Which protocol is responsible for controlling sessions between computers in a network?

The AppleTalk Session Protocol is specifically designed to manage and control sessions between computers within an AppleTalk network. It plays a crucial role in establishing, maintaining, and terminating sessions by coordinating the data flow and ensuring that communication is orderly and efficient. This protocol facilitates the interaction between different applications on networked devices, allowing them to exchange data in a structured way. In essence, the AppleTalk Session Protocol is essential for maintaining the integrity of communications during a session, ensuring that both endpoints properly synchronize their interactions and understand each other's status.

The other protocols listed, such as the Appletalk Transaction Protocol, Ethernet, and ARUP, serve different functions within networking. For instance, Ethernet is a physical and data link layer technology that defines how data packets are placed on the network. The Appletalk Transaction Protocol is more about facilitating specific data transactions rather than managing sessions themselves. ARUP (AppleTalk Remote Access Protocol) is used for remote access and does not focus on session control. Hence, the AppleTalk Session Protocol is the correct response for the specific role of controlling sessions in a network environment.