New technology for trunking gigE switches

Greg Lindahl lindahl at
Fri Aug 1 19:05:47 EDT 2003

What good timing: Broadcom just released public info about their new
generation of gigE switch chips, which are capable of using
inexpensive 4-wire copper 10gig uplinks between boxes. The neat thing
about this is that instead of having to buy a bunch of 10gig optics,
which are very expensive, it uses a 4-wire 3.125 gbit copper
interconnect, same as InfiniBand.

You should expect to see this showing up in stackable 24 to 48 port
switches, allowing up to 384 gigE ports in a single blob, at around
$100/gigE port. The center is an 8-port 10gigE switch, so as you can
see, you have the same issue of the ratio of uplink bandwidth to local
bandwidth that you had in the fast ethernet stackables with 1gig
uplinks. You will note, however, that the Broadcom blurb says you can
get much better total fabric bandwidth than just one of those
chips. They don't explain how, and so I can't mention it -- but if
anyone finds a public explanation, please let me know. I believe that
it should be able to hit the quoted 640 gbits of total traffic,
i.e. at 384 ports, you can build a switch which almost has perfect
bisection. The total switch latency also shouldn't be so bad: say ~35
usec for first bit in to last bit out, which is just over double of
what you'll see with a standalone gigE switch. (The total latency seen
by an application using TCP/IP will be higher, of course.)

The HP Procurve guys had a quote in one of the press releases, but I'm
sure that other vendors will ship products based on this too; Broadcom
is already a high volume producer of chips used in ethernet switches.

-- greg
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