What is the purpose of the seven protocols?

Answer 1

I think you are referring to the seven layers of the ISO model. It is a framework that defines the process of moving information from one point to another. That is a complex process with many steps.... too difficult to deal with as one process. The model breaks the process into seven "layers" with each layer defining a part of the process. Each layer defines a result that must be achieved without specifying how to acheive it...so for each layer there can be and are multiple options.

The first layer, for instance, requires a method or "protocol" that can transfer a stream of two values (1 and 0) between 2 sites. Any process that can do that is a layer one protocol. Examples include twisted pair wires, microwave, fiber optic, thicknet, thinnet, etc.

Layer two describes how to prevent two users from talking at the same time and how to group the ones and zeros into meaningful segments. Token Ring, Ethernet, IPX, etc.

Whole books have been written on the subject.