, Volume 11, Issue 4, pp 419-434

a high-throughput path metric for multi-hop wireless routing

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Abstract

This paper presents the expected transmission count metric (ETX), which finds high-throughput paths on multi-hop wireless networks. ETX minimizes the expected total number of packet transmissions (including retransmissions) required to successfully deliver a packet to the ultimate destination. The ETX metric incorporates the effects of link loss ratios, asymmetry in the loss ratios between the two directions of each link, and interference among the successive links of a path. In contrast, the minimum hop-count metric chooses arbitrarily among the different paths of the same minimum length, regardless of the often large differences in throughput among those paths, and ignoring the possibility that a longer path might offer higher throughput.

This paper describes the design and implementation of ETX as a metric for the DSDV and DSR routing protocols, as well as modifications to DSDV and DSR which allow them to use ETX. Measurements taken from a 29-node 802.11b test-bed demonstrate the poor performance of minimum hop-count, illustrate the causes of that poor performance, and confirm that ETX improves performance. For long paths the throughput improvement is often a factor of two or more, suggesting that ETX will become more useful as networks grow larger and paths become longer.

This research was supported by grants from NTT Corporation under the NTT-MIT collaboration, and by MIT’s Project Oxygen.
Douglas De Couto received his Ph.D. in Computer Science from MIT in June 2004 for work in multi-hop wireless routing. He was a member of MIT’s Computer Science and Artificial Laboratory. He also received his S.B. and M.Eng. degrees in Computer Science and Electrical Engineering from MIT, in 1998. His research interests include multi-hop wireless networks, sensor and embedded networks, and applications of GPS. E-mail: decouto@csail.mit.edu
Daniel Aguayo is a graduate student in MIT’s EECS department and a member of MIT’s Computer Science and Artificial Intelligence Laboratory. He received an S.B. in Computer Science and Electrical Engineering from MIT in 2001, and an M.Eng. in 2002. His research interests are focused on multi-hop wireless networks. E-mail: aguayo@csail.mit.edu
John Bicket is a graduate student in MIT’s EECS department and a member of MIT’s Computer Science and Artificial Intelligence Laboratory. He received a B.S. from Cornell University. His research interests include multi-hop rooftop 802.11 networks and device drivers. E-mail: jbicket@csail.mit.edu
Robert Morris is an associate professor in MIT’s EECS department and a member of MIT’s Computer Science and Artificial Intelligence Laboratory. He received a Ph.D. from Harvard University for work on modeling and controlling data networks with large numbers of competing connections. He co-founded Viaweb, an e-commerce hosting service. His current interests include routing in multi-hop rooftop 802.11 networks, modular software-based routers, distributed hash tables, and peer-to-peer file storage. He has received a Sloan Fellowship, an NSF Career award, and the ITT Career Development Chair at MIT. E-mail: rtm@csail.mit.edu