Why it is necessary to have layering in a network?

A computer network is a very complex system. It becomes very difficult to execute as a single entity. The layered approach divides a very complex task into small pieces each of which is independent of others and it allow a structured approach in implementing a network. The basic idea of a layered architecture is to divide the design into small pieces. Every layer adds to the services given by the lower layers in such a manner that the highest layer is given a full set of services to manage communications and run the applications.