Framework for Real-Time Text over IP Using the Session Initiation Protocol (SIP)
RFC 5194

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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 2008

Table 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
   10. References ....................................................27
      10.1. Normative References .....................................27