Rules that Govern Communications

A group of inter-related protocols necessary to perform a communication function is called a protocol suite. Protocol suites are implemented by hosts and networking devices in software, hardware or both.

One of the best ways to visualize how the protocols within a suite interact is to view the interaction as a stack. A protocol stack shows how the individual protocols within a suite are implemented. The protocols are viewed in terms of layers, with each higher level service depending on the functionality defined by the protocols shown in the lower levels. The lower layers of the stack are concerned with moving data over the network and providing services to the upper layers, which are focused on the content of the message being sent.

As the figure shows, we can use layers to describe the activity occurring in our face-to-face communication example. At the bottom, the physical layer, we have two people, each with a voice that can say words out loud. In the middle, the rules layer, we have an agreement to speak in a common language. At the top, the content layer, there are words that are actually spoken. This is the content of the communication.

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