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.
Direct Inward Dialing Support. This function is offered by telephone companies with the goal that ATC clients could connect all range of company numbers to one or several lines. The aim is to give a personal number to every employee without having to connect it to a separate phone line. Thus, all telephone traffic can be divided and controlled more efficiently.