Annex 6 to AVC-553R

Source:	Experts Group for ATM Video Coding in SG15
Title:	Cell loss correction method for AAL Type 1 to support H.320 terminals in B-ISDN

Contact:	Sakae OKUBO
	Visual Media Laboratory (Room 922A)
	NTT Human Interface Laboratories
	1-2356 Take, Yokosuka-shi
	238-03 Japan
	Phone	: +81 468 59 2814
	Fax	: +81 468 59 2829/3573
	E-mail	: okubo@nttvdt.ntt.jp

At the twelfth meeting of the SG15 Experts Group for ATM Video Coding held during 7-9 July in Boston, we reviewed the following two contributions regarding the subject matter;

AVC-521	Correction method for cell loss and bit error in AAL Type 1 (Japan)	
AVC-538	Method for the correction of cell losses for low bit-rate signals transport with the AAL Type 1 (France)	

Our fundamental position is that a sufficient level of network performance (cell loss ratio) should be available to allow simple terminal implementation.  Before deciding adoption of the cell loss correction technique under discussion, we would like to confirm that this additional functionality of AAL Type 1 is really necessary 

The attached material is summary of the discussion, comparing the following two methods in delay, cell loss correction capability and some other aspects;

•	separable FEC interleaving matrix as contained in AVC-521,
•	its modification to the non-separable matrix as proposed in AVC-538.

We welcome any comments of SG13 on this comparison.  We also seek advice on the method of synchronizing the interleaver matrices between the transmitting and receiving AALs as discussed in §4 of AVC-521, particularly on what combination of SRTS and SDT should be considered for supporting H.320 terminals on B-ISDN, including the B-N interworking situations.

Document AVC-521 is attached for your consideration (Note: AVC-538 has already been input to SG13 from France).

END

* SEPARABLE MATRIX: AVC-459(521)

RS(4844)FEC frame x 16 <=> 16 cells
(Closed form of Error Correction Matrix)
- Each cell Contains only one sector of each FEC frame.
- First sector of each FEC frame is also first sector of each cell.

* NON-SEPARABLE MATRIX : AVC-459(521)+AVC-538

RS(48,44) FEC frame x 16 ~16cells
(Open form of Error Correction Matrix)

* COMPARISON

- Correction Capability

  RS(48,44) corrects    

In both cases....
One sector from each FEC frame is in one cell.
  ------------->  correction capability is the same.

- Processing Delay (Case of 384Kbps)

Separable Matrix
      48(Bytes) x 8(bits) x 16(cells) x 2(sites)/384 x 103=32(msec)

Non-separable Matrix
   136(sectors) x 3(Bytes) x 8(bits) x 2(sites)/384103=17(msec)

- Applicability

Separable Matrix
     Applicable for multiplexing in unit of 16 cells
     Applicable for VBR
     Applicable at users level as well

Non-Separable Matrix
      Applicable for non-multiplexing, CBR
      Needs special treatment at Start and End (see next page)

* DATA TRANSPORT (Case of 384 kbps) ALL Type 1