Which of the following is an example of a specification in the Network Layer?

The correct answer is routing protocols, which are essential components of the Network Layer in the OSI (Open Systems Interconnection) model. The Network Layer is primarily responsible for determining how data is sent from the source to the destination across multiple nodes and networks. Routing protocols facilitate this by enabling routers to communicate with each other, share information about network topology, and make decisions regarding the most efficient paths for data transmission.

Routing protocols such as RIP (Routing Information Protocol), OSPF (Open Shortest Path First), and BGP (Border Gateway Protocol) play a crucial role in maintaining accurate routing tables and ensuring that data packets are delivered reliably and efficiently. Their specifications define how these processes are executed, making them a clear example of the functions performed at the Network Layer.

Other options refer to different layers or functions that do not fall under the specific characteristics of the Network Layer. For instance, physical address management pertains to the Data Link Layer, application service delivery relates to the Application Layer, and session control is a feature of the Session Layer. Therefore, routing protocols aptly represent a specification within the Network Layer's scope of responsibilities.