In a peer-to-peer (P2P) overlay network, a peer process (peer) communicates with other peers and manipulates objects like databases in the peers. Service of each peer is characterized in terms of types of methods and quality of objects supported by the peer. It is critical to obtain service information on what peers support what service. In a fully distributed, unstructured P2P network, there is no centralized coordinator like index and super peer. Each peer has to communicate with its acquaintance peers and obtain service information of other peers. It is critical for a peer to identify which acquaintance is trustworthy since acquaintances may support obsolete service information and may be faulty. There are subjective and objective types of the trustworthiness, of each acquaintance peer. In the subjective approach, a peer obtains the trustworthiness of an acquaintance peer by itself through communicating with an acquaintance. On the other hand, a peer takes trustworthiness opinions on an acquaintance from other peers, that is, how other peers trust the acquaintance peer in the objective approach. In this chapter, a peer only takes opinions of trustworthy peers by excluding faulty peers differently from the traditional reputation concepts. The types of trustworthiness on an acquaintance peer are not always similar. A peer has to decide on which trustworthiness type is taken. In this chapter, we postulate the more confident of its trustworthiness opinion the peer is, the more significantly the subjective trustworthiness is taken into account. If the peer is less confident, the subjective and objective types of trustworthiness are taken respectively. We also discuss how to define the confidence.
In this chapter, we discuss a fully distributed, unstructured peer-to-peer (P2P) overlay network where there is no coordinator like centralized index Napster (1999) and super peer KazaA (2003) and each process is peer and autonomous. Peer processes (peers) on computers are cooperating by not only exchanging messages but also manipulating objects like databases in P2P overlay networks. There are many discussions on how to detect a target peer which holds an object like flooding algorithms as studied by Crespo and Garcia-Molina (2002), Egemen, Deepa & Hanan, (2002), Ripeanu (2001), Watanabe,
Hayashibara and Takizawa, (2005), and Ratnasamy, Francis, Handley, Karp and Schenker (2001), Rowstron and Druschel, (2001), Stoica, Morris, Karger, Kaashoek and Balakishnan, (2003) and Zhao, Kubiatowicz and Joseph, (2001). A peer has to manipulate a target object in addition to detecting which peer holds the target object. Only a peer that is granted an access right can manipulate a target object in an authorized way. For an object o, services supported by peers are classified into holder peers where the object o is stored, manipulation peers, which are allowed to manipulate the object o, and authorization peers, which can grant access rights of the object o to other peers Watanabe et al., (2005).
Key Terms in this Chapter
Confidence: Degree at which a peer is confident of its own opinions on the trustworthiness of an acquaintance peer.
P2P Overlay Network: Peer-to-peer systems are distributed systems consisting of interconnected nodes able to self organize into network topologies with the purpose of sharing resources such as content, CPU cycles, storage and bandwidth, capable of adapting to failures and accommodating transient populations of nodes while maintaining acceptable connectivity and performance, without requiring the intermediation or support of a global centralized server or authority.
Subjective Trustworthiness: Trustworthiness of an acquaintance peer which a peer itself obtains through communication with the acquaintance peer.
Trustworthiness: Degree at which a peer trusts another peer.
Access Right: What a peer can manipulates what an object in what method.
QoS: Quality of Service, for example, number of colors, frame rate of a multimedia content.
Acquaintance Peer: Another peer with which a peer can communicate and whose service the peer perceives.
Objective Trustworthiness: Trustworthiness of an acquaintance peer which is obtained from the acquaintance peer.