ITU Telecommunication Standardization Sector	Document AVC-578R
Study Group 15	September 10, 1993
Experts Group for ATM Video Coding	
(Rapporteur's Group on Part of Q.2/15)

Source:	RAPPORTEUR (Sakae OKUBO)	
Title:	REPORT OF THE THIRTEENTH EXPERTS GROUP MEETING IN BRUSSELS (September 2-10, 1993) - Part I and Part II	
Purpose:	Report	

-----------------------

Part I	General
Part II	Sole sessions in Boston
Part III	Joint sessions in New York (see AVC-554R)

Part I  General

The twelfth meeting of the Experts Group was held in Brussels, Belgium, as follows;

- 	ITU-TS sole sessions during 2-3 September at the kind invitation of BELGACOM, 
- 	Joint sessions with ISO/IEC JTC1/SC29/WG11 (MPEG) during 6-10 September at the kind invitation of Commission of the European Communities, DGXIIIB - Advanced Communication.

The list of participants appears at the end of this document. 

Part II  Sole Sessions

Contents

1. 	Introduction
2. 	Documentation
3. 	Tape demonstration
4. 	Review of the previous meetings
5. 	Video source coding
6. 	Network aspects
7. 	Profiles
8. 	Work plan
9. 	Progress report to SG15
10.	Joint sessions with MPEG
11.	Future meetings

1. Introduction

The ITU-TS sole sessions were held at BELGACOM during 2-3 September 1993 at the kind invitation of BELGACOM.  At the opening session, Mr. O. Poncin made a welcoming address on behalf of the hosting organization.  

At the end of the sessions, Chairman thanked the hosting organization for the meeting facilities provided and the excellent secretarial support.

We had also a short closing session on 10 September under chairmanship of Mr. G. Morrison to review both sole and joint sessions as well as to prepare for the Daejeon/Seoul meeting.

Key words headed by • at the start of Section indicate items for discussion in this report.

2. Documentation (TD-2)

For the sole sessions, 26 AVC-numbered documents and 10 Temporary Documents have been made available as listed in Annex 1.

3. Tape demonstration (TD-3)

Two video tape demonstrations in D1 format were given to present experimental results as detailed in Annex 2 .  

4. Review of the previous meetings 

4.1 Sole sessions in Boston (AVC-553R)

There were no comments to the meeting report.

4.2 Joint sessions in New York (AVC-552,554R,555,556)

Chairman highlighted the following items which had been identified as needing responses of the ITU-T group at the New York joint sessions;

	- H.261 compatibility
	- Data Partitioning

5. Video source coding

5.1 VBV specifications (Annex C to AVC-555, AVC-563; TD-8)

		• handling of 3:2 pulldown
		• low delay operational mode (M=1)

The meeting supported the solution in AVC-563 for determination of the data removal timing just after an initial frame.

TD-8 indicated that the current VBV specification is not straightforward for the "low delay operational mode (M=1)" for 3:2 pulldown, but the meeting concluded that this is acceptable because such use would be very unlikely.

Mr. Haskell pointed out that there may be some bitstreams where it is not easy to simultaneously meet VBV in video and STD in systems 

5.2 Error resilience by use of Data Partitioning (§3.1/AVC-554R,AVC-565,576,577)

		• necessity for ATM environments
		• description in the video coding standard (normative?  informative?)
		• description in the application standard (H.32X?)

The discussion is summarized as follows;

1)	Tools currently available in the Video WD can provide cell loss resilience for the single layer coding up to around 10-3 CLR.  Hence DP as a means of layered coding becomes useful when we use it under lossy environments of CLR higher than that value.

2)	To secure the base layer, its bit rate should be constant.  Hence, DP should allow fine rate control in the base layer requiring PBP change in the slice header.

3)	Price advantage of splitting the bitstream into two channels with different QoS is not certain at this moment.

4)	AVC-577 provides specifications for the Data Partitioning as a tool.  Though it needs addition of slice layer syntactic elements, this addition does not affect the SP/MP/NP decoder implementation.

