Early Media and Ringing Tone Generation in the Session Initiation Protocol (SIP)
RFC 3960
Document | Type | RFC - Informational (December 2004; No errata) | |
---|---|---|---|
Authors | Henning Schulzrinne , Gonzalo Camarillo | ||
Last updated | 2015-10-14 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 3960 (Informational) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Allison Mankin | ||
Send notices to | rohan@cisco.com, dean.willis@softarmor.com |
Network Working Group G. Camarillo Request for Comments: 3960 Ericsson Category: Informational H. Schulzrinne Columbia University December 2004 Early Media and Ringing Tone Generation in the Session Initiation Protocol (SIP) 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. Copyright Notice Copyright (C) The Internet Society (2004). Abstract This document describes how to manage early media in the Session Initiation Protocol (SIP) using two models: the gateway model and the application server model. It also describes the inputs one needs to consider in defining local policies for ringing tone generation. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Session Establishment in SIP . . . . . . . . . . . . . . . . . 3 3. The Gateway Model. . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Forking. . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Ringing Tone Generation. . . . . . . . . . . . . . . . . 5 3.3. Absence of an Early Media Indicator. . . . . . . . . . . 7 3.4. Applicability of the Gateway Model . . . . . . . . . . . 8 4. The Application Server Model . . . . . . . . . . . . . . . . . 8 4.1. In-Band Versus Out-of-Band Session Progress Information. 9 5. Alert-Info Header Field. . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations. . . . . . . . . . . . . . . . . . . . 9 7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.1. Normative References . . . . . . . . . . . . . . . . . . 11 8.2. Informative References . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 13 Camarillo & Schulzrinne Informational [Page 1] RFC 3960 Early Media and Ringing Tone Generation December 2004 1. Introduction Early media refers to media (e.g., audio and video) that is exchanged before a particular session is accepted by the called user. Within a dialog, early media occurs from the moment the initial INVITE is sent until the User Agent Server (UAS) generates a final response. It may be unidirectional or bidirectional, and can be generated by the caller, the callee, or both. Typical examples of early media generated by the callee are ringing tone and announcements (e.g., queuing status). Early media generated by the caller typically consists of voice commands or dual tone multi-frequency (DTMF) tones to drive interactive voice response (IVR) systems. The basic SIP specification (RFC 3261 [1]) only supports very simple early media mechanisms. These simple mechanisms have a number of problems which relate to forking and security, and do not satisfy the requirements of most applications. This document goes beyond the mechanisms defined in RFC 3261 [1] and describes two models of early media implementations using SIP: the gateway model and the application server model. Although both early media models described in this document are superior to the one specified in RFC 3261 [1], the gateway model still presents a set of issues. In particular, the gateway model does not work well with forking. Nevertheless, the gateway model is needed because some SIP entities (in particular, some gateways) cannot implement the application server model. The application server model addresses some of the issues present in the gateway model. This model uses the early-session disposition type, which is specified in [2]. The remainder of this document is organized as follows: Section 2 describes the offer/answer model in the absence of early media, and Section 3 introduces the gateway model. In this model, the early media session is established using the early dialog established by the original INVITE. Sections 3.1, 3.2, and 3.4 describe the limitations of the gateway model and the scenarios where it is appropriate to use this model. Section 4 introduces the application server model, which, as stated previously, resolves some of the issues present in the gateway model. Section 5 discusses the interactions between the Alert-Info header field in both early media models. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", " NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in thisShow full document text