Wireless Channel

[BostonDan]

Hi - I was checking out the articles 'How To Fix Your Wirless Network' series and 'When Wireless LANs Collide'. Can someone explain why you would stick to channels 1, 6, and 11 if there are already neighbor SSID's using those channels? In my case, I have several neighboring access points which are as follows:

Channel 6: (4 neighbor SSID's)

Channel 1: (3 neighbor SSID's)

All the neighbor SSD's show RSSI<signal> at -75 and lower

I set up two access points:
WAP-1 is in my main living area while WAP-2 is in my basement.
WAP-1 using Channel 11 for all my wireless N clients and
WAP-2 using Channel 3 for all of my wireless G clients. - I picked Channel 3 because inSSIDer showed it as having the most unobstructed traffic in the graphic where they show each channels bandwidth usage.
My SSD's show a RSSI signal at -50 (Channel 3) and -30 (Channel 11)

Am I making the best choice for WAP-2, or is it better to choose a standard 1,6,11 Channel and fully overlap these other SSID's.
Appreciate the feedback.

 

[thiggins]

When you use channels other than 1, 6 and 11, your signal may appear as noise to users on those channels. More noise can cause more retransmits, which can increase traffic needlessly.

802.11's CSMA/CA mechanism can work only when it receives all the data in a packet. You're better off being on a common channel so that your traffic can be properly coordinated.

 

[BostonDan]

Hi Tim,

Thanks for the response. I'm still having a tough time understanding which is worse:
1) Keeping it on Channel 3, where my router and my neighbor 7 routers have to deal with noise, retransmits, and increase traffic.
2) Move it to Channel 1, where my router has to compete/coordinate with my 3 neighbor routers using that same channel

I keep reasoning that by going in the middle,
1) I'm using bandwidth not being utilized
2) I'm only partially overlapping Channels 1 and 6, resulting in less impact on neighboring routers, because my router is now being shared among 7 neighboring routers compared to 3.
3) Channels 1 and 6, dealing with a little noise is less impact than sharing that bandwidth with another router.
4) I'm assuming the router is designed to deal with noise, as if generated by something else in the home.
I don't have the technical background in this to back up any of the assumptions I'm jumping to. I've moved my router to Channel 1, but still desire to understand the reasoning why. Can you help me understand?

 

[thiggins]

1) I'm using bandwidth not being utilized

Not true. If you look at real spectrum plots, you'll see that part of each main channel signal spills into adjacent channels. This is because 802.11 channels need 20 MHz of bandwidth and 2.4 GHz channels are separated only by 5 MHz.

2) I'm only partially overlapping Channels 1 and 6, resulting in less impact on neighboring routers, because my router is now being shared among 7 neighboring routers compared to 3.

Your router isn't being "shared". And as shown above, your signal is raising the noise level in two non-overlapping channels.

3) Channels 1 and 6, dealing with a little noise is less impact than sharing that bandwidth with another router.

Again, noise causes retransmissions, which wastes bandwidth resending old information. Operating in-channel means data gets through the first time, releasing more bandwidth for new data.

4) I'm assuming the router is designed to deal with noise, as if generated by something else in the home.

Today's radios are great, but not perfect. Some products are better at dealing with non 802.11 "noise", i.e. cordless phones, microwaves, by automatically changing the channel to move away from noise. Noise is by definition something that isn't and can't be understood / decoded. If you're in a noisy room trying to hear a quiet speaker, you need to either get everyone else to quiet down or get the speaker to speak louder.

In the end, the best choice is a commonly used channel with the least use.

If you still don't understand my point, maybe someone else can jump in with a more understandable explanation.

 

[BostonDan]

Channel Overlap - Makes Sense

Hi Tim - Thanks again for your help. I just figured out the flaw in my logic. inSSIDer shows the bandwidth of each channel more narrow than what is real. I now see the extent of the overlap and the bandwidth I thought was available, isn't really available. Appreciate your help very much.