Network Working Group A. van Wijk, Ed.
Request for Comments: 5194 G. Gybels, Ed.
Category: Informational June 2008
Framework for Real-Time Text over IP Using
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.
Abstract
This document lists the essential requirements for real-time Text-
over-IP (ToIP) and defines a framework for implementation of all
required functions based on the Session Initiation Protocol (SIP) and
the Real-Time Transport Protocol (RTP). This includes interworking
between Text-over-IP and existing text telephony on the Public
Switched Telephone Network (PSTN) and other networks.
van Wijk & Gybels Informational [Page 1]RFC 5194 Framework for TOIP using SIP June 2008Table of Contents
1. Introduction ....................................................3
2. Scope ...........................................................4
3. Terminology .....................................................4
4. Definitions .....................................................4
5. Requirements ....................................................6
5.1. General Requirements for ToIP ..............................6
5.2. Detailed Requirements for ToIP .............................8
5.2.1. Session Setup and Control Requirements ..............9
5.2.2. Transport Requirements .............................10
5.2.3. Transcoding Service Requirements ...................10
5.2.4. Presentation and User Control Requirements .........11
5.2.5. Interworking Requirements ..........................13
5.2.5.1. PSTN Interworking Requirements ............13
5.2.5.2. Cellular Interworking Requirements ........14
5.2.5.3. Instant Messaging Interworking
Requirements ..............................14
6. Implementation Framework .......................................15
6.1. General Implementation Framework ..........................15
6.2. Detailed Implementation Framework .........................15
6.2.1. Session Control and Setup ..........................15
6.2.1.1. Pre-Session Setup .........................15
6.2.1.2. Session Negotiations ......................16
6.2.2. Transport ..........................................17
6.2.3. Transcoding Services ...............................18
6.2.4. Presentation and User Control Functions ............18
6.2.4.1. Progress and Status Information ...........18
6.2.4.2. Alerting ..................................18
6.2.4.3. Text Presentation .........................19
6.2.4.4. File Storage ..............................19
6.2.5. Interworking Functions .............................19
6.2.5.1. PSTN Interworking .........................20
6.2.5.2. Mobile Interworking .......................22
6.2.5.2.1. Cellular "No-gain" .............22
6.2.5.2.2. Cellular Text Telephone
Modem (CTM) ....................22
6.2.5.2.3. Cellular "Baudot mode" .........22
6.2.5.2.4. Mobile Data Channel Mode .......23
6.2.5.2.5. Mobile ToIP ....................23
6.2.5.3. Instant Messaging Interworking ............23
6.2.5.4. Multi-Functional Combination Gateways .....24
6.2.5.5. Character Set Transcoding .................25
7. Further Recommendations for Implementers and Service
Providers ......................................................25
7.1. Access to Emergency Services ..............................25
7.2. Home Gateways or Analog Terminal Adapters .................25
7.3. User Mobility .............................................26
van Wijk & Gybels Informational [Page 2]RFC 5194 Framework for TOIP using SIP June 2008
7.4. Firewalls and NATs ........................................26
7.5. Quality of Service ........................................26
8. Security Considerations ........................................26
9. Contributors ...................................................27
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