1 Asynchronous vs Synchronous Input-Queued Switches

Abstract—Input-queued (IQ) switches are one of the reference architectures for the design of high-speed packet switches. Classical results in this field refer to the scenario in which the whole switch transfers the packets in a synchronous fashion, in phase with a sequence of fixedsize timeslots, tailored to transport a minimum-size packet. However, for switches with large number of ports and high bandwidth, maintaining an accurate global synchronization and transferring all the packets in a synchronous fashion is becoming more and more challenging. Furthermore, variable size packets (as in the traffic present in the Internet) require rather complex segmentation and reassembly processes and some switching capacity is wasted due to partial filling of timeslots. Thus, in this work we consider a switch able to natively transfer packets in an asynchronous fashion thanks to a simple and distributed packet scheduler. We investigate the performance of asynchronous IQ switches and show that, despite their simplicity, their performance is comparable or even better than those of synchronous switches. These results highlight the great potential of the asynchronous approach for the design of high-performance switches.

Scheduling algorithms for high-speed switches

The virtual output queued (VOQ) switching architecture was adopted for high speed switch implementation owing to its scalability and high throughput. An ideal VOQ algorithm should provide Quality of Service (QoS) with low complexity. However, none of the existing algorithms can meet these requirements. Several algorithms for VOQ switches are introduced in this dissertation in order to improve upon existing algorithms in terms of implementation or QoS features. Initially, the earliest due date first matching (EDDFM) algorithm, which is stable for both uniform and non-uniform traffic patterns, is proposed. EDDFM has lower probability of cell overdue than other existing maximum weight matching algorithms. Then, the shadow departure time algorithm (SDTA) and iterative SDTA (ISDTA) are introduced. The QoS features of SDTA and ISDTA are better than other existing algorithms with the same computational complexity. Simulations show that the performance of a VOQ switch using ISDTA with a speedup of 1.5 is similar to that of an output queued (OQ) switch in terms of cell delay and throughput. Later, the enhanced Birkhoff-von Neumann decomposition (EBVND) algorithm based on the Birkhoff-von Neumann decomposition (BVND) algorithm, which can provide rate and cell delay guarantees, is introduced. Theoretical analysis shows that the performance of EBVND is better than BVND in terms of throughput and cell delay. Finally, the maximum credit first (MCF), the Enhanced MCF (EMCF), and the iterative MCF (IMCF) algorithms are presented. These new algorithms have the similar performance as BNVD, yet are easier to implement in practice

On Asymptotic Optimality of Dual Scheduling Algorithm In A Generalized Switch

Generalized switch is a model of a queueing system where parallel servers are interdependent and have time-varying service capabilities. This paper considers the dual scheduling algorithm that uses rate control and queue-length based scheduling to allocate resources for a generalized switch. We consider a saturated system in which each user has infinite amount of data to be served. We prove the asymptotic optimality of the dual scheduling algorithm for such a system, which says that the vector of average service rates of the scheduling algorithm maximizes some aggregate concave utility functions. As the fairness objectives can be achieved by appropriately choosing utility functions, the asymptotic optimality establishes the fairness properties of the dual scheduling algorithm. The dual scheduling algorithm motivates a new architecture for scheduling, in which an additional queue is introduced to interface the user data queue and the time-varying server and to modulate the scheduling process, so as to achieve different performance objectives. Further research would include scheduling with Quality of Service guarantees with the dual scheduler, and its application and implementation in various versions of the generalized switch model