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Cisco Bug: CSCun81693 - Interop issues when doing T.38 fax transmission via SIP-MGCP

Last Modified

Nov 26, 2019

Products (1)

  • Cisco Unified Communications Manager (CallManager)

Known Affected Releases

9.1(1.98100.2)

Description (partial)

Symptom:
Fax Transmission Method: 

T.38 Protocol. 

Call Flow: 

Fax - VG2XX - mgcp-CUCM-sip-CUBE-sip-ITSP

Fax call fails with Unacceptable media, during switch over. In this cal flow, Cisco call manager sends an mid-call INVITE with c=0.0.0.0 , m=image & attribute as sendrecv. Which is causing this interoperability issue. As CUBE will send it's own IP address while extending mid-call RE-INVITE to ITSP. Which causes ITSP to complete T.38 Fax switch over. 

Later CUCM sends an INVITE again, when it gets 200 OK from VG2XX , which cause call to get fail, as on ITSP leg switch over had already completed.

Conditions:
Fax call fails with Unacceptable media, during switch over. In this cal flow, Cisco call manager sends an mid-call INVITE with c=0.0.0.0 , m=image & attribute as sendrecv. Which is causing this interoperability issue. As CUBE will send it's own IP address while extending mid-call RE-INVITE to ITSP. Which causes ITSP to complete T.38 Fax switch over. 

Later Cisco UCM sends an INVITE again, when it gets 200 OK from VG2XX , which cause call to get fail, as on ITSP leg switch over had already completed.
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