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IP phone user experiences one-way voice when a call is established across a Cisco IOS voice gateway

Core Issue

Issuing the h323-gateway voip bind srcaddr command on an interface causes one-way audio due to Cisco bug ID CSCdw69681.

The caller using the IP phone is unable to hear the caller in the Public Switched Telephone Network (PSTN).

Resolution

These are among the symptoms:

  • Issuing the debug voip rtp command indicates the audio stream is open in both directions, and Real Time Protocol (RTP) packets are being transmitted and received.

    Note: The debug voip rtp command severely impacts performance and should be used only for single-call debug capture. The command became available in Cisco IOS  Software Releases 12.2(2)XB and 12.2(8)T. It is similar in function to the hidden debug cch323 rtp command.

  • Issuing the show call active voice brief command indicates RTP packets are being transmitted and received for both call legs.

  • Call statistics on the IP phone, however, show that RTP packets are not being received. A sniffer trace confirms this.

  • This problem was reproduced in the lab using a 2611 and 3640 router running the IP plus feature set of Cisco IOS 12.2(6b).

For a workaround, consider these options:

  • Remove the h323-gateway voip bind srcaddr command to restore two-way audio.
  • Reissue the h323-gateway voip bind srcaddr command to bind the IP address of a loop back interface instead of a physical interface.
  • Cisco bug ID CSCdw69681 is resolved in Cisco IOS versions 12.2(9.1), 12.2(9.1)T, 12.2(9.2)S, and 12.2(9.4)DA.

To resolve one-way voice issues, refer to the Additional Information: Verify One-Way Audio section of Troubleshooting One Way Voice Issues.

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