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Cisco Unity plays system prompts but the audio is not detected by the caller, and the voice mail message is blank


Core Issue

If callers can hear Cisco Unity prompts, but Cisco Unity does not transmit any audio when a caller speaks, Cisco Unity can have a dual Network Interface Card (NIC) misconfiguration. The message waiting indicator (MWI) functions normally, and it can be turned on and off.


When dual NICs are configured in a Cisco Unity system with separate interface IP addresses, this can prevent the correct receipt of Real-Time Transport Protocol (RTP) packets for voice transmissions.

This problem is recorded in the log and trace files as silence detection filtering because Cisco Unity does not receive any audio and the wave driver reports silence detection on all recordings. This problem can also occur when a second NIC is installed in the Cisco Unity server but is not configured or connected to the network.

When dual NICs are installed on a Cisco Unity server, both NICs must be configured to share the same IP address. Refer to Configuring and Troubleshooting Dual NICs for Cisco Unity for more information.

Complete the steps in the Configuring Dual NICs section of Hardware in order to confirm or change NIC configuration settings.

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