Flow Control in the Switcherland Interconnection Structure

Switcherland is a scalable interconnection structure based on crossbar switches. It can be used as a desk area network as well as a local area network. Switcherland implements a distributed shared memory, that is, all communication is performed by load and store operations. Data transfers are characterized either as variable bit rate (VBR) traffic or constant bit rate (CBR) traffic and differ in the guarantees provided by the switches. For CBR traffic, the switches provide bounded transmission delays. For VBR traffic, buffer space is reserved in the switches, thereby guaranteeing that cells are never dropped due to overflowing buffers. Switcherland employs end-to-end flow control rather than link-by-link flow control. This is possible since the diameter of the interconnection structure is limited to ten switches. Flow control for VBR traffic is credit-based, while flow control for CBR traffic is rate-based. In both cases, only the processor and I/O nodes but not the switches are involv..