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.
Cisco 7931G is considered as one of the best multifunctional phones with 24 phone line keys. Due to high number of keys (24 line keys with backlight and 4 interactive menu keys with all features and possibilities of the phone), this model can work independently from CP7915 and CP7916 panels, what makes the organization of the office cheaper.