Gallaudet's Chapel Hall with U.S. Capitol dome in backgroundGallaudet's new logo with TAP wording below

Accessible real-time conversational service: 
Summary of overviews, specifications and standards.

Gunnar Hellström, Omnitor
May 25, 2006

This is an overview of specifications related to accessible real time conversation, including Total Conversation and Text Telephony.  The reader must be aware of that the work in the standards groups move on, and new versions of the referenced specifications may take effect. For implementation, only the versions retrieved directly from the standard bodies shall be used and verifying that the version is valid.

Some overviews and presentations are also included.

For 3GPP, the specifications can be found in the "Document area" under  

For ITU-T, the recommendations can be found under .

For IETF, the specifications can be found under .

For ETSI, the specifications can be found under .

All 3GPP specifications related to text telephony and total conversation are accepted as ETSI technical specifications and are listed under ETSI below.


Overviews, articles, regulations, policy statements



Full name



COCOM 04-08

INCOM Report

Report on eAccessibility to EU regulatory group COCOM 

Priority action requirements
TCAM 17(64) TCAM eAccessibility Request to TCAM for terminal related action for accessibility action request from EC
TCAM 17(64) presentation TCAM eAccessibility Presentation to TCAM 17 on real time conversation needs Powerpoint presentation
ITU-T Web pages on Accessibility ITU-T SG 16 Work on Accessibility Summary of work in ITU-T Multimedia group and related Web site

Accessibility presentation in IMTC-NGN workshop


Accessibility in New Emerging Networks and Services Presentation made for joint ITU-T / IMTC workshop 2006 PDF of Powerpoint


Standards and specifications


IETF accessibility specific documents

Standard   Full Name of Standard Explanation   Type Status



Registration of text/red


MIME registration of text with redundancy


MIME reg




IETF RFC 4103 RTP Payload for Text Conversation.   RTP Payload for T.140 text conversation. MIME Registered as "text/t140", used in H.323 and SIP and 3GPP Transport Approved

RFC 2793

draft-ietf-sipping-toip-04   Framework of requirements for real-time text conversation using SIP   Requirements Draft


User Requirements for the Session Initiation Protocol (SIP)
in Support of Deaf, Hard of Hearing
and Speech-impaired Individuals

Handles transcoding and other value added services invoked through SIP.

Requirements Approved
draft-ietf-sipping-transc-conf The session Initiation Protocol Conference bridge transcoding model Mentioned that it can be used for invocation of relay services Procedure specification Draft
IETF RFC 4351 RTP Payload for Text Conversation interleaved in an audio stream RTP Payload for text, intended for transit gateways where number of ports may be an issue. Transport Approved.

IETF General documents of specific interest for accessibility

Specification Title Explanation Type Status

 IETF RFC 2327

SDP;  Session Description Protocol

Parameters and formats for call setup in SIP

Call control Approved
IETF RFC 3261 SIP; Session Initiation Protocol Session initiation Protocol – used to connect Voice over IP (Internet Protocol) phone calls. Call control Approved

IETF  RFC 2833

RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals

Encoding and transport of tones over IP

Transport Approved
draft-ietf-mmusic-sdp-new-26 Session Description Protocol Contains "text" as an allowable media type. Intended to replace RFC3261 Call control Draft, for approval
IETF RFC 2198 Redundancy for RTP payloads Used in RFC4103 for reliability of text traffic Transport Approved
IETF RFC 3840 Indicating User Agent Capabilities in
the Session Initiation Protocol (SIP)
Can be useful for preference and capability indication for service invocation Call control Approved
IETF RFC 3841 Caller Preferences for the Session Initiation Protocol Can be useful for preference and capability indication for service invocation Call control Approved
draft-ietf-avt-rfc2833bisdata Definition of Events For Modem, FAX, and Text Telephony Signals Text telephone signals expanded, will replace RFC2833 Transport Approved by Working group, publication requested
IETF RFC 4504 SIP Telephony Device Requirements and Configuration Text requirements included, referring to RFC 4103 Device requirements Approved
IETF RFC 3550 RTP; Real Time Protocol Media protocol in SIP and others Transport Approved
IETF RFC 3711 SRTP; Secure Real Time Protocol Encryption etc on RTP Transport Approved
draft-ietf-ecrit-requirements-09.txt Requirements for Emergency Context Resolution with Internet Technologies Requirements for emergency services in IP, including real time teext Service requirements Draft


ITU Accessibility specific documents




Type Status

ITU-T Rec.  V.18

Operational and Interworking Requirements for DCE:s Operating in the Text Telephone Mode

Includes automatic interworking with most legacy text telephones.

