Optik çoğuşum anahtarlamalı ağlarda çoğuşum oluşumunun tcp performansına etkisi

ABSTRACTEFFECT OF BURST ASSEMBLY OVER TCPPERFORMANCE IN OPTICAL BURST SWITCHINGNETWORKSGüray Gürelu uM.S. in Electrical and Electronics EngineeringSupervisor: Assoc. Prof. Dr. Ezhan KaraşansJuly, 2006Optical Burst Switching (OBS) is proposed as a short-term feasible solutionthat is capable of efficiently utilizing the optical bandwidth of the future Inter-net backbone. Performance evaluation of TCP traffic in OBS networks has beenunder intensive study, as TCP constitutes the majority of Internet traffic. Sinceburst assembly mechanism is one of the fundamental factors that determine theperformance of an OBS network, we focus our attention on burst assembly andspecifically, we investigate the influence of the number of burstifiers on TCP per-formance for an OBS network. We start with a simple OBS network scenariowhere very large flows are considered and losses resulting from the congestionin the core OBS network are modeled using a burst independent Bernoulli lossmodel. Then, a background burst traffic is generated in order to create contentionat a core node realizing burst-length dependent losses. Finally, simulations arerepeated for Internet flows where flow sizes are modeled using a Bounded Paretodistribution. Simulation results show that for an OBS network employing timer-based assembly algorithm, TCP goodput increases as the number of burst as-semblers is increased for each loss model. The improvement from one burstifierto moderate number of burst assemblers is significant, but the goodput differ-ence between moderate number of buffers and per-flow aggregation is relativelysmall, implying that a cost-effective OBS edge switch implementation should usemoderate number of assembly buffers per destination. The numerical studies arecarried out using nOBS, which is an ns2 based OBS simulation tool, built withinthis thesis for studying the effects of burst assembly, scheduling and contentionresolution algorithms in OBS networks.Keywords: Optical Burst Switching, Burst Assembly, TCP Performance.iii