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.
Resolution
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.
