Institute for Systems Research
Permanent URI for this communityhttp://hdl.handle.net/1903/4375
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Item Push-Based Information Delivery in Two Stage Satellite-Terrestrial Systems(2000) Ercetin, Ozgur; Tassiulas, Leandros; ISR; CSHCNSatellite broadcast data delivery has inherent advantages in providing global access to information to everyone. However, users of satellite communications need expensive and cumbersome equipment to receive and transmit satellite signals. Furthermore, as the amount of information being broadcast increases, average user latency increases as well. In many situations, users in a locality may have similar interests and hence they can be better served by a local broadcast schedule. A two stage satellite-terrestrial wireless broadcast system can provide more efficient service. In such a system, main server broadcasts information via satellite to the geographically distributed local ground stations. Every station has limited buffer capacity to store the items broadcast by the satellite. According to their cache content, and the interests of their users, local stations deliver the information to their users via terrestrial wireless channel. We develop novel methods for the joint cache management and scheduling problem encountered in these systems. Our results demonstrate that two stage systems can provide more efficient data delivery compared to the single stage systems.Item Functioning of TCP Algorithms over a Wireless Link(1999) Anjum, Farooq M.; Tassiulas, Leandros; Tassiulas, Leandros; ISR; CSHCNIn this paper, we investigate the behavior of the various algorithms of TCP, the Internet datatransport protocol, over wireless links with correlated packet losses. For such ascenario, we show that the performance of NewReno is worse than theperformance of Tahoe in many situations and even OldTahoe in a few situations on account of the inefficientfast recovery method of NewReno.We also show that random loss leads tosignificant throughput deterioration when either the product of the squareof the bandwidth-delay ratio and the loss probability when in the good state exceeds 1 or the product of the bandwidth-delay ratio and the packet successprobability when in the bad state is less than two.
The performance of Sackis always seen to be the best and the most robust thereby arguing for theimplementation of TCP SACK over the wireless channel. We also show thatunder certain conditions the performance depends not only on thebandwidth-delay product but also on the nature of timeout, whether coarse orfine. We have also investigated the effects of reducing the fast retransmitthreshold.
Item Balanced-RED: An Algorithm to Achieve Fairness in the Internet(1999) Farooq M. Anjum; Tassiulas, Leandros; Tassiulas, Leandros; ISR; CSHCNThe problem of fair bandwidth sharing among adaptive (TCP) and non-adaptive(i.e. CBR-UDP) flows at an Internet gateway is considered. An algorithm thatdrops packet preventively, in an attempt to actively penalize the non-adaptivetraffic that attempts to "steal" buffer space, and therefore bandwidth from theadaptive traffic flows, is presented. The algorithm maintains minimal flow stateinformation and is therefore scalable. The performance of the algorithm iscompared with other gateway algorithms, and it is shown that, in the presence of non-adaptive traffic, it achieves a more balanced bandwidth allocation among thedifferent flows. The behavior of a flow subjected to the given algorithm has also been analyzed in detail.Item Fair Allocation of Discrete Bandwidth Layers in Multicast Networks(1999) Sarkar, Saswati; Tassiulas, Leandros; Tassiulas, Leandros; ISRWe study fairness when receivers in a multicast network can not subscribeto fractional layers. This case arises whenthe source hierarchically encodes its signal and the hierarchical structureis predetermined. Unlike the case of the fractional layer allocation,which has been studied extensively in a previous work, bandwidth canbe allocated in discrete chunks only. Fairness issues becomevastly different. Computation of lexicographically optimal rateallocation becomes NP-hard in this case, while lexicographicallyoptimal rate allocation is polynomial complexity computablewhen fractional layers can be allocated. Furthermore, maxmin fair rate vector may not exist in this case.We introducea new notion of fairness, maximal fairness.We propose a polynomialcomplexity algorithm for computation of maximally fair ratesallocated to various source-destination pairs. Even though, maximal fairnessis a weaker notion of fairness, itcoincides with lexicographic optimality and maxmin fairness, when maxmin fair rate allocation exists. So the algorithmfor computing maximally fair rate allocation computes maxmin fairrate allocation, when the latter exists.Item Distributed Algorithms for Computation of Fair Rates in Multirate Multicast Trees(1999) Sarkar, Saswati; Tassiulas, Leandros; Tassiulas, Leandros; ISRWe study fairness in arbitrary networks with multicast capabilities.Multicast traffic in internet and ATM provides a motivationfor studying these networks. A study of fairness in multicastnetworks poses several interesting problems e.g., the issueof {it intra-session} fairness in addition to thatof {it inter-session} fairness in unicastnetworks. We develop a mathematical frameworkto model the fair allocation of bandwidth in multicast networkswith minimum and maximum rate constraints. We presentdistributed algorithms for computation of maxmin fair ratesallocated to various source-destination pairs.