[Show abstract][Hide abstract] ABSTRACT: It is well known that network coding can enhance the performance of peer-to-peer (P2P) content distribution systems since it benefits block scheduling. In this paper, we introduce our P2P content distribution system "SmartCode" with sparse network coding on PlanetLab. SmartCode uses pre-checking to avoid linearly dependent blocks being transmitted. Under the same system architecture, we also implement two systems "Ecode" and "LRF". Ecode is also based on sparse network coding, but without pre-checking. LRF is BitTorrent- like, using local-rarest-first for block scheduling. We conduct extensive experiments to compare the performances among the three systems. Experimental results show that the distributing time of SmartCode is reduced by 11% on average and up to 19% compared with LRF, and by 7% on average and up to 16% compared with Ecode. We also conduct experiments to analyze robustness among the three systems under the assumption that peers join in and leave a content distribution session dynamically and the seed leave the session after it has transmitted a fixed percentage of blocks over the total blocks of the content. In dynamical cases, SmartCode outperforms evidently than Ecode and LRF in downloading time and the times of peers completing the downloading.
[Show abstract][Hide abstract] ABSTRACT: In this paper we consider the design issue of sensor networks by placing a few powerful aggregate nodes into a dense sensor network such that the network lifetime is significantly prolonged when performing data gathering. Specifically, the problem is to place K aggregate nodes into a dense sensor network of n sensor nodes with KÂ¿n such that the lifetime of the resulting network is maximized, subject to the constraints that both the maximum transmission range of an aggregate node and the maximum transmission delay between an aggregate node and a sensor node covered by the aggregate node are met. Clearly, this is a joint optimization problem of aggregate node placement and the communication structure, which is NP-hard. We approach the problem by devising a fast and scalable heuristic algorithm. We also conduct experiments by simulation to evaluate its performance, and the experimental results show that the proposed algorithm outperforms a commonly equal distance placement schema significantly.
[Show abstract][Hide abstract] ABSTRACT: With network coding, intermediate nodes between source and destination node(s) encode the incoming packets into new ones and forward them to their outgoing links. The original content is decoded at the destination node(s). Recent theoretical results show that network coding is beneficial for peer-to-peer(P2P) content distribution. To evaluate the benefit of network coding, we implement a P2P content distribution system based on the sparse linear network coding method. In our system, we use the Chord protocol to construct the system topology. We determine the proper encoding density so as to reach a high probability of generating independent encoded blocks, and to reduce the computational complexity of encoding packets at each peer. To improve the system performance, we use the encoding interval to reduce the probability of transmitting linear dependent packets and dependency test to avoid accepting linear dependent packets possibly from cyclic topology. Lastly, we carry out extensive experiments to show in terms of average downloading time at peers, total distribution time and system throughput, the system with network coding slightly outperforms a BitTorrent-like non-coding system using the local-rarest-first chunk selection policy.