دانلود رایگان مقاله توزیع محتوای هاپ توسط هاپ با برنامه نویسی شبکه در شبکه بی سیم چند جهشی

Abstract

The predominant use of today's networks is content access and distribution. Network Coding (NC) is an innovative technique that has potential to improve the efficiency of multicast content distribution over multihop Wireless Mesh Networks (WMNs) by allowing intermediate Forwarding Nodes (FNs) to encode and then forward data packets. Practical protocols are needed to realize the benefits of the NC technique. However, the existing NC-based multicast protocols cannot accurately determine the minimum number of coded packets that a FN should send in order to ensure successful data delivery to the destinations, so that many redundant packets are injected into the network, leading to performance degradation. In this paper, we propose HopCaster, a novel reliable multicast protocol that incorporates network coding with hop-by-hop transport. HopCaster completely eliminates the need for estimating the number of coded packets to be transmitted by a FN, and avoids redundant packet transmissions. It also effectively addresses the challenges of heterogeneous multicast receivers. Moreover, a cross-layer multicast rate adaptation mechanism is proposed, which enables HopCaster to optimize multicast throughput by dynamically adjusting wireless transmission rate based on the changes in the receiver population and channel conditions during the course of multicasting a coded data chunk. Our evaluations show that HopCaster significantly outperforms the existing NC-based multicast protocols.

6. Conclusions

There are many challenges in designing an intra-flow NC based protocol for efficient reliable multicast over WMNs, including how many coded packets a FN should send and how to handle the bandwidth heterogeneity of multicast receivers. In this paper, we have designed HopCaster, a novel reliable multicast protocol that incorporates intra-flow NC with hop-by-hop transport. Compared to the existing intra-flow NC-based multicast protocols, HopCaster eliminates the need for estimating the number of coded packets each FN should send, avoids redundant transmissions, as well as simplifies multicast management and congestion control. We have also proposed a cross-layer rate adaptation mechanism that enables HopCaster to optimize data transmission rate in hop-by-hop multicast by taking into account the changing population of multicast receivers and the wireless channel variations. Our simulations show that compared to Pacifier, a state-of-the-art intra- flow NC-based multicast protocol, HopCaster greatly reduces the number of required transmissions over the wireless network to deliver multicast data, and achieves higher throughput. Furthermore, we show that the advantages of HopCaster are more prominent in the situation that a new node dynamically requests joining the multicast.