Fax is not working on H323

Question

Hello All,
I have an issue with fax, it is connected to an fxs port on my h323 gateway. When a call comes from PRI and get connected to fax after I hear the fax tone the fax drops. IOS is Version 15.0(1)M4, and DSP is PVDM3.
My analysis:
The external calls hit gateway and it matches the pots dialpeer where my fax connected to. From the "debug voip vtsp all", I see Primary Fax Protocol=CISCO_FAX_RELAY, which is not enabled and we are using T38 relay and modem passthrough method for faxing. I believe PVDM3 does not work with Cisco Relay and couldn't allocate any dsp resources for the call and it drops. But still I wonder how gateway takes cisco relay.
Config:
voice service voip
allow-connections h323 to h323
fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback none
h323
  emptycapability
modem passthrough nse codec g711ulaw
dial-peer voice 1001 pots
tone ringback alert-no-PI
description PSTN Incoming, Pattern:.
translation-profile incoming PSTN-to-PhoneDN
incoming called-number .
direct-inward-dial
dial-peer voice 999030 pots
tone ringback alert-no-PI
destination-pattern 3027898
progress_ind setup enable 3
port 0/3/0
Output of vtsp debug
Oct  4 20:30:07: //6824/97F0D7BD8350/VTSP:(0/1/0:15):7:1:1/vtsp_dsm_save_fax_config: 
   Fax Relay=ENABLED
   Primary Fax Protocol=CISCO_FAX_RELAY, Fallback Fax Protocol=NONE_FAX_RELAY
   Fax Relay CM Suppression :=ENABLED, Fax Relay ANS Suppression :=DISABLED
   Fax Parameters Set By=Dialpeer, Peer=999030 (this is the peer where my fax connected to)
I have converted the port to MGCP and found its working, while faxing I see vtsp outputs
Oct  4 23:57:29: //7181/8FE17FEF8379/VTSP:(0/3/0):-1:1:2/vtsp_dsm_save_fax_config:
   Fax Relay=DISABLED - MGCP Application
   Primary Fax Protocol=IGNORE_FAX_RELAY, Fallback Fax Protocol=IGNORE_FAX_RELAY
   Fax Relay CM Suppression :=ENABLED, Fax Relay ANS Suppression :=DISABLED
   Fax Parameters Set By=MGCP Call Type --> I believe MGCP disabled the cisco fax relay and switch over to T38.
Oct  4 23:57:40: //7181/8FE17FEF8379/VTSP:(0/3/0):-1:1:2/vtsp_dsm_save_fax_config:
   Fax Relay=ENABLED
   Primary Fax Protocol=T38_FAX_RELAY, Fallback Fax Protocol=NONE_FAX_RELAY
   Fax Relay CM Suppression :=ENABLED, Fax Relay ANS Suppression :=DISABLED
   Fax Parameters Set By=MGCP Call Type
Can some one kindly suggest how to make it work on H323, also how we can force disabling cisco fax relay?

Answer 1

As I mentioned earlier, we are using MGCP for that particular fax port and the gateway we use as H323.
Even I'm not pretty sure about using mixed protocol, I believe this gateway gonna used to support call center calls. SInce MGCP is easy for configs they might have confiugred only the port as MGCP endpoint.
Now its not working with both the cases, not in mgcp as well as fallback mode. Can you reveiw the debugs and see why I have to remove "modem passthrough" command from voice service voip section which of our standard config and works well with all other gateway of ours. Please help here.