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After installing Cisco VT Advantage, a PSTN call from the 7970 phone to an IOS gateway is disconnected as soon as the last digit is entered

Core Issue

This problem will be observed  with 7940, 7941, 7960, 7961, 7970, and 7971 IP phones associated with a camera fail to complete a call after the installation of Cisco VT Advantage

Cisco CallManager uses Unrestricted Digital bearer capability to send audio calls to the voice gateway for this kind of phone. The Unrestricted Digital bearer capability includes both voice and video capabilities.

This is how a failed call appears in the output of the debug isdn q931 command:

May 22 09:12:54.010: ISDN Se0/1/0:23 Q931: TX -> SETUP pd = 8  callref = 0x7A3D
  Bearer Capability i = 0x8890A3
  Standard = CCITT
  Transer Capability = Unrestricted Digital

A successful call appears like this:

Sep 14 09:12:54.010: ISDN Se3/0:15 Q931: TX -> SETUP pd = 8  callref = 0x7A3D
  Bearer Capability i = 0x8890A3
  Standard = CCITT
  Transer Capability = Speech

Resolution

Verify whether:

  • Cisco VT Advantage is used
     
  • Video must be sent on the same PRI

If the new PRI Telco does not accept any bearer capability other than speech, configure bearer-cap speech under the voice port. This forces the gateway to overwrite the bearer capability as speech.

However, if video capability is necessary, request the Telco to modify the PRI to accept the Unrestricted Digital bearer capability.

For more information, refer to:

IP Phone Call Failure with VT Advantage - Bearer Capability

IP Phone Models

7970G

7940G

7960 series

7971G-GE

7941G-GE

7961G-GE

Version history
Revision #:
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Last update:
‎06-22-2009 04:05 PM
Updated by:
 
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