2002 Reports

On Buffered Clos Switches

Krishnan, Santosh; Schulzrinne, Henning G.

There is a widespread interest in switching architectures that can scale in capacity with increasing interface transmission rates and higher port counts. Furthermore, packet switches that provide Quality of Service (QoS), such as bandwidth and delay guarantees, to the served user traffic are also highly desired. This report addresses the issue of constructing a high-capacity QoS-capable, multi-module switching node. Output queued switches provide the best performance in terms of throughput as well as QoS but do not scale. Input queued switches, on the other hand, require complex arbitration procedures to achieve the same level of performance. We enumerate the design constraints in the construction of a packet switch and present several approaches to build a system composed of lower-capacity memory and space elements, and analyze their performance. Towards this goal, we establish a new taxonomy for a class of switches, which we call Buffered Clos switches, and present a formal framework for optimal packet switching performance, in terms of both throughput and QoS. Within the taxonomy, we augment the existing combined input-output queueing (CIOQ) systems with Aggregation and Pipelining techniques. Furthermore, we present the design and analysis of a novel parallel packet switch architecture. For the items in the taxonomy, we present algorithms that provide optimal throughput and QoS, in accordance with the above performance framework. While some of the presented ideas are still in the investigative stage, we believe that the current state of the work, especially the formal treatment of switching, will be beneficial to the ongoing research in the field.