QuickProbe

Abstract

An accurate estimate of the available (or unused) bandwidth in a network path can be useful in many applications, including route selection in an overlay or multi-homed network, initial bit-rate selection for video streams or improving the slow start phase of existing TCP protocols. Previously proposed methods for estimating available bandwidth include Pathload [2], PTR [1], Spruce [4], and references therein. The Pathload technique has been shown to be reasonably accurate under a wide range of conditions by independent researchers [3,5]. PTR is more efficient and has been shown to have accuracy similar to Pathload in a more limited set of experiments [1]. With an accurate measure of the bottleneck link capacity, Spruce has been found to be more accurate than Pathload when a new cross traffic stream with known rate is injected. The principal drawback of these techniques is that they require on the order of hundreds of probe packets, and several to several tens of seconds to obtain the available bandwidth estimate. This paper develops a new bandwidth estimation technique, ‘QuickProbe’, that uses 19 probe packets to obtain a conservative estimate of the available bandwidth within a single round trip, and then uses 9-17 further probe packets in each subsequent round trip to refine the estimate. We have compared the QuickProbe and Pathload estimates for hundreds of Internet paths between PlanetLab and other nodes. The paths have measured round-trip times in the range of 20-800 milliseconds, capacities in the range of 0.1 600 Mb/s, and ratios of available bandwidth to capacity in the range of 5-95%. Over such paths, ‘QuickProbe’ obtains conservative available bandwidth estimates after two round trips that are a within a factor of 0.7 1.0 times the Pathload estimate.