7.3 Ports and Sockets
TCP uses what is termed port addressing to deliver information to the appropriate application-layer program. A port is a 16-bit address. The term socket refers to the concatenation of the IP address of the node and the port number used by the application-layer program. The concept of opening a socket in an application layer program facilitates multiple sessions on a single network node.
For example, two V+ tasks, or sessions, on the same controller may communicate simultaneously with a network server. Because both tasks run on the same network node, they have the same IP address. However, through the use of sockets, the combination of the IP address and a port number uniquely identifies the task to which TCP needs to route the information, provided that the port numbers are different for each task.