ITU-T Telecommunication Standardization Sector	Document AVC-598R
Study Group 15	November 5, 1993
Experts Group for Video Coding and Systems 
in ATM and Other Network Environments

Source:	RAPPORTEUR (Sakae OKUBO)	
Title:	REPORT OF THE FOURTEENTH EXPERTS GROUP MEETING IN DAEJEON AND SEOUL (October 27 - November 5, 1993) - Part I and Part II	
Purpose:	Report	

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

Part I	General 
Part II	Sole sessions in Daejeon
Part III	Joint sessions in Seoul (see AVC-599R)

Part I  General

The fourteenth meeting of the Experts Group was held in Daejeon and Seoul, Korea, as follows;

- 	ITU-T sole sessions in Daejeon during 27-29 October at the kind invitation of ETRI, and
- 	Joint sessions with ISO/IEC JTC1/SC29/WG11 (MPEG) in Seoul during 1-5 November at the kind invitation of KBS.

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 coding - H.26X
6. 	ATM terminal and system - H.32X
7. 	Network adaptation - H.22X/AAL
8. 	Audiovisual communication systems over LANs - H.32Z
9. 	Work plan and work method
10.	Joint sessions with MPEG in Seoul
11.	Future meetings

1. Introduction

The ITU-T sole sessions were held at ETRI during 27-29 October 1993 at the kind invitation of ETRI.  At the opening session, Mr. Jae-Woo Yang, Director of Human Interface Department, ETRI 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 5 November to review both sole and joint sessions as well as to prepare for the next meeting in Geneva and Paris.

2. Documentation (TD-2)

For the sole sessions, 20 AVC-numbered documents and 12 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 Brussels (AVC-578R)

Rapporteur briefly presented the outcome of the sole sessions in Brussels, noting Annexes 3 and 4 both of which had been presented at the Working Party 1/15 meeting in Geneva.

4.2 Joint sessions in Brussels (AVC-579)

Each representative of the Experts Group presented the outcome of the sub-group in charge; Requirements (B. Haskell), Video (S. Okubo on behalf of G. Bjoentegaard), Systems (D. Schinkel) and Implementation (G. Morrison).

4.3 SG15 meetings (AVC583,584; TD-6)

Rapporteur presented the outcome of the Working Party 1/15 meeting held in Geneva in September, drawing attention of the members to the following items;

•	new structure of SG15 (TD-6)
•	new rules (Attachments 1,2,3/AVC-584)
•	time schedule for audiovisual systems Recommendations (Annex 2/AVC-583)
•	reorganization of the Experts Group (AVC-584)
•	intellectual property (§4.2.1 i)/AVC-583)

As to the last item, Rapporteur requested support of the Experts Group members for collection of patent information and patent licensing policy statements regarding H.26X|MPEG-2 Video.  Rapporteur's letters of request have been sent to the organizations which indicated holding of patents relevant to MPEG-1 and MPEG-2.

5. Video coding - H.26X

5.1 Picture skipping (AVC-596; TD-7)

AVC-596 gave clarification to picture skipping whose purpose is to keep low delay in the steady state and to related VBV operation.  The meeting appreciated this clarification so that the feature be maintained in Committee Draft of MPEG-2 Video and Systems.  

During the discussion a comment was raised that the picture skipping has still some ambiguity in the spatial scalability.  In response to this, a clarification document was produced as in Annex 3, which the meeting agreed for submission to the joint sessions in Seoul.  An essential point is that the encoder (Video, Systems, together with network access, such as use of multiple VCs, if relevant) is responsible to deliver base layer picture data prior to the time of decoding its corresponding upper layer coded picture.

It was noted that a term "VBV underflow" is used to describe the situation that the VBV buffer does not contain complete coded picture data at a timing of data removal (i.e. decoding).

The meeting considered shortly whether more restrictions other than low_delay = 1 is necessary to the use of picture skipping.  As to 3/2 pulldown, the Brussels meeting recognized that use of picture skipping would be very unlikely in practice (see §5.1/AVC-578R).

5.2 VBR

	5.2.1 VBR application examples

The meeting listed the following as possible VBR coding applications;

•	ATM network services where input traffic can be varied but is to be regulated,
•	Local Area Networks where packet retransmission is involved,
•	Video servers where peak rate can be high but average rate is restricted,
•	Disks where all bits in a picture are read out in a picture time,
•	CD ROM where start/stop operation is involved.

Since VBR characteristics look different for respective cases, they should be analyzed and well defined.

