[SIPForum-discussion] FAX T.38

Wed Jan 16 16:09:53 UTC 2013

Talking about confusion,

All that has been said about the b-party having to initiate the T.38 in SIP is valid for V.17. if the fax call is in super G3 (V.34), the roles are reversed. When receiving an ANSAM (instead of the CED in V.17), the a-party must initiate the T.38 change...

Cheers,
SBL

-----Original Message-----
From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Steve Underwood
Sent: Saturday, January 12, 2013 12:52 AM
To: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] FAX T.38

Its worth pointing out what gives rise to this confusion. In the H.323 part of T.38 it says the egress gateway should be the one to initiate T.38. In the SIP section is doesn't specify. It makes more sense to initiate from the egress gateway, and many people follow that practice with SIP. Others do the dumbest thing that stays within the letter of the spec.

T.38 is the Gruyere of specifications.

Steve

On 01/11/2013 09:40 PM, Mike Coffee wrote:
>
> Moh, you have received answers to your important question that were 
> conflicting and, in some cases, would not be helpful to you if 
> followed.  However, if you were to simply accept Eric's response as 
> comprehensive and 100-percent correct, you would be fine.
>
> Mike Coffee
> Co-Chair, FoIP Task Group
> SIP Forum
>
>
>
>
>
> "Jastak, Eric" <Eric.Jastak at adp.com> on 01/10/2013 12:38:30 PM
>
> To:   "Moh, Yee-Kuang" <ykmoh at pccwglobal.com>, "discussion at sipforum.org"
>        <discussion at sipforum.org>
> cc:    (bcc: mcoffee)
>
> Subject:  Re: [SIPForum-discussion] FAX T.38
>
>
>
> Yes, you can configure the "sending" device (A-party) to send the 
> re-invite.  Of course, the B-party device needs to be able to handle 
> an incoming re-invite for T.38...some devices (gateways) don't handle 
> that so well.  I've done this type of configuration in the past with Cisco 2102 ATAs, but it's not recommended.
> One of the downsides is that you can run into glare issues if both A and
> B-parties send T.38 re-invites simultaneously.   This can result in failed
> negotiations and, ultimately, inconsistent results.   The exact behavior depends
> on the CPE and Fax gateways in the path; for example, if you fax a 
> variety of different voice gateways (e.g., T.38 to different carriers) 
> you will likely end up with an unreliable fax solution.
>
> With that said, my advice is to stick with the T.38 recommendation 
> that only the receiving party (B-party) send the T.38 re-invite.
>
> From: discussion-bounces at sipforum.org 
> [mailto:discussion-bounces at sipforum.org]
> On Behalf Of Moh, Yee-Kuang
> Sent: Monday, January 07, 2013 9:35 PM
> To: discussion at sipforum.org
> Subject: [SIPForum-discussion] FAX T.38
>
> Hi,
>
> Good day. Wondering using Fax T.38, isn't that B-party has always send 
> Re-INVITE
> T.38 upon codec negotiation? Can A-party send Re-INVITE T.38 if B 
> -party doesn't?
>
> Thanks in advance.
>
> Regards
> moh
>
>

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