Connection Reuse in the Session Initiation Protocol (SIP)
RFC 5923

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Internet Engineering Task Force (IETF)                   V. Gurbani, Ed.
Request for Comments: 5923             Bell Laboratories, Alcatel-Lucent
Category: Standards Track                                        R. Mahy
ISSN: 2070-1721                                             Unaffiliated
                                                                 B. Tate
                                                               BroadSoft
                                                               June 2010

       Connection Reuse in the Session Initiation Protocol (SIP)

Abstract

   This document enables a pair of communicating proxies to reuse a
   congestion-controlled connection between themselves for sending
   requests in the forwards and backwards direction.  Because the
   connection is essentially aliased for requests going in the backwards
   direction, reuse is predicated upon both the communicating endpoints
   authenticating themselves using X.509 certificates through Transport
   Layer Security (TLS).  For this reason, we only consider connection
   reuse for TLS over TCP and TLS over Stream Control Transmission
   Protocol (SCTP).  This document also provides guidelines on
   connection reuse and virtual SIP servers and the interaction of
   connection reuse and DNS SRV lookups in SIP.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc5923.

Gurbani, et al.              Standards Track                    [Page 1]
RFC 5923                  SIP Connection Reuse                 June 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 ....................................................4
   3.  Applicability Statement ........................................5
   4.  Benefits of TLS Connection Reuse ...............................5
   5.  Overview of Operation ..........................................6
   6.  Requirements ..................................................10
   7.  Formal Syntax .................................................11
   8.  Normative Behavior ............................................11
     8.1.  Client Behavior ...........................................11
     8.2.  Server Behavior ...........................................13
     8.3.  Closing a TLS Connection ..................................14
   9.  Security Considerations .......................................14
     9.1.  Authenticating TLS Connections: Client View ...............14
     9.2.  Authenticating TLS Connections: Server View ...............15
     9.3.  Connection Reuse and Virtual Servers ......................15
   10. Connection Reuse and SRV Interaction ..........................17
   11. IANA Considerations ...........................................17
   12. Acknowledgments ...............................................17
   13. References ....................................................18
     13.1. Normative References ......................................18
     13.2. Informative References ....................................18

Gurbani, et al.              Standards Track                    [Page 2]
RFC 5923                  SIP Connection Reuse                 June 2010

1.  Introduction

   SIP entities can communicate using either unreliable/connectionless
   (e.g., UDP) or reliable/connection-oriented (e.g., TCP, SCTP
   [RFC4960]) transport protocols.  When SIP entities use a connection-
   oriented protocol (such as TCP or SCTP) to send a request, they
   typically originate their connections from an ephemeral port.

   In the following example, A listens for SIP requests over TLS on TCP
   port 5061 (the default port for SIP over TLS over TCP), but uses an
   ephemeral port (port 49160) for a new connection to B.  These