	5.2.2 Definition of bit_rate, vbv_delay in CD (AVC-588,591; AVC-396; TD-8)

AVC-588 proposed that since it is impossible to know future transmission rates the current definition is not appropriate for VBR and that correct VBR decoding is possible only with the support of Systems.  AVC-591 provided a particular example where the current definition is workable; vbv_delay value is set constant as a picture time.  It also proposed insertion of the corresponding illustration in CD.  

After some discussion, the meeting reached a conclusion that the general solution is to use PTS/DTS for indicating correct decoding timing for VBR (including CBR as a degenerate case), thus vbv_delay be reverted back to 'FFFF'.  As to bit_rate, it is concluded to be 'undefined' since it does not help decoding process but room should be left for its future use.  It was also concluded that the illustration in CD can be as it is with necessary editorial modifications according to the above conclusion.

The meeting prepared a clarification and proposal document as in Annex 4 for submission to the joint sessions in Seoul.

	5.2.3 Relation between video parameters in the header and the traffic descriptors
	          (AVC-592)

AVC-592 discussed what implications the definition of VBR bit_rate and vbv_delay has to the traffic descriptors at the user-network interface, concluding that the current definition does not directly correspond to the parameters which the networks require for establishing a VBR connection.  We need to continue this study cooperating with SG13 toward clear definition of traffic descriptors.

5.3 Spatial scalability (AVC-597)

AVC-597 proposed some modifications to the spatial scalability parts in WD based on the bitstream exchange experiments.  The meeting would rely on the bitstream exchange contributors.

5.4 Video mixing bridge for continuous presence multipoint 
       (AVC-581; Annex 3 to AVC-578R, §4.3.5/AVC-583; TD-9)

AVC-591 provided HRD and delay consideration, experimental results and clarification to the Brussels summary report.  The discussion focused on whether delay accumulates at the video mixing bridge.  It was clarified that even if the case of p.18/AVC-578R is repeated, the second series do not suffer additional delay because no more stuffing is necessary due to buffering at the video mixing bridge inputs (see Figure 2/TD-9).  Namely, the additional delay due to stuffing at the bridge does not exceed a certain bound.

During this discussion, the meeting was drawn attention to the delay measurement method, though a method is described in Annex C of Recommendation H.261.

The meeting agreed to the proposed action that the Experts Group should not recommend either of the video combiner and transcoding approaches if the video mixing approach is technically feasible, but leave the choice to the market since both can co-exist.

6. ATM terminal and system - H.32X

AVC-590 reminded the meeting of an open issue of picture format(s) for the H.32X terminal, proposing mandatory formats of local ITU-R 601 one plus common format(s).  The Experts Group suspended the format study at the Ipswich meeting in October 1992 (§5.2/AVC-398R), summarizing that; "in the light of lacking clear application possibilities, H.26X should be a generic coding standard and the 'application profiles' study should be commenced when appropriate which will include picture formats, bit rates and other parameters".

The meeting recognizes that the situation has not changed so much since then, thus we should not restrict the applications to a specific one, rather we should characterize the applications and list desirable format(s) for each 'application profile'.

Me. Haskell introduced a recent e-mail discussion on Pel Aspect Ratio (PAR) and Image Aspect Ratio (IAR), stating that one finding is that conversion of IAR may be rather easy but exact PAR conversion may be expensive, thus restriction of IAR values to ITU-R 601 values plus square pel aspect ratio may help us.

When we discuss the format issue, we should bear in mind the fact that the H.26X|MPEG-2 Video decoders can decode any formats inside the defined upper bound.  Mr. Schinkel clarified that the half SCIF (720 pels/line, 576 lines per picture, 29.97 progressive pictures per second), which was considered in the definition of Next profile at Main Level, had been raised for reserving a possibility for communication purpose, not for proposing at the moment.

The meeting also noted an early contribution from Canada (AVC-59) which proposed to use CIF as a common format for interregional conversational services.  Possibility of HHR (Half Horizontal Resolution of 4:2:0) was pointed out.  For these low resolution formats, Mr. Tabatabai made a comment that full resolution ITU-R 601 format would provide better overall picture quality as AVC-394 (Daimler Benz) had indicated.

7. Network adaptation - H.22X/AAL

7.1 Framework for the network adaptation (AVC-586; TD-5)

Mr. Dunstan reported the correspondence group activities regarding the network adaptation in AVC-586.  Rapporteur presented a protocol model, required functions, existing or planned protocol elements in TD-5.  Both documents give a framework for our future study of the network adaptation.

