Performance evaluation of TCP over software-defined optical burst-switched data centre network

In this paper, we consider the performance of TCP when used in data centre networks (DCNs) featuring optical burst switching (OBS) using two-way reservation. The two-way reservation is not suitable in wide-area OBS networks due to high bandwidth-delay product (BDP). The burst loss using traditional methods of one-way reservation can be mistakenly interpreted by the TCP layer as congestion instead of contention in OBS network, leading to serious degradation of the TCP performance. The reduced BDP in DCNs allows the use of two-way reservation that results in zero burst loss. The modelled architecture features fast optical switches in a single hop topology. We apply different workloads with various burst assembly parameters to evaluate the performance of TCP. Our results show significant improvement in TCP performance as compared to traditional methods of OBS as well as to a conventional electronic packet switching DCN

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

Analysis of TCP over Optical Burst-Switched Networks with Burst Retransmission

Due to the bufferless nature of OBS networks, random burst losses may occur, even at low traffic loads. For optical burst-switched (OBS) networks in which TCP is implemented at a higher layer, these random burst losses may be mistakenly interpreted by the TCP layer as congestion in the network, leading to serious degradation of the TCP performance. In this paper, we reduce random burst losses by a burst retransmission scheme in which the bursts lost due to contention in the OBS network are retransmitted at the OBS layer. The OBS retransmission scheme can then reduce the probability that the TCP layer falsely detects congestion, thereby improving the TCP throughput. We analyze the TCP throughput when OBS networks employ the burst retransmission scheme and develop a simulation model to validate the analytical results. Based on our simulation results, we show that an OBS layer with burst retransmission provides an improvement of up to ten times the TCP throughput over an OBS layer without burst retransmission. This significant improvement is primarily because the TCP layer triggers fewer time-out based retransmissions when the OBS retransmission scheme is used

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