[SIPForum-discussion] Would the fax call fail if there is amistmatch between SDP Attributes

[Rob Maxwell]

I believe those parms are "declarative" meaning they are sent to inform the other user of what the senders capabilities are for  T.38. The receiver should "NOT" fail a call based on mismatch of those values. The 0 in the image port is important because that is canceling the stream and there should be no further communication on that stream. In my experience, which is not that great, this is seen when there are 2 "m-line" descriptors in SDP as is seen in T.38 annex E support.







From: mustafa aydin 
Sent: Tuesday, August 24, 2010 7:28 AM
To: discussion at sipforum.org 
Subject: [SIPForum-discussion] Would the fax call fail if there is amistmatch between SDP Attributes


Hello Guys,

In my scenario, the receiving gateway sends a reinvite (to negotiate t38) with the following SDP attributes;

Media Attribute (a): T38FaxVersion:0
Media Attribute (a): T38FaxMaxBuffer:1100
Media Attribute (a): T38FaxMaxDatagram:612
Media Attribute (a): T38MaxBitRate:14400
Media Attribute (a): T38FaxRateManagement:transferredTCF
Media Attribute (a): T38FaxUdpEC:t38UDPRedundancy

However, the emitting  gateway responds only with the  attributes below in 200 OK;

Media Attribute (a): T38FaxRateManagement:transferredTCF
Media Attribute (a): T38MaxBitRate:14400

Then the recieving gateway sends another reinvite with removing the "T38FaxUdpEC:t38UDPRedundancy" attribute, but this time the emitting gw responds with a 200 which has "0" at it`s image port.

My questions are; whether the mismatch between these attributes is a reason for a failure ? If so, should not  the emitting gw respond back with a failure message instead of a 200 OK ?  

"draft-mule-sip-t38callflows-02.txt" indicates that only T38FaxMaxBuffer  and T38FaxMaxDatagram are optional, does it mean that all other attributes must reside at the SDP ? 

Best Regards,
Mustafa Aydin




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