Congestion window-based adaptive burst assembly for TCP traffic in OBS networks

Burst assembly is one of the key factors affecting the TCP performance in optical burst switching (OBS) networks. When the TCP congestion window is small, the fixed-delay burst assembler waits unnecessarily long, which increases the end-to-end delay and thus decreases the TCP goodput. On the other hand, when the TCP congestion window becomes larger, the fixed-delay burst assembler may unnecessarily generate a large number of small-sized bursts, which increases the overhead and decreases the correlation gain, resulting in a reduction in the TCP goodput. In this paper, we propose adaptive burst assembly algorithms that use the congestion window sizes of TCP flows. Using simulations, we show that the usage of the congestion window size in the burst assembly algorithm significantly improves the TCP goodput (by up to 38.4% on the average and by up to 173.89% for individual flows) compared with the timerbased assembly, even when the timer-based assembler uses the optimum assembly period. It is shown through simulations that even when estimated values of the congestion window size, that are obtained via passive measurements, are used, TCP goodput improvements are still close to the results obtained by using exact values of the congestion window. © Springer Science+Business Media, LLC 2010

Performance issues in optical burst/packet switching

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-01524-3_8This chapter summarises the activities on optical packet switching (OPS) and optical burst switching (OBS) carried out by the COST 291 partners in the last 4 years. It consists of an introduction, five sections with contributions on five different specific topics, and a final section dedicated to the conclusions. Each section contains an introductive state-of-the-art description of the specific topic and at least one contribution on that topic. The conclusions give some points on the current situation of the OPS/OBS paradigms

Network level performance of differentiated services (diffserv) networks

The Differentiated Services (DiffServ) architecture is a promising means of providing Quality of Service (QoS) in Internet. In DiffServ networks, three service classes, or Per-hop Behaviors (PHBs), have been defined: Expedited Forwarding (EF), Assured Forwarding (AF) and Best Effort (BE). In this dissertation, the performance of DiffServ networks at the network level, such as end-to-end QoS, network stability, and fairness of bandwidth allocation over the entire network have been extensively investigated. It has been shown in literature that the end-to-end delay of EF traffic can go to infinity even in an over-provisioned network. In this dissertation, a simple scalable aggregate scheduling scheme, called Youngest Serve First (YSF) algorithm is proposed. YSF is not only able to guarantee finite end-to-end delay, but also to keep a low scheduling complexity. With respect to the Best Effort traffic, Random Exponential Marking (REM), an existing AQM scheme is studied under a new continuous time model, and its local stable condition is presented. Next, a novel virtual queue and rate based AQM scheme (VQR) is proposed, and its local stability condition has been presented. Then, a new AQM framework, Edge-based AQM (EAQM) is proposed. EAQM is easier to implement, and it achieves similar or better performance than traditional AQM schemes. With respect to the Assured Forwarding, a network-assist packet marking (NPM) scheme has been proposed. It has been demonstrated that NPM can fairly distribute bandwidth among AF aggregates based on their Committed Information Rates (CIRs) in both single and multiple bottleneck link networks

A Unified End-to-End Communication Paradigm for Heterogeneous Networks

The aim of this thesis research is to develop a unified communication paradigm that provides an end-to-end bursting model across heterogeneous realms. This model generates end-to-end bursts, thereby eliminating edge node burst assembly and its effect on TCP performance. Simulation models are developed in ns-2 to validate this work by comparing it with edge burst assembly on OBS networks. Analysis shows improved end-to-end performance for a variety of burst sizes, timeouts, and other network parameters

Congestion window based adaptive burst assembly for TCP traffic in optical burst switching networks

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent Univ., 2008.Thesis (Master's) -- Bilkent University, 2008.Includes bibliographical references leaves 51-55.Burst assembly is one of the key factors affecting the TCP performance in Optical Burst Switching (OBS) networks. Timer based burst assembly algorithm generates bursts independent of the rate of TCP flows. When TCP congestion window is small, the fixed-delay burst assembler waits unnecessarily long, which increases the end-to-end delay and decreases the TCP goodput. On the other hand, when TCP congestion window becomes larger, the fixed-delay burst assembler may unnecessarily generate a large number of small-sized bursts, which increases the overhead and decreases the correlation gain, resulting in a reduction in the TCP goodput. Using simulations, we show that the usage of the congestion window (cwnd) size of TCP flows in the burst assembly algorithm consistently improves the TCP goodput (by up to 38.4%) compared with the fixed-delay timer based assembly even when the timer based assembler uses the optimum assembly period threshold value. One limitation of this proposed method is the assumption that the exact value of the congestion window is available at the burst assembler. We then extend the adaptive burstification algorithm such that the burst assembler uses estimated values of the congestion winpassive measurements at the ingress node. It is shown through simulations that even when estimated values are used, TCP goodput can achieve values close to the results obtained by using exact values of the congestion window. dow that are obtained viaÖzsaraç, SeçkinM.S

