Modem Relay Codec's

hltelle

Quick questions... At work we are running CUCM 8.6 we use codec 7.11 or 7.29 for calls and there are no issues. We do not have a fax server so we are routing them through the gateways to vg224's on the bottom the screen on the device page there is a choice of gateway controlled, modem relay, modem passthrough or both. I did my research because we was having issues with faxes being garbled and it recommended that without a server to run modem relay. The question I have on this is that modem relay uses codec T.38. Im not sure that this codec is even set up or where to check to see if it is or isnt. We just had this system built and we are deploying the phones and are learning on the fly so bare with me. I am studying for my icnd1 and sort of new to the networking side.

shodown

Kinda all over the place

I can't really give you much advice until I under stand your call flow and call setup. Usually when a call goes out of a fax it goes though the VG device which is usually setup SCCP or MGCP. Then out to the PSTN gateway which can be SIP/MGCP/H323, then out to the actual PSTN which can be a SIP trunk or PRI or FXO port. We would need your call flow and the signaling method. 1 other thing faxes will not work if they are seing G729 anywhere in your call flow, I see this often with Site to Site faxing or Centralized dialing where there is 1 pstn gateway and multiple sites use it.