Design and performance of FDL buffers in optical switches

A key technique for reducing packet blocking in optical switches is by temporarily buffering packets in fiber delay lines (FDLs). The packet blocking probability depend on the FDLs design as well as on how packets are scheduled to the FDL buffers. This study compares between the blocking probabilities of the following design and buffer scheduler options: (i) input vs output port FDLs; (ii) shared vs port-dependent FDLs; (iii) forward vs feedback FDLs; (iv) variable vs fixed size FDLs; and (v) FIFO vs non-overlapping buffer schedulers. The comparison results reveals several interesting facts. The first one is that feedback FDL design can reduce the number of required buffers by 75% compared with a forward FDL design. Another observed fact is that fixed-size FDLs is very wasteful, specifically, the length of a fixed size FDL has no affect on the blocking probability. The third observation is that a non-overlapping buffer scheduler can reduce the number of required FDLs by 30% compared with a FIFO scheduler.