Network latency metrics for server proximity

This paper investigates network latency metrics in the context of the server proximity problem. Using a combination of experimentation and statistical analysis, we study the correlation among number of network and administrative system (AS) hops, and round-trip time (RRT). We ran experiments involving 601 Internet sites spanning 5 continents. Our results show reasonably strong AS hop-network hop correlations of up to 70%. We also observe an average RTT-number of hop correlation close to 50%, which represents a considerable improvement over what Crovella and Clark observed in 1995. Based on our results, we argue that, when choosing a single metric for network latency, RTT should be the metric of choice when trying to reduce clients' perceived latency. However, hop counts are good indicators of network resource usage. Another factor that favors RTT is that it is the least expensive metric to measure.