Abstract
Asynchronous optical packet switching seems to a suitable transport technology for the next-generation Internet due to the variable lengths of IP packets. Optical buffers in the output port are an integral part of solving contention by exploiting the time domain. Fiber delay lines (FDLs) are a well-known technique for achieving optical buffers, and various optical buffer architectures using FDLs have been proposed. These are generally classified into two types of structure: feed-forward (FF) or feedback (FB). In the FF buffers, optical packets are delayed at the output ports by passing through step-increasing-length multiple FDLs to avoid contentions, and in the FB buffers, optical packets are delayed by being fed back in re-circulating loop FDLs to avoid contentions. We report the detailed characteristics of optical FB buffers with the Post-Reservation (PostRes) policy and clarify the superiority of the FB buffers through simulations. For comparison, we also show the characteristics of FBSI (FB with step-increasing-length FDLs) and FF buffers. We found that 1) the blocking probabilities in the FB buffer were about 10-2 lower than those in the FF buffer and 2) the blocking probabilities for the deterministic case in the FB buffer sharply dropped at D=1.0, where the packet length was equal to the FDL loop length. We carried out 108 packet simulations. The results can be applied to the design of WDM optical packet switches and networks with the maximum throughput.
Highlights
The ultimate capacity of the Internet may be constrained by energy density limitations and heat dissipation considerations rather than by the bandwidth of the physical components
Observing that the average circulation numbers in the FB buffer were almost twice the averages in the FBSI buffer, we found that the buffer ability of the FB was twice that of the FBSI, making the blocking probabilities in the FB much lower than those in the FBSI buffer
1) The blocking probabilities in the FB buffer became about 10-2 lower than those in the FF buffer, and the buffer number of the FB buffer can be reduced to 1/2 ( ρ = 0.5 ) - 1/7 ( ρ = 0.8 ) that of the FF buffer when the blocking probabilities require equal values
Summary
The ultimate capacity of the Internet may be constrained by energy density limitations and heat dissipation considerations rather than by the bandwidth of the physical components. In the FF buffers, optical packets are delayed at the output ports by passing through step-increasing-length multiple FDLs to avoid contentions [3, 5]. In the FB buffers, optical packets are delayed by being fed back in re-circulating loop FDLs to avoid contentions when another packet already occupies the output, and they arrive again at the input of the switch. For a cost-efficient packet switch architecture, a share-per-node optical FB butter configuration has been proposed and has been extensively investigated [8, 14,15], where FDLs are shared among the output ports of a node in a feedback configuration.
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