Efficient Mechanisms to Improve TCP Performance over OBS Networks

Abstract : Transmission Control Protocol (TCP) performance over Optical Burst Switching (OBS) is experimentally investigated on an OBS network testbed, concluding that burst losses will lead to a significant drop in the available TCP bandwidth. Two mechanisms are introduced to improve TCP performance. One is concerning the burst assembly optimization and another is based on the novel as-sembly and scheduling mechanism to reduce the burst losses. Key words : OBS; ACK; TCP; burst loss probabil-ity; scheduling algorithm I. IntroductIon Optical Burst Switching (OBS), which combines the best of Optical Circuit Switching (OCS) and Optical Packet Switching (OPS), is a promising technology for the future optical networks[1]. Given that TCP is today’s prevailing transport protocol and likely to be adopted in future optical networks, the evaluation of TCP performance over OBS networks is an important issue. TCP perform-ance over OBS has been discussed theoretically and experimentally in detail[2][3], with the conclu-sion that burst losses lead to a network-wide drop in the available TCP bandwidth, thus degrading the performance of networks[4]. [5] proposed a fast TCP to improve TCP performance. All these work tend to optimize the TCP protocol to match OBS. In these previous studies, the impact of ACK loss on TCP connection was discussed and some new scheduling mechanisms in OBS layer were proposed[6]. In this paper, a Labeled OBS (LOBS) testbed with the support of Multi-Protocol Label Switch-ing (MPLS) is firstly reported, which is developed based on the testbed in [7]. The influence of burst losses on TCP performance is investigated ex-perimentally in this testbed. Two mechanisms are introduced to improve TCP performance. One is based on the burst assembly optimization. Experi-ments show that there exists a specific assembly period to maximize the available TCP bandwidth. This optimal assembly period is independent of burst loss probability. The other is Retransmission-based Group-scheduling algorithm with Multiple

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