TimeWeaver: Opportunistic One Way Delay Measurement via NTP

Abstract

One-way delay (OWD) between end hosts has important implications for Internet applications, protocols, and measurement-based analyses. We describe a new approach for identifying OWDs via passive measurement of Network Time Protocol (NTP) traffic. NTP traffic offers the opportunity to measure OWDs accurately and continuously from hosts throughout the Internet. Based on detailed examina- tion of NTP implementations and in-situ behavior, we develop an analysis tool that we call TimeWeaver, which enables assessment of precision and accuracy of OWD measurements from NTP. We apply TimeWeaver to a ~1TB corpus of NTP traffic collected from 19 servers located in the US and report on the characteristics of hosts and their associated OWDs, which we classify in a precision/accuracy hierarchy. To demonstrate the utility of these measurements, we apply iterative hard-threshold singular value decomposition to estimate OWDs between arbitrary hosts from the high- est tier in the hierarchy. We show that this approach results in highly accurate estimates of OWDs, with average error rates on the order of less than 2%. Finally, we outline a number of applications---in particular, IP geolocation, network operations and management---for hosts in lower tiers of the precision hierarchy that can benefit from TimeWeaver, offering directions for future work.