[SIPForum-discussion] FAX Call Identification

[Kevin P. Fleming]

On 01/05/2011 10:19 PM, Ashoke Kumar Ghosh wrote:
> Dear All,
> We have SIP Application server platform that works in B2BUA mode. The
> platform handles the prepaid charging as well.
> The Application Servere receives SIP request from the NGN Elements,
> applies account validation and initiates one new SIP Dialog with NGN for
> routing towards B party. The Application Server maintains two separate
> dialog for A party and B party.
> We have observed that Re-INVITE message is received for normal voice
> calls for heart beating purpose for both legs of the call. The
> Application Server sends 200 OK on receipt of Re-INVITE message without SDP.
> *_/PROBLEM STATEMENT:/_*
> We are having one problem in terms of identifying the fax calls. Sample
> traces taken show that for fax calls are being set up initially like
> normal voice calls. After dialog confirmation, Re-INVITE message is
> being received from A party side with modified SDP. Since Application
> Server considers Re-INVITE as heart beating message, it is simply
> generating 200 OK without SDP. As a result, fax calls are failing.

This completely broken. Your Application Server must treat re-INVITE 
request as what they are, and process them according to the RFCs 
involved. What this processing means for your system (charging, 
communicating the session changes to another SIP session, etc.) is 
outside the scope of SIP itself.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kfleming at digium.com
Check us out at www.digium.com & www.asterisk.org