A telecom codec is the piece of hardware that connects a data line to the customers local network. In the computer world, a codec is a piece of software that compresses and decompresses digital audio or video. Sending data in both directions at the same time. Usually higher quality, but requires more bandwidth. In video conferencing, full duplex will be much more natural and useable.
Cheap speakerphones are half duplex, whereas more expensive ones are full duplex.
A family of ITU standards for audio compression. In the H.323 world, the gatekeeper provides several important functions. First, it controls access to the network, allowing or denying calls and controlling the bandwidth of a call. Second, it helps with address resolution, making possible email type names for end users, and converting those into the appropriate network addresses. They also handle call tracking and billing, call signaling, and the management of gateways.