Network speed mystery
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October 6, 2012, 01:35 PM
Join Date: Apr 2010
Location: East Van
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Trendnet figures that some customers will run a LAN with more than two nodes. Someone might choose to use a 500 Mbps adapter with gig ethernet at their router and home server, another gig-capable adapter at their office PC, and a 100Mbps max "nano" adapter for the HTPC and the kid's PC and etc. All of these adapters talk to each other using the same 500 Mbps modulation scheme.
They call it 200 Mbps* on their spec sheet. Of course it's 100base-T, which is 250 MHz signalling, 125 Mbaud, 100 Mbps after coding, and full duplex, which means it's 100 Mbps each way at the same time. It's kinda lame to say full duplex = 2x speed, but that's what marketing does these days. Likewise there's not much chance you'll ever get a real 500 Mbps out of the units with gig ports. The adapters are a sort of radio and modem combo to modulate the signal on the power lines, and like wifi the speed they make in the real world is dependent on the radio environment on the power lines they have to work with.
Well that's because that's 500 Mbps over your power line, which technically are thicker (lower cage wires) so they can handle a lot more bandwidth or current compared to your smaller twisted pair CAT cables.
Power line is thicker, lower gauge wire, so it can carry a lot more current, but current capacity and bandwidth potential are not related much at all. The power lines are in practice a much worse enviornment than your usual CAT5 cable because of a whole bunch of reasons, like instead of point-to-point it's tapped cables in a weird forking topology that causes reflections and ringing, power lines are loaded up with all sorts of major noise sources driving the cable with low impedance, there's been no attempt made to balance the cable impedance or maintain an even twist rate, etc etc. That's why the power line adapters are designed more like wifi adapters than simple NIC cards... because they really have to work hard (DSP) for that 500 Mbps.
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