There has been much work on developing techniques for estimating the capacity and the available bandwidth of network paths based on end-point measurements. The focus has primarily been on settings where the constrained link can be modeled as a point-to-point link with a well-defined bandwidth, serving packets in FIFO order. In this paper, we point out that broadband access networks, such as cable modem and 802.11-based wireless networks, break this model in various ways. The constrained link could (a) employ mechanisms such as token bucket rate regulation, (b) schedule packets in a non- FIFO manner, and (c) support multiple distinct rates. We study how these characteristics impede the operation of the various existing methods and tools for capacity and available bandwidth estimation, and present a new available bandwidth estimation technique, Probe- Gap, that overcomes some of these difficulties. Our evaluation is based on experiments with actual 802.11a and cable modem links.
Capacity, Available bandwidth, Broadband networks, Network measurement
There has been much work on developing techniques for estimating the capacity and available bandwidth1 of network paths based on end-point measurements. Capacity is defined as the bandwidth of the narrow link (i.e., the link with the smallest bandwidth) on a path.
Available bandwidth refers to the headroom on the tight link; more precisely, it is the maximum rate that a new flow can send at without 1In this paper, we use the term bandwidth to mean the data rate of links or paths, expressed in bits per second; we are not referring to the spectrum
bandwidth at the PHY layer. The bandwidth is, in general, a function of the
packet size, due to per-packet overhead. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are
not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. impacting the rate achieved by the existing flows on the tight link. As noted in prior work , the motivation behind bandwidth estimation
has been the potential for applications and end-host-based protocols to take advantage of bandwidth information in making intelligent choices on server selection, TCP ramp-up, streaming media