Constructing Incentive Oriented Overlay on Mobile Peer-to-Peer Networks Feng Hong1 Yuan Feng1 1 Dept. of Comp. Sci. & Eng. Ocean University of China
[email protected] [email protected]
Abstract In mobile peer-to-peer networks, the incentive mechanism has to be provided for peers’ participation as both resource suppliers and intermediaries(routers). In this paper we propose our solution to the incentive problem for intermediaries of message routing. We provide the dominationset-based peer-to-peer searching algorithm with economic models, which achieves motivating peers’ corporation in the whole overlay. Simulation results prove the functionality of our solution.
Minglu Li2 Zhongwen Guo1 2 Dept. of Comp. Sci. & Eng. Shanghai Jiao Tong University
[email protected] [email protected]
connected-dominating-set(CDS) based peer-to-peer searching overlay with economic models to provide incentive. IOMP2P aims to achieves such goals as (1) dealing with the resource discovery problem in MANETs and (2)providing incentives that more cooperation peers get more utility. The remainder of the paper proceeds as follows. The CDS based peer-to-peer searching overlay is presented in Section 2, Section 3 introduces our economic models of incentive. Section 4 shows the simulation environments and provides the simulation results. Section 5 summarizes this paper and future work.
2. CDS Calculation 1. Introduction The mobile peer-to-peer network is a set of moving nodes that communicate via short-range wireless technologies such as IEEE 802.11. With such communication mechanisms, a moving node receives information from its direct neighbors, or from remote peers of multi-hop transmission relayed by intermediate moving nodes. One killer application of mobile peer-to-peer networks is resource discovery in transportation. However, according to the mobility of peers, the underlying communication network is subject to topology changes and disconnecting. So the structured peer-to-peer overlay which requires pre-defined data access structures such as Tapestry [8], Pastry [5], CAN [4] and Chord [6], are impractical in such environments. Meanwhile, because every node should act as routers of message transmission in mobile peer-to-peer networks, incentive should be provided for participation as both suppliers and intermediaries(routers). As most incentive mechanisms of peer-to-peer networks have demonstrated the incentive problem between suppliers and consumers [2], this paper concentrates on dealing with incentives for intermediaries of message transmission, which is the main difference of incentive mechanism between original peer-to-peer networks and mobile peer-topeer networks. We propose Incentive Oriented overlay on Mobile Peer-to-Peer networks(IOMP2P), which consists of
2007 International Conference on Parallel Processing Workshops (ICPPW 2007) 0-7695-2934-8/07 $25.00 © 2007
The CDS based peer-to-peer searching overlay of IOMP2P defined below tries to minimize the searching cost and realize resource discovery. No global information is needed to construct and reduce CDS using marking and reduction rule. Meanwhile, IOMP2P achieves equity in some degree in searching process with our economic models which will illustrate in Section 4. This section focuses on the illustration of calculation of CDS in mobile peer-topeer networks. A CDS of the graph is a connected subset of nodes of the graph from which all nodes in the network can be reached in one hop. And the shortest path between any two nodes does not include any non-CDS node as an intermediate node. Finding a minimum CDS is NP-complete for most graphs. Wu’s marking and reduction process gives a simple and distributed algorithm for calculating CDS [7]. Wu’s algorithm consists of the marking process and two rules of reduction. Specifically, the marking process is a localized algorithm which nodes interact only with others in a restricted vicinity. In MANETs it is that two nodes located closely together within wireless transmission range of each other. Each node performs exceedingly simple tasks such as maintaining and propagating information markers. Collectively, these hosts achieve a desired global objective of finding a small CDS. The marking process marks every vertex in a given connected and simple graph G = (V ; E). m(v) is a marker for
