Caller Preferences for the Session Initiation Protocol (SIP)
RFC 3841
Network Working Group J. Rosenberg
Request for Comments: 3841 dynamicsoft
Category: Standards Track H. Schulzrinne
Columbia University
P. Kyzivat
Cisco Systems
August 2004
Caller Preferences for 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 (2004).
Abstract
This document describes a set of extensions to the Session Initiation
Protocol (SIP) which allow a caller to express preferences about
request handling in servers. These preferences include the ability
to select which Uniform Resource Identifiers (URI) a request gets
routed to, and to specify certain request handling directives in
proxies and redirect servers. It does so by defining three new
request header fields, Accept-Contact, Reject-Contact, and Request-
Disposition, which specify the caller's preferences.
Rosenberg, et al. Standards Track [Page 1]
RFC 3841 Caller Preferences for SIP August 2004
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 4
5. UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Request Handling Preferences . . . . . . . . . . . . . . 6
5.2. Feature Set Preferences . . . . . . . . . . . . . . . . 6
6. UAS Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Request-Disposition Processing . . . . . . . . . . . . . 9
7.2. Preference and Capability Matching . . . . . . . . . . . 9
7.2.1. Extracting Explicit Preferences . . . . . . . . . 10
7.2.2. Extracting Implicit Preferences . . . . . . . . . 10
7.2.2.1. Methods. . . . . . . . . . . . . . . . . 10
7.2.2.2. Event Packages . . . . . . . . . . . . . 11
7.2.3. Constructing Contact Predicates . . . . . . . . . 11
7.2.4. Matching. . . . . . . . . . . . . . . . . . . . . 12
7.2.5. Example . . . . . . . . . . . . . . . . . . . . . 16
8. Mapping Feature Parameters to a Predicate. . . . . . . . . . . 17
9. Header Field Definitions . . . . . . . . . . . . . . . . . . . 19
9.1. Request Disposition . . . . . . . . . . . . . . . . . . 20
9.2. Accept-Contact and Reject-Contact Header Fields . . . . 21
10. Augmented BNF . . . . . . . . . . . . . . . . . . . . . . . . 22
11. Security Considerations . . . . . . . . . . . . . . . . . . . 22
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
14.1. Normative References . . . . . . . . . . . . . . . . . . 24
14.2. Informative References . . . . . . . . . . . . . . . . . 24
15. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25
16. Full Copyright Statements. . . . . . . . . . . . . . . . . . . 26
1. Introduction
When a Session Initiation Protocol (SIP) [1] server receives a
request, there are a number of decisions it can make regarding the
processing of the request. These include:
o whether to proxy or redirect the request
o which URIs to proxy or redirect to
o whether to fork or not
o whether to search recursively or not
Rosenberg, et al. Standards Track [Page 2]
RFC 3841 Caller Preferences for SIP August 2004
o whether to search in parallel or sequentially
The server can base these decisions on any local policy. This policy
can be statically configured, or can be based on execution of a
program or database access.
However, the administrator of the server is the not the only entity
with an interest in request processing. There are at least three
parties which have an interest: (1) the administrator of the server,
(2) the user that sent the request, and (3) the user to whom the
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