Requirements for Multiple Address of Record (AOR) Reachability Information in the Session Initiation Protocol (SIP)
RFC 5947

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Internet Engineering Task Force (IETF)                         J. Elwell
Request for Comments: 5947             Siemens Enterprise Communications
Category: Informational                                        H. Kaplan
ISSN: 2070-1721                                              Acme Packet
                                                          September 2010

     Requirements for Multiple Address of Record (AOR) Reachability
          Information in the Session Initiation Protocol (SIP)

Abstract

   This document states requirements for a standardized SIP registration
   mechanism for multiple addresses of record (AORs), the mechanism
   being suitable for deployment by SIP service providers on a large
   scale in support of small to medium sized Private Branch Exchanges
   (PBXs).  The requirements are for a solution that can, as a minimum,
   support AORs based on E.164 numbers.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5947.

Elwell & Kaplan               Informational                     [Page 1]
RFC 5947            Multiple AOR reachability in SIP      September 2010

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. Problem Statement ...............................................4
      3.1. Issues with the REGISTER Transaction .......................5
           3.1.1. Mishandling by SIP-Aware Middleboxes ................5
           3.1.2. REGISTER Response Growth ............................6
           3.1.3. Illegal "Wildcard" Syntax ...........................6
      3.2. Issues with Routing Inbound Requests to the SIP-PBX ........6
           3.2.1. Loss of Target Information ..........................6
           3.2.2. Inconsistent Placement of Target URI
                  Information in Inbound Requests .....................6
           3.2.3. Request-URI Misrouting ..............................7
      3.3. Policy-Related Issues ......................................7
           3.3.1. Authorization Policy Mismatches .....................7
           3.3.2. PAI or PPI URI Mismatches ...........................7
   4. Requirements ....................................................8
   5. Desirables .....................................................10
   6. Non-Requirements ...............................................11
   7. Security considerations ........................................11
   8. Acknowledgements ...............................................12
   9. References .....................................................12
      9.1. Normative References ......................................12
      9.2. Informative References ....................................12

Elwell & Kaplan               Informational                     [Page 2]
RFC 5947            Multiple AOR reachability in SIP      September 2010

1.  Introduction

   The Session Initiation Protocol (SIP) [RFC3261], together with its
   extensions, supports multiple means of obtaining the connection
   information necessary to deliver out-of-dialog SIP requests to their
   intended targets.  When a SIP proxy needs to send a request to a
   target address of record (AOR) within its domain, it can use a
   location service to obtain the registered Contact Universal Resource
   Identifiers (URIs), together with any associated path information
   [RFC3327], and build a route set to reach each target user agent
   (UA).  The SIP REGISTER method can be used to register Contact URIs
   and path information.  SIP-outbound [RFC5626] enhances this mechanism