Fast Packet Switching for Integrated Services

As the communications industry continues to expand two current trends are becoming apparent: the desire to support an increasing diversity of communications services (voice, video, image, text, etc.) and the consequent requirement for increased network capacity to handle the expected growth in such multi-service tra c. This dissertation describes the design, performance and implementation of a high capacity switch which uses fast packet switching to o er the integrated support of multi-service tra c. Applications for this switch are considered within the public network, in the emerging metropolitan area network and within local area networks. The Cambridge Fast Packet Switch is based upon a non-bu ered, multi-path switch fabric with packet bu ers situated at the input ports of the switch. This results in a very simple implementation suitable for construction in current gate array technology. A simulation study of the throughput at saturation of the switch is rst presented to select the most appropriate switch parameters. Then follows an investigation of the switch performance for multi-service tra c. It is shown, for example, that for an implementation in current CMOS technology, operating at 50 MHz, switches with a total tra c capacity of up to 150 Gbits/sec may be constructed. Furthermore, if the high priority tra c load is limited on each input port to a maximum of 80% of switch port saturation, then a maximum delay across the switch of the order of 100 secs may be guaranteed, for 99% of the high priority tra c, regardless of the lower priority tra c load. An investigation of the implementation of the switch by the construction of the two fundamental components of the design in 3 m HCMOS gate arrays is presented and close agreement is demonstrated between the performance of the hardware implementation and the simulation model. It is concluded that the most likely area of application of this design is as a high capacity multi-service local area network or in the interconnection of such networks.