Flow Control in the Switcherland Interconnection Structure

Hans Eberle, Erwin Oertli
Swiss Federal Institute of Technology (ETH), Institute of Computer Systems, 
CH-8092 Zurich, Switzerland

Abstract

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 involved in flow control.