Which layer of the Data Over Cable Service Interface Specification (DOCSIS) system is utilized by the cable modem termination system (CMTS) to identify cable modems?

The layer utilized by the cable modem termination system (CMTS) to identify cable modems is the Media Access Control (MAC) layer. This layer is responsible for managing protocol access to the physical network medium, meaning it governs how devices on a network uniquely identify themselves and communicate with each other.

In DOCSIS systems, each cable modem is assigned a unique MAC address which the CMTS uses to recognize and communicate with that specific modem. The MAC layer handles essential functions such as framing, addressing, and managing protocol control for data transmission, which are crucial for maintaining multiple simultaneous connections efficiently.

The other layers mentioned do not serve this particular identification function in the context of DOCSIS. The Transmission Control Protocol (TCP) layer deals primarily with ensuring reliable transmission of data segments between devices rather than identification. The Internet Protocol (IP) layer is focused on routing packets across networks using IP addresses, which is more about locating devices on a broader scale rather than the distinctive task of identifying individual cable modems. The Data Link layer includes operations that facilitate data transfer across a shared physical medium, but it is the MAC sublayer that specifically manages device identification and access to that medium.