Doubling Memory Bandwidth for Network Buffers

Memory bandwidth is frequently a limiting factor in the design of high-speed switches and routers. In this paper, we introduce a buffering scheme called ping-pong buffering, that increases memory bandwidth by a factor of two. Ping-pong buffering halves the number of memory operations per unit time, allowing faster buffers to be built from a given type of memory. Alternatively, for a buffer of given bandwidth, ping-pong buffering allows the use of slower, lower-cost memory devices. But ping-pong buffers have an inherent penalty: they waste a fraction of the memory. Unless additional memory is used, the overflow rate is increased; in the worst case, half of the memory is wasted. Although this can be compensated by doubling the size of the memory, this is undesirable in practice. Using simulations, we argue that the problem is eliminated by the addition of just 5% more memory. We show that this result holds over a wide range of traffic and switch types, for low or high offered load, and continues to hold when the buffer size is increased.