Request-Grant Scheduling For Congestion Elimination in Multistage Networks

This thesis considers buered multistage interconnection networks (fabrics), and investigates methods to reduce their buer size requirements. Our con- tribution is a novel o w and congestion control scheme that achieves performance close to that of per-o w queueing while requiring much less buer space than what per-o w queues would need. The new scheme utilizes a request-grant pre-approval phase, as many contemporary buerless networks do, but its operation is much sim- pler and its performance is remarkably better. Traditionally, the role of requests in buerless networks is to reserve an available time slot on each link along a packet's route, where these time slots are contiguous in time along the path, so as to guar- antee non-conicting packet transmission. These requirements impose a very heavy toll on the scheduling unit of such buerless fabrics. By contrast, our requests do not reserve links for a specic time duration, but instead only reserve space in the buers at their entry points; eectiv ely, the scheduling decisions that concern dif- ferent links are decoupled among themselves, leading to a much simpler admission process. The proposed scheduling subsystem comprises independent single-resource schedulers, operating in a pipeline; they operate asynchronously to each other. In this thesis we show that the reservation of buers in front of critical network links {links that are unable to carry the potential aggregate demand{ eliminates congestion, in