Modem transport Approved

ITU-T Study Group 16

Text Telephony over IP

Text Telephony transit through IP.

Gateway Approved

ITU-T Rec. F.703

Multimedia conversational services

Defines Text Telephony and Total Conversation services

Service description Approved

ITU-T Rec. H.224 

A real time control protocol for simplex applications using the H.221 LSD/HSD/HLP channel.

Addition of client id=2 for T.140 text transport

Transport Approved

ITU-T Rec. H.323 Annex G

Text Conversation and Text SET.

Defines T.140 text inclusion in H.323 IP Multimedia

Call control Approved
ITU-T Rec H.323 Annex G v2

Text Conversation and Text SET.

Defines T.140 text inclusion in H.323 IP Multimedia

Call control Approved

ITU-T Rec.T.134

Text Chat Application Entity

Application for text conversation in the T.120 data conferencing concept.

Transport Approved

ITU-T Rec.  T.140

Protocol for multimedia application text conversation.

Text conversation protocol for multimedia application. With amendment 1 (2000).

Presentation level Approved

ITU-T Rec.T.140  - Addendum

Marking of missing characters

Replacement for characters  missing after transmission

Presentation Approved

ITU-T H Series Supplement 1

Video Quality for sign language and lip reading

Quality characteristics of video transmission of importance for sign language and lip-reading use.

Requirement Approved
ITU-T Rec. H.248.2v2 Packages for fax, text and call discrimination Text telephony to text over IP gateway. Approved revision. Gateway Approved


ITU general documents of accessibility interest


Full Name of Standard


Type Status

ITU-T Recommendation H.248

Gateway control protocol

 Control of gateways.

Gateway Approved
ITU-T Recommendation H.248.21 Controlled multimedia conferences Includes text Conference control protocol Approved

ITU-T Rec. F.700

Framework Recommendation for multimedia services, Annex A.3.

Multimedia Framework, including real time text

Service description Approved

ITU-T Rec.V.250

Serial asynchronous automatic dialling and control

Contains modem control for V.18 

Call control Approved

ITU-T Recommendation

Procedures for starting sessions of data transmission over the public switched telephone network

Contains call function = text telephony

Call control Approved

ITU-T Recommendation
V.8 bis

Procedures for the identification and selection of common modes of operation between Data Circuit-terminating Equipments (DCEs) and between Data Terminal Equipments (DTEs) over the public switched telephone network

Contains procedures for starting simultaneous voice and text in V.18.

Call control Approved


Modem transit over IP

International  Recommendation for transport of Modem over IP

Gateway Approved

ITU-T Rec.V.152

Procedures for supporting Voice Band Data over IP networks

Usable for text telephony transit through IP networks

Gateway Approved

ITU-T Rec.H.324

Terminal for low bit-rate multimedia communication

Addition of data channel for T.140 text

Multimedia system Approved

ITU-T Rec.  V.61

Analog simultaneous voice and data (permits Voice carry over with ASCII modems

Possible to use under V.18 

Modem transport Approved

ITU-T Rec.H.320

ISDN visual telephone systems and terminal equipment.

Text conversation added 

Multimedia system Approved

ITU-T Rec. H.245

Control Protocol for Multimedia Communication

Multimedia Control protocol, includes setup of text channels

Call control Approved

ITU Y.1541  


Network performance objectives for IP-based services  






NGN Release 1 Scope Scope for next generation network Real time text included Requirements Draft
NGN Release 1 Requirements Requirements for next generation networks Accessibility additions proposed Requirements Draft
F.724 IP Videophone service description Real time text included Service description Approved
F.733 Multimedia conference services Real time text included Service description Approved
F.742 Service description and requirements for distance learning services Real time text included Service description Approved


ETSI and 3GPP Accessibility specific documents




Type Status


Text Telephony, User Requirements And Recommendations

Describes user needs for text conversation and guidelines for standardisation

Requirement Approved.

