Toward Representative Internet Measurements

Efforts to characterize and understand the structure and behavior of the Internet have a long history in the network research community. Though our understanding of the network has evolved, our knowledge of its configuration, workload, and failure modes still is far from complete. Characterizing the operation of the current Internet infrastructure and its usage patterns is essential to improve the understanding of the Internet and shape its future. Despite the numerous studies of Internet properties, there has been little work to understand how to measure the network in terms of the number and distribution of measurement sites. Research studies that aim to collect and analyze Internet data from end-hosts are typically limited to a relatively small number of probes, located primarily at universities or research institutions. Naturally, the authors of such studies express caveats to their results, and offer some justification of the limited perspective. Some examples of this reasoning in studies of Internet path properties include statements such as “routes between the 37 hosts are plausibly representative” [10], “we believe that measuring the paths between our sources and a wide variety of different ISPs would provide a representative view” [2], and “the testbed topology contains paths that traverse most of the ‘large’ AS’s in the Internet” [8]. Some recent work delves into this issue in the context of discovering the Internet router-level topology [5], concluding that having more than 1 or 2 vantage points does not improve discovery of nodes and links. The authors also point out, however, that it is impossible to claim that the measurement sites used in the study are representative, and that their conclusions are unavoidably sensitive to the choice of measurement sites. While deploying and maintaining a large-scale measurement infrastructure is extremely challenging, it is clear that further guidance as to the representativeness of results obtained using existing measurement testbeds is a crucial missing element of current network measurement research. In this paper we argue that for measurements of traffic, paths, workloads, etc., to be representative, data should be collected from locations actually used by a large portion of Internet users (with an obvious trade-off between “large” and the degree of representativeness). For the common client-server communication pattern, this means that measurement infrastructure should be placed at, or near, places (i.e., stub networks, ingress points, egress points) that are sources or destinations for most of the traffic flowing in the Internet. For popular peer-to-peer applications, measurement probes should be placed at concentration points (i.e., close to busy dial-up access servers or broadband central offices and cable head-ends). Given enough resources, a more complete approach would be to place a measurement probe at every access point in the Internet. This would allow, for example, studies of general properties of the entire network, such as a survey of delays along all paths regardless of their usage. Our view is that though such studies might be valuable, it is more important and interesting, not to mention more practical, to characterize the network based on common usage.