Multiple Dialog Usages in the Session Initiation Protocol
RFC 5057
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RFC - Informational
(November 2007; No errata)
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2015-10-14
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IETF
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RFC 5057 (Informational)
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Jon Peterson
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Network Working Group R. Sparks
Request for Comments: 5057 Estacado Systems
Category: Informational November 2007
Multiple Dialog Usages in the Session Initiation Protocol
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
Several methods in the Session Initiation Protocol (SIP) can create
an association between endpoints known as a dialog. Some of these
methods can also create a different, but related, association within
an existing dialog. These multiple associations, or dialog usages,
require carefully coordinated processing as they have independent
life-cycles, but share common dialog state. Processing multiple
dialog usages correctly is not completely understood. What is
understood is difficult to implement.
This memo argues that multiple dialog usages should be avoided. It
discusses alternatives to their use and clarifies essential behavior
for elements that cannot currently avoid them.
This is an informative document and makes no normative statements of
any kind.
Sparks Informational [Page 1]
RFC 5057 Multiple Dialog Usages November 2007
Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Examples of Multiple Usages . . . . . . . . . . . . . . . . . 4
3.1. Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Reciprocal Subscription . . . . . . . . . . . . . . . . . 6
4. Usage Creation and Destruction . . . . . . . . . . . . . . . . 9
4.1. Invite Usages . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Subscribe usages . . . . . . . . . . . . . . . . . . . . . 9
5. Proper Handling of Multiple Usages . . . . . . . . . . . . . . 9
5.1. A Survey of the Effect of Failure Responses on Usages
and Dialogs . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Transaction Timeouts . . . . . . . . . . . . . . . . . . . 15
5.3. Matching Requests to Usages . . . . . . . . . . . . . . . 16
5.4. Target Refresh Requests . . . . . . . . . . . . . . . . . 17
5.5. Refreshing and Terminating Usages . . . . . . . . . . . . 17
5.6. Refusing New Usages . . . . . . . . . . . . . . . . . . . 18
5.7. Replacing Usages . . . . . . . . . . . . . . . . . . . . . 18
6. Avoiding Multiple Usages . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
10. Informative References . . . . . . . . . . . . . . . . . . . . 24
1. Overview
This is an informative document. It makes no normative statements of
any kind. This document refines the concept of a dialog usage in the
Session Initiation Protocol (SIP [1]), and discusses what led to its
existence. It explores ambiguity associated with processing multiple
dialog usages that share a dialog. In particular, it surveys the
effect of SIP failure responses on transaction, dialog usage, and
dialog state. This document will help the implementer understand
what is required to process multiple dialog usages correctly, and
will provide information for future standards-track work that will
clarify RFC 3261 and other related documents. Finally, the document
explores single-usage dialog alternatives (using SIP extensions) to
multiple dialog usages.
2. Introduction
Several methods in SIP can establish a dialog. When they do so, they
also establish an association between the endpoints within that
dialog. This association has been known for some time as a "dialog
usage" in the developer community. A dialog initiated with an INVITE
request has an invite usage. A dialog initiated with a SUBSCRIBE
Sparks Informational [Page 2]
RFC 5057 Multiple Dialog Usages November 2007
request has a subscribe usage. A dialog initiated with a REFER
request has a subscribe usage.
Dialogs with multiple usages arise when a usage-creating action
occurs inside an existing dialog. Such actions include accepting a
REFER or SUBSCRIBE issued inside a dialog established with an INVITE
request. Multiple REFERs within a dialog create multiple
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