Performance Evaluation of TCP over Optical Channels and Heterogeneous Networks

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Next generation optical networks will soon provide users the capability to request and obtain end-to-end all optical 10 Gbps channels on demand. Individual users will use these channels to exchange large amounts of data and support applications for scientific collaborative work. These new applications, which expect steady transfer rates in the order of Gbps, will very likely use either TCP or a new transport layer protocol as the end-to-end communication protocol. In this paper, we investigate the performance of TCP and newer TCP versions over High Bandwidth Delay Product Channels (HBDPC), such as the on demand optical channels described above. In addition, we investigate the performance of these new TCP versions over wireless networks and according to old issues such as fairness. This is particularly important to make adoption decisions. Using simulations, we show that (1) the window-based mechanism of current TCP implementations is not suitable to achieve high link utilization and (2) congestion control mechanisms, such as the one utilized by TCP Vegas and Westwood are more appropriate and provide better performance. We also show that new TCP proposals, although perform better than current TCP versions, they still perform worse than TCP Vegas. In addition, we found that even though these newer versions improve TCP's performance over their original counterparts in HBDPC, they still have performance problems in wireless networks and present worse fairness problems than their old counterparts. We conclude that all these versions are still based on TCP's AIMD strategy or similar and therefore continue to be fairly blind in the way they increase and decrease their transmission rates. TCP will not be able to utilize the foreseen optical infrastructure adequately and support future applications if not redesigned to scale.

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