Politecnico di Bari

Latest Content From Politecnico di Bari

Whitepaper: TCP Congestion Control Over 3G Communication Systems: An Experimental Evaluation of New Reno, BIC and Westwood+

by Politecnico di BariJan 01, 2008

In this paper the authors focus on the UMTS wireless scenario and report a campaign of measurements that involved around 3000 flows and more than 40 hours of measurements using three different TCP stacks, TCP NewReno, which is the congestion control algorithm standardized by IETF, TCP BIC which is the default congestion control algorithm adopted by the Linux operating system. The experimental evaluation has been carried out by accessing the public Internet using an UMTS card. Distribution of measurements of goodputs, RTTs over time, packet loss ratios, number of timeouts and Jain Fairness Indices are reported through cumulative distribution functions.

Whitepaper: An Experimental Investigation of the Congestion Control Used by Skype VoIP

by Politecnico di BariJan 01, 2008

The explosive growth of VoIP traffic poses a potential challenge to the stability of the Internet that, has been guaranteed by the TCP congestion control. In this paper, the authors investigate how Skype behaves in the presence of time-varying available bandwidth in order to discover if some sort of congestion control mechanism is implemented at the application layer to match the network available bandwidth and cope with congestion. Finally, it is also found that when more Skype calls are established on the same link, they are not able to adapt their sending rate to correctly match the available bandwidth.

Whitepaper: Performance Evaluation of TCP Congestion Control Algorithms Over UMTS

by Politecnico di BariJan 01, 2008

TCP congestion control was designed and optimized for wired networks. During recent years, however, the popularity of wireless network infrastructures enabling ubiquitous Internet access, such as Universal Mobile Telecommunication System (UMTS), has grown considerably. This paper investigates the performance of TCP congestion control over UMTS networks. Author focused the attention on the interactions between UMTS RLC error recovery, and New Reno or Westwood+ TCP congestion control algorithms.

Whitepaper: Issues in Performance Evaluation of New TCP Stacks in High Speed Networks

by Politecnico di BariJan 01, 2008

This paper presents present a simulation study of new congestion control algorithms proposed to overcome the TCP well known problem in high bandwidth-delay networks. Using the ns simulator in a single bottleneck scenario with few or many sender entities, it analyzes the performance of different proposals also with respect to different buffer size provisioning. Simulation results show interesting and complex behavior of TCP stacks. In particular, STCP has shown significant lacking of airness, HTCP and HSTCP have shown low goodputs in the presence of buffer with size smaller than the bandwidth delay product.

Whitepaper: Performance Evaluation of a Feedback Based Dynamic Scheduler for 802.11e MAC

by Politecnico di BariJan 01, 2008

The 802.11 Medium Access Control (MAC) employs a mandatory contention-based channel access scheme called Distributed Coordination Function (DCF), which is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and an optional centrally controlled channel access scheme called Point Coordination Function (PCF). This paper compares the performance of standard access methods proposed by the 802.11e working group with a novel Feedback Based Dynamic Scheduler (FBDS), which is compliant to 802.11e specifications.

Whitepaper: Performance Evaluation of Westwood+ TCP Congestion Control

by Politecnico di BariJan 01, 2008

Due to the fundamental end-to-end principle, classic Tahoe/Reno TCP congestion control implements a self-clocked Additive Increase Multiplicative Decrease (AIMD) sliding window algorithm to probe the network bandwidth capacity. It employs two control variables: the congestion window (cwnd), which limits the number of segments transmitted by the source and not yet acknowledged by the receiver, and the slow start threshold (ssthresh), which varies the way the cwnd is increased. This research paper report experimental results that have been obtained running Linux 2.2.20 implementations of Westwood+, Westwood and Reno TCP to ftp data over an emulated WAN and over Internet connections spanning continental and intercontinental distances.

Whitepaper: An Experimental Investigation of the End-to-End QoS of the Apple Darwin Streaming Server

by Politecnico di BariJan 01, 2008

Video content distribution over the traditional best-effort, store-and-forward Internet Protocol is of ever increasing importance due to the great success of new web services such as personal video broadcast or television over IP (IPTV). This paper investigates the end-to-end Quality of Service (QoS) that is provided by the Apple Darwin Streaming Server and the Quick-Time client player in the presence of time-varying available bandwidth and multiple concurrent streaming sessions.