I had an interesting scenario where customer logged a case with us regarding their RightFax server not working. Those of you who don’t know what is a RightFax server can read about it here. When you dial the fax number from outside, it reaches the gateway and you hear one ringback and then a fast busy. The call flow was something like this:
0XXXX23422 >>>> Birmingham GW FXO >>> on CCM we have FXO port with number 3422 >> on CCM there was a RP 3422 with a RL pointing towards an Intercluster trunk to 192.168.10.39. The 192.168.10.39 was the Right Fax server.
I could ping 192.168.10.39 which proved no issues between CCM and Right fax server.
I then opened debug voip ccapi inout and observed the Ringback and fast busy tone which was not very helpful. I then asked the customer if fax calls through any other gateway are working and luckily I found one gateway where they had successful fax calls. I compared the MGCP config on both gateways and found one line missing from this gateway which was not working.
The MGCP commands common to both:
ccm-manager redundant-host BELL
no ccm-manager fax protocol cisco
ccm-manager config server 192.168.10.25
mgcp call-agent MICKEY 2427 service-type mgcp version 0.1
mgcp rtp unreachable timeout 1000 action notify
mgcp modem passthrough voip mode nse
mgcp package-capability rtp-package
mgcp package-capability sst-package
mgcp package-capability pre-package
no mgcp package-capability res-package
no mgcp timer receive-rtcp
mgcp sdp simple
mgcp fax t38 ecm
mgcp bind control source-interface FastEthernet0/0
mgcp bind media source-interface FastEthernet0/0
mgcp profile default!
The command which was missing was this:
mgcp rtp payload-type g726r16 static
I added that command and Fax started working.