Dear SG16 colleagues,
Attached please find my correspondence with Seung ho SHIN, Korean Telecom, regarding the phase change from A4 (logical channels setup) to B (audiovisual communication) in H.310 terminals. The same discussion will apply to the phase change from D (initialization) to E (communication) in H.324 terminals.
I hope my understanding in the reply is correct.
Best regards,
Sakae OKUBO (Mr.) ******************************************************************** Graphics Communication Laboratories Phone: +81 3 5351 0181 6F ANNEX TOSHIN BLDG. Fax: +81 3 5351 0184 4-36-19 Yoyogi, Shibuya-ku, Tokyo e-mail: okubo@gctech.co.jp 151 Japan ********************************************************************
Dear Seung ho SHIN,
In phase A4(logical channels setup), which is one of H.310 call phases for native H.310 communication, H.310 terminal establishes multiple logical channels. After completing logical channels setup, H.310 terminal transit from phase A4 to phase B. The out-going terminal can know the instant that H.245 completes multiple logical channels setup. But the in-coming terminal can't know it.
The in-coming terminal can't know how many the out-going terminal attempts to setup logical channels. Therefore, the in-coming terminal doesn't know when it transits from phase A4 to phase B.
How can I solve this problem?
Communication phases set out in Section 7 of H.310 are to describe the communication steps from the start to the end of an H.310 call, not necessarily to specify state machines of the terminal.
In case of moving from phase A4 (logical channels setup) to Phase B (audiovisual communication), there is no clear state transition of the terminal as a whole. As soon as a logical channel is in the ESTABLISHED state, its corresponding media content (either of audio, video, data, or video frame synchronous signalling) can be transmitted, thus communication can start. Transmission of multiple media contents can be synchronous, or can be audio first and video later, or can be left as they start according to the terminal design. Data, in particular, may usually start some time after audio and video communications have started.
Therefore even in the transmitting side, transition from phase A4 to phase B differs from one logical channel to another. Identification of phase transition at the receiving side similarly depends on each logical channel.
Please note, however, that H.245 defines state machines for their signalling entities to assure their operation.
I hope this information would help your resuming H.310 terminal implementation.
END