The meeting concluded that the Experts Group support the proposal of AVC-577 as a useful error resilience tool for our possible future use.

5.3 H.261 compatibility by use of spatial scalability (AVC-564,571)

		• parameter setting in video syntax
		• support of external sub-systems
		• do we need it?

The H.32X terminal should be able to use the following video coding modes;

	Communication configuration	Video coding mode in H.32X terminal	
1)	Point to point communication between two H.32X terminals	H.26X without embedded H.261	
2)	Point to point interworking between an H.32X terminal and an H.320 terminal	H.261 (H.32X should operate in an H.320 emulation mode)	
3)	Multipoint* among H.32X terminals through video servers such as MCUs	H.26X without embedded H.261	
4)	Multipoint* among mixture of H.32X and H.320 terminals through video servers such as MCUs	The following possibilities should be considered;
-	two layer H.26X with embedded H.261,
-	H.26X without embedded H.261 (video server makes transcoding to/from H.261),
-	simulcast of H.26X without embedded H.261 and H.261	

*Multipoint includes interactive services (e.g. videoconferencing) and distributive services (e.g. remote video presentation).

At this moment we can not reach a firm conclusion on the choice of the video coding mode for the multipoint operation because of uncertainties both in service and network developments.  Hence we conclude that the solution of the "two layer H.26X with embedded H.261" should be covered by the generic video coding standard H.26X|MPEG-2 Video for our possible future use.

5.4 Video mixing bridge for continuous presence multipoint (AVC-501,559,560,575; TD-10)

		• technical feasibility of the Bellcore method
		• recommendations to WP1/15

AVC-575 is forwarded to SG15 as our reply with the following amendments;

-	appreciation of the Bellcore challenge in this new video coding field
-	delay implication of increasing HRD buffer size
-	reflection of AVC-560
-	QCIF only terminals which suffer from receiving lower quality pictures due to limited bit rate in the remote sending side

with conclusion that the current method of video mixing is not yet fully proven to be advantageous compared to the conventional transcoding approach.  Annex 3 contains the outcome of this meeting.

Bellcore informed the meeting of the hardware system being experimented which uses PCs as platform, H.261 chipsets operating at up to 384 kbit/s, TCP/IP and Ethernet.  A plan of replacing the Ethernet with N-ISDN was also informed.

5.5 Upsampling filters for spatial scalability (§2(3)/AVC-564,AVC-573)

		• clarification of specifications in WD

The meeting took note of the experimental results with tape demonstration showing that the simplified upsampling filters does not affect the coding efficiency.  It was stated that applicability of this simplification to sampling ratios other than 2:1 is yet to be examined.

Corrections to WD listed in §2(3)/AVC-564 should be conveyed to the joint sessions.

6. Network aspects

6.1 Requirements to H.22X/AAL (AVC-562,567,570)

1) Video clock recovery

AVC-562 provided experimental results showing that asynchronous operation between encoder and decoder are acceptable depending on applications.  The meeting appreciated this input based on hardware experiments.

2) Strategy for detection/correction of bit error and cell loss

AVC-567 raised a fundamental question regarding the strategy we should take for bit errors and cell loss.  The choice will affect the structure of H.22X/AAL.  Since both of network performance and service requirements are uncertain, this is an area where we should apply good engineering sense.  Members are requested to respond to this question at the next meeting.

3) PES semantics for PES_packet_length field

The meeting supported the proposal in AVC-570 to decouple the semantics of unspecified PES packet length with the nature of elementary stream in the interest of low delay requirement to H.22X/AAL.

At the closing session on 10 September, it was reported that MPEG Systems had not accepted this proposal.  It was decided to establish a small correspondence group under Mr. Stuart Dunstan to continue the study.  The mandate is to identify a suitable interworking point for MPEG-2 systems on packet oriented networks.

6.2 AALs 

	6.2.1 Asynchronous clock recovery (AVC-557)

		• SRTS for PDH networks
		• jitter performance of the adaptive clock method

The meeting became aware of the SG13 activities to elaborate AAL Type 1.  There was a comment that asynchronous clock recovery can also be recovered by user methods such as time stamps of MPEG Systems.

