Sizing router buffers (redux)

The queueing delay faced by a packet is arguably the largest source of uncertainty during its journey. It therefore seems crucial that we understand how big the buffers should be in Internet routers. Our 2004 Sigcomm paper revisited the existing rule of thumb that a buffer should hold one bandwidth-delay product of packets. We claimed that for long-lived TCP flows, it could be reduced by √N, where N is the number of active flows, potentially reducing the required buffers by well over 90% in Internet backbone routers. One might reasonably expect that such a result, which supports cheaper routers with smaller buffers, would be embraced by the ISP community. In this paper we revisit the result 15 years later, and explain where it has succeeded and failed to affect how buffers are sized.