[SIPForum-discussion] FAX T.38

Tue Jan 22 23:52:48 UTC 2013

Hi all,

I worked with lots of different media gateways which are not accept T38 in originial invite. So, declaring T38 in originial invite may cause you problems with some of the gateways, even B party in this scenario supports it.

Also you may configure your A side to send reinvite to swtich fax mode.

Regards,

________________________________
 From: Sebastien BOIRE-LAVIGNE <Sebastien.Boire-Lavigne at sagemcom.com>
To: mahdi salah <mahdi.salah0 at gmail.com> 
Cc: discussion at sipforum.org 
Sent: Tuesday, January 22, 2013 10:46 PM
Subject: Re: [SIPForum-discussion] FAX T.38

Yeah offering both G.711 and T.38 can confuse the B-party. I don’t see why, but it would not be a first since T.38 call flows are not always bullet proof. Can you enable T.38 on the A-Party without advertising it in the initial invite an just offer G.711?
SBL

From:discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of mahdi salah
Sent: Tuesday, January 22, 2013 4:05 AM
To: Sebastien BOIRE-LAVIGNE
Cc: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] FAX T.38

In fact, a first test was done without the support of T38 at A party side, so the INVITE is sent with only G711, then the audio RTP media link is correctly established and the re-INVITE for T.38 is successfully initiated by B Party, but the call is failed because A party does not support T.38.
Then we activated the support of T.38 at A party, and so the INVITE is sent including both Codecs G711 first and T.38 second. Also for this case the audio RTP media link is established correctly but there was no re-INVITE initiated by B Pa rty, and the Fax is successfully sent with G711.

So it seems like when there is T.38 in the first invite, B party won't initiate a re-INVITE.

Equipments:

A party : Huawei MGCF
B party : Alcatel Lucent MGCF   

Thanks

On Mon, Jan 21, 2013 at 11:16 PM, Sebastien BOIRE-LAVIGNE <Sebastien.Boire-Lavigne at sagemcom.com> wrote:
Unless you can figure out the reason why the B-party doesn’t make the switch, you have little choice but to initiate the re-invite yourself.  Putting a muted T38 media is unlikely to  improve much, if the B-party is not even supporting the “basic” call flows. But it is trial and error at this point.

Do you know the type of hardware/software of the B-party?
SBL

From:discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of mahdi salah
Sent: Monday, January 21, 2013 10:20 AM
To: discussion at sipforum.org; Yee-KuangMoh

Subject: Re: [SIPForum-discussion] FAX T.38

Dear All,

I am facing a problem with initiating the re-INVITE for T.38 by the B party.
The A party INVITE is sent including both media G711A and T.38 and then an RTP media link (G711) is correctly established for audio,
But there is no re-INVITE for T.38 sent by the B Party.

What should be the problem? 
Is putting the T38 media to inactive in the first INVITE a solution ?

Thanks
Mahdi
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