LS - H.245



COM 16 – ILS 15 – E


STUDY PERIOD 2001-2004


English only

Original: English


1/16 ( WP 2/16 )

Geneva, 16-26 November 2004



IMTC – 3G-324M Activity Group


LS on Windowed Transport of H.245 Messages



ITU-T SG 16 - Questions 1/16


SG 16 Chairman (on behalf of IMTC)


IMTC – 3G-324M Activity Group




November 2004


J. A. Polizotto

IMTC Secretariat

2400 Camino Ramon, Suite 375

San Ramon, CA 94583, USA

Tel: +1.650.328.0194

Fax: +1.650.618.2799



Albert Wong

Dilithium Networks Inc

California, USA

Tel:   +1-415-9251100

Fax:   +1-415-9252277



IMTC 3G-324M Activity Group (AG) thanks for your Liaison Statement (LS) request with document number Q11C17.

Our AG has had the discussion and reviewed the topic and currently made the following points:

  1. Regarding to the request for comments on the use of LAPM/V.42, our AG thinks this procedure would not offer much gain with the following reasons:

•  To Use LAPM/V.42, it requires LAPM/V.42 capability to be indicated through H.223 capability in the H.245 TerminalCapabilitySet (TCS) Request message.   This restricts us from using the LAPM/V.42 since the beginning of the call.   Typically, TCS is a large message and may require multiple round trips to convey.   WNSRP does not have this restriction, and so WNSRP can be used from the beginning of the call.

•  WNSRP overhead is less than LAPM/V.42 overhead on the bitstream.   WNSRP has the overhead of 4 bytes whereas LAPM/V.42 has the overhead of 5 Bytes (for 16 bits FCS) or has overhead of 7 Bytes (for extended FCS 32 bits).

•  SRP/NSRP protocol is widely used across many 3G-324M Vendors.   Implementing WNSRP on top of SRP/NSRP is relatively easier and should take lesser time and effort.   Also, SRP/NSRP is well interoperability tested across 3G-324M vendors.    The effort of enhancing to WNSRP and the interoperability testing will be less.

•  To use LAPM/V.42, we need to implement V.42 partially as a minimum.   Since many 3G324M vendors usually use SRP/NSRP protocol, switching to LAPM/V.42 is very unlikely because of the effort to implement it and its low usage popularity.

  1. WNSRP aims on the improvement on the reduced H.245 message round trips.   It can co-exist with other potential future call startup improvement proposals.
  2. At the same time, we are on the way to evaluate other call startup improvement proposal and techniques received and arisen by the group.
  3. Technically, there is no issue on the WNSRP proposal with majority of the members supporting the techniques.   Amongst all members, 11 are for, 1 is neutral, 3 without response.

From the position of our AG, we also focus on the interoperability of the proposal.   We would like to obtain further experimental information and the original proposer has agreed to provide the information.   The focus on the information includes:

  1. Practical call setup time improvement.   Apart from the time required for the H.245 message exchange, the comparison should include the time needed for initial mobile level setup, which is the beginning of Phase D of terminal procedures as described in C.5/H.324.
  2. Interoperability with existing deployed H.324/M systems.



By the time this LS was prepared, the above information has not been completed yet.   Therefore, we would likely recommend your option a) “Accept the proposed WNSRP mode, as it can be used immediately upon connection” on condition that satisfactory experimental information is available.


Our Activity Group approves unanimously to the above recommendation.