[SIPForum-discussion] Fax call flow

vidyut gupta vidyut_gupta at yahoo.com
Mon Aug 23 10:01:24 UTC 2010


Hi ridhuan,

The SDP exchange will be different for both the call flows, in case of T.38 the SDP will have image in "m=" line and corresponding parameters in "a=" line. Generally UA tries for send the fax using t.38 but in case other party does not supports, the it fall back to pass through fax.You see T.38 SDP in second or third INVITE because initially they might have established the audio call and after that fax would have initiated. have a look at the following draft, it will surely help you : 

draft-ietf-sipping-realtimefax-01

--Vidyut


--- On Fri, 8/20/10, ridhuan yusof <mridhuan at gmail.com> wrote:

From: ridhuan yusof <mridhuan at gmail.com>
Subject: [SIPForum-discussion] Fax call flow
To: discussion at sipforum.org
Date: Friday, August 20, 2010, 9:08 PM

Folks,

I really not understand which are the correct call flow for fax..in my case i have 2 different codec i.e. using g.711passthrough and t.38. Can u explain for me how to differentiate those fax flow... Sometime i noticed that the SDP carried T.38 in 2nd and 3rd INVITE msg..Any reference/standard can be referred?


Regards,
Ridhuan


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