Gotta go with the old head scratch on that one...

Imagine the packet zipping down a wire. It hits a router. It slows down. Why? Because (until very recently) wire-speed != processing speed != backplane speed... This is called 'blocking'. The packet has to wait somewhere while the prior packet is being processed and fed through the backplane.

Very recently vendors started offloading tasks from a single processor to sub-processors and ASICs in a more distributed manner. This has led to routers that are faster than the wire (in contrast to the above stated routers that were slower than the wire). In this situation, buffering allows a greater port density: that is to say, more channels at a slower speed (the speed of the wire) rather than less channels at a higher speed (faster than the wire).

Apart from the fact that I have been building these (PC/Sparc based) routers since the early '90s is neither here nor there. My point in general was to actualy try to make people explain why there is a 'marketing' relationship between the size of buffers and a magical bandwidth x delay product of (normally) line rate x one second. I fully understand (in case it appeared otherwise) the issues of interface contention when aggregating traffic and also the need for buffering in QoS implementations, but the perceived wisdom of 'you must have at least one seconds buffer on each *interface*' still seems very shoddy and marketing driven. Still haven't heard it (a good reason), but then again I haven't gone to read Van Jacobson's paper that was referenced in an earlier reply. And that paper probably makes too good a point and bears no relation to the marketing drivel we have been getting for many years. BTW The faster than line rate / slower than line rate forwarding engine stuff is an ongoing and iterative thing that has been the simple result of capacity growth and in turn a has spurred the development of each new generation of router - just like any growth industry - and this will continue until we run out of electrons and photons and god-knows-what-else to move around. Peter