Core Issue
When using a voice gateway that runs Media Gateway Control Protocol (MGCP), there is a high pitch tone for several seconds after the first ring followed by a normal media cut-through when a Foreign Exchange Station (FXS) line answers a public switched telephone network (PSTN) call. If you answer during the first ring, you can hear this high pitch tone on the device. This causes problems especially on a port that goes to a paging system. The paging system picks up on the first ring, and the beeps are heard on the overhead speakers.
This issue is documented by Cisco bug ID CSCsa97827.
This symptom is observed on all voice gateways that run Cisco IOS Software Release 12.3(14) or a later.
Resolution
Downgrade the router from Cisco IOS Software Release 12.3(14) to any of these releases:
- Cisco IOS Software Release 12.3(11)T5
- Cisco IOS Software Release 12.3(11)T6
- Cisco IOS Software Release 12.3(11)T7
Note:
This problem is also resolved in the resolved in the 12.4(5a) IOS version
You can download the required Cisco IOS software from the Software Center (Downloads)-Cisco IOS Software page.
The temporary workaround is to wait for the analog phone to ring three or four times before you answer the phone.
