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.
Multiple call arrangement - allows the user to receive several calls simultaneously, even if they came by the same line. This stops the redirection of incoming calls directly to voice mail in case the line is busy or if the user is already involved in an active call.