Identification of H.22X specific functions await consideration of the participating members.  Mr. Schinkel drew attention of the meeting that §2.5.7 of Systems WD specifying Program and Elementary Stream Descriptors, which should cover our audiovisual communication requirements.  These descriptors may be sufficient for "assignment of media identification" listed in TD-5.

In response to the action proposed in AVC-586 on clarification of the desirable use of PES as an independent interface point, the meeting produced a document of request as contained in Annex 5 for submission to the joint sessions in Seoul.  It points out three places in WD implying possible use of PES for the above mentioned purpose.

7.2 Evaluation of alternative solutions (AVC-585,593)

Both of AVC-585 and 593 attempted comparison of possible network adaptation solutions.  Particularly, AVC-585 proposed 'pipelining' for shorter delay and 'alignment between cell and picture structure' for error resilience.  It also presented a 'reference system' which was intended as a default solution if improvements in other methods were not outstanding.  This reference system idea for network adaptation study is to be considered as a tool to make progress.

The meeting recognized that the performance parameters to be evaluated are;

•	delay
•	packing efficiency
•	error resilience
•	timing recovery
•	implementation

which should be quantified as tried in AVC-585.  It also recognized that the comparison should also be in terms of whether each alternative solution provides required functionalities .

We should study delay budget for the total system so that the network adaptation performance comparison can be practical in delay.  This needs action of the members.

As to the error strategy for real time audiovisual systems, the meeting agreed to adopt the one raised in §2.2/AVC-585; "to pass the errored data unit to the decoder along with error indication flags so that the decoder can take necessary actions such as suspending to decode, concealing errors, etc.".

As to implementation, it was thought that ATM demultiplexer and TS packet demultiplexer need hardware while PES packet demultiplexer can be handled by software.  {how about AAL? - Rapporteur}  Chips for AAL Type 5 are now available, those for AAL Type 3/4 SAR would come earlier than Type 1 chips.  Furthermore, AAL hardware quantity is much more small than that for video decoding, thus it would not be a problem in the longer term, but hardware trial of mid 1995 need be worried about in this respect.

A small group discussion for elaborating the comparison and identifying action points took place in the evening of Thursday, October 28 under leadership of Mr. Dunstan.  Its outcome is contained in Annex 6.

Rapporteur raised the following points which may affect the choice of alternative solutions for the network adaptation;

•	impact of the mandatory B-N interworking requirement for H.32X terminals which requires inclusion of AAL Type 1 circuit emulation,
•	utilization of ATM cell characteristics

One of the opportunities of ATM is deemed as variable bit rate operation which can provide low delay characteristics.

7.3 TS packet delivery (AVC-594)

AVC-594 provided elaboration of the cell interleaving scheme presented in Brussels (AVC-569) and another new cell interleaving scheme for TS packet deliver.  The issues are; 

•	required functionalities,
•	error correction methods.

We have now four alternatives for the TS packet delivery; three others are listed in AVC-568 (considered in Brussels).  Members are requested of the comparison study.

During the discussion, it was questioned how cell interleaving might affect the spectrum distribution of cell arrival jitter after de-interleaving.

Mr. Dunstan gave a comment that AAL should absorb cell delay jitter which is generated inside the ATM network.

The meeting confirmed that the use of cell interleaving with ring buffer for the AAL Type 1 circuit emulation is converging, while the 'closed form' method proposed in Brussels (AVC-569; see Figure 2/Annex 2 to AVC-594) is still awaiting comments.  If there will be no more reactions, this will be put forward to the joint meeting with SG13 AAL Type 1/2 experts.

Mr. M-T. Sun gave a brief overview of ATM Forum which recently initiated the study on AAL for the TS packet delivery, expressing a desire that the activities among relevant bodies be coordinated .

7.4 Agenda items for the joint meeting with SG13 AAL Type 1/2 experts

The meeting confirmed that we should make progress for the following items at the joint meeting with SG13 AAL Type 1/2 experts in March 1994;

•	cell loss correction method for AAL Type 1
•	AAL Type 2 for video services support
•	AAL for TS packet delivery

Members are requested to prepare good input materials through correspondence toward this joint meeting.

It was pointed out that clarification of the network restrictions for VBR traffic should also be included, but this item might not be under responsibility of the AAL experts.  Rapporteur will consult with Mr. K. Yamazaki on this matter.

7.5 Action items

As summary of the Daejeon/Seoul meeting discussion, a list of action items for the network adaptation study has been made as in Annex 7.

