I'm not here to ask help but to share some info on CISCO gw fax sending and have the comment of NetPRO people.
We use cisco UGw (5300,5350,5400) as VoIP terminations in SIP. We often find interops problems with third party devices when we try to send fax in T.38.
Recently we have discovered the reason of all these problems is on CISCO IOS T.38 negotiation.
If Re-Invite is made by CISCO gw and third party ATA or IAD use different port for T.38 respect to voice, CISCO
gw ACK the change but doesn't use the new port: T.38 packets are sent to previous RTP port used for voice.
FAX works if third party device use same
port for audio codec and T.38.
I don't think is a standard behavior.
I understand that CISCO takes as standard using the same port but why acknowledging the 200 OK with a different port?
Only if third party device makes ReInvite
before CISCO does, port can be changed.
According to me, changing ports should be
permitted on CISCO IOS (we have changed a lot of versions but nothing changes).
I'd like to know your opinion about this.
Thanks in advance.