A codec is a device or software capable of encoding or decoding a digital data stream or signal. Audio codecs can encode or decode a digital data stream of audio. Video codecs encode or decode digital video streams.
This chapter describes the basics of encoding digital voice samples using codecs and how to configure them.
Cisco Unified Border Element (CUBE) uses codecs to compress digital voice samples to reduce bandwidth usage per call.
Configuring codecs allows the CUBE to act as a demarcation point on a VoIP network and allows calls on a specific dial peer to be established only if the desired codec criteria are satisfied. Also, preferences can be used to determine which codecs are selected over others.
If codec filtering is not required, CUBE also supports transparent codec negotiations. The codec filtering enables negotiations between endpoints with CUBE leaving the codec information untouched.
The following illustrations show how codec negotiation is performed on CUBE. Two VoIP clouds must be interconnected. In this scenario, both VoIP 1 and VoIP 2 networks have G.711 a-law that is configured as the preferred codec.
In the first example, the CUBE router is configured to use the G.729a codec. This can be done by using the appropriate codec command on both VoIP dial peers. When a call is set up, CUBE accepts only G.729a calls, thus influencing the codec negotiation.
In the second example, the CUBE dial peers are configured with a transparent codec and this leaves the codec information that is contained within the call signaling untouched. Because both VoIP 1 and VoIP 2 have G.711 a-law as their first choice, the resulting call is a G.711 a-law call.
H.323 protocol is no longer supported from Cisco IOS XE Bengaluru 17.6.1a onwards. Consider using SIP for multimedia applications.