Comparing Routing Metrics & Protocols in Multi-Radio Wireless Mesh Networks, Papers of Computer Science

Download Comparing Routing Metrics & Protocols in Multi-Radio Wireless Mesh Networks and more Papers Computer Science in PDF only on Docsity! Paper Critique Joseph Jefferson COSC7397 January 30, 2007 “Routing in Multi-Radio, Multi-Hop Wireless Mesh Networks”, Draves, R.,Padhye, J., Zill, B The authors of this paper attempt to address the problem of lost capacity in wireless mesh networks. They suggest that the problem is due to transmission interference. They propose to address the problem by using multiple radios on each node in the wireless network. The side effect of using multiple radios is that the standard routing algorithm which uses the shortest-path metric doesn’t perform well in a multi-radio environment. To solve this performance problem the authors propose a new routing metric, WCETT, and implement this metric as part of the LQSR routing protocol. The Weighted Cumulative Expected Transmission Time, WCETT, is used as the routing metric within a modified version of the Link Quality Source Routing protocol, MR- LQSR. This metric is unique in that it considers two link characteristics simultaneously: loss rate and bandwidth. A parameter, , is used to give more weight to one or the other. The goal of the new metric is to try to balance the path throughput and delay. The new protocol was implemented as a Windows driver and operates between the network layer and the link layer. The positive contributions of this research include a routing metric that provides good performance within a multi-radio ad-hoc mesh environment. The metric balances two aspects of a wireless link such that it can take advantage of the additional capacity provided by the second radio. This metric is a positive step toward increasing the available capacity in wireless networks. A second positive contribution is the implementation of the WCETT metric within a new routing protocol. This new protocol was implemented in a different way since it resides between two traditional layers so that it can be used on existing hardware. The new protocol along with the WCETT metric takes advantage of the additional capacity provided by the additional radio on each node. Previous routing metrics showed poor performance in this environment. The shortcomings of the paper include the approach to estimate bandwidth accuracy. As stated in the paper, their technique is inaccurate for high data rates. The issue is that their metric uses this estimate to distinguish between high-bandwidth and low-bandwidth links. A second negative of the paper is that their experimental results are constrained by their choice of implementation. Since they chose to implement the protocol in an operating system with less flexibility, they could not test nodes with identical radios. Given these negatives, I believe the conclusions presented in the paper still hold and the positives outweigh the negatives. Some improvements available to the authors are to experiment with the affect of node density on the performance of the protocol and metric. The reported results include a deliberately high node density environment. Another future work possibility is to report on the performance of the metric under high network load. This would give insight to how the protocol would perform on a more realistic test environment which may include more interference. ExOR: Opportunistic Multi-Hop Routing for Wireless Networks. Biswas, S., Morris, R. This paper describes the design and evaluation of the ExOR routing protocol. This new protocol uses the broadcast mechanism in the MAC layer as a part of the routing protocol. The use of broadcasting allows the protocol to take advantage of the links which traditional routing would typically try to ignore. The authors show that the new protocol improves on existing solutions to the routing problem by increasing throughput over an ETX based route. The ExOR protocol coordinates the sending of data between the nodes using a timed scheduling algorithm that gives preference to higher priority nodes. This scheduling ensures that collisions do not occur. The authors show that the new protocol is an improvement by implementing the protocol on Linux systems using the Roofnet mesh network. This test bed was used to measure throughput between 65 random nodes. The protocol was measured against a traditional routing protocol that uses ETX as the metric. The authors show that the ExOR protocol improves throughput by a factor of 2 or 4 over ETX since it uses multiple relay nodes to forward the packet to its destination. This broadcast and forward approach takes advantage of ‘lucky’ situations in which unanticipated receivers close to the destination can help packets make progress. The most important positive contribution of the paper is the ExOR protocol and its use of broadcasting to route packets. According to the authors, this is a new approach to the routing problem. The cooperative diversity technique used is unique as well as the fact that it runs on existing hardware nodes which makes it practical. Another positive about the paper is that the protocol provides scheduling among the nodes without extra control communication to decide when a node transmits. This is accomplished using a transmission timer that is adaptable based on observed traffic. One negative about the paper is that the authors propose a solution that incurs variable packet overhead. The extra header data required for the batch map and the forward list