It is a device capturing and controling all the signals, which are being created by the whole system, especially the made and received phone call signals. The device is mostly used for connecting regular phone system with the Internet and backwards.
A device or a program, which is makes the transformation of data or
signal. Codecs can both code flow/signal (often for transfer, storage or
encoding) and decoding – for review or changes in the size, more suitable also
for these operations. Codecs are often used during the digital processing of
video and sound.