Performance of slotted store-and-forward (sSnF) optical circuit-switched networks - a simulation study

Increasing bulk data transfers have been overwhelming the Internet. To overcome this, optical circuit-switched (OCS) networks are equipped with assistive storage, so that bulk data that are delay tolerant can be temporarily stored at intermediate nodes and forwarded at later times. But, the use of storage greatly complicates the routing problem, since data storage must be incorporated into routing. This motivates us to simplify this issue by applying slotted operations for the network. Intuitively, the slotted network suffers from degraded network performance due to the inefficient utilization incurred by the slot constraint. However, our simulation shows that when the slot size equals to half the mean duration, the blocking probability is reduced from 0.076 to 8.5×10−5, and the number of network reconfigurations is reduced by a factor of 5, compared to the unslotted case. We reveal that in spite of the inefficient utilization, the slotted operations mitigate bandwidth fragmentation. This suggests in the slotted case, more bandwidth gaps on the links are available for accommodating other requests, and they are aligned with each other in time. Requests hence are delivered with less store-and-forward (SnF) operations being performed. Thus, when the number of SnF allowed for routing each request is limited (in order to reduce the computational complexity of routing), requests are more easily served in the slotted than in the unslotted cases. Our research provides clue for designing scalable slotted OCS networks with assistive storage.