The client-server model firmly differentiates the roles of the client and server. According to this model, the client requests services that are provided by the server. The peer-to-peer model doesn’t have such severe roles. In actual fact, all nodes in the system are considered peers and thus may act as either clients or servers or both. A node may request a service from any more peers, or the node may in fact give such a service to other peers in the system.
For instance, let’s consider a system of nodes that share cooking recipes. Under the client-server model, all formulas are stored with the server. If a client wishes to access a recipe, it must ask for the recipe from the specified server. Using the peer-to-peer model, a peer node could ask other peer nodes for the particular recipe. The node (or perhaps nodes) with the requested recipe could give it to the requesting node. Notice
How each peer may perform as both a client (i.e. it may request recipes) and as a server (it may give recipes.)