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 scheduling input queued cell switches

Output-queued switching, though is able to offer high throughput, guaranteed delay and fairness, lacks scalability owing to the speed up problem. Input-queued switching, on the other hand, is scalable, and is thus becoming an attractive alternative. This dissertation presents three approaches toward resolving the major problem encountered in input-queued switching that has prohibited the provision of quality of service guarantees. First, we proposed a maximum size matching based algorithm, referred to as min-max fair input queueing (MFIQ), which minimizes the additional delay caused by back pressure, and at the same time provides fair service among competing sessions. Like any maximum size matching algorithm, MFIQ performs well for uniform traffic, in which the destinations of the incoming cells are uniformly distributed over all the outputs, but is not stable for non-uniform traffic. Subse-quently, we proposed two maximum weight matching based algorithms, longest normalized queue first (LNQF) and earliest due date first matching (EDDFM), which are stable for both uniform and non-uniform traffic. LNQF provides fairer service than longest queue first (LQF) and better traffic shaping than oldest cell first (OCF), and EDDEM has lower probability of delay overdue than LQF, LNQF, and OCF. Our third approach, referred to as store-sort-and-forward (SSF), is a frame based scheduling algorithm. SSF is proved to be able to achieve strict sense 100% throughput, and provide bounded delay and delay jitter for input-queued switches if the traffic conforms to the (r, T) model

Minimizing the communication overhead of iterative scheduling algorithms for input-queued switches

Communication overhead should be minimized when designing iterative scheduling algorithms for input-queued packet switches. In general, the overall communication overhead is a function of the number of iterations required per time slot (M) and the data bits exchanged in an input-output pair per iteration (B). In this paper, we aim at maximizing switch throughput while minimizing communication overhead. We first propose a single-iteration scheduling algorithm called Highest Rank First (HRF). In HRF, the highest priority is given to the preferred input-output pair calculated in each local port at a RR (Round Robin) order. Only when the preferred VOQ(i,j) is empty, input i sends a request with a rank number r to each output. The request from a longer VOQ carries a smaller r. Higher scheduling priority is given to the request with a smaller r. To further cut down its communication overhead to 1 bit per request, we design HRF with Request Compression (HRF/RC). The basic idea is that we transmit a single bit code in request phase. Then r can be decoded at output ports from the current and historical codes received. The overall communication overhead for HRF/RC becomes 2 bits only, i.e. 1 bit in request phase and 1 bit in grant phase. We show that HRF/RC renders a much lower hardware cost than multi-iteration algorithms and a single-iteration algorithm π-RGA [11]. Compared with other iterative algorithms with the same communication overhead (i.e. SRR [10] and 1-iteration iSLIP [6]), simulation results show that HRF/RC always produces the best delay-throughput performance. © 2011 IEEE.published_or_final_versionProceedings of the IEEE Global Telecommunications Conference (GLOBECOM 2011), Houston, TX, USA, 5-9 December 201