Telecomm. Standardization Sector		Document # AVC-834
								LBC-95-305
Study Group 15
Experts Group for Video Coding and Systems 	October 1995
in ATM and other network environments


Title:  Proposal for adding a simple ACK/NACK data protocol to H.245
Source: Barry G. Haskell and Amy R. Reibman (AT&T Bell Laboratories)
Purpose: Informational and Proposal

This document presents an H.245 example of how to send video using the 
modified Data Partitioning syntax to achieve reliable transmission on ATM 
networks.  It also proposes a minor modification to the existing H.245 syntax.

1.  Introduction.

H.222.1 describes a method for sending video across two virtual channels
so as to achieve reliable transmission.  The base layer is decodable by all
decoders.  The enhancement layer uses a modified Data Partitioning syntax
and consists only of header information.  It should be transported reliably.
The base layer need not have 100% reliable transmission.

To initiate transmission of such a signal with reliable transport for the 
enhancement layer, H.245 can be used to set up a video logical channel for 
transporting the base layer, and a data-application logical channel with  
acknowledgements for transporting the enhancement layer.  The data sent on the  
second channel happens to be H.222.1 video data.

2.  Modified syntax for H.245

Currently, there is no simple data application that can be selected to transport 
the H.222.1 video data reliably with acknowledgements.  We propose that a code-
point be added to "DataApplicationCapability" and its twin, "DataMode" to achieve 
this.  The code-point to be added is "h222", which indicates that the data to be 
sent is comprised of H.222 information.  In our application, the H.222 information 
happens to be H.222.1 video data.

This proposed modification would change DataApplicationCapability to be:

DataApplicationCapability		:=CHOICE
{
  nonStandard				NonStandardParameter
  t120					DataProtocolCapability
  dsm-cc				DataProtocolCapability
  userData				DataProtocolCapability
  t84					SEQUENCE
  {
     t84Protocol			DataProtocolCapability
     t84Profile				T84Profile
  }
  t434					DataProtocolCapability
  h224					DataProtocolCapability
  nlpid					SEQUENCE
  {
     nlpidProtocol			DataModeProtocol
     nlpidData				OCTET STRING
   }
  h222					DataProtocolCapability	<- add this
  ...
}

and DataMode to be:

DataMode					:=CHOICE
{
  nonStandard				NonStandardParameter
  t120					DataModeProtocol
  dsm-cc				DataModeProtocol
  userData				DataModeProtocol
  t84					DataModeProtocol
  t434					DataModeProtocol
  h224					DataModeProtocol
  nlpid					SEQUENCE
  {
     nlpidProtocol			DataModeProtocol
     nlpidData				OCTET STRING
   }
  h222					DataModeProtocol     <- add this
  ...
}

3.  Modified Semantic Text for H.245

At the end of Section 7.2.2.7, the following should be inserted.

h222 indicates the capability to support H.222 applications.

At the end of section 7.5.1.3, the following text should be inserted.

h222 requests the use of an H.222 application on a data channel.

4.  Example Usage

The following example illustrates the channel setup for the enhancement layer 
channel, using this new code-point.  A bi-directional logical channel is opened by 
issuing an OpenLogicalChannel signal using an appropriate logicalChannelNumber.  
The forwardLogicalChannelParameters have an appropriate portNumber,  
dataType=data, and 
logicalChannelMultiplexParameters = h222LogicalChannelParameters.

The DataApplicationCapability sent for dataType=data should be h222,
with DataProtocolCapability=v42lapm.   V.42 LAPM is a fairly simple 
retransmision protocol.

The H222LogicalChannelParameters in the forward channel consist only of 
virtualChannelID and subChannelID values.

The reverseLogicalChannelParameters in the OpenLogicalChannel signal again 
have an appropriate portNumber, dataType=data, and 
logicalChannelMultiplexParameters = h222LogicalChannelParameters.
The DataApplicationCapability sent for dataType=data should be identical
to that for the forward channel, namely h222, with 
DataProtocolCapability=v42lapm.
The H222LogicalChannelParameters again consist only of virtualChannelID
and subChannelID values.

5.  Description in H.310

In section 7 (7.1) of H.310, a paragraph should be included describing the
intended operation.  The following paragraph may be appropriate.

To achieve reliable transmission of video information or other
H.222 information, a bi-directional channel can be initiated using
dataType=data, DataApplicationCapability=h222, with 
DataProtocolCapability=v42lapm.