Browsing by Subject "Optical Burst Switching"

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Open Access
Congestion window based adaptive burst assembly for TCP traffic in optical burst switching networks
(2008) Özsaraç, Seçkin
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 via
Open Access
Effect of burst assembly over TCP performance in optical burst switching networks
(2006) Gürel, Güray
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.
Open Access
Joint path and resource selection for OBS grids with adaptive offset based QOS mechanism
(2007) Köseoğlu, Mehmet
It is predicted that grid computing will be available for consumers performing their daily computational needs with the deployment of high bandwidth optical networks. Optical burst switching is a suitable switching technology for this kind of consumer grid networks because of its bandwidth granularity. However, high loss rates inherent in OBS has to be addressed to establish a reliable transmission infrastructure. In this thesis, we propose mechanisms to reduce loss rates in an OBS grid scenario by using network-aware resource selection and adaptive offset determination. We first propose a congestion-based joint resource and path selection algorithm. We show that path switching and network-aware resource selection can reduce burst loss probability and average completion time of grid jobs compared to the algorithms that are separately selecting paths and grid resources. In addition to joint resource and path selection, we present an adaptive offset algorithm for grid bursts which minimizes the average completion time. We show that the adaptive offset based QoS mechanism significantly reduces the job completion times by exploiting the trade-off between decreasing loss probability and increasing delay as a result of the extra offset time.
Open Access
Research in optical burst switching within the e-Photon/ONe network of excellence
(Elsevier BV, 2007) Aracil, J.; Akar, N.; Bjornstad, S.; Casoni, M.; Christodoulopoulos, K.; Careglio, D.; Palacios, J. F.; Gauger, C.; Dios, O. G.; Hu, G.; Karasan, E.; Klinkowski, M.; Morato, D.; Nejabati, R.; Overby, H.; Raffaelli, C.; Simeonidou, D.; Stol, N.; Tossi-Beleffi, G.; Vlachos, K.
This paper presents a summary of Optical Burst Switching (OBS) research within the VI framework program e-Photon/ONe network of excellence. The paper includes network aspects such as routing techniques, resilience and contention resolution, together with burst switch architectures. On the other hand, we also discuss traffic analysis issues, Quality of Service (QoS) schemes, TCP/IP over OBS and physical layer aspects for OBS.