A High-Throughput Path Metric for
Multi-Hop Wireless Routing
Douglas S. J. De Couto
M.I.T. Computer Science and Artificial Intelligence Laboratory
decouto, aguayo, jbicket, rtm
This paper presents the
expected transmission count
metric (ETX), which
finds high-throughput paths on multi-hop wireless networks.
mizes the expected total number of packet transmissions (including retrans-
missions) required to successfully deliver a packet to the ultimate destina-
tion. 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
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.
Categories and Subject Descriptors
]: Network Archi-
tecture and Design—
; C.2.2 [
]: Network Protocols—
Design, Experimentation, Measurement, Performance
Multi-hop wireless networks, Ad hoc networks, Rooftop networks,
Wireless routing, Route metrics, 802.11b, DSR, DSDV, ETX
This research was supported by grants from NTT Corporation un-
der the NTT-MIT collaboration, and by MIT’s Project Oxygen.
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September 14–19, 2003, San Diego, California, USA.
Copyright 2003 ACM 1-58113-753-2/03/0009 .
Much of the recent work in ad hoc routing protocols for wireless
networks [25, 15, 26] has focused on coping with mobile nodes,
rapidly changing topologies, and scalability.
Less attention has
been paid to finding high-quality paths in the face of lossy wireless
links. This paper presents measurements of link loss characteris-