Hi ALL, I understand that there is no standard way to re-negotiate the T.38 media parameters. However during my experience I have discussed following approaches.
1. Calling and called party are in voice state. Calling party detects CNG from FAX machine and initiates Re-Invite. After re-negotiation both calling and called party move to FAX state. 2. Calling and called party are in voice state. Called party detects V.21 preamble (DIS) from FAX machine and initiates Re-Invite. After re-negotiation both calling and called party move to FAX state. 3. Calling and called party are in voice state. Calling party detects CNG from FAX machine and further forward to called party as a voice. Now when called party detect CNG on its network side, called party initiate Re-Invite for T.38 negotiation. After re-negotiation both calling and called party move to FAX state. CNG is a MUST tone in G3 fax machine while ANS/CED is a optional tone. BR, Sachin Rastogi On Tue, Jul 21, 2009 at 2:37 PM, Andrea Rizzi <andrea.ri...@yahoo.it> wrote: > There's no a standard way to renegotiate the T.38 media. Usually it is the > called party that issues the reINVITE, but there are implementations where > the reINVITE is sent by the calling party once the CNG is detected (of > course in the most common scenario where the calling party is the one > sending the fax), so you must be prepared to handle correctly any scenario. > On the called side, fax detection should be done on the HDLC flags (to be > sure it is a fax and not a modem) but it is quite common to find > implementation based on CED detection (much easier to implement). There are > pros and cons of different ways, but it is not a subject for this mailing > list ... > > Andrea > > _______________________________________________ > Sip-implementors mailing list > Sip-implementors@lists.cs.columbia.edu > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
