mechanism are exactly the same as defined in [draft-gin].
   The [draft-gin] Path and Service-Route model has no dependency on
   the AoR being an E.164.

8. Open Issues

   This document has several open issues, which were noted previously.
   They center around the handling of Local-Numbers.  Local-Numbers are
   difficult because they are doubly-scoped: once at the URI level by
   the domain name, and internally by the phone-context URI user
   parameter.  The authoritative system for the Local-Number user
   portion (the system(s) which knows what they are and how to process
   them) is not necessarily identified by the URI's domain name, but
   rather may be identified by the phone-context's value.

   If the phone-context identifies the SSP domain, all's well - but
   that's rarely the case.  More likely is that it identifies an E.164
   number, or a sub-domain of the SSP, or another domain entirely.
   This causes issues with certain functions such as the reg-event
   package, which has been identified as an open issue.

9. Examples

   These will be fleshed out more in later versions of the draft, with
   explanations of the processing performed at each step.  For the time
   being, they just show the basic syntax described above.

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9.1. Usage Scenario: Basic Registration case

   This example shows a basic bulk REGISTER transaction, followed by an
   INVITE addressed to one of the registered terminals, for a Local-
   Number AoR.

   Internet                        SSP                              PBX
   |                                |                                 |
   |                                |REGISTER                         |
   |                                |Contact:<sip:;f=b;bnc>|
   |                                |<--------------------------------|
   |                                |                                 |
   |                                |200 OK                           |
   |                                |-------------------------------->|
   |                                |                                 |
   |INVITE                          |                                 |
   |sip:1234;ext=678                |                                 |
   | ;phone-context=+1212555        |                                 |
   | @ssp.example.com               |                                 |
   |------------------------------->|                                 |
   |                                |                                 |
   |                                |INVITE                           |
   |                                |sip:1234;ext=678                 |
   |                                | ;phone-context=+1212555         |
   |                                | @;f=b               |
   |                                |-------------------------------->|

   REGISTER sip:ssp.example.com SIP/2.0
   Via: SIP/2.0/UDP;branch=z9hG4bKnashds7
   Max-Forwards: 70
   To: <sip:pbx123@ssp.example.com>
   From: <sip:pbx123@ssp.example.com>;tag=a23589
   Call-ID: 843817637684230998sdasdh09
   CSeq: 1826 REGISTER
   Proxy-Require: gin
   Require: gin
   Supported: path
   Contact: <sip:;f=b;bnc>
   Expires: 7200
   Content-Length: 0

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   INVITE sip:1234;ext=678;phone-context=+1212555
       @ssp.example.com SIP/2.0
   Via: SIP/2.0/UDP foo.example;branch=z9hG4bKa0bc7a0131f0ad
   Max-Forwards: 69
   To: <sip:2145550105@some-other-place.example.net>
   From: <sip:alice@rabbithole.example.org>;tag=456248
   Call-ID: f7aecbfc374d557baf72d6352e1fbcd4
   CSeq: 24762 INVITE
   Contact: <sip:line-1@>
   Content-Type: application/sdp
   Content-Length: ...

   <sdp body here>

   INVITE sip:1234;ext=678;phone-context=+1212555
       @;f=b SIP/2.0
   Via: SIP/2.0/UDP foo.example;branch=z9hG4bKa0bc7a0131f0ad
   Via: SIP/2.0/UDP ssp.example.com;branch=z9hG4bKa45cd5c52a6dd50
   Max-Forwards: 68
   To: <sip:2145550105@some-other-place.example.net>
   From: <sip:alice@rabbithole.example.org>;tag=456248
   Call-ID: 7ca24b9679ffe9aff87036a105e30d9b
   CSeq: 24762 INVITE
   Contact: <sip:line-1@>
   Content-Type: application/sdp
   Content-Length: ...

   <sdp body here>

10.  IANA Considerations

   This document makes no request of IANA.

11.  Security Considerations

   This section is still TBD, but it should follow/have the same issues
   as [draft-gin].

12.  Acknowledgements

   Thanks to Adam Roach for providing text copied from [draft-gin].

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13.  Informative References

   [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., Schulzrinne, H., "Session Initiation
              Protocol (SIP): Locating SIP Servers", RFC 3263, June

   [RFC3327]  Willis, D., and Hoeneisen, B., "Session Initiation
              Protocol (SIP) Extension Header Field for Registering
              Non-Adjacent Contacts", RFC 3327, December 2002.

   [RFC3455]  Garcia-Martin, M., Henrikson, E., and Mills, D., "Private
              Header (P-Header) Extensions to the Session Initiation
              Protocol (SIP) for the 3rd-Generation Partnership Project
              (3GPP)", RFC 3455, January 2003.

   [RFC3608]  Willis, D., and Hoeneisen, B., "Session Initiation
              Protocol (SIP) Extension Header Field for Service Route
              Discovery During Registration", RFC 3608, October 2003.

   [RFC3966]  Schulzrinne, H., "The tel URI for Telephone Numbers", RFC
              3966, December 2004.

   [RFC4244]  Barnes, M. (ed.), "An Extension to the Session Initiation
              Protocol (SIP) for Request History Information", RFC
              4244, November 2005.

   [RFC5486]  Malas, D., and Meyer, D., "Session Peering for Multimedia
              Interconnect (SPEERMINT) Terminology", RFC 5486, March

   [draft-gin] Roach, A. B., "Registration for Multiple Phone Numbers
              in the Session Initiation Protocol (SIP)", draft-ietf-
              martini-gin-01, April 2010.

   [draft-4244bis] Barnes, M., et al, "An Extension to the Session
              Initiation Protocol (SIP) for Request History
              Information", draft-ietf-sipcore-rfc4244bis-00, February

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Author's Address

   Hadriel Kaplan
   Acme Packet
   71 Third Ave.
   Burlington, MA 01803, USA
   Email: hkaplan@acmepacket.com

Appendix A - Why Local-Numbers may need processing by SSPs

   There is some debate about how a non-E.164 AoR could even be
   received by the SSP for processing to begin with.  This section
   describes how such could be the case.

   It should be noted that this document only deals with SIP AoRs of
   the same URI domain name as that of the REGISTER's To URI - namely
   the SSP's domain.

   A SIP Request targeted to a Local-Number could require processing by
   the SSP because:
      - The SSP provides IP-Centrex type services for some of the AoRs
        of an Enterprise, for example for small branches, while
        providing SIP-Trunk service to the main IP-PBX(s).  Requests
        from the IP-Centrex UAs will thus be targeted to Local-numbers
        as they are received by the SSP Proxy on their way to the IP-
      - The SSP provides inbound extension dialing, for example by
        offering private calling-card services, such that a E.164
        number call is terminated by an Application Server of the SSP
        which authenticates the caller belongs to an Enterprise and
        then allows private extension dialing, as a UAC, thereby
        originating a new SIP session Request using a Local-Number
      - The SSP provides inter-branch private dialing, by routing on
        some number of leading digits of a Local-Number.

   There are other possibilities as well, of course, but this section
   is only intended to provide some basic rational for why it is
   possible for a local-number AoR to be used and appear in the SSP.

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