Representing Trunk Groups in tel/sip Uniform Resource Identifiers (URIs)
RFC 4904
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RFC - Proposed Standard
(June 2007; No errata)
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2015-10-14
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IETF
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RFC 4904 (Proposed Standard)
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Jon Peterson
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Network Working Group V. Gurbani
Request for Comments: 4904 Bell Laboratories, Alcatel-Lucent
Category: Standards Track C. Jennings
Cisco Systems
June 2007
Representing Trunk Groups in tel/sip
Uniform Resource Identifiers (URIs)
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 IETF Trust (2007).
Abstract
This document describes a standardized mechanism to convey trunk
group parameters in sip and tel Uniform Resource Identifiers (URIs).
An extension to the tel URI is defined for this purpose.
Gurbani & Jennings Standards Track [Page 1]
RFC 4904 Trunk Groups in tel/sip URIs June 2007
Table of Contents
1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Requirements and Rationale . . . . . . . . . . . . . . . . . . 5
4.1. sip URI or tel URI? . . . . . . . . . . . . . . . . . . . 5
4.2. Trunk Group Namespace: Global or Local? . . . . . . . . . 5
4.3. Originating Trunk Group and Terminating Trunk Group . . . 6
4.4. Intermediary Processing of Trunk Groups . . . . . . . . . 6
5. Trunk Group Identifier: ABNF and Examples . . . . . . . . . . 6
6. Normative Behavior of SIP Entities Using Trunk Groups . . . . 8
6.1. User Agent Client Behavior . . . . . . . . . . . . . . . . 9
6.2. User Agent Server Behavior . . . . . . . . . . . . . . . . 10
6.3. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . 10
7. Example Call Flows . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Reference Architecture . . . . . . . . . . . . . . . . . . 11
7.2. Basic Call Flow . . . . . . . . . . . . . . . . . . . . . 12
7.3. Inter-Domain Call Flow . . . . . . . . . . . . . . . . . . 14
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. IANA considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . . 17
Gurbani & Jennings Standards Track [Page 2]
RFC 4904 Trunk Groups in tel/sip URIs June 2007
1. Background
Call routing in the Public Switched Telephone Network (PSTN) is
accomplished by routing calls over specific circuits (commonly
referred to as "trunks") between Time Division Multiplexed (TDM)
circuit switches. In switches, a group of trunks that connect to the
same target switch or network is called a "trunk group".
Consequently, trunk groups have labels, which are used as the main
indication for the previous and next TDM switch participating in
routing the call.
Formally, we define a trunk and trunk group and related terminology
as follows (definition of "trunk" and "trunk group" is from [5]).
Trunk: In a network, a communication path connecting two
switching systems used in the establishment of an end-to-end
connection. In selected applications, it may have both its
terminations in the same switching system.
Trunk Group: A set of trunks, traffic engineered as a unit, for
the establishment of connections within or between switching
systems in which all of the paths are interchangeable. A single
trunk group can be shared across multiple switches for redundancy
purposes.
Digital Signal 0 (DS0): Digital Signal X is a term for a series
of standard digital transmission rates based on DS0, a
transmission rate of 64 kbps (the bandwidth normally used for one
telephone voice channel). The European E-carrier system of
transmission also operates using the DS series as a base multiple.
Since the introduction of ubiquitous digital trunking, which resulted
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