Kent D. Benson

Throughput of crossbar switches using maximal matching algorithms

Crossbar switch fabrics are simple and inexpensive. Maximal matching algorithms can be used to schedule packets through a crossbar switch at a reasonable computational complexity. This paper establishes conditions that guarantee the departure rate of each of a switchs input/output pairs will equal each pairs arrival rate if the switch is using a crossbar fabric and any maximal matching algorithm. These conditions bound each pairs arrival rate in relation to the switchs speedup and the sum of the arrival rates of the other input/output pairs that share either the input or the output of the pair in question. In particular, for speedups less than 2, bounding the sum of the rates passing through each input and output independently is overly restrictive, especially if rates tend to be a sizable fraction of the line rates. This paper also establishes that the speedup required to ensure that each input/output pairs departure rate equals its arrival rate for switches using maximal matching is less than 2 if all non-zero arrival rates are equal to or greater than some minimum rate.

A simple shaping scheme for frame-based bandwidth allocation

Packet switching devices that rely on input buffering to prevent cell loss in the switch fabric must regulate the arrival pattern of data packets to the input links of the switch fabric. Frame-based bandwidth allocation can be used in cell-based switch fabrics to regulate the number of cells from a flow entering the fabric during a fixed-length frame of cell slots. We present a simple cell slot assignment algorithm for distributing each flows cell slot allocations within a frame. The algorithm controls the inter-cell spacing for each flow and bounds fabric queues to a small number independent of the frame length. The simplicity of the algorithm supports per-frame changes in the allocated rates.