https://www.mdu.se/

With a better understanding of how probe packets and cross-traffic packets interact with each other, more accurate measurement methods based on active probing can be developed. Several existing measurement methods rely on packet-train probing schemes. In this article, we study and describe the interactions between probe packets and cross-traffic packets. When one packet within a packet train is delayed, the dispersion (i.e. packet separation) of at least two (and possibly more) probe packets will change. Furthermore, the dispersions are not independent, which may bias calculations based on statistical operations. Many methods use dispersion averages, such as the mean, in the calculation of bandwidth estimates and predictions. We describe cross traffic effects on packet trains. The interaction results in mirror, chain and quantifi- cation patterns. Experiments have been performed in a testbed to explore these patterns. In histograms of delay variations for adjacent probe packets, these patterns are manifested as different identifiable signatures. Finally, we also discuss the effect of these patterns on the mean and median operations.

For active, probing-based bandwidth measurements performed on top of the unifying IP layer, it may seem reasonable to expect the measurement problem in wireless networks to be no different than the one in wired networks. However, in networks with 802.11 wireless bottleneck links we show that this is not the case. The results from the experiments presented in this paper show that the measured available bandwidth is dependent on the probe packet size (contrary to what is observed in wired networks). Another equally important finding is that the measured link capacity, using the well known TOPP model, is dependent on the probe packet size and on the cross-traffic intensity. The underlying reasons for the observed differences are analyzed by incorporating the characteristics of 802.11 wireless networks into the TOPP model. The extended model is applicable to other end-to-end bandwidth measurement methods as well, such as BART, Pathload and PTR.

Available bandwidth measurement methods have be- ome more and more a epted to be used when seeking the status of a network path. To measure the end-toend available bandwidth without a ess to the path routers, these methods inje t UDP based probe pa kets into the network path. The probe-pa ket load an transiently be high and thus it is important to study the impa t on the existing network ows. In this paper, we show and dis uss our simulation results on how the TCP ows are ae ted when inje ting probe pa kets with dierent ight patterns into the network path. We investigate the relation between the amount of inje ted probe pa kets and the redu tion in TCP performan e. Further, we suggest a quantitative denition of the term network friendly probing.