Pattabhiraman Krishna

Algorithms for providing bandwidth and delay guarantees in input-buffered crossbars with speedup

Investigates some issues related to providing QoS guarantees in input-buffered crossbars with speedup. We show that a speedup of 4 is sufficient to ensure 100% asymptotic throughput with any maximal matching algorithm employed by the arbiter. We present several algorithms which ensure different delay guarantees with a range of speedup values between 2 and 6. We demonstrate that with relatively simple arbitration algorithms and a speedup that is independent of the switch size, it is possible to ensure delay guarantees which are comparable to those available for output-buffered switches.

On the speedup required for work-conserving crossbar switches

Describes the architecture for a work-conserving server using a combined input-output buffered crossbar switch. The switch employs a novel algorithm based on output occupancy-the Lowest-Occupancy-Output-First Algorithm (LOOFA)-and a speedup of only 2. A work-conserving switch provides the same throughput performance as an output buffered switch. The work-conserving property of the switch is independent of the switch size and input traffic pattern. We also present a suite of algorithms that can be used in combination with LOOFA. These algorithms determine the fairness and delay properties of the switch. We also describe a mechanism to provide delay bounds for real-time traffic using LOOFA. These delay bounds are achievable without requiring output buffered switch emulation.