| |
Buffer Sizing in the Internet |
Buffer Sizing ProblemUntil quite recently, Internet routers were widely believed to need large buffers. Commercial routers today have huge packet buffers, often storing millions of packets, under the assumption that large buffers lead to good statistical multiplexing and hence efficient use of expensive long-haul links. A widely-used rule-of-thumb states that, because of the dynamics of TCP's congestion control mechanism, a router needs a bandwidth-delay product of buffering, in order to fully utilize bottleneck links. Here, bandwidth refers to the router's capacity, and delay refers to the average two way propagation delay of packets going through the router. We have developed an analytical model that suggests that router buffers of core routers could be decreased by about two order of magnitude. This result has been validated by thousands of ns2 simulations as well as experiments done on Stanford's dormitory traffic, University of Wisconsin's WAIL testbed, Internet2, and some commercial operational backbones. This result has significant implications in router design. If big electronic routers require only tens of thousands of packet buffers, it could reduce their complexity, making them easier to build and easier to scale. A typical router linecard today contains about one million packet buffers, using many external DRAM chips. The board space the DRAMs occupy, the pins they require, and the power they dissipate all limit the capacity of the router. By Reducing the buffer size to tens of thousands of pacets, then packet buffers could be incorporated inside the network processor (or ASIC) in a small on-chip SRAM. Not only would external memories be removed, but it would allow the use of fast on-chip SRAM, which scales in speed much faster than DRAM. Recently, we have shown that the under certain constraints we can reduce the buffer size of Internet routers even more, to just 10-20 packets without any degradation in performance. While this is an interesting intellectual exercise in its own right, there would be practical consequences if it were possible. It could facilitate the building of all-optical routers. With recent advances, it is now possible to perform all-optical switching, opening the door to routers with huge capacity and lower power than electronic routers. Recent advances in technology make possible optical FCFS packet buffers that can hold a few dozen packets in an integrated opto-electronic chip. Larger all-optical buffers remain infeasible, except with unwieldy spools of optical fiber (that can only implement delay lines, not true FCFS packet buffers). We are interested in exploring the feasibility of an operational all-optical network with just a few dozen optical packet buffers in each router. Papers
Talks
Other Interesting PapersAdaptive Routing and Congestion Control
Deflection Routing
Congestion Control
|