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:
- 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.
- 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.
- At the same time, we are on the way to evaluate other call startup improvement
proposal and techniques received and arisen by the group.
- 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:
- 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.
- Interoperability with existing deployed H.324/M systems.
Conclusion
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.
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