vertex v ∈ V , which is either T (marked) or F (unmarked). The marking process consists of: (1) Initially, assign marker F to each v in V . (2) Each v exchanges its open neighbor set N (v) with all its neighbors. (3) Each v assigns its marker m(v) to T if there exists two unconnected neighbors. It is shown that given a graph G = (V ; E) that is connected but not completely connected, the vertex subset V , derived from the marking process, forms a connected dominating set of G. Two localized reduction rules 1 and 2 are provided to reduce the size of the CDS in [7]: if the neighbor set of node u in the CDS is covered by that of another node v or those of two connected nodes v and w in the CDS, then node u can be removed from the CDS. In this case, u is said to be covered by v (or by v and w). To avoid simultaneous removal of two nodes covering each other, each node u is assigned a distinct id. A node is removed from the CDS when it is covered by node(s) with higher id(s). In this paper, we modify reduction rules 1 and 2 by using the special virtual currency counting, denoted as coins, of each node as the priority to break a tie. coins, is defined as the total number of virtual currency(coin) of node v. The complete descriptions of coins is given in the Section 4 when we illustrate our economic models. Here are the modified rules 1 and 2 of reduction: Rule 1: Consider two vertices v and u in CDS V . If N (v) ⊂ N (u) in G and coins(v) < coins(u), change the marker of v to F if node v is marked. Rule 2: Assume that u and w are two marked neighbors of marked vertex v in V . If N (v) ⊂ N (u) ∪ N (w) in G and coins(v) = min(coins(v), coins(u), coins(w)), change the marker of v to F . The above proposed CDS calculation process needs only local information. Wu has proven that the calculation process of CDS only takes O()2 time with direct neighborhood information, where is the maximum node degree in the network. Our modified reduction rules 1 and 2 do not change the complexity of the calculation of the CDS. Meanwhile, a lot of nodes of mobile peer-to-peer networks are in motion which will let some parts of CDS be invalid. So the marking and reduction process should be executed periodically per predefined time interval.
3. Peer-to-Peer Searching Algorithm For a mobile peer-to-peer network, we can use the above CDS calculation process to get a CDS and use this subset of nodes for searching in the overlay. The CDS based searching algorithm is discussed in detail in this section, which includes its preliminary and its search algrithm.
2007 International Conference on Parallel Processing Workshops (ICPPW 2007) 0-7695-2934-8/07 $25.00 © 2007
3.1. Preliminary It has been proven by Wu that the shortest path between any two nodes does not include any non-CDS node as an intermediate node in [7]. So Our CDS based searching algorithm aims to minimize the searching cost by restricting search in the CDS set. As the search target is to do resource discovery for the search requester, the search path will be restricted to CDS and the search request will be fulfilled only by means of that CDS have all the resource indexes. This can be achieved by the none-CDS nodes publish their resource indexes to its neighbor CDS nodes. This publishing process should also be executed periodically by none-CDS node, because there may be changes in the resource which it presents, and because the topology will be changed by the motion of itself or its neighbors. As this preliminary fulfills, it can be concluded that the search path of IOMP2P only consists of hops in CDS with at most two hops between none-CDS node to CDS node. These two hops of search path are: (1) the first hop between search requester and its neighbor CDS node if the requester is not in CDS; and (2) the last hop between one CDS node and the resource supplier if the supplier is not in CDS.
3.2. Search Algorithm The routing process in IOMP2P can be divided into four parts: (1)The request source sends out the query message, which format is illustrated in Table.1. If the source is one unCDS node, it forwards the message its adjacent CDS node of lowest coins. which is called source CDS node. (2)The source CDS node acts as a new source to route the message in CDS’s graph generated from the marking and reduction process. The routing algorithm is is illustrated in Fig.1. (3)Eventually, the message reaches the destination CDS node, which is the destination host itself or a CDS node of the destination un-CDS node. In the latter case, there is one more hop from the CDS node directly to the destination node. (4)The destination node change the flag of message to identify that it is the answer message and send it back reversely along the query path. However, the query message will be discarded when its coins all consumed, as illustrated in Fig.1. This action happens no matter the message is the query message or the answer one. This is because the rules of our economic model of IOMP2P, which will be illustrated further in the next section.
Table 1. Format of Routing Message Attribute Comments ID unique value in whole MP2P source the query source node query structure to describe the target resource coins the virtual currency to pay the intermediaries passed recording the path for the answer return flag identify it’s query or answer message nextHop(Message m){ //Current message will be discarded, //if it has consumed all its coins. if(m.coins
