Cisco IOS Voice Troubleshooting and Monitoring -- FXS Interfaces - DocWiki

Cisco IOS Voice Troubleshooting and Monitoring -- FXS Interfaces - DocWiki

Ring Voltage Problems

Voltage problems can cause three types of problems:

• Answering and Call Initiation Problems with Automated Telephony Devices
• Ringing Problems
• FXS Ring Failure in the United Kingdom

Certain automated devices, such as fax machines, answer machines, multiline phones and voice mail systems, look at the line voltage in order to deduce if the line is busy or idle. If another device is off hook, then the line voltage drops, and the automated system does not answer or initiate a call. If the threshold being used is close to -24 V or higher, this can cause the device not to work as expected.

Certain phones might not ring when the default ring voltage and ring frequency are applied from the Cisco FXS interface.

For situations where the line voltage is not high enough, a ring booster can be installed between the interface card and the network.