Network Working Group G. Camarillo
Request for Comments: 4032 Ericsson
Updates: 3312 P. Kyzivat
Category: Standards Track Cisco Systems
March 2005
Update to the Session Initiation Protocol (SIP)
Preconditions Framework
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 updates RFC 3312, which defines the framework for
preconditions in SIP. We provide guidelines for authors of new
precondition types and describe how to use SIP preconditions in
situations that involve session mobility.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Defining New Precondition Types . . . . . . . . . . . . . . . 3
3.1. Precondition Type Tag . . . . . . . . . . . . . . . . . 3
3.2. Status Type . . . . . . . . . . . . . . . . . . . . . . 3
3.3. Precondition Strength . . . . . . . . . . . . . . . . . 3
3.4. Suspending and Resuming Session Establishment . . . . . 3
4. Issues Related to Session Mobility . . . . . . . . . . . . . . 4
4.1. Update to RFC 3312 . . . . . . . . . . . . . . . . . . . 5
4.2. Desired Status . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
Camarillo & Kyzivat Standards Track [Page 1]
RFC 4032 SIP Preconditions Framework March 2005
8.2. Informational References . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
RFC 3312 [3] defines the framework for SIP [2] preconditions, which
is a generic framework that allows SIP UAs (User Agents) to suspend
the establishment of a session until a set of preconditions are met.
Although only Quality of Service (QoS) preconditions have been
defined so far, this framework supports different types of
preconditions. (QoS preconditions are defined by RFC 3312 as well).
This document updates RFC 3312, provides guidelines for authors of
new precondition types and explains which topics they need to discuss
when defining them. In addition, it updates some of the procedures
in RFC 3312 for using SIP preconditions in situations that involve
session mobility as described below.
RFC 3312 focuses on media sessions that do not move around. That is,
media is sent between the same end-points throughout the duration of
the session. Nevertheless, media sessions established by SIP are not
always static.
SIP offers mechanisms to provide session mobility, namely re-INVITEs
and UPDATEs [5]. While existing implementations of RFC 3312 can
probably handle session mobility, there is a need to explicitly point
out the issues involved and make a slight update on some of the
procedures defined there in. With the updated procedures defined in
this document, messages carrying precondition information become more
explicit about the current status of the preconditions.
Specifically, we now allow answers to downgrade current status values
(this was disallowed by RFC 3312). We consider moving an existing
stream to a new location as equivalent to establishing a new stream.
Therefore, answers moving streams to new locations set all the
current status values in their answers to "No" and start a new
precondition negotiation from scratch.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
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