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

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 29node 802.11b test-bed demonstrate the poor performance of minimum hopcount, 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.

MUSTER: Adaptive Energy-Aware Multisink Routing in Wireless Sensor Networks

“…In absence of LQI, we use the inverse of the hop-count to a sink, a metric potentially inaccurate, yet used successfully in real deployments [6]. Since this functionality is decoupled from the rest of MUSTER, alternative metrics (e.g., ETX [13]) can be easily integrated. The Router module determines the parent (i.e., neighbor with maximum Q) based on the data structure shown in Figure 11 for a given neighbor.…”

An ETX Based Positioning System for Wireless Ad-Hoc Networks

“…Expected Transmission Count (ETX) is one such link quality indication parameter. ETX metric was first proposed in [11] to model the expected number of transmissions required to send a unicast packet over a link, including retransmissions. It is calculated by taking into account the successfully transmitted and received packets between a node and its neighbor within a certain time period.…”

“…Our experiments show favorable results which strengthen our claim that, ETX could be used as a location estimation parameter similar to RSS. We choose ETX as a location estimation parameter for ad-hoc networks for the following reasons: i) it is readily available as an extension to the popular ad-hoc routing protocols, e.g., DSR, DSDV, OLSR, etc [11,9], ii) it is an efficient proximity indication metric which will be elaborately discussed in Section 3.2, and iii) since it is a network layer metric, no interoperability issue across different NICs as discussed in case of RSS.…”

Quality-Aware Routing Metrics in Wireless Mesh Networks

“…These metrics are Hop Count, Per-hop Round Trip Time (RTT, [8]), Per-hop Packet Pair Delay (PktPair), quantized loss rate [9], Expected Transmission Count (ETX, [10]), modified ETX (mETX, [11]) and Effective Number of Transmissions (ENT, [11]). …”

“…ETX is a metric proposed by [10] for 802.11-based radios employing link-layer retransmissions to recover from frame losses. Basically, the ETX of a radio link is the estimated average number of {data frame, ACK frame} transmissions necessary to transfer a packet successfully over the wireless link.…”