a b s t r a c tThis paper compares four different architectures for sharing wavelength converters in asynchronous optical packet switches with variable-length packets. The first two architectures are the well-known shared-per-node (SPN) and shared-per-link (SPL) architectures, while the other two are the shared-per-input-wavelength (SPIW) architecture, recently proposed as an optical switch architecture in synchronous context only, which is extended here to the asynchronous scenario, and an original scheme called shared-per-output-wavelength (SPOW) architecture that we propose in the current article. We introduce novel analytical models to evaluate packet loss probabilities for SPIW and SPOW architectures in asynchronous context based on Markov chains and fixed-point iterations for the particular scenario of Poisson input traffic and exponentially distributed packet lengths. The models also account for unbalanced traffic whose impact is thoroughly studied. These models are validated by comparison with simulations which demonstrate that they are remarkably accurate. In terms of performance, the SPOW scheme provides blocking performance very close to the SPN scheme while maintaining almost the same complexity of the space switch, and employing less expensive wavelength converters. On the other hand, the SPIW scheme allows less complexity in terms of number of optical gates required, while it substantially outperforms the widely accepted SPL scheme. The authors therefore believe that the SPIW and SPOW schemes are promising alternatives to the conventional SPN and SPL schemes for the implementation of next-generation optical packet switching systems.
This work considers contention resolution in optical packet switches and proposes a switch architecture empowered by available technology which exploits a combination of wavelength and time domains to solve packet contention. An hybrid switch architecture based on space switching matrix and re-circulating links, equipped with wavelength converters and electronic buffers is described. The forwarding procedure is implemented by suitable scheduling which minimizes the number of wavelength conversions needed. Switch performance is evaluated by simulation to show the effects of combination of wavelength conversion and electronic queuing. The hybrid switch characteristics are exploited to design the switch in relation to application needs. To this end, service differentiation schemes are applied to traffic forwarding and evaluated. The results obtained outline how switch design optimization take advantage of the relationships between the employed technology and traffic needs.
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