Have two voice gateways (3845) terminating PRIs in an NFAS configuration. So the router's config is H323 based. Have 6 VG224s deployed in H323 as well, because a majority of the devices involved are fax and modems. Since forced authrorization code is a requirement for dialing long distance calls (even from fax machines and modems), running into an issue with H323 on the VG224. Analog gateways cannot play tones required for forced auth codes and hence FAC/CMC are not supported with H323.
So I changed the configs from H323 to MGCP on the VG224s (my PSTN gateways are still H323 due to NFAS). After this change, FAC codes seem to work on analog devices properly. I had enabled Cisco fax relay initially on the PSTN gateway (h323) and MGCP enabled VG224. This didnt seem to help much, so i changed the configs to use T38 fax relay. Fax seem to start working immediately after i changed to T38. But this behaviour seems to be very inconsistent. Sometimes it work, sometimes it doesnt.
Configs on H323 PSTN gateway..
dial-peer voice 2 voip
description Dialpeer to Match Incoming Voip leg
incoming called-number .
fax-relay ecm disable
fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback cisco
ip qos dscp cs3 signaling
Configuration of MGCP VG224.
no ccm-manager fax protocol cisco
mgcp call-agent <CM-ip> 2427 service-type mgcp version 0.1
mgcp dtmf-relay voip codec all mode out-of-band
mgcp rtp unreachable timeout 1000 action notify
mgcp ip qos dscp cs3 signaling
mgcp package-capability rtp-package
no mgcp package-capability res-package
mgcp package-capability sst-package
no mgcp package-capability fxr-package
no mgcp timer receive-rtcp
mgcp sdp simple
<b>no mgcp fax t38 ecm
no mgcp fax t38 inhibit (default)</b>
mgcp rtp payload-type g726r16 static
VG224 is running 12.4.12 (LD).
The H323 gateway is a 3845 running 12.3.14T7. The reason this gateway is running this version due to a bug with NFAS configuration in the 12.4 code (all of them are affected, so we had to downgrade to 12.3 until a fix for it arrives).
Any suggestions or improvements in the config above to make this work ?