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New Member

CUBE and T.38 - passthrough fax interworking

I'd like exchange faxes between 3rd party H.323 gateway which requires to use T.38 fax relay and ATA which doesn't support T.38. ATA is controlled with SCCP by CUCM 6.0 and there is H.323 trunk between CUCM and 3rd patry GW.

My idea is to use CUBE (IP-IP GW) but it looks like it doesn't support fax protocol transcoding.

Can anyone confirm if this feature is supported on Cisco UBE?



Cisco Employee

Re: CUBE and T.38 - passthrough fax interworking

Your suspicion is correct, Petr. CUBE does not support T.38 fax to fax passthrough transcoding.

The type of transcoding that CUBE will do is for example one leg of the call uses G.711 and the other leg using G.729, and then overlaying a T.38 or fax passthough fax on top of that session. Both call legs on the CUBE, however, would need to use the same fax protocol.

Hope this helps.



New Member

Re: CUBE and T.38 - passthrough fax interworking

Thank you, Michael.


New Member

Hi guys,I know this topic is

Hi guys,

I know this topic is very old but ( already has six years) , but someone can tell me if this is already supported ( Fax interworking T38 with G711a (passthrough)  in CUBE? Protocol is SIP v2.
I have a cube (Cisco 2921 ios 15.4 - C2900-universalk9-mz.SPA.154-1.T2.bin) in the middle of a OXE R11 (PBX Alcatel) and an SIP operator. The operator only supports fax's in G711A and the x in T38 v.0

OXE (T38) <---sip-----> C2921 <---sip-----> Service Provider (G711A-law)


I have tried to setup a solution that forced the dial-peer to the OXE side in T38 and the Operator in G711a but does not work, and I see in the traces that can not force the protocol (the call comes from OXE in T38 and goes to the operator in T38 and the other way the call came from  the operator in G711A and goes to OXE in G711A). The router is not doing nothing, does not interworking.

Best Regards