Hi All,

I was trying to send FAX over IP network.

I enabled G729 and t.38 codec on both endpoints.

While checking the Wireshark trace of the session, i saw that first negotiation was done with G729 and media started flowing using this codec.

After some time re-negotiation happened with t.38 codec and FAX was properly transmitted.

But in the Wireshark trace could not see RTP packets with t.38 codec. RTP using G729 was still flowing even after the successfull negotiation with t.38. However the SSRC of the new G729 stream was changed to 0x0000(earlier it was a different value).

Moreover, i could see "Unknown RTP version 0" in the Wireshark trace after the second negotiation(negotiation with t.38).

I am not sure whether FAX was transmitted using G729 or t.38.

Could anyone help me out for the above scenario?

Regards.

Sanjeeb