On Wed, 14 Oct 2009 11:50:42 +0200, Uwe Klein wrote: > Rick Jones wrote: >> Uwe Klein <[email protected]> wrote: >> >>>With switches the problem tends to be the strategy for handling >>>(potentially) colliding traffic. >>>"Passthrough", "store-and-forward", "drop/cause resend" have >>>massively different transit times. >>>Depending on traffic density any single switch will use a mix of all >>>transfertypes. >> >> >> I don't think it is what you meant by "drop/cause resend" but >> something else "new" in 1 Gigabit Ethernet relative to old 10/100 is >> support for pause and resume (moral equivalent to xon/xoff?) flow >> control. > > No, the traffic that passes through the _switch_ hardware. > > if the destination port is idle you get passthrough. > i.e. you get just enough bittimes delay to read the > target MAC address from the paket header. > I dont think many switches are passthrough nowadays. But it can be a problem that the path to the switch matix is oversubscribed. One example I know of is that on a 48 port card every 8 ports share 1Gbit to/from the backplane. Depending on the traffic by the other 7 this will create jitter. (Cisco 450x has 6*1Gbit per slot, 450xE has 8*3G per slot) /hjj
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