SERVICE ORIENTED COOPERATION AMONG TRUSTWORTHY PEERS

Abstract

Various types of applications make access to objects distributed in peer-to-peer (P2P) overlay networks. Even if the locations of target objects are discovered by some look-up algorithm such as flooding and distributed hash table (DHT), applications cannot manipulate the target objects without access rights. It is critical to perceive which peer can manipulate an object in which method, i.e. only a peer authorized with an access right is allowed to manipulate an object. Hence, an application has to find peers which can manipulate a target object rather than detect the location of the target object. Due to the scalability, variety, and autonomy of peers, it is difficult, may be impossible to maintain a centralized directory showing in which peer each object is distributed. An acquaintance peer of a peer p is a peer whose service the peer p knows and with which the peer p can directly communicate. We discuss types of acquaintance relations of peers with respect to what objects each peer holds, is allowed to manipulate, and can grant access rights on. Acquaintance peers of a peer may notify the peer of different information on target peers due to communication and propagation delay. Here, it is critical to discuss how much a peer trusts each acquaintance peer. We first define the satisfiability of an acquaintance peer, i.e. how much a peer is satisfied by issuing an access request to the acquaintance peer. For example, if a peer p locally manipulates a target object o and obtains a response, p is mostly satisfied. On the other hand, if the peer p has to ask another peer to manipulate the object o, the peer p is less satisfied. We define the trustworthiness and ranking factor of an acquaintance peer obtained by accumulating the satisfiability of each interaction with the acquaintance peer. Differently from traditional reputation concepts, trustworthiness information only from trustworthy acquaintance peers can be used to obtain the ranking factor. The trustworthiness of an acquaintance peer shows how much a peer can trusts the acquaintance peer while the ranking factor of an acquaintance peer shows how much the acquaintance peer is trusted by other trustworthy acquaintance peers. Then, we evaluate the trustworthiness and ranking factor in presence of faulty peers.