Eric Carroll;173946 Wrote: > > The simple fact is that the cut through time (time from first bit in to > first bit out with no queueing delay) on a two port bridge (which is > what the SB3 is) is measured in microseconds.
I think that could only be true of an hardware ethernet switch (in silicon), or some architecture where the controller/CPU has the ability to start putting an outgoing frame on the wire before it is fully received. Obviously having the destination MAC as the first thing in the frame header makes this possible. However a software bridge or access point typically would store and forward, for a number of reasons - your first bit doesn't go back out until the last bit is in. One thing that is interesting about the Ubicom platform we use is that they implement the ethernet MAC in software. So as a bridge, the implementation would be considered somewhere between a minimal-latency silicon implementation and a "software plus ordinary ethernet interfaces". The advantage it has is that a packet coming in on the ethernet port goes straight into memory as it comes off the wire, so the step of copying the packet from an external ethernet chip's RX buffer is eliminated. The OS does not do any copies internally, and of course the reverse is also true for the TX direction. This is probably faster than most access points, but not as fast a hardware ethernet switch. So, while I'd rather have a 10-hop connection with 10ms latency than a 2-hop connection with 100ms latency, I wouldn't go as far as saying that hops don't matter... they don't matter much at very high interface speeds, but as you talk about slower link speeds the time for a packet to get in and out of the buffers becomes material. -- seanadams ------------------------------------------------------------------------ seanadams's Profile: http://forums.slimdevices.com/member.php?userid=3 View this thread: http://forums.slimdevices.com/showthread.php?t=31850 _______________________________________________ discuss mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/discuss
