I am searching my dim T.120 memory (it's been a while) as well as some of the documents and here's my recollection:
In essence, you do not need the TSAP-ID parameters at all and can leave them empty (they are optional as far as I remember X.224/0). The TSAP-IDs constitute a way for addressing tranport layer entities and thus for multiplexing transport connections in the OSI model (similar to TCP port numbers). However, if you are using T.120, there is typically no such additional muxing required: either you use X.224/0/TPKT/TCP/IP in which cse you will make use of the well-defined T.120 port (1503, for stand-along applications) or you will negotiate a port number for data conferencing using e.g. H.245 OpenLogicalChannel procedures; in neither case you need an additional muxing point, so you can leave the TSAP-IDs empty. If don't have an IP-based network, you are likely to be running T.120 in the context of another H.32x system where, again, use may use H.242 or H.245 for assigning logical channels for T.120 data so that you do not need an additional muxing layer and can leave the TSAP-IDs empty. If you run a stand-alone T.120 system, the T.120 standards assume that you do not have other OSI applications running in parallel (which seems pretty likely :-) so that you don't need TSAP-IDs in this case, too.
Leaving TSAP-IDs empty is allowed according to X.224 (11/93) para 6.5.4 (b) and encouraged following T.123 section 6 (second to last paragraph or so).
Hope this helps, Joerg
Pl. help Vish - Radhika
-----Original Message----- From: vish@jlonline.com [SMTP:vish@jlonline.com] Sent: Friday, December 24, 1999 4:50 AM To: Roy, Radhika R, ALARC Subject: about t120
Hi Mr Radhika, In X.224 13.3.4,the TSAP-ID parameter in CR PDU header is not defined,the x.224 does not specify which recommendation is used,where can I find the encoding method of the TSAP-ID parameters? Could you help me?thank you very much!
Merry Christmas
vish