Why CUBE Needs Codecs
CUBE uses codecs to compress digital voice samples to reduce bandwidth usage per call. Refer to Table 2 to see the relationship between codec and bandwidth utilization.
Configuring codecs on a device (configured as CUBE) allows the device to act as a demarcation point on a VoIP network and allows a dial peer to be established only if the desired codec criteria are satisfied. Additionally, preferences can be used to determine which codecs are selected over others.
If codec filtering is not required, CUBE also supports transparent codec negotiations. This enables negotiations between endpoints with CUBE leaving the codec information untouched.
The illustrations below show how codec negotiation is performed on CUBE. Two VoIP clouds need to be interconnected. In this scenario, both VoIP 1 and VoIP 2 networks have G.711 a-law 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 will accept 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 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 will be a G.711 a-law call.
Restrictions for Voice-Class Codec Transparent
While using the voice-class codec transparent, only the offer is passed transparently (without filtering). Codec filtering is done on the SDP present in answer and the first codec is passed to other side.
CUBE does not support Early-Offer to Delayed-Offer (EO-DO) call flows.
You can use 'pass-thru content sdp', if you do not want to involve CUBE in the codec negotiation.