دانلود رایگان مقاله خواص و کاربرد گام های تصادفی زمانی در شبکه های فرصت طلب

Abstract

Opportunistic networks are a special case of DTNs that exploit systematically the mobility of nodes. When node contacts occur, routing protocols can exploit them to forward messages. In the absence of stable end-to-end paths, spatio-temporal paths are created spontaneously. Opportunistic networks are suitable for communications in pervasive environments that are saturated by other devices. The ability to self-organize using the local interactions among nodes, added to mobility, leads to a shift from legacy packet-based communications towards a message-based communication paradigm. Usually, routing is done by means of message replication in order to increase the probability of message delivery. Instead, we study the use of Temporal Random Walks (TRWs) on opportunistic networks as a simple method to deliver messages. TRW can adapt itself to the self-organizing evolution of opportunistic networks. A TRW can be seen as the passing of a token among nodes on the spatio-temporal paths. Since the token passing is an atomic operation, we can see it as forwarding one simple message among nodes. We study the drop ratio for message forwarding considering finite buffers. We then explore the idea of token-sharing as a routing mechanism. Instead of using contacts as mere opportunities to transfer messages, we use them to forward the token over time. The evolution of the token is ruled by the TRW process. Finally, we use the TRW to monitor opportunistic networks. We present the limits and convergence of monitoring the interact time between participating nodes.

6. Conclusions

In the following we present the main conclusions to each part of our work. 6.1. TRW architecture for opportunistic networks Random walks on temporal networks were studied in previous work as a sampling method. In this work we used them to provide a computer communication architecture. In Section 4, we de- fined and discussed the main elements necessary to use temporal random walks over opportunistic networks, defining our own Temporal Random Walk (TRW) architecture. Indeed, we formalized the concept of dynamic overlay for opportunistic networks. We defined a dynamical mapping function that links nodes in the opportunistic network with nodes in the overlay and we defined the token as a virtual device symbolizing who is the walker at a given time. The dynamic mapping is defined at each instant as the nodes in the opportunistic network that are holding a token in the overlay. The progression of the tokens follows a random walk in the temporal network. We then discussed the link between TRW and message forwarding.