8. Audiovisual communication systems over LANs - H.32Z

8.1 Packetization (AVC-587)

AVC-587 presented a possibility to encapsulate H.221 multiplexed signal into LAN packets, which requires study for packet loss impacts.  Its advantage is more use of existing H.320 terminal protocols for LAN adaptation.  To use H.221 or not for H.32Z terminals has been recognized as one of the issues which need early decision.

During the discussion, Mr. Hall clarified that the audiovisual part of protocols can be rather independent of the LAN protocols; LAN may be Ethernet, Token Ring, FDDI or ATM LAN.

Mr. C-C. Li informed the meeting that Internet "IETF" has activities relevant to the scope of H.32Z.

8.2 Implementation examples (AVC-595)

AVC-595 provided information on an implementation of audiovisual terminal for LAN application with accompanied tape demonstration, covering protocol stack, congestion control techniques and interworking with H.320 terminals accommodated in N-ISDN.

During the discussion, interest in achieved delay was expressed.

Information of other implementation examples is requested toward the next meeting.

8.3 Items to be standardized

The following is a preliminary list of items which are to be tackled with for drafting H.32Z.

•	protocol stack
•	interworking with N-ISDN and B-ISDN systems
•	whether H.221 be retained or H.22Z be needed
•	clock recovery aspects
•	congestion control

9. Work plan and work method

9.1 Hardware trials (AVC-589)

AVC-589 requested members to propose experimental H.32X hardware specifications by attaching a straw man.  Mr. M-H Chan raised whether error resilience verification extends to layered coding such as DP or simple form of scalability (SNR scalability).  This possibility should be sought, but the verification of basic configuration should be given priority.

Rapporteur stressed that at least two independent hardwares are necessary for the verification and requested consideration of laboratories to commit.

9.2 Work method (AVC-584)

	9.2.1 Work progress through correspondence

According to the guidance of the ITU-T for making progress between the meetings, we will continue discussion through e-mail among concerned members.  PTT Research volunteered to offer an e-mail reflector for this purpose.  If technically feasible, this international reflector plus necessary number of national reflectors may be a better solution.

Rapporteur will establish a list of correspondents.

	9.2.2 Editor for each target Recommendation

The meeting supported the Rapporteur's proposal to appoint Editor for each target Recommendation.  Editor's tasks are as follows;

•	to generate draft Recommendation
•	to lead the correspondence work
•	to lead detailed discussion at the meeting

At this meeting, the following volunteers have been obtained;

Rec.	Title	Editor	
H.26X	Video coding for ATM environments	S. Okubo*	
H.22X	Multimedia multiplex and synchronization for audiovisual communication in ATM environments	S. Dunstan	
H.32X	Broadband audiovisual communication systems and terminal equipment	C-C. Li**	
H.32Y	Adaptation of H.320 terminals to B-ISDN	S. Okubo*	
H.32Z	Adaptation of H.320 terminals to LANs	G. Morrison	
	* provisional until volunteers are found
	** indication was obtained after the meeting

	9.2.3 Information/document distribution

For efficient distribution of the Experts Group information and documents, each country has her point of distribution.  The following members undertake this role;

FRG	Mr. B. Hammer	Siemens	
Australia	Mr. M. Biggar	Telecom Australia	
Belgium	Mr. O. Poncin	BELGACOM	
Canada	Mr. S. Sabri	BNR	
Korea	Mr. J-Y. Nam	ETRI	
Denmark	Mr. E. Nielsen	Telecom Denmark	
USA	Mr. C-C. Li	AT&T	
France	Mr. G. Eude	CNET	
Italy	Ms. L. Conte	CSELT	
Japan	Mr. T. Tanaka	NTT	
Norway	Mr. G. Bjoentegaard	Norwegian Telecom	
Netherlands	Mr. D.A. Schinkel	PTT Research	
UK	Mr. D.G. Morrison	BT Labs	
Sweden	Ms. C. Verreth	Telia Research	
Switzerland	Ms. M.L.M. Pralong	SWISS TELECOM PTT	

We used to exchange advance copies of contributions by telefax, but e-mail is a much more convenient means for distribution among concerned members in each country.  The meeting agreed to adopt this e-mail distribution from now on using;

•	Microsoft Word for Windows 2.0 (US version)
•	uuencode only (not compress)
•	recommended file naming: "no more than eight characters" + ".doc" extension

or plain text (if drawings or tables are not involved) as interchange format.

