Indication of Support for Keep-Alive
RFC 6223

Internet Engineering Task Force (IETF)                       C. Holmberg
Request for Comments: 6223                                      Ericsson
Category: Standards Track                                     April 2011
ISSN: 2070-1721

                  Indication of Support for Keep-Alive

Abstract

   This specification defines a new Session Initiation Protocol (SIP)
   Via header field parameter, "keep", which allows adjacent SIP
   entities to explicitly negotiate usage of the Network Address
   Translation (NAT) keep-alive mechanisms defined in SIP Outbound, in
   cases where SIP Outbound is not supported, cannot be applied, or
   where usage of keep-alives is not implicitly negotiated as part of
   the SIP Outbound negotiation.

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/rfc6223.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Holmberg                     Standards Track                    [Page 1]
RFC 6223                       Keep-Alive                     April 2011

Table of Contents

   1. Introduction ....................................................2
      1.1. Use-Case: Dialog from Non-Registered UAs ...................3
      1.2. Use-Case: SIP Outbound Not Supported .......................3
      1.3. Use-Case: SIP Dialog Initiated Outbound Flows ..............3
   2. Conventions .....................................................3
   3. Definitions .....................................................4
   4. User Agent and Proxy Behavior ...................................4
      4.1. General ....................................................4
      4.2. Lifetime of Keep-Alives ....................................5
           4.2.1. General .............................................5
           4.2.2. Keep-Alives Associated with Registration ............5
           4.2.3. Keep-Alives Associated with Dialog ..................6
      4.3. Behavior of a SIP Entity Willing to Send Keep-Alives .......6
      4.4. Behavior of a SIP Entity Willing to Receive Keep-Alives ....7
   5. Keep-Alive Frequency ............................................8
   6. Connection Reuse ................................................9
   7. Examples ........................................................9
      7.1. General ....................................................9
      7.2. Keep-Alive Negotiation Associated with
           Registration: UA-Proxy .....................................9
      7.3. Keep-Alive Negotiation Associated with Dialog: UA-Proxy ...11
      7.4. Keep-Alive Negotiation Associated with Dialog: UA-UA ......13
   8. Grammar ........................................................15
      8.1. General ...................................................15
      8.2. ABNF ......................................................15
   9. IANA Considerations ............................................15
      9.1. "keep" Via Header Field Parameter .........................15
   10. Security Considerations .......................................15
   11. Acknowledgements ..............................................16
   12. References ....................................................17
      12.1. Normative References .....................................17
      12.2. Informative References ...................................17

1.  Introduction

   Section 3.5 of SIP Outbound [RFC5626] defines two keep-alive
   mechanisms.  Even though the keep-alive mechanisms are separated from
   the rest of the SIP Outbound mechanism, SIP Outbound does not define
   a mechanism to explicitly negotiate usage of the keep-alive
   mechanisms.  In some cases, usage of keep-alives can be implicitly