Effect of burst assembly over TCP performance in optical burst switching networks

Cataloged from PDF version of article.Optical Burst Switching (OBS) is proposed as a short-term feasible solution that is capable of efficiently utilizing the optical bandwidth of the future Internet backbone. Performance evaluation of TCP traffic in OBS networks has been under intensive study, as TCP constitutes the majority of Internet traffic. Since burst assembly mechanism is one of the fundamental factors that determine the performance of an OBS network, we focus our attention on burst assembly and specifically, we investigate the influence of the number of burstifiers on TCP performance for an OBS network. We start with a simple OBS network scenario where very large flows are considered and losses resulting from the congestion in the core OBS network are modeled using a burst independent Bernoulli loss model. Then, a background burst traffic is generated in order to create contention at a core node realizing burst-length dependent losses. Finally, simulations are repeated for Internet flows where flow sizes are modeled using a Bounded Pareto distribution. Simulation results show that for an OBS network employing timerbased assembly algorithm, TCP goodput increases as the number of burst assemblers is increased for each loss model. The improvement from one burstifier to moderate number of burst assemblers is significant, but the goodput difference between moderate number of buffers and per-flow aggregation is relatively small, implying that a cost-effective OBS edge switch implementation should use moderate number of assembly buffers per destination. The numerical studies are carried out using nOBS, which is an ns2 based OBS simulation tool, built within this thesis for studying the effects of burst assembly, scheduling and contention resolution algorithms in OBS networks.Gürel, GürayM.S

Adaptive traffic distribution in optical burst switching networks

Master'sMASTER OF ENGINEERIN

Transport Control Protocol (TCP) over Optical Burst Switched Networks

Transport Control Protocol (TCP) is the dominant protocol in modern communication networks, in which the issues of reliability, flow, and congestion control must be handled efficiently. This thesis studies the impact of the next-generation bufferless optical burst-switched (OBS) networks on the performance of TCP congestion-control implementations (i.e., dropping-based, explicit-notification-based, and delay-based). The burst contention phenomenon caused by the buffer-less nature of OBS occurs randomly and has a negative impact on dropping-based TCP since it causes a false indication of network congestion that leads to improper reaction on a burst drop event. In this thesis we study the impact of these random burst losses on dropping-based TCP throughput. We introduce a novel congestion control scheme for TCP over OBS networks, called Statistical Additive Increase Multiplicative Decrease (SAIMD). SAIMD maintains and analyzes a number of previous round trip times (RTTs) at the TCP senders in order to identify the confidence with which a packet-loss event is due to network congestion. The confidence is derived by positioning short-term RTT in the spectrum of long-term historical RTTs. The derived confidence corresponding to the packet loss is then taken in to account by the policy developed for TCP congestion-window adjustment. For explicit-notification TCP, we propose a new TCP implementation over OBS networks, called TCP with Explicit Burst Loss Contention Notification (TCP-BCL). We examine the throughput performance of a number of representative TCP implementations over OBS networks, and analyze the TCP performance degradation due to the misinterpretation of timeout and packet-loss events. We also demonstrate that the proposed TCP-BCL scheme can counter the negative effect of OBS burst losses and is superior to conventional TCP architectures in OBS networks. For delay-based TCP, we observe that this type of TCP implementation cannot detect network congestion when deployed over typical OBS networks since RTT fluctuations are minor. Also, delay-based TCP can suffer from falsely detecting network congestion when the underlying OBS network provides burst retransmission and/or deflection. Due to the fact that burst retransmission and deflection schemes introduce additional delays for bursts that are retransmitted or deflected, TCP cannot determine whether this sudden delay is due to network congestion or simply to burst recovery at the OBS layer. In this thesis we study the behaviour of delay-based TCP Vegas over OBS networks, and propose a version of threshold-based TCP Vegas that is suitable for the characteristics of OBS networks. The threshold-based TCP Vegas is able to distinguish increases in packet delay due to network congestion from burst contention at low traffic loads. The evolution of OBS technology is highly coupled with its ability to support upper-layer applications. Without fully understanding the burst transmission behaviour and the associated impact on the TCP congestion-control mechanism, it will be difficult to exploit the advantages of OBS networks fully

Deflection Routing Strategies for Optical Burst Switching Networks: Contemporary Affirmation of the Recent Literature

A promising option to raising busty interchange in system communication could be Optical Burst Switched (OBS) networks among scalable and support routing effective. The routing schemes with disputation resolution got much interest, because the OBS network is buffer less in character. Because the deflection steering can use limited optical buffering or actually no buffering thus the choice or deflection routing techniques can be critical. Within this paper we investigate the affirmation of the current literature on alternate (deflection) routing strategies accessible for OBS networks