HIgh-Throughput Path Metric for Multi-Hop Wireless Routing

This paper introduces a metric for discovering routes on wireless ad-hoc networks which performs better than the usual minimum hop-count metrics from wired networks. The previous paper used a metric that looked at the "expected transmission time" of a message based on the throughput and reliability of each link; in this paper, the presented algorithm refines this by looking at the expected transmission count. Unlike other metrics, this is not dependent on the momentary load characteristics of the network.

Minimum hop routing works when the shortest path is also the fastest; however, because of the characteristics of wireless networks, this is often not the case (for example, intermediate nodes in routing can interfere with acknowledgements from the previous node because transmitting the packet may override transmitting an ACK).

The algorithm looks at delivery ratios both TO other nodes and the delivery ratios of the ACKS, which is a good refinement. Based on these ratios, it decides which route to take. Because the link probes are sent at some fixed known rate, each node can calculate the delivery ratios even without full knowledge of the link state. However, I noticed this calculation could be somewhat off since the probes are jittered; couldn't this lead to artificially low ratios in some cases?

The paper analyzes adding ETX to DSDV and DSR. I thought their test methodology was a little odd because they use a snapshotted route table instead of allowing it to evolve through the test for DSDV. I'm not sure if this makes the numbers suspect, but it is something to keep in mind. Nevertheless, the measurements show ETX+DSDV is better than plain DSDV (although this may not hold if the tables evolve under heavy load...). However, ETX+DSR is not better than DSR; ETX uses rather small probes even to check for how the network route performs for large messages.

A simple modification to this algorithm could make performance better. Even doing something like using exponentially distributed probe sizes (and having them occur far apart for larger sizes) would give a better image of what the network routing actually will do for various size messages. Routes could be picked based on message size. Even using two different sizes ("small" and "large") may give a better view.