Final answer:
Frame Relay is the connection-oriented packet-switched network service that works at the Data Link Layer, providing a way to connect WANs using virtual circuits for data packet transmission.
Step-by-step explanation:
The protocol that fits the description of being a connection-oriented packet-switched network service operating at the Data Link Layer is Frame Relay. Frame Relay is designed to provide a cost-effective way to connect wide area networks (WANs) by using shared network equipment. Unlike circuit-switched networks which require a dedicated path between endpoints, Frame Relay creates a virtual circuit between the source and destination, which can be shared with others, thus optimizing the use of available network bandwidth.
Once a connection is established, data packets are forwarded in sequences called frames, and each frame contains enough addressing information to route it through the network to its intended destination. Frame Relay ensures the reliable delivery of frames by using error checking and flow control mechanisms. While this technology was quite prevalent in the 90s and early 2000s, it has been largely superseded by newer technologies such as MPLS (Multiprotocol Label Switching) and Ethernet WAN services.