Cisco Support Community

Clicking sound on Cisco IP phone on calls through digital gateways DT24+/DE30+

Core Issue

On calls coming through a DT24+, some current IP phone to PSTN calls hear a clicking sound. It sounds like someone hanging up.

Scenario 1:

  • Phone A (PSTN) calls IP phone 1 - no clicking.
  • Phone B (PSTN) calls IP phone 2 - no clicking.
  • Phone C (PSTN) calls IP phone 2 - IP phone 1 hears a click.

Scenario 2:

  • Phone A (PSTN) calls IP phone 1 - PSTN phone A hears a click.

This bug is believed to be caused by the absense of a jitter buffer on the DT-24+. It becomes apparent in environments where jitter and/or packet loss exists.

The load on the DT24+ is D003N300 Cisco CallManager version 3.0(10), but the problem also occurs on later releases. The load on the DE30+ is D003J300. This bug is documented in Cisco bug ID CSCdv21826.


These  workarounds are currently available:

  • Eliminate excess jitter from the data network.
  • Make use of the G711 codec if possible.
  • Change the gateway that is being used.