Question

A CUBE connects an internal CUCM cluster to an ITSP SIP trunk. Voice calls work perfectly, but every T.38 fax call fails during the switchover to fax. A debug shows that when CUBE sends the re-INVITE to the ITSP, the SDP media line reads 'm=image 4000 udptl t38', while the ITSP's own documentation states its equipment only accepts the media transport token 'UDPTL' followed by 'TCP/UDPTL' capability and rejects lowercase 'udptl'. You must modify the outbound signaling toward the ITSP without affecting the internal leg. Which configuration approach resolves this?

Accepted Answer

Apply an outbound SIP profile with an SDP rule that rewrites the m=image line transport token to the format the ITSP expects, and associate it to the outbound dial peer facing the ITSP

Answer

Configure a voice translation-rule on the outbound dial peer to substitute the udptl string in the called-number field

Answer

Enable fax protocol pass-through g711ulaw globally under voice service voip to bypass the T.38 negotiation entirely

Answer

Add an inbound SIP profile on the CUCM-facing dial peer to change the SDP media transport before the call reaches CUBE