TCP or RTP for text conversation in H.323

[Scott Bradner]

note that any transport protocol will need to be able to react to
congestion in the network - a good reason to use TCP where one can

Scott

From: Gunnar Hellstrom <gunnar.hellstrom at OMNITOR.SE>
Subject:      TCP or RTP for text conversation in H.323

I have one furter area of discussion:

When selecting the transport protocol for the text conversation, the
current draft (APC 1504) specifies TCP or UDP. It would be good to be able
to specify only one of them.

I realize that there are situations where TCP must be avoided. One such
situation is a sub-titled
H.332 transmission. Also other multi-casting situations is better off with
a UDP based transport protocol.
I am therfore now leaning towards using RTP as the transport for text
conversation. With RTP we can discover dropped frames and possibly invent a
mechanism to mark dropped or destroyed text in the text stream for T.140 to
display. If we
have less than 3 % dropped frames, and these occations are clearly marked,
I think the users could accept it.

Questions

1. Do you agree that there are situations when TCP should be avoided, and
a UDP based protocol preferred?
(H.332, conferencing, connecting through many chained networks, connections
including sattellite links...)

2. Do you agree that RTP is a good alternative, with a thin transport
protocol for
error indications to the user?

3. Most packets will carry only 1-4 characters . Can anyone give me an
indication on the expected packet loss rates in different situations for
such packets. Or a document giving such figures. Is max 3% loss reachable?

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

Tel +46 751 100 501
Fax +46 8 556 002 06

E-mail: gunnar.hellstrom at omnitor.se
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