Annex 5 to AVC-673R

Source:	Hayder Radha
Title:	Summary of H.32Y Discussions and H.320/H.32X Interoperability Issues
Purpose:	Report

1. Introduction

This report summarizes the AVC Experts Group discussions regarding Recommendation H.32Y.  In addition, discussions regarding the interoperability and interworking between existing H.320 terminals and H.32X terminals are also outlined.

2. Summary of H.32Y Discussions

1)	H.32Y terminals will support AAL Type 1 for the adaptation of H.320 over ATM.

2)	There are two possible implementations of H.32Y terminals: (1) an integrated solution including both H.320 and AAL-1 capabilities in one terminal equipment (B-TE), and (2) a two-component solution which consists of an H.320 terminal and an AAL-1 broadband adaptor (B-TA).

3)	H.32Y terminal types will follow the same terminal types specified by Recommendation H.320.  In addition, AAL-1 tools and capabilities will be defined for H.32Y.

4)	By the next AVC meeting, the group should decide the level of support of  the SDT pointer capability by H.32Y terminals.  The level of support may be optional, mandatory, or none.

5)	AVC-653 provided AAL-1 and Q.2931 parameters for circuit emulation mode of H.32Y terminals.  Based on the parameters shown, it was noted that multiple B and H0 connections supported by H.320 terminals will be mapped onto the corresponding number of ATM virtual connections.

6)	The number of virtual channels supported by an H.32Y terminal will be the same as the number of B or H0 channels supported by the corresponding H.320 terminal type.

7)	By the next meeting the group should decide the level of support of the short interleaver FEC capability by H.32Y terminals.

8)	Currently, the support of both the short interleaver FEC and SDT pointer is not possible.  This issue is under consideration by Study Group 13 as noted by Mr. Yamazaki contribution on circuit emulation (AVC-634).

9)	As noted in AVC-653, N-ISDN circuit emulation includes the SDT pointer.  This excludes the usage of the short interleaver FEC approach.  This issue should be clarified with SG13.

10)	It is not clear if the signaling of AAL-1 tools (e.g., FEC) can be achieved among H.32Y terminals, AAL-1 terminal adaptors, and interworking units.  If such AAL capabilities are not communicated, it is not clear how terminals and adaptors will decide when to use these capabilities.  This issue should be addressed with SG13.

11)	It was noted that the short interleaver FEC method, which protects against one cell loss in a 16-cell block, may not be required under several transmission conditions.  However, a simpler FEC approach which only protects the data against BER conditions (i.e., no cell loss protection) might be desired.  Currently, AAL-1 does not support such a mechanism (i.e., error correction capability only).  This issue will be addressed with SG13.

12)	A preliminary experiment for the deployment of H.320 codecs over ATM networks was conducted by BT (AVC-651) between Ipswich and London.  The experiment was based on AAL-1 with adaptive clock recovery.  No visual degradation was observed based on this experiment.  However, it was emphasized that the results were very preliminary.  Future experiments and their results will be shared with the AVC Experts Group.

3. H.32X Support of H.320/Y capabilities

1)	It was agreed that a minimum set of H.320/Y capabilities should be defined for their support by H.32X terminals.  This minimum set will reflect, as much as possible, the common features and capabilities found in existing H.320 terminals.

2)	AVC-667 provided a proposed set of H.320 capabilities to be supported by H.32X terminals.  The following summarizes some of the major capability modes to be supported:

•	Transfer modes B, 2B, H0, H11, and H12.  Other modes are optional.
•	G.711, G.722, and G.728 audio coding modes.
•	H.261 video mode.
•	MLP and H-MLP data modes.
•	H.221 multiframe structure and a minimum of two service channels.  The support of a higher number of service channels (i.e., 3-6 service channels) is optional.
•	H.261 BCH, H.221 CRC4, and BAS double-error correction codes.

3)	The definition of the above set of capabilities will be extended to include AAL-1 tools that H.32Y terminals will support.  This will provide a comprehensive frame-work for the inter-working between H.32X and H.32Y terminals.  

4)	It was agreed that identifying a Class 1 (or Type A) H.32X terminal which only supports H.320/Y  capabilities will not be required.  Therefore, all H.32X terminal types will support some level of high-end capabilities (e.g., H.262 video) and a minimum set of H.320/Y features as explained above.

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