A survey of traffic-based routing metrics in family of expected transmission count for self-organizing networks

•We survey the traffic-based routing metrics in self-organizing networks.•We present our viewpoints on the principle for designing routing metrics.•Different routing metrics may suit for different scenarios or different kinds of network.•Balance or tradeoff among the considered factors becomes very important.

Self-Organizing Networks (SONs) are attractive for applications where flexibility, resilience, and a large network service area are required. In order to meet the requirements of those applications, the principal issue is to guarantee efficient routing in SONs. Hence, the design and selection of appropriate routing metrics is important. A mass of metrics have been proposed in the past several decades. Among all the metrics, Expected Transmission Count (ETX) has drawn the most attention. Since the proposal of ETX, many ETX-based or extended metrics have been proposed. ETX and its descendants compose the ETX family. This paper is an attempt to analyze, compare and summarize traffic-based routing metrics in the ETX family. Details of each routing metric are presented and analyzed. Some of our viewpoints on the principal for designing metrics in SONs are presented.