Last modified 3 years ago Last modified on 05/26/2014 03:10:43 PM

Learn about OLSR (Optimized Link State Routing Protocol)

This page is created for ones who wish to learn about technical details of OLSR routing protocol.

Studies and protocol comparisons

The Optimized Link-State Routing protocol can be divided into three main modules:

  • Neighbor/link sensing
  • Optimized flooding/forwarding (MultiPoint Relaying)
  • Link-State messaging and route calculation

OLSR presentations:


ETX is a reliability metric designed to find paths requiring the fewest transmissions. Although all packets in 802.11 are acknowledged using Automatic Repeat Request (ARQ), retransmissions result in a loss of airtime and hence, bandwidth.

ETX calculates the probability of successful transmissions in both directions over a wireless link.

To determine these statistics, every node periodically broadcasts a configured number of probes. Receivers calculate the number of probes received; against the number expected. As links are asymmetric, it is important to measure the success rate of probes in both directions. To obtain this information, each node will place its own ETX values in the probes sent. The formula for calculating the ETX of a link is shown in equation:

There are well documented problems with ETX, perhaps the biggest problem is that ETX does not incorporate bandwidth. This may cause ETX to favour fewer slow long distance links over a larger number of high speed links. Despite these problems, ETX is used by numerous routing protocols such as OLSR and Babel.