Can the CUBE forward T.38 fax on a call leg to another leg using pass-thru?

[T-Boens]

Hello Everyone,

My first post on this forum...

I have a CUBE that sits in the middle between my VoIP network to the ISP.

Our fax machines, currently, connects to analog voice gateways (VG224, etc), and are using T.38 throughout our organization.

We are trialing SIP Trunking from one of our providers, but they do not do T.38; only pass-through.

Can we not terminate the T.38 at the CUBE and have the CUBE initiate a passthru to the ISP?  sorta like store-and-forward on the fly?  I can't seem to find any reference to confirm if this is possible or not possible.  Ultimately, I think this will be a deal breaker for us to move to SIP trunking.

*** Don't ask why we are still doing faxing today... ***   --facepalm--

Cheers,

Trev.

[Anthony Holloway · Accepted solution]

Last time I looked into this, you had to have a two port PRI card in CUBE connecting port 0 to port 1, kind of like a loopback. This way the IP leg inside connects to port 0, then port 1 connects to the IP leg outside, thus allowing you to have two different fax relay technologies on the same fax call.

[T-Boens]

Thanks, Anthony!
I was pondering the same setup; but was hopeful that the CUBE could terminate and reinitiate the media.
--Trev.

[Vaijanath Sonvane]

Hi,

“Fax Passthrough” refers to the passthrough transport method using an NSE switchover to pass faxes over G.711. In Fax Passthrough mode, gateways do not distinguish a fax call from a voice call. Fax communication between the two fax machines is carried in its entirety in-band over a voice call. It only support G.711. CUBE does not support transcoding of T.38 to G.711. For T.38 to work on your fax machine side, your ISP must support T.38. Or you need to change Fax protocol on your fax machine side to match with your ISP.

[T-Boens]

Thanks, Vai!
Is there a reference document that would reinforce that the CUBE is not capable of such transcoding?
--Trev.

[Vaijanath Sonvane · Accepted solution]

Here is the reference URL:

https://community.cisco.com/t5/collaboration-voice-and-video/t-38-fax-over-ip-design-best-practices-questions-and-answers/ta-p/3116604

Below is the exact questions asked in this live webcast:

Q. If the SIP trunk provider doesn't support T.38, can I use a Cube to transform from T.38 to G.711 to the provider and if yes is their an example IOS config I can use?

A. No. Cube can't transcode from T.38 to G.711.