1. Layered protocol architecture: basic concepts

To achieve communication between two entities, several choices are possible when it comes to grouping the rules to be followed. They can be combined in a single protocol, grouping together all the functions required for communication. The drawback of this solution is that it does not simply allow the introduction of improvements; the entire protocol has to be reworked to add or change a rule. The classic solution, found in many architectures, is to group rules into layered protocols that stack one on top of the other. The most classical architecture is that described in the ISO reference model (see the article Open Systems Interconnection (OSI) in the Computer Science treatise [H 3 220] ); it contains seven protocol levels. The N ^th level will be referred to...