Performance evaluation of all-optical switching architectures with feedback or feed-forward optical buffers.

摘要

Optical buffering, which is realized using Fiber Delay Lines (FDLs) is employed to avoid collision of optical packets or bursts in all-optical switches. Two main optical buffering schemes are studied and evaluated. The first scheme, output optical buffering, is realized by employing feed-forward FDLs at the output ports of an optical switch. Packets that are addressed to the same output fiber only share a single output buffer. The second scheme is the optical shared buffering, which is realized by employing feedback FDLs that are shared among all inputs of an optical switch.; Two different packet-forwarding algorithms for switches with output buffers are evaluated: a simple forwarding algorithm (SFA) that is easier to implement, and an enhanced forwarding algorithm (EFA) that provides better performance in terms of both probability of blocking and packet average delay. Most of the proposed forwarding algorithms utilize the FDLs under FIFO discipline where the outgoing stream of packets from the buffer can have inter-packet gaps that are not utilized. The enhanced forwarding algorithm utilizes the output buffer more effectively by filling the inter-packet gaps. Analytical models are derived to evaluate the performance of both algorithms. Simulation results are used to verify the accuracy of both of the analytical models Finally, the same architecture is shown to be capable of supporting Quality of Service (QoS).; A Surjective-Mapping based Model (SMM) is developed to evaluate the performance of an optical shared buffer switch. The resulting model is accurate, and overcomes the explosion of states that occurs with Markovian based models for moderate to large switches employing shared optical buffers. For example, a Markovian based analysis requires solving a set of 922 equations for a switch with 16 x 16 nodal degree and 8 feedback FDLs, while a set of only 24 equations is generated using the SMM approach to study the same switch. The SMM provides a complete characterization of the switch including the distribution of the occupancy of the delay lines. A simulator is developed to verify results of the SMM model for switches of different sizes and number of delay lines.