(Cable Modem Termination System) A computerized device that enables cable modems to send and receive packets over the Internet. It inserts IP packets from the Internet into MPEG frames and transmits them to the cable modems via an RF signal. It does the reverse process coming from the cable modems.

A DOCSIS-compliant CMTS enables customer PCs to dynamically obtain IP addresses by acting as a proxy and forwarding DHCP requests to DHCP servers. A CMTS may provide filtering to protect against theft of service and denial of service attacks or against hackers trying to break into the cable operator's system. It may provide traffic shaping in order to guarantee a specified quality of service (QoS) to selected customers. A CMTS may also provide bridging or routing capabilities.