Quote:
Originally Posted by billymac /forum/post/21418389
can you please elaborate? not everything you say here makes sense to me. i don't believe there is an "auto" in the speed drop down. the choices on these netgears appear as "up to XXX".
When 40 MHz channels are used in 802.11n at 2.4GHz, 82% of the legal spectrum is allocated to that "One" channel. That means there's an 82% likelihood that your neighbors will be interfering with you...whether they're using 40MHz or 20MHz.
So basically, if YOU are using 40MHz channels, and your neighbors have WiFi of *ANY* sort in the 2.4GHz band, 82% chance they will interfere with yours.
2.4 GHz has only THREE channels that are considered "Non Overlapping." In reality, there is a LITTLE overlap. The channels are 1, 6, and 11.
Channel 1 overlaps with channels 1 thru 3.
Channel 6 overlaps with channels 4 thru 8.
Channel 11 overlaps with channels 9 thru 13.
If you use 40 MHz channels, then Channel 5 overlaps with channels 1 thru 7, and channel 9 overlaps with channels 3 thru 11. See? No matter WHICH channel you use, they overlap the others with an 82% likelihood.
This is based on United States frequency allocation. Other "regulatory domains" have different results.
So basically, 40 MHz channels are a HUGELY TERRIBLE thing to do in a "Shared" space. Only if you live out in the forest, or roughly 500 feet from the nearest neighbor, will you EVER get a clean spectrum. And if your city has Municipal Wifi: It's ALL OVER.
If your boxes do NOT have an Auto channel-width, then you are far better off using 20 MHz channels.
If you are using *ANY* 802.11b/g devices, you're better off leaving your max throughput set to 54Mbit / second, because there's VERY LITTLE advantage to having 802.11n in "Mixed Mode" with other devices.
All of these things I'm describing are generally called "Coexistence Problems." And it's a major limitation of WiFi. But it's NECESSARY to guarantee interoperability with older devices. The presence of so much as ONE 802.11b client in an 802.11b/g network slows performance dramatically. The presence of ONE 802.11 b or g device in a 802.11n network severely limits performance.
It's just the way it is.
Read the "Backward Compatibility" section of this wiki article:
http://en.wikipedia.org/wiki/802.11n
to see more.
That's why WD stresses in the user manual: "The recommended setting on Wireless N routers is 802.11n-only..." because they know that "Mixed Mode" destroys high-throughput WiFi capabilities.