A Taxonomy of Session Initiation Protocol (SIP) Back-to-Back User Agents
RFC 7092
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RFC - Informational
(December 2013; No errata)
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2015-10-14
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IETF
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WG Document
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Document shepherd |
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Christer Holmberg
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(last changed 2013-06-12)
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RFC 7092 (Informational)
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Gonzalo Camarillo
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Internet Engineering Task Force (IETF) H. Kaplan
Request for Comments: 7092 Oracle
Category: Informational V. Pascual
ISSN: 2070-1721 Quobis
December 2013
A Taxonomy of Session Initiation Protocol (SIP) Back-to-Back User Agents
Abstract
In many SIP deployments, SIP entities exist in the SIP signaling path
between the originating and final terminating endpoints, which go
beyond the definition of a SIP proxy, performing functions not
defined in Standards Track RFCs. The only term for such devices
provided in RFC 3261 is for a Back-to-Back User Agent (B2BUA), which
is defined as the logical concatenation of a SIP User Agent Server
(UAS) and User Agent Client (UAC).
There are numerous types of SIP B2BUAs performing different roles in
different ways; for example, IP Private Branch Exchanges (IPBXs),
Session Border Controllers (SBCs), and Application Servers (ASs).
This document identifies several common B2BUA roles in order to
provide taxonomy other documents can use and reference.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7092.
Kaplan & Pascual Informational [Page 1]
RFC 7092 Taxonomy of B2BUAs December 2013
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. B2BUA Role Types . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Signaling Plane B2BUA Roles . . . . . . . . . . . . . . . 4
3.1.1. Proxy-B2BUA . . . . . . . . . . . . . . . . . . . . . 4
3.1.2. Signaling-only . . . . . . . . . . . . . . . . . . . 4
3.1.3. SDP-Modifying Signaling-only . . . . . . . . . . . . 5
3.2. Signaling/Media Plane B2BUA Roles . . . . . . . . . . . . 5
3.2.1. Media Relay . . . . . . . . . . . . . . . . . . . . . 5
3.2.2. Media Aware . . . . . . . . . . . . . . . . . . . . . 6
3.2.3. Media Termination . . . . . . . . . . . . . . . . . . 6
4. Mapping SIP Device Types to B2BUA Roles . . . . . . . . . . . 6
4.1. SIP PBXs and Softswitches . . . . . . . . . . . . . . . . 6
4.2. Application Servers . . . . . . . . . . . . . . . . . . . 7
4.3. Session Border Controllers . . . . . . . . . . . . . . . 7
4.4. Transcoders . . . . . . . . . . . . . . . . . . . . . . . 7
4.5. Conference Servers . . . . . . . . . . . . . . . . . . . 8
4.6. P-CSCF and IBCF Functions . . . . . . . . . . . . . . . . 8
4.7. S-CSCF Function . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Informative References . . . . . . . . . . . . . . . . . . . 9
Kaplan & Pascual Informational [Page 2]
RFC 7092 Taxonomy of B2BUAs December 2013
1. Introduction
In current SIP deployments, there are numerous forms of Back-to-Back
User Agents (B2BUAs), operating at various levels of transparency and
for various purposes, with widely varying behavior from a SIP
perspective. Some act as pure SIP proxies and only change to the
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