Electronic Thesis/Dissertation

 

Time Slotted Optical Networks: Architectures and Performance Evaluation Open Access

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In an effort to reduce the bottleneck between electronic sources and high speed wavelength channels, optical time division multiplexing is proposed. In such Time-Wavelength Switched Networks (TWSNs), time on every wavelength is slotted and the Time-Wavelength-Space-Routers (TWSRs) are configured to switch time-slots within a frame. Connections are assigned one or more slots per frame. A bank of Fiber delay lines (FDLs) can be further utilized to increase the flexibility of slot scheduling and decrease the connection blocking probability. We consider the two broad scenarios of sharing a bank of FDLs: shared per output link (SPL) and shared per crossconnect (SPC). We present several TWSR architectures and develop graph formulations that can be used to optimally solve the scheduling problem. We also incorporate the provision of wavelength conversion and FDL feedback in these architectures, and study the impact of various FDL configurations on a TWSR's performance by looking at its ability to schedule as many connections as possible from a given traffic matrix. Results using numerical simulations show that the FDL configuration does in fact affect the performance of the TWSR. With this in mind, we also consider the problem of optimally constructing a bank of FDLs with limited number of recirculations through the FDL bank. Specifically, given a time frame consisting of M slots, and an FDL bank of D FDLs, we develop a method to find a set of delay values D = {d1, d2, . . .dD}, such that the set of achievable delay values using no more than R recirculations through the bank is maximized. Maximizing the set of achievable delay values provides more flexibility in slot scheduling and is expected to decrease the connection blocking probability. We investigate the impact of this FDL configuration on a TWSR's performance. Our results indicate that the optimal FDL construction presented here for static traffic achieves better blocking under dynamic traffic as well. We also present a solution to the FDL bank design problem for an optical packet switch, and show through simulations that packet drop probability is considerably reduced by using this optimal FDL configuration. Another kind of time slotted network proposed in the literature is the Time-Domain-Wavelength-Interleaved Network (TWIN), which eliminates time switching within the network by using a non-reconfigurable core and an intelligent edge utilizing a fast tunable laser to emulate fast switching. A drawback of the TWIN network is that it assigns a unique wavelength to each node in the network. Thus it requires a total of W = N wavelengths for an N-node network and hence is not scalable. We first compare the performance of the TWIN to the TWSN and also propose to design a wavelength-constrained (i.e., W < N) TWIN network with no switching (TWIN-NS) by using a multicasting strategy. We also propose a variant of the TWIN network which possesses switching capabilities only at the edge nodes (TWIN-ES) and compare the performances of these TWIN networks to that of the TWSN. Overall, we provide a detailed analysis of the various TWSR architectures incorporating FDL banks and compare the performance of the TWSN to the TWIN which renders useful insight to the advantages one gains by using a reconfigurable switch (TWSR) as opposed to a non-reconfigurable router.

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