Performance Evaluation of Virtual Cut-Through Multistage Packet Switches

Asynchronous transfer mode (ATM) has been widely accepted as a well-suited transmission and switching principle for a variety of services including video, hi-fi sound and high-speed data communication. Many of the ATM switch architectures which support broadband services efficiently employ multistage interconnection networks. In such switch architectures, multistage interconnection networks play an important role in determining the overall performance of high-speed data communication. At present, many multistage interconnection networks used in ATM switches employ packet switching to relay cells from input ports, stage by stage, toward the specified output ports of the networks. In this thesis, we look into the virtual cut-through switching mechanism for multistage interconnection networks. In the case of virtual cut-through switching, cells which do not come across blocking are passed through stages toward their destination in just one network cycle. When blocked, cells are temporarily buffered at the stages until blocking is cleared. At that moment, cells move across as many stages as they can until the next blocking stage is encountered. Virtual cut-through has an apparent merit in statistically multiplexing cells such that multistage interconnection networks can be better utilized and network latency can be significantly reduced. This paper aims to study performance of the virtual cut-through alternative in multistage interconnection networks. We introduce a general analytical model for the evaluating virtual cut-through multistage interconnection networks. Closed form analysis and simulation experiments are conducted our performance evaluation study. We compare the analytical results with the simulation results in order to verify their correctness.