fax-relay ans-disable command breaks modems

[arudolph_emd]

Hello,

I have a vg224 with a mix of fax machines, modems, and analog phones attached to it and a 2811 router as the PSTN gateway.  Both are configured as h323 gateways.  In order for faxing to work, I had to enter the "fax-relay ans-disable" and "fax-relay sg3-to-g3" commands under "voice service voip" on both devices so that faxes would not negotiate sg3 speeds and fail.  Now the modems cannot dial out.  If I remove the "fax-relay ans-disable" command from just the 2811 gateway, the modems work again but faxes to/from sg3 capable fax machines fail.  Is there any way to disable / enable the ans tones based on the calling source at the 2811 gateway?

Thanks,

Andy

[ksaheta · Accepted solution]

ANSam tone is shared by SG3 Fax and Modems. 
SG3 faxes do not work with older 12.4T IOS releases, and the work-around you
 are using breaks Modem calls.

What you should do is use 15.1.3 T IOS code which enables support for SG3 faxes
 (so you don¹t have to ignore the ANSam tones).

Details on how to enable this feature: T38 Fax supports SG3 faxing
"This feature provides support for V.34 fax relay based on the ITU
Specification T.38 version 3 (04/2007) and for fax pass-through at SG3
speed"
[..]
"Beginning in Cisco IOS Release 15.1(1)T, full SG3 fax support is
enabled on Cisco TDM-IP voice gateways and Cisco UBE platforms"

http://www.cisco.com/en/US/docs/ios/voice/fax/configuration/guide/vf_cfg_t38_fxrly_ps10592_TSD_Products_Configuration_Guide_Chapter.html#wp1179536

To enable it, both gateways should run 15.1.3T or later and have:-
voice service voip
fax protocol t38 version 3

This feature provides support for V.34 fax relay based on the ITU
Specification T.38 version 3 (04/2007) and for fax pass-through at SG3
speed. Prior to Cisco IOS Release 15.1(1)T, SG3-to-SG3 calls would fail
because the V.34 modulation was not supported. A fallback solution
allowed SG3-to-SG3 connections to be made, but the transmission speed
was set to G3 levels.

For T.38 fax sessions to operate at SG3 speeds, all the endpoints
involved must support T.38 Version 3 (v3) configuration and have
negotiated T.38 v3.