	9.2.4 Alignment of the meetings with MPEG and LBC ones

According to the new work phase, the collaboration with MPEG can be through Liaison Representative after March 1994.  However, if many participants attend both meetings, keeping synchronization will help them.  Furthermore, Mr. Schaphorst's LBC Experts Group intends to have its meetings synchronized with MPEG to collaborate in Phase 4.  Some members of this Experts Group intend to participate in the LBC meetings.  The rule of ITU-T requires that our meeting schedule between May 1994 and March 1995 should be approved by the SG15 meeting in May 1994.

Taking these factors into consideration, we should decide the future meeting plan for after March 1994.  This matter will be further discussed through correspondence.

10. Joint sessions with MPEG in Seoul

10.1 Documents

As outcome of the sole session discussion, the following clarification / proposal documents have been forwarded to the joint sessions with MPEG in Seoul;

• TD-7 	Spatial scalability when the base layer includes picture skipping (for clarification)	Video, Systems	
• TD-8	Decoding start-up algorithm for VBR coded bitstream (for clarification and proposal)	Video, Systems	
• TD-11	Use of Packetized Elementary Stream as an interface point (for clarification)	Systems	

10.2 Representatives

The Experts Group is represented by the following members at the joints sessions;

	ITU-TS EG		S. Okubo
	Requirements 	B. Haskell
	Video			K. Sakai
	Systems		S. Dunstan
	Implementation	G. Morrison

11. Future meetings

Meeting	Date	Sole sessions	Joint sessions with MPEG	Joint sessions with SG13 	
15th	March 1994	March 16-18 at CNET in Paris	March 21-25 in Paris	March 14 in Geneva	
16th	July 1994?			-	

END

*    *    *

Annexes

Annex 1	Documentation	
Annex 2	List of tape demonstrations	
Annex 3	Spatial scalability when the base layer includes picture skipping	
Annex 4	Decoding start-up algorithm for VBR coded bitstream 	
Annex 5	Use of Packetized Elementary Stream as an interface point 	
Annex 6	Report of meeting to discuss ATM Network Adaptation - H.22X/AAL	
Annex 7	List of action items for the network adaptation study	

Participants of the fourteenth meeting of the Experts Group 
for Video Coding and Systems in ATM and Other Network Environments
27 October - 5 November 1993 in Daejeon and Seoul

			D	S	
FRG	Mr. Bernard Hammer	Siemens	X	X	
	Mr. Istvan Sebestyen	Siemens	X	X	
					
Australia	Mr. Ming H. Chan	Telecom Australia	X	X	
	Mr. Stuart Dunstan	Siemens Ltd.	X	X	
	Mr. Stephen Hall	Monash University	X	X	
					
Belgium	Mr. Olivier Poncin	BELGACOM	X	X	
					
Korea 	Mr. Dong-Sok Ha	Korea Telecom	X	-	
	Mr. Cheul-Hee Hahm	KAIST	X	-	
	Mr. Yo-Sung Ho	ETRI	X	X	
	Mr. Dong-Beum Jeong	ETRI	X	-	
	Mr. Jae-Dong Kim	Korea Telecom	X	X	
	Mr. Yong-Han Kim	ETRI	X	-	
	Mr. Young-Sik Kim	ETRI	X	-	
	Mr. Jae-Yeal Nam	ETRI	X	X	
					
USA	Mr. Christopher Bennett	Tiernan Communications Inc.	X	X	
	Mr. Barry G. Haskell	AT&T Bell Labs	X	X	
	Mr. Chia-Chang Li	AT&T Bell Labs	X	X	
	Mr. Ming-Ting Sun	Bellcore	X	X	
	Mr. Ali Tabatabai	Tektronix	X	X	
	Mr. Yi-Tong Tse	CLI	X	X	
					
France	Mr. Gerard Eude	CNET	X	X	
					
Italy	Ms. Luisa Conte	CSELT	-	X	
					
Japan	Mr. Tokumichi Murakami	Mitsubishi	X	X	
	Mr. Yasuyuki Nakajima	KDD	X	X	
	Mr. Sakae Okubo	NTT	X	X	
	Mr. Kiyoshi Sakai	Fujitsu	X	X	
	Mr. Tomoaki Tanaka	NTT	X	-	
	Mr. Toshiaki Watanabe	Toshiba	X	X	
					
Netherlands	Mr. Dolf Schinkel	PTT Research	X	X	
					
UK	Mr. Geoff Morrison	BT	X	X	
					
Sweden	Mr. Leif Bengtsson	Telia Research 	X	X