Abstract:

This paper describes a general purpose queue architecture for an ATM switch capable of supporting both real-time and non-real-time communication. The central part of the architecture is a kind of searchable, self-timed FIFO circuit into which are merged the queues of all virtual channels in the switch. Arriving cells are tagged with numerical values indicating the priorities, deadlines, or other characterizations of the order of transmission, then they are inserted into the queue. Entries are selected from the queue both by destination and by tag, with the earliest entry being selected from among a set of equals. By this means, the switch can schedule virtual channels independently, but without maintaining separate queues for each one. This architecture supports a broad class of scheduling algorithms at ATM speeds, so that guaranteed qualities of service can be provided to real-time applications. It is programmable because the tag calculations are done in microprocessors at the interface to each physical link connected to the switch.