Core Issue
Review this configuration example:
Cisco CallManager > MGCP Gateway > 2821> NM-HDV > PRI > PSTN
The media stream of the voice calls to the Public Switched Telephone Network (PSTN) is not secured or encrypted, but the IP phone to IP phone calls are encrypted normally.
The debug mgcp all command shows the Skipping Crypto Suite Selection. No Secure RTP info specified in LCO or SDP message.
The show mgcp connection command displays information for active connections that are controlled by the Media Gateway Control Protocol (MGCP).
Resolution
For the High-Density Voice/Fax Network Module (NM-HDV) only, the codec complexity secure command must be enabled under the voice-card configuration in order to enable the digital signal processor (DSP) to encrypt the media traffic.
Refer to Media and Signaling Authentication and Encryption Feature for Cisco IOS MGCP Gateways, which mentions this configuration and its support.
The codec complexity secure command is also applicable to the MGCP voice gateways. The NM-HDV for secure Real-Time Protocol Priority (RTP) in the MGCP is now supported in Cisco IOS Software Release 12.3(14)T as well.
