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I have a 50 Mbps connection through Comcast. When connected to my router via ethernet cable, every speed test that I perform consistently reports a 50-55 Mbps download speed. However, when I connect to my router via wireless N the same speed tests report download speeds in the range of 20 Mbps.

What's even stranger is that when connected wirelessly I can download files from other PCs on my network at speeds of 40-50 Mbps.

So in summary, wired I can download data from both within and outside of my network at speeds of 40-50 Mbps, but when connected via wireless N I can download data within my network at 40-50 Mbps but only at 20 Mbps from sources outside of my network.

Does anyone know why this issue occurs and how I might correct it?

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What router do you have? –  David Schwartz Aug 23 '13 at 6:50

1 Answer 1

It could just be a poorly designed router whose CPU is underpowered. Modern Wi-Fi radio designs do a lot of work in the driver on the host CPU to save money and complexity on the Wi-Fi chipset. If your router's CPU is not fast enough to do NAT and Wi-Fi at full speed at the same time, that could explain what you've measured. It's pretty common for cheap routers to have underpowered CPUs. That's one of the corners they cut to make them cheap.

I know from my own testing that both Apple's new 2013 AirPort Extreme and Time Capsule with 802.11ac, and Asus's RT-AC66U 802.11ac router, have all the CPU they need to do NAT and 802.11ac at the same time with good throughput.

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This is about the only explanation that makes sense. If it was slow WiFi, then Wifi-to-Wifi should be worse. If it was slow Internet, wired shouldn't be much better. –  David Schwartz Aug 23 '13 at 6:50

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