Paul:

729 and 729A do indeed use the same encoder. Only the decoder is different. Performance of 729A is poorer, particularly with respect to tandeming.

I can see that it may sometimes be beneficial to control whether the 729 or 729A algorithm (if a choice is available) is used by the decoder in order to prevent significant degradation of audio quality. If that is a real scenario, then it becomes more than "a local issue".

Perhaps others can comment on the "realness" of this possibility.

Charles (Chuck) Hutton Strategic Architecture Engineering Wireless Local Technology Group AT&T Wireless Services PO Box 97059 Redmond, WA 98073 (USPS only) 9461 Willows Road Redmond, WA 98052 (FEDEX/UPS) 425-702-2938 Voice 425-702-2518 FAX charles.hutton@attws.com

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From: Paul Long[SMTP:plong@SMITHMICRO.COM] Reply To: Mailing list for parties associated with ITU-T Study Group 16 Sent: Wednesday, March 01, 2000 10:00 AM To: ITU-SG16@mailbag.cps.intel.com Subject: Re: Errors / ambiguities / problems found in specs at last week's int erop

Reinhard,

I have responded to each of the items you listed.

• I've wondered myself why there is a separate codepoint for G.729a. From

my understanding, the use of G.729 or G.729a is a local issue and does not change the bits on the wire. Maybe we need to state in a future version of H.323 that they are equivalent with respect to signaling.

• Are you saying that a GK cannot return a TTL in RCF that is larger than

the TTL in the corresponding RRQ or that it cannot subsequently increase the TTL without first having received a lightweight RRQ? I believe that a GK could return a larger value, but you are correct that there is no way for it to update this value without responding to a lightweight RRQ.

I don't see how the mandatory-parameters issue is related to TTL. Regardless, this points out a general weakness in semantics for later additions to H.245 (since H.245v2) and especially H.225.0. IMO, the description of all SEQUENCE OF and SET OF components should include the semantics for these situations, even if it is "obvious" to the author what the semantics should be: - OPTIONAL component whose encoding is absent - zero components (empty) - exactly one component - more than one component - component order (we should also use SEQUENCE OF and SET OF where appropriate)

We continue to have interoperability problems due to the differing interpretations as to what these mean.

• Regarding call reference value, since H.323 is the top-level

Recommendation that references H.225.0, if there is a conflict, H.323 is always normative. This is true in all referencing relationships between Recommendations, e.g., between H.225.0 and Q.931.

• I can't find in H.323 where destinationAddress is required. H.225.0v2

does require it, though, "if available" (whatever that means).

• The audio framing expressed in H.245 is _not_ ambiguous. It is clearly

stated that this is the maximum framing. B.2.2.6/H.245v5: "When an H.225.0 multiplex is used, these numbers indicate the maximum number of audio frames per packet." The problem is that some _implementations_ do not support variable framing, e.g., some DSPs used in GWs can only process 30ms frames. Possible solutions: "fix" decoders so that they support variable framing, reframe into fixed-size frames before passing along to decoder, add ability to express fixed framing in H.245.

• MCU prefix. I surprisingly have nothing to say about this one. :-)

• What is a "BE message format?"

• CRV. Wasn't this already described in a previous item?

Paul Long Smith Micro Software, Inc.

-----Original Message----- From: Reinhard Scholl [mailto:Reinhard.Scholl@etsi.fr] Sent: Wednesday, March 01, 2000 10:34 AM To: 'h323implementors@imtc.org'; 'ITU-SG16@MAILBAG.INTEL.COM'; TIPHON_WG6 Subject: Errors / ambiguities / problems found in specs at last week's int erop

The following errors / ambiguities / problems were reported at last week's ETSI-TIPHON/IMTC interop event at ETSI:

• Terminal capabilities for G.729 and G.729 Annex A. Though mutually

compatible, TCS often fails if vendors only specify support for one or the other. E.g. 729 <--> 729a should work but TCS fails.

• H323: GK cannot increase TTL in RCF. Mandatory parameters of type

SEQUENCE OF ... can have empty list.

• H.225 says that call reference value should be same in ARQ and SETUP.

H.323 says that call reference value should be different in ARQ and SETUP.

• In H.323, the destination address in UUIE in SETUP is mandatory, in

H.225.0 it is not.

• H.245: if a capability being sent includes G.711 "20 msec", the other

side may think that the sender supports both "20 msec" and "10 msec" rates. But it can be that the originator supports only 20 msec. Ambiguity.

• MCU should probably also have "prefix", not just the gateway.

• Need BE message formats so that packet dumps can be quickly

interpreted.

• When using a GK, should the CRV in the admission and setup be the

same?

    Reinhard Scholl
    ETSI