	6.2.2 Error correction in AAL (AVC-557,569)

		• response to SG13's questions (interleaving method, polynomial)
		• adaptation to VBR 

The meeting agreed on acceptance of the SG 13's method for cell loss correction for delay sensitive signal transport of AAL Type 1; use of RS(94,88) with diagonal interleaving.  We also agreed on adoption of the polynomial (x8+x7+x2+x+1).

As to the closed form of interleaving in Figure 2/AVC-569, the meeting recognized that this implies 706 Bytes packet transmission.  Members are requested to react to this proposal at the next meeting in the light of audiovisual communication applications.

It was clarified that the methods in Figures 1 and 2 in AVC-569 are not compatible because the time order of read out cells at the decoder are different.

	6.2.3 Delivery of TS packets over ATM connection (AVC-568,569)

		• alternatives
		• evaluation items

We will continue the work comparing the alternatives listed in AVC-568 and the one proposed in AVC-569.  AVC-569 method can be added to Table 2/AVC-568 as follows;

	Case 2'
Use of FEC/CRC and interleave matrix	
Cell loss correction		
Cell loss detection		
Bit error correction		
Quick synchronization		
Transmission efficiency	 95.87 (47/48 x 188/192)	
Generic AAL	 (new type)	
Transmission clock recovery	 (188x47=8836 bytes packet)	
Variable bit rate		

7. Profiles (AVC-572,574)

1) Minimum scalability profile

AVC-572 proposed a new profile (Main + SNR scalability) between Main and Next which is optimized for such applications as graceful degradation, WS/networks with different capabilities.  The meeting concluded that we need more time to support this proposal because we should be careful to define new profiles.

It was recognized that proliferation of profiles is against the objective to allow cross application bitstream interchange, but at the same time too big a profile may not be implemented allowing eventual proprietary solutions optimized for particular applications.

Use of DP is another factor to affect this consideration; profile containing DP can not be in the onion ring structure.

2) Level parameters for the Next Profile

The meeting supported the AVC-574 proposal to define the maximum pel rate in terms of the sum of luminance and chrominance pels, since luminance and chrominance pels need the same resource in terms of processing power and memory size.  An implication is that NP@ML can handle half SCIF (720x576x29.97, 4:2:0, progressive).

8. Work plan

8.1  Network standardization (AVC-557,558)

AVC-558 provides for the release time tables of network standardization.

We will continue to contribute to the use of IVS Baseline Document as a coordination tool by providing our study results.

8.2 Hardware trials (AVC-566)

		• significance
		• time schedule
		• system configuration

The AVC-566 proposal to carry out field trails in mid-1995 was generally accepted.  Ms. Conte and Mr. Schinkel stated relevant hardware projects in their organizations which might be extended to the proposed field trial.

The meeting concluded to make efforts to materialize the proposed plan, expecting this will assist in encouraging corresponding plans in member organizations.

8.3 H.320 adaptation to LANs (AVC-561)

		• timescale
		• initial activities for standardization (understanding the state of the arts)

AVC-561 provided a view that H.32X is a long term target but the needs are ambiguous but H.320 over LANs is an urgent short term target, thus the standardization program should reflect the situation.  Since we already recognized the necessity to work on audiovisual systems over LANs at the previous meeting, an issue will be weighting on the ongoing ATM work and this new work.  We will handle these in parallel for the moment; if it is appropriate, splitting the group may be a solution.

Mr. Morrison requested the participants to ask their commercial people what standards they require.

As a first action for the H.320 over LANs, members are requested to present the state of arts at the next meeting, particularly addressing protocol stack and interworking aspects 

The meeting was called attention to that H.32X over ATM LANs should also be in the scope and that network interconnection is going on among ISDN, LAN and ATM.

