A cable modem termination system (CMTS) is a component that exchanges digital signals with cable modems on a cable network. A cable modem termination system is located at the local office of a cable television company.
A data service is delivered to a subscriber through channels in a coaxial cable or optical fiber cable to a cable modem installed externally or internally to a subscriber's computer or television set. One television channel is used for upstream signals from the cable modem to the CMTS, and another channel is used for downstream signals from the CMTS to the cable modem. When a CMTS receives signals from a cable modem, it converts these signals into Internet Protocol (IP) packets, which are then sent to an IP router for transmission across the Internet. When a CMTS sends signals to a cable modem, it modulates the downstream signals for tranmission across the cable to the cable modem. All cable modems can receive from and send signals to the CMTS but not to other cable modems on the line.