Telecommunication Standardization Sector         Document AVC-837 
Study Group 15                                          Version 1
Experts Group for Video Coding and Systems          Oct. 16, 1995
in ATM and Other Network Environments

SOURCE   :  JAPAN
TITLE    :  Considerations on H.310 communication protocol
PURPOSE : Discussion
                -----------------------------

1. Introduction
  Some signalling procedures are defined as tools in draft Rec. H.245.
Draft Rec. H.310 should define upper layer communication procedures,
which include the usage of each H.245 signalling procedure and error
handling and recovery procedure.
  This document discusses the concept of H.310 protocol definition and
also shows examples of procedure with the relation to H.245.

2. Approach toward the H.310 communication procedure definition
  In H.245 procedures, irregular situations which are not expected are
indicated as error to the upper H.310 Call Management layer. H.310
should define handling and recovery procedure of those errors.
  There are two candidate approaches for this protocol definition.
  (1) Error indications from H.245 is indicated to a user, that is
      more upper layer than H.310. Rec. H.310 define nothing for error
      handling, leaving it for human user's decision or implementation.
  (2) H.310 defines how to deal with and recover from error situation.
      The H.310 protocol will guarantee the completion of the
      procedure against error conditions.

  We think that above (2) is more desirable, because the interworking
among different manufacturer's H.310 terminals by detailed definition
in H.310 as well as that in H.245. However, enough time for this
detailed definition does not remain until Nov. SG15 meeting where
draft Rec. H.310 will be frozen. It is suggested that we should
concentrate on the definition of necessary minimum set of procedures
at this stage, leaving optional or extendable mechanisms for further
study.

3. Example of H.310 procedure
  The followings are examples of H.310 protocol definition based on
the concept described in section 2 (2).
 
3.1 Example of Capability Exchange (outgoing).
    (a) H.310 sets the terminal capability to CAPTABLE parameter and
        issues TRANSFER.request H.245 primitive.
    (b) H.310 waits for a primitive from H.245.
      (b-1) If TRANSFER.confirm is received from H.245, capability
            transmission is successfully completed.
      (b-2) If REJECT.indication is received, H.310 should check
            SOURCE and CAUSE parameters in the primitive.
            H.310 issues TRANSFER.request primitive again.
    (c) H.245 is capable to deal with new TRANSFER.request during
        AWAITING RESPONSE state. But procedure of H.310 for duplicate
        TRANSFER.request if for further study.

3.2 Example of Logical Channel Signalling (outgoing).
    (a) H.310 sets the requesting mode of communication to DATATYPE
        and LC_PARAM parameter and issues ESTABLISH.request primitive.
    (b) H.310 waits for a primitive from H.245.
      (b-1) If ESTABLISH.confirm is received from H.245, the logical
            channel is successfully established.
      (b-2) If REJECT.indication is received, H.310 should check
            SOURCE and CAUSE parameters in the primitive.
            H.310 may issue ESTABLISH.request primitive again.
    (c) Once a logical channel is established, the channel will be
        maintained until H.310 issues RELEASE.request primitive or
        RELEASE.indication primitive is received from H.245.
    (d) If ERROR.indication is received for the RELEASED logical
        channel, mismatch of H.245 state with the remote terminal may
        have been occured. H.310 is prefered to issue RELEASE.request
        for that logical channel to reset both remote and local H.245
        state to RELEASED.
    (e) H.310 can issue ESTABLISH.request primitive for the logical
        channel, even when that logical channel is not completely
        released, i.e. waiting for responce to RELEASE.request. The
        H.310 procedure of this case is for further study.

4. Conclusion
  This document has been discussed the concept of H.310 procedures and
suggested to define necessary minimum set of procedures including
recovery process from error. Examples of H.310 procedure definition
has been also shown.

END