Abstract-This paper is ahout high capacity switches and routers that give guaranteed throughput, rate and delay guarantees. Many routers are built using input queueing or combined input and output queueing (CIOQ), using crossbar switching fabrics. But such routers require impractically complex scheduling algorithms to provide the desired guarantees. We explore how a buffered crossbar -a crossbar switch with a packet buffer at each crosspoint -can provide guaranteed performance (throughput, rate, and delay), with less complex, practical scheduling algorithms. We describe scheduling algorithms that operate in parallel on each input and output port, and hence are scalable. With these algorithms, buffered crossbars with a speedup of two can provide 100% throughput, rate, and delay guarantees. A. me BufJered Crossbar- Figure 1 shows a 3 x 3 buffered crossbar, with line-rate R. To prevent head-of-line blocking, the inputs maintain virtual output queues (VOQs). Fixed length packets' wait in the VOQs to be transferred across the switch. Each crosspaint contains a buffer that can hold one cell. The buffer between input z and output 2 is denoted as &; when the buffer holds a cell, B,, = 1, else B,, = 0. Because the packets are all the same length, time is slotted, with a time slot equal to the time it takes for a cell to arrive on the external line. Internally, the switch runs faster than the external line, and the ratio between the two IS the speedup. If the switch can remove S cells from each input and transfer 5' cells to each output in a time slot, then it has a speedup of S . Throughout most of this paper we will assume that 5' = 2, and so the switch has output queues. we'll see that the scheduler for a buffer4 crossbar is much unbuffered crossbar. 0-7803-
REF studied practical scheduling algorithms for buffered crossbar switches.
Practical algorithms for performance guarantees in buffered crossbars
Proceedings IEEE 24th Annual Joint Conference of the IEEE Computer and Communications Societies.
Proceedings IEEE 24th Annual Joint Conference of the IEEE Computer and Communications Societies.
Computer Science