Annex 3 to AVC-743R

Liaison to SG8 on multiple VCs and error free transport protocol for H.24X

SOURCE	:  Q.2/15
TITLE	:  Liaison to SG8 on multiple VCs and error free transport protocol for H.24X 
PURPOSE	:  Response to a previous Liaison and request for comments

CONTACT	: Sakae OKUBO
		  Rapporteur for Q.2/15
		  Graphics Communication Laboratories
		  6F ANNEX TOSHIN BLDG, 4-36-19 Yoyogi,
		  Shibuya-ku, Tokyo 151 Japan
		     Phone : +81 3 5351 0181
		     Fax     : +81 3 5351 0185
		     e-mail :  okubo@gctech.co.jp

  Experts Group for Video Coding and Systems in ATM and Other Network Environments further discussed the highly reliable transmission for conveying H.24X negotiation information taking the harmonization with Q10/8 into consideration toward the service integration in B-ISDN generation. We tried to define the protocol stack of H.24X channel. We could reach a conclusion that H.24X should have X.214 (COTS) interface with the lower layer to be applicable to various network environments. That is the same approach as T.120 series protocol which is being studied in Q10/8. According to our progress of work, Experts Group for Video Coding and Systems in ATM and Other Network Environments makes the following comment as a reply to the liaison statement from Q10/8.

Transparent data channel in single VC
  SSCOP was examined as a candidate for our protocol stack in case of multiple VC usage. We also considered the support of H.24X information transmission in single VC, using the multiplex mechanism with audio and video provided by H.222.1. In this case, H.222.1 can use either AAL type 1, 2 or 5, and data channel should be transparent and reliable for the purpose of H.24X information transmission. ATM specific method, e.g. SSCOP, cannot be applied, because H.222.1 is located just above the one of AALs in the protocol model.
  Another important issue is alignment with H.24P, which is the negotiation protocol for low bitrate PSTN videophone also studied under Q2/15, the same question as B-ISDN audiovisual terminals. H.24P will use V.42 (LAPM) as underlying transport mechanism.
  As the result of discussion, we decided to use LAPF (Q.922) combined with X.224 class 0 as a lower layer protocol for H.24X channel, considering the LAPM has very similar functionality and characteristics to LAPF. Proposed protocol stack is shown in the attached figure.
  We can now have common protocol stack providing X.214 service for both single VC and multiple VC. We think that T.120 protocol can be embedded in H.222.1 multiplexed stream for single VC without any change. T.120 protocol stack for ATM environment will be hopefully the same as our H.24X protocol stack. Advice and comments from Q10/8 are highly appreciated for further collaborative and harmonized development of audiovisual Recommendations..

Q.2931 vs. H.24X
  We have decided that indication via Q.2931 should be kept minimum. Signaling using Q.2931 information elements is focused on terminal type and stream type indication at the start up of the call. Our scope of H.24X is now capability exchange, e.g. video coding/decoding capability, audio coding/decoding capability etc. The transmission mechanism of H.230 like video frame asynchronous C&I signals will be specified in H.222.1.

ATTACHMENTS:	H.24X Protocol Stack (Fig. 1 in Annex 3 to AVC-743R)
			H.32X  Protocol Reference Model (Annex 9 to AVC-743R)

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