What type of signaling involves sending messages over a separate channel from the voice channel?

Common Channel Signaling is the correct type of signaling that involves sending messages over a separate channel distinct from the main voice channel. This method enhances communication efficiency by allowing control signals to be exchanged independently of the traffic channels that carry actual voice or data. This separation reduces the chances of interference with the voice communication, as control messages can be transferred without occupying the same bandwidth required for conversations.

This type of signaling is especially valuable in modern telecommunications environments where a high volume of simultaneous calls and services is common. It also supports advanced features such as call setup, teardown, and various supplementary services without impacting the quality of the voice channel in use.

Other signaling methodologies do not utilize a separate channel in the same manner, as in-band signaling uses the same channel for both voice and signaling, and robbed-bit signaling modifies the voice channel itself for signaling purposes, hence not sending messages over a completely separate channel. Channel Associated signaling maintains a single connection for each call, where signaling information travels alongside the voice channel rather than separately.