1. Summary of P2P and characteristics of the
P2P means "point to point" or "end-to-end" also known as peer-to-peer computing, is a kind of in a centralized mode of use of distributed resources to complete some of the key tasks of system and the application of P2P network, as a distributed network, break the traditional Client/Server (C/S) model, each node in the network status are equivalent, has many characteristics of the distributed network,
From the above description of P2P, unknown P2P at least the following three characteristics:
(1) the P2P network is equivalent interconnected network, between nodes of a network are equivalent, partner relationship,
(2) resource transfer between P2P network nodes from one point to another, and each node is both resource providers and resource consumers,
(3) resources in P2P network is dependent on the existence of the node, and resources can dynamically join or quit,

2. The P2P network topology structure is divided into the following kinds,
(1) centralized P2P network
In this kind of network structure, there is a central server, it is used to record information sharing as well as the response to the information query, this also has the characteristics of centralized network structure, but it has essential difference between with C/S structure, in the C/S structure, all the information and resources in the server, and between the client and the client doesn't have the ability to interact with each other, but in peer-to-peer (P2P), a central server to keep only the index of resource information, users find the resources in the center server's users, and communicate with resources the user access to information, rather than on the server to download information,
(2) the fully distributed unstructured peer-to-peer (P2P)
The structure fully utilizes the flooding search and random way forward, the Gnutella system adopted the structure, as for the structure works, in is detailed introduce the work principle of the Gnutella again
(3) fully distributed structured P2P
(4) hybrid P2P