ETSI TR 101 806  


Guidelines for Telecommunication Relay Services for text and video

Guidelines for Telecommunication Relay Services for text and video

Requirement Approved

ETSI TS 122 226

3GPP TS 22.226

Global Text Telephony Service Stage 1

Global Text and Total conversation (GTT) service description

Service Approved

ETSI TS 123 226  

3GPP TS 23.226

Global Text Telephony Architecture Stage 2

GTT Specific description of network architecture for text conversation and especially CTM text telephony

Architecture Approved

ETSI TS 126 226  

3GPP TS 26.226

CTM Modem, General description

Robust  and error tolerant modem for text telephony specified for mobile networks.

Modem transport Approved

ETSI TS 126 235  

3GPP TS 26.235

Packet Switched Conversational Multimedia , default codecs

Includes text conversation using T.140 in RTP as RFC 2793.

Profile Approved
ETSI TS 126 236

3GPP TS 26.236

Packet switched conversational multimedia, transport. Includes text conversation transport RFC 2793 Profile Approved
ETSI EG 202 320 Duplex Universal Speech and Text Communication  Guide for text as a mainstream call component Requirements and implementation framework Approved


ETSI and 3GPP general documents of accessibility interest




Type Status

ETSI TS 122 101

3GPP TS 22.101

Service principles

Brief description of mobile text conversation

Service Approved

ESI TS 126 110  

3GPP TS 26.110

Circuit Switched Multimedia Telephony
( 3G.324 )

Includes text conversation using T.140 in AL1 channel

Multimedia call control Approved
ETSI TS 124 008

3GPP TS 24.008

Terminal indicators CTM indicator from terminal is defined here Call control Approved
3GPP TS 26.114 IMS Multimedia Telephony codec principles Real-time text, video and audio are included Profile and codec details Draft


EIA/TIA Accessibility specific Documents


Full Name of Standard


Type Status

TIA/EIA 825a

A Frequency Shift Keyed Modem  for use on  the Public Switched Telephone Network

The standard for TTY signals, which permitted mainstream industry to design for compatibility with TTY as technologies moved to digital.

Modem transport Approved

TIA 1001 

Standards for text over IP (TIA 1001) transit gateway

U.S. effort to develop standard methods for carrying Baudot over IP  networks, using voice band data and gateway approaches.

Gateway Approved

TIA- 504-A

Telecommunications-Telephone Terminal Equipment-Magnetic Field and Acoustic Gain Requirements for Headset Telephones Intended for Use by the Hard of Hearing


Requirement Approved


Telecommunications - Telephone Terminal Equipment - Technical Requirements for Connection of Terminal Equipment to the Telephone Network


Requirement Approved

TR 45


2.5 mm Audio Interface For Mobile Wireless Handsets - Text Telephones (TTY)

Connector standard for wireless telephones and TTYs

Physical Approved


ANSI C.63.19

American National Standard for Methods of Measurement of Compatibility between Wireless Communication Devices and Hearing Aids

Measurements of wireless telephone emissions and hearing aid immunity, with predicted performance based on measures.  (Now in use in an FCC order)

Interference Approved

TIA IS-823

TTY/TDD Extension to TIA/EIA 136-410 Enhanced Full Rate Speech Codec




TIA -IS-840

Minimum Performance Standards for Text Telephone Signal Detector and Text Telephone Signal Regenerator





2.5 mm Audio Interface For Mobile Wireless Handsets - Text Telephones (TTY)





EIA/TIA General documents with accessibility interest.


Full Name of Standard


Type Status

TIA IS-127-2

Enhanced Variable Rate Codec, Speech Service Option 3 for Wideband Spread Spectrum Digital Systems - Addendum 2


 Speech codec


TIA IS-707-A-2

Data Services Options for Spread Spectrum Systems - Radio Link Protocol Type 3 - Addendum No. 2




TIA IS-733-1

High Rate Speech Service Option 17 for Wideband Spread Spectrum Communications Systems




 TIA IS-789A

 Electrical Specification for the Portable Phone to Vehicle Interface





DTE/DCE Interface For Digital Cellular Equipment





American National Standard for Operations Administration and Maintenance and Provisioning (OAM&) – Network Tones and Announcements

Provides and industry standard way for network routing messages to be conveyed in TTY in addition to voice.



Black Line Back to home page

Valid XHTML 1.0 Strict

Optimized for a width of 800 - This page last updated: July 12, 2018
© Copyright 2007 by the Technology Access Program - All Rights Reserved