8.4 Terms of reference of the group (TD-7)

		• from pure video coding (H.26X) to total system (H.32X)?
		• skeleton of H.32X

Chairman queried the members whether the terms of reference of the group be extended to H.32X from pure video H.26X.  Since there was no negative comment expressed during the discussion, this was put forward to the consideration of WP1/15 held in the following week.

TD-7 presented a skeleton of Recommendation H.32X.  Comments are welcome by correspondence.

9. Progress report to SG15 (TD-5)

		• items needing guidance and/or consideration of SG15

The meeting reviewed the draft progress report and made some editorial amendments.  This was presented at the WP1/15 meeting of the following week.  Annex 4 contains the outcome of this week with subsequent slight editorial modifications made by WP1/15 and attached to its meeting report.

10. Joint sessions with MPEG

10.1 Documents

	- information and discussion documents
	- proposal documents

Conclusions obtained in the sole sessions will be put forward to the joint sessions;

Section # in this document	Item	Relevant document	
§5.1	VBV	AVC-563	
§5.2	Data Partitioning	AVC-577	
§5.3	H.261 backward compatibility	none	
§5.5	Correction to WD	§2(3)/AVC-564	
§6.1 3)	PES_packet_length semantics	AVC-570	
§7 2)	Definition of pel rate	AVC-574	

10.2 Representatives

	ITU-T EG		G. Morrison
	Requirements 	B. Haskell
	Video			G. Bjoentegaard
	Systems		D. Schinkel
	Implementation	G. Morrison

11. Future meetings

Meeting	Date	Sole sessions	Joint sessions with MPEG	Joint sessions with SG13 	
14th	October - November 1993	October 27-29 in Daejeon
(See AVC-535)	November 1-5 in Seoul	-	
15th	March 1994	March 16-18 in Paris (?)	March 21-25 in France	March 14 in Geneva (?)	

Synchronization of the meetings of this Experts Group and MPEG should be reviewed in the light of new work phase.

END
*    *    *

Annexes

Annex 1	Documentation	
Annex 2	List of tape demonstrations	
Annex 3	Video Coding Aspects of the Bellcore 4 QCIF to CIF mixing proposal	
Annex 4	Fifth progress report of the Experts Group for ATM Video Coding	

Participants of the thirteenth meeting of Experts Group for ATM Video Coding 
2-10 September 1993 in Brussels

			S*	J*		
						
Australia	Mr. M. Biggar	Telecom Australia	X	X	CM	
						
Belgium	Mr. O. Poncin	BELGACOM	X	X	CM	
						
Korea 	Mr. J-Y. Nam	ETRI	X	X	CM	
						
USA	Mr. C-T. Chen	Bellcore	X	X		
	Mr. B. Gifrig	Tektronix		X		
	Mr. B.G. Haskell	AT&T Bell Labs	X	X		
	Mr. A. Luthra	Tektronix		X	(CM)	
	Mr. P. Rao	CLI	X	X		
	Mr. G. Thom	DIS	X	X	(CM)	
	Ms. A. Wong	Bellcore	X	X		
						
France	Mr. J. Guichard	CNET	X	X	CM	
						
Italy	Ms. L. Conte	CSELT	X	X	CM	
						
Japan	Mr. K. Asai	Mitsubishi	X	X		
	Mr. Y. Kosugi	Tokyo Electric Power Company	X	X		
	Mr. T. Murakami	Mitsubishi	X	X		
	Mr. Y. Nakajima	KDD	X	X	(CM)	
	Mr. S. Okubo	NTT	X	X	Chairman	
	Mr. K. Sakai	Fujitsu	X	X		
						
Norway	Mr. G. Bjøntegaard	NTR	X	X	(CM)	
						
Netherlands	Mr. D. Schinkel	PTT Research	X	X	CM	
						
UK	Mr. D. Beaumont	BT	X	-		
	Mr. G. Morrison	BT	X	X	CM	
						
Sweden	Mr. P. Tholin	Telia Research 	X	-		
	Ms. C. Verreth	Telia Research 	X	X	CM	

								S: Sole sessions
								J: Joint sessions with MPEG
								CM: Coordinating Member
								(CM): Substitute for CM