[Foip] FoIP-TG: Issues with V.8/V.34/V.152 call flows.

[Steve Underwood]

Hi,

Is advertising version 3 support really supposed to imply that the T.38 
system supports V.34? A lot of people seem to interpret the version code 
that way, but its a rather weird idea. What if there's a version 4 with 
cleanups we propose from the current activity? Will only V.34 capable 
machines be able to support it? Most T.38 machines today are only 
capable of V.17, and a *lot* of commercial T.38 gateways restrict things 
further, to only 9600bps. I suspect that will always be the case.

Steve


gboulay.ext at orange-ftgroup.com wrote:
> Hi,
> Concerning the first point, it seems to me that the best way to know, 
> during the T.38 negotiation, if a GW manages 14400 b/s rate in V.17 or 
> V.34 is to look at the version parameter sent in the T38 parameters of 
> the T.38 SIP negotiation. If it is version 3, it is V.34, otherwise 
> for lower versions, it is V.17. And if the parameter is absent, the 
> defaut value is 0.
> Gerard
>
> ------------------------------------------------------------------------
> *De :* foip-bounces at sipforum.org [mailto:foip-bounces at sipforum.org] 
> *De la part de* Chen, Ximing M (Michael)
> *Envoyé :* mardi 23 juin 2009 22:01
> *À :* Wang, Chris; foip at sipforum.org
> *Objet :* Re: [Foip] FoIP-TG: Issues with V.8/V.34/V.152 call flows.
>
> Hi, Chris,
> Please see my following comments to your questions. I agree that we 
> still need to sort out a few things.
>
> 1. "For Study Case #2, how would Emitting GW determine it only support 
> G3? Is it via some prior signaling with Receiving GW?"
>
> The emitting GW knows the other GW's capabilities via SIP/SDP 
> negotiation for T.38. The question are when such a negotiation should 
> start, and which GW should initiate the negotiation. In this 
> particular case, the emitting GW can start the SIP/SDP negotiation for 
> T.38 after V.8 CM is received from the local fax machine. One problem 
> with the negotiation is that in T.38 only the maximum data rate (not 
> modulation type) is included in negotiation parameters. So if both 
> sides agrees on 14400 bps, does it mean V.17 14400 or V.34 14400? My 
> guess is that people may simply assume G3 fax if the max rate is less 
> than (and equal to )14400, but V.34 does support the data rate all the 
> way to 2400 bps.
>
> 2. "Does the Receiving GW need to jam/stop the CM from reaching 
> answering FD?"
>
> Most T.38/V.17 GWs do not have capability to detect V.8 CM. It 
> probably makes more sense to let the emitting GW to jam the CM in this 
> case.
>
> 3. "How would answering FD fallback to G3 gracefully? By timing out or 
> somehow receiving a modified CM with V.34 modulation capability 
> removed in modn0 octet?"
>
> The answering FD will fallback to G3 if CM is not detected. If the 
> answering FD does not detect valid CMs during ANSam (~5 s), it will 
> switch to G3 and start to generate v.21 preambles.
>
> Regards,
>
> Michael
>
> ------------------------------------------------------------------------
> *From:* foip-bounces at sipforum.org [foip-bounces at sipforum.org] On 
> Behalf Of Wang, Chris [cwang at sonusnet.com]
> *Sent:* Tuesday, June 23, 2009 11:41 AM
> *To:* foip at sipforum.org
> *Subject:* Re: [Foip] FoIP-TG: Issues with V.8/V.34/V.152 call flows.
>
> A few comments/questions regarding V8-V34-V152 document.
>
> For Study Case #2, how would Emitting GW determine it only support G3? 
> Is it via some prior signaling with Receiving GW?
>
> Does the Receiving GW need to jam/stop the CM from reaching answering FD?
>
> How would answering FD fallback to G3 gracefully? By timing out or 
> somehow receiving a modified CM with V.34 modulation capability 
> removed in modn0 octet?
>
> Best regards,
>
> Chris Wang
>
> Sonus Networks
>
> ------------------------------------------------------------------------
>
> *From:* foip-bounces at sipforum.org [mailto:foip-bounces at sipforum.org] 
> *On Behalf Of *Chen, Ximing M (Michael)
> *Sent:* Monday, June 22, 2009 10:46 PM
> *To:* Neil Weldon; foip at sipforum.org
> *Subject:* [Foip] FoIP-TG: Issues with V.8/V.34/V.152 call flows.
>
> Hi all,
>
> Instead of looking into the call flows for all possible system/network 
> configurations (which will be many), it probably makes more sense for 
> us to concentrate on a few cases where clarification/guidance is 
> needed from TG. Attached are brief descriptions of two possible cases. 
> Both of them are related to fallbacks from V.34 to V.17, which are not 
> specified in T.38. Please comment on these two cases and/or add any 
> other cases that you think TG should look into and provide 
> recommendations.
>
> Regards,
>
> Michael
>
> ------------------------------------------------------------------------
>
> *From:* foip-bounces at sipforum.org [foip-bounces at sipforum.org] On 
> Behalf Of Neil Weldon [Neil.Weldon at dialogic.com]
> *Sent:* Thursday, June 18, 2009 5:41 AM
> *To:* foip at sipforum.org
> *Subject:* [Foip] June 17th Meeting Minutes.
>
> Hi all,
>
> Minutes from yesterday are attached. I’ll follow-up with the updated 
> Problem statement.
>
> Next meeting will be called by Michael Chen, via this list. Please 
> ensure you review material that Michael will provide over the coming 
> weeks so we can gather some momentum for dealing with the identified 
> problems.
>
> Regards,
>
> Neil
>
> Neil Weldon
> Director of Technology
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>
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