Text over IP existing standards- requirements - use cases - solutions

Gunnar Hellström gunnar.hellstrom at OMNITOR.SE
Fri Feb 21 02:21:33 EST 2003

Dear all,

The discussion about solutions for text over IP is moving on. One goal for
Q.H/16 is to have a requirement spec agreed from the rapporteurs meeting
March 18-19 in UK.

I have collected some material belonging to this work in
- An overview presentation over standards and solutions made for the ATIS
seminar on Jan.13.
- A small discussion presentation around the proposed requirement spec, a
proposed division in use cases and one brief solution.
- A draft requirement spec, intended to go as a contribution to the Q.H

Please review the draft requirement spec, and comment directly to me or as
contributions to the Q.H meeting.
Please also remember to sign up for the announced Q.H/16 rapporteurs meeting
not later than Feb. 26.

I have noticed that it is good to have a list of already approved standards
at hand when discussiong this topic.

Already approved from standards groups of importance in the TVoIP

- ITU-T F.700 Multimedia framework. Appendix 3, Defines media, among them
Conversational text in two quality levels T1 and T2.  T1 alows 1% errors. T2
allows 0.2 % error rate.

- ITU-T F.703 Multimedia Conversation Service Description. Defines among
other services Text Telephony and Total Conversation, and gives basic
characteristics and requirements. This should be the starting point for the
current work.

- ITU-T V.18, an automoding text telephony standard including Baudot TTY.
When it is specified "V.18 or any of its legacy submodes", it can be
interpreted "Baudot TTY" in USA if you want.

- ITU-T T.140, a presentation level text conversation protocol based on
Unicode. Used in all multimedia environments to add a simple text dialogue
to it. The natural choice for any effort to make TTY-like text conversations
in other networks.

- ITU-T H.323 Annex G Text Conversation and Text SET. Both the text
telephone for H.323 VoIP networks, and the text component to add to H.323
Multimedia environment.

- IETF RFC 2793, RTP Packetization for T.140. A description of how to pack
T.140 text in packets for transmission with the RTP protocol, commonly used
for media transmission in both H.323 and SIP multimedia and VoIP. Includes a
standardised method for repeating information in sequential packets for
increasing reliability.  Includes also the MIME registration so that
text/t140 can be started in a SIP textphone or multimedia phone.

- ITU-T H.248.2 Text and Fax and call discrimination packages for the H.248
gateway protocol. Makes use of V.18, and other standards for discrimination
between voice fax and and text telephony on PSTN lines, and has methods for
establishing and transmitting text over the IP network with T.140 and RFC
2793. The application of V.18 principles in H.248.2 allows configuration to
only support one or a few text telephone types ( e.g. Baudot and native
V.18 )
H.248 is one of the dominating gateway architectures for VoIP.

- 3GPP 26.235, 22.226, 23.226 reuses T.140 with RFC2793 in SIP connections
with text in 3G wireless environments and gatewayes with H.248.2 to TTY and
other textphones.

- 3GPP 26.226 CTM describes a robust method to transport T.140 text over a
voice channel, with possible conversion in both ends to other forms of text
telephony, e.g. V.18 or Baudot TTY. Used in GSM wireless networks.

These standards form a good base when now defining the application in ToIP.


Gunnar Hellström
Omnitor AB
Renathvägen 2
SE 121 37 Johanneshov
+46 8 556 002 03
Mob: +46 708 204 288
Gunnar.Hellstrom at Omnitor.se

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