Fax outbound rings once 4321 SRST FXS Port

[Joe Mullis]

I have a new Cisco Phone system, we are using CUCM and at this particular site have a 4321 ISR . The fax line is plugged into port 0/2/0. Inbound faxes come through but when sending outbound faxes it rings one time then cuts out. On the receiving end we get the top quarter of the fax ( about one rings worth apparently) and the rest of the page is blank. The machine end and the receiving end also print out a report page saying fax has failed due to communication issue. I have attached my config. 

[R0g22]

Add the following to your config -

no ccm-manager fax protocol cisco
no mgcp fax t38 inhibit
mgcp package-capability fxr-package
mgcp default-package fxr-package
no mgcp fax t38 ecm
mgcp fax t38 nsf 000000

You have ECM enabled which might cause issues. Also if you have an analog phone plugged into the same FXS port as the fax machine, do outbound calls complete with two way audio ?

[Joe Mullis]

Yes I get two way audio when I plug a phone in. How do I disable ECM ?

[R0g22]

Do it on your fax machines. All modern ones have an option. Add the configuration that I added in my other post as well. You can add "fax-relay ecm disable" command on VoIP dial-peers as well. With this added, the DSP fax-relay FW will modify the "DIS" T.30 message in both directions so as to force the ECM disable even if the other gateway does not have it disabled.