Cisco VG202 - T.38 configuration over SCCP

[Enric92]

Hello everyone,

We have VG202 (Version 15.4(3)M3) registered in sccp over CUCM (11.5 SU4).

On CUCM, we have sip trunk to an SBC which is connected to SIP provider.

When there is incoming SIP invite containing T38 in the SDP.

m=image 21112 udptl t38
c=IN IP4 172.22.156.54
a=T38FaxVersion:0
a=T38MaxBitRate:14400
a=T38FaxMaxBuffer:1800
a=T38FaxMaxDatagram:150
a=T38FaxRateManagement:transferredTCF
a=T38FaxUdpEC:t38UDPRedundancy

The CUCM reject the SIP invite with a "SIP/2.0 488 Not Acceptable Media".

I dig a bit in the CUCM Call Manager log and found the following error:

AppInfo  |DET-SIPInterface-(990763):SDPOfferInd: T38-SIP: Rejecting T38 only incoming offer-INVITE_NOT_ACCEPTABLE_HERE. The called party is a SCCP endpoint. mPeerXferMode=4, mFarEndXferMode=0

Do you have an idea why?

VG should be compatibly with SCCP this current firmware no?

Thanks a lot for your help.

[R0g22 · Accepted solution]

SCCP cannot do a protocol based switchover, which is what T.38 is doing at the moment. The only flavor of T.38 that SCCP does support is NSE based switchover but since you have a ITSP sip trunk, it won't be supported since NSE is Cisco Proprietary and as long as your ITSP does not use Cisco gear, they won't understand it.
Your options are to have either MGCP, SIP or H.323 for your VG-202.

[Enric92]

Thanks alot for your feedback, that answer my question !