Fixing slow Wireless LAN - the damn Multicast Rate setting

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Published on July 25th 2012 - Listed in Internet Windows Android Hardware Personal


I've recently installed a completely new home network, including a 20Mbit/s Internet line. On the computer, directly connected to the main router by LAN, it is as fast as I expect. But on Wireless devices, like my Android SGS2 the speed was bloody slow. 

At the begin I expected a low range of the signal due to walls and floors but once I installed a repeater the speed didn't increase at all. As if I didn't already had enough to do, troubleshooting at home became inevitable ;-).

On the computer I used the famous www.speedtest.net  website to determine the speed. It came up to almost the full speed of the Internet line (19Mbit/s), which, as we all know, is almost never the full speed of what your contract says it is (best effort anyway). For Android there's an app for that, called Speed Test (also from speedtest.net) and I launched it. Android's data speed was at surprising 230Kbit/s !

I made some tests with the different 802.11 modes, switched forth and back to b/g/n, tested different settings. None of them had an impact. Just on top of that setting on my Zyxel router is another option called "Multicast Rate" which was set to 18Mbit:

High Multicast Rate causing slow WiFi

By looking at it I thought "man, this is slow!" but instead of changing it, I wanted to know what "Multicast Rate" actually means. One of the first results in a search engine beginning with a G was this site: Why is My Apple Wi-Fi So Damn Slow, a blog of Terry Blanchard. In my case I don't have an Apple device, but indeed, my Wi-Fi is damn slow so I gave it a shot. And this guy, Terry Blanchard, answered the question about Multicast Rate in the following way:

Essentially, the multicast rate is the minimum speed that a wireless device must be able to communicate at in order to connect to the router. So, the lower the multicast rate, the further away, or more accurately, the weaker the wireless signal, are allowed to connect. Therefore, turning up your multicast rate will decrease the range of your wireless network. If you are experiencing your wireless devices constantly losing their wireless connections, and then restoring those connections automagically seconds later; check this setting. It’s probably too high.

Dude, you're so right.

I switched it to a much lower setting, to 1Mbit/s:

Multicast Rate set to 1Mbit per second increased Wireless Speed

Then I retested the speed with the Speed Test app. Hell, the needle jumped up to 18Mbit/s!

Troubleshooting done successfully, and that even on my birthday!


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