Protocol Stacks

Protocol Stacks

Figure 2.1 illustrates the origin of the term protocol stack. The OSI model (and other non-OSI protocol standards) break the complex process of network communication into layers. Each layer represents a category of related tasks. A protocol stack is an implementation of this layered protocol architecture. The protocols and services associated with the protocol stack interact to prepare, transmit, and receive network data.

Two computers must run compatible protocol stacks before they can communicate because each layer in one computer’s protocol stack must interact with a corresponding layer in the other computer’s protocol stack. Figure 2.2, for example, shows the path of a message that starts in the Transport layer. The message travels down the protocol stack, through the network medium, and up the protocol stack of the receiving computer. If the Transport layer in the receiving computer understands the protocols used in the Transport layer that originated the message, the message can be delivered.

As long as their protocol stacks are compatible, computers of different types can communicate. TCP/IP, for example, is available for almost all current computers and operating systems. If a Macintosh and a Unix workstation both run TCP/IP, the Mac can access files on the Unix workstation.