Session Timers in the Session Initiation Protocol (SIP)
RFC 4028
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RFC - Proposed Standard
(May 2005; Errata)
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2015-10-14
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IETF
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RFC 4028 (Proposed Standard)
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Allison Mankin
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<rohan@cisco.com>
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Network Working Group S. Donovan
Request for Comments: 4028 J. Rosenberg
Category: Standards Track Cisco Systems
April 2005
Session Timers in the Session Initiation Protocol (SIP)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document defines an extension to the Session Initiation Protocol
(SIP). This extension allows for a periodic refresh of SIP sessions
through a re-INVITE or UPDATE request. The refresh allows both user
agents and proxies to determine whether the SIP session is still
active. The extension defines two new header fields:
Session-Expires, which conveys the lifetime of the session, and
Min-SE, which conveys the minimum allowed value for the session
timer.
Donovan & Rosenberg Standards Track [Page 1]
RFC 4028 Session Timer April 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of Operation . . . . . . . . . . . . . . . . . . . 4
4. Session-Expires Header Field Definition . . . . . . . . . . 6
5. Min-SE Header Field Definition . . . . . . . . . . . . . . . 8
6. 422 Response Code Definition . . . . . . . . . . . . . . . . 8
7. UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Generating an Initial Session Refresh Request . . . . 9
7.2. Processing a 2xx Response . . . . . . . . . . . . . . 9
7.3. Processing a 422 Response . . . . . . . . . . . . . . 11
7.4. Generating Subsequent Session Refresh Requests . . . . 11
8. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Processing of Requests . . . . . . . . . . . . . . . . 13
8.2. Processing of Responses . . . . . . . . . . . . . . . 14
8.3. Session Expiration . . . . . . . . . . . . . . . . . . 15
9. UAS Behavior . . . . . . . . . . . . . . . . . . . . . . . . 15
10. Performing Refreshes . . . . . . . . . . . . . . . . . . . . 17
11. Security Considerations . . . . . . . . . . . . . . . . . . 18
11.1. Inside Attacks . . . . . . . . . . . . . . . . . . . . 18
11.2. Outside Attacks . . . . . . . . . . . . . . . . . . . 19
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 19
12.1. IANA Registration of Min-SE and Session-Expires
Header Fields . . . . . . . . . . . . . . . . . . . . 19
12.2. IANA Registration of the 422 (Session Interval Too
Small) Response Code . . . . . . . . . . . . . . . . . 20
12.3. IANA Registration of the 'timer' Option Tag . . . . . 20
13. Example Call Flow . . . . . . . . . . . . . . . . . . . . . 20
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
15.1. Normative References . . . . . . . . . . . . . . . . . 25
15.2. Informative References . . . . . . . . . . . . . . . . 26
Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 26
Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
The Session Initiation Protocol (SIP) [2] does not define a keepalive
mechanism for the sessions it establishes. Although the user agents
may be able to determine whether the session has timed out by using
session specific mechanisms, proxies will not be able to do so. The
result is that call stateful proxies will not always be able to
determine whether a session is still active. For instance, when a
user agent fails to send a BYE message at the end of a session, or
when the BYE message gets lost due to network problems, a call
stateful proxy will not know when the session has ended. In this
situation, the call stateful proxy will retain state for the call and
Donovan & Rosenberg Standards Track [Page 2]
RFC 4028 Session Timer April 2005
has no method to determine when the call state information no longer
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