T38

[Robert Craig]

My ITSP only supports G711 Pass-Through for faxing. I want to experiment with T38 internally. Can I implement T38 on the inside of my network by applying it to the dial-peer going to my CUCM, and keep pass-through on the dial-peer going to my ITSP? I can't find anything saying that T38 has to be carried all the way through or it can be changed at a certain hop. Any help is appreciated. Thanks!                  

[Steven Griffin]

Robert,

The T.38 protocol is, for all intents and purposes, a codec.  As I understand it there currently* isn't a transcoder or MTP that can terminate a T.38 call and replay it as a G.711 call when doing IP to IP calls.  Thus the answer is, currently*, no.

-Steven

* Currently = IOS 15.1(4)M5

[Robert Craig]

OK, so more than likely if I sent T38 towards the internal side, the end fax machine will just utilize pass through because there won't be a terminating device/gateway accepting or offering T38. I spoke to my provider and he is having the same problem. No one all the way up the line that will carry T38. Thanks for your help though.

[Jonathan Schulenberg · Accepted solution]

Correct assuming you configure a fallback option on the gateway/CUBE.

voice service voip
 fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw

Please remember to rate helpful responses and identify helpful or correct answers.

[Robert Craig]

Yup, thats what I did and it did exactly that. I am experimenting with Flowroute as we speak. They support T.38 throughout their network. Thanks for the tip!

[asafayan1]

Hi Robert,

Would you mind reaching out to me to discuss your success/failures with T.38 faxing and flowroute?  We have a fax upgrade project and I'm looking at various options to move away from the traditional 1FB - analog fax machine model.

Thanks,

Amir