H.Chat vs. T.Chat

Gunnar Hellstrom gunnar.hellstrom at OMNITOR.SE
Thu Oct 30 16:38:45 EST 1997

Toby Nixon asks if there really is a need for a simple logical channel
approach for text chatting with T.140 in H.323, or if we could do with the
T.120-based T.134 solution for all H.323 implementations.

If you remember how this started in March in Geneva, I came in with the
view that the T.120 solution for text conversation would mean maximum
compatibility for least work. However, first recations came from the H.324
side, asking for a simple solution in a logical channel. 
Then, in the Herliza meeting, apparently text chatting was discussed in a
group that was aiming at the simple Internet Phone applications, who said
that there should be a similar solution in H.323 if I wanted full coverage
in H.323 products. 

I agree that it complicates the implementations to have T.120 as the
solution to invoke if we turn out to enter a multipoint situation, and
otherwise use plain H.323 data channel for point-to-point.

It is easy for Toby to say that T.120 should be the base. He usually has
enough power and memory around. I would like to get the view from Internet
Phone people as well. If this is the text telephone of the future, it
should be suiable to attach to any implementation of voice and video

On H.320 dedicated simple videophones, it seems to be common to have a
connector that can be used for T.120 application attachment. Can that be
the way to add T.120 to Internet phones also?

A summary of Sunriver activities in the text chat area:
-A general purpose character by character text chat protocol based on
Unicode was determined, named T.140.
-A way to carry T.140 in a simple T.120 APE was determined, named T.134.
-A way to carry T.140 in a simlpe H.324 logical channel was edited into
H.324 and H.245.
-V.18 - the PSTN text telephone modem - was changed to point at T.140
instead of having its own presentation layer.
-Work was initiated to define a way to carry T.140 in a simple data channel
in H.323 - H.245 - H.225.0

If you want to take a look at T.140 and T.134, they are available in

Can all H.323 producers have room for T.120LITE and  T.134 ?

Best regards
Gunnar Hellström

Gunnar Hellström
Alsnögatan 7, 4tr
S-116 41 Stockholm

Tel +46 701 100 501
Fax +46 8 556 002 06

E-mail: gunnar.hellstrom at omnitor.se
WWW:    public-www.pi.se/~omnitor

More information about the sg16-avd mailing list