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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical gigabit router (was Re: Getting a "portable" /19 or /20)
In message <[email protected]>, "R ichard A. Steenbergen" writes: >Don't be absurd, I can walk into fry's and pick up a motherboard with >64bit/66mhz PCI, some Netgear GA620's, and all the other components for a >1GHz computer for under $1000. OK, so your bus has 4.2 Gb/s of bandwidth. But, alas, you're in a PC so you have to copy each packet from the line card, into main memory, examine it, and push it back out to a line card. So each packet consumes twice its size in bus bandwidth. So 2 1 Gb/s line cards will consume 4 Gb/s backplane. Assuming you can run the PCI at full rate (which in my experience is a big big if), you can connect two Ethernets. Incidentally, this isn't the full story either. You have to do a route lookup on each of those packets. That's typically 5 to 10 memory accesses... 5 memory access times 1 Mpps per gigabit times 2 gigabits is 10 million lookups per second or 100 ns per lookup. Allowing for time spent getting through the chip to the pins, you probably need 60 or 70ns DRAM, which is doable. Except, oops!, that completely consumes your memory bandwidth... where are you going to find the cycles to get the packets in and out? Craig PS: Side note, this illustrates where router vendors earn their bucks. Find a way to move data over each bus only once (double your bandwidth!). Design your memory subsystems to keep packets and routing data separate (increase your memory bandwidth!). Find a processor that doesn't waste cycles doing virtual memory (improve your memory access times!). Oh yes, and then add hot board swap, a working BGP implementation (quick, where's Tony Li working these days:-)), a CLI, and a power subsystem for a CO, and you're in business. *************** Craig Partridge Chief Scientist BBN Technologies
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