Fax issue on SIP/MGCP gateway

[LAJITH POTHU VARAKKAL]

Hi All,

I would require all your help to make our my fax machine working. Kindly find my flow below.

Analog phone --> FXS --> MGCP GW (IDDGW1) --> CUCM 9.1.2 --> SIP Trunk --> SIP GW (IDDGW1) --> E1 ISDN

The gateway IDDGW1 communicates to CUCM using SIP protocol, but the FXS endpoints alone are registered as MGCP endpoints.

Now the problem is, every time I make outbound fax it fails with communication error result. I have done some troubleshooting from my end and the failure reason I could see from SIP side as 488 and 415 error messages. I have T.38 and Modem pass through enabled from CUCM MGCP GW page as well as in gateway side. The primary fax protocol is configured as T.38 and fall back as modem pass through. Since I felt the gateway is having some issues in processing T.38 media, I have configured it to do pass though but no luck.

I see posts saying about fax protocol between IP networks, but in this case the gateway is connected to an ISDN provider. Could you tell me how the fax works in this setup and what is the recommended mechanism for this type of setup to work?

I even tried adjusting baud rate to 14000 since I found codec is being used was G711, and also zeroed the NSF values. But no luck.

Could some one help me here with right direction?

Thank You,

Lajith

[aboubakr1]

Hi,

Did you use T38 protocol or Cisco T38 fax relay?

[Francisco Granados]

Lajith,

I can help you. Please post your "sh run" output so I can see what you have configured. 

I will share some of my configuration, please do not copy and paste unless you fully understand the impact this will have on your network =].

Please make sure the FXS port shows "registered". Take a look at the 2 attachments and compare your config.

Thanks,

Francisco Granados

CCIE# 47169

[LAJITH POTHU VARAKKAL]

Thank you much for looking in to this Francisco. I really appreciate it.

The configuration that I have and the one you suggested to be the same.

With my little knowledge in traces and logs, I have found the signalling side is OK. The gateway and CUCM negotiates for standard T.38. So I had suggested the site to verify the fax cards on the machine as well as for any configuration tuning to TELCO. The HP engineer upgraded the firmware for fax card in HP machine and it appears fax in/out to be working now.

[Francisco Granados]

Excellent! Let me know if you need anything else.

[LAJITH POTHU VARAKKAL]

Sure. Thank You :)