Why does setting a fixed wireless network speed cause hosts to lose their connection?

Question

Why do some of the hosts on our home network drop when I change the transmission rate from auto to 130Mbps or 270Mbps? Is it because their wireless NIC can not support such rate?

Answer 1

Based on signal strength, which is a measurement that is constantly fluctuating and affected by many environmental factors that are out of your control, the maximum possible practical transfer rate changes over time.

If you force the router to only accept connections at a certain bit rate, you are forcing any nodes that are only able to communicate at a lower bitrate to be knocked off the network, either due to the hardware not supporting that speed, or signal strength.

Imagine you are in a quiet room having a conversation with someone. Now gradually start adding an increasingly loud background noise, like the sound of running water. Eventually when it's loud enough, even speaking in a loud tone won't be enough for you to be able to effectively communicate; you'll have to say "what?" and get them to say things twice or three times over before you can understand it.

Whenever signal strength decreases, a smart wifi node will adjust its max. line bitrate downwards, for improved stability. If you declare that your bitrate is lower, it's easier to reliably achieve that lower bitrate, i.e. the error rate will be lower, but if you increase the bitrate, you have more data going back and forth, and it's harder to keep track of all the errors, resends, dropped packets, etc. and it becomes really impractical.

Another way to look at it is that a reliable connection can still be made even on a "noisy" medium at a low bitrate, but in order to attain higher bitrates with any sort of reliability, you need to reduce the noise. When you have factors influencing your signal strength, noise can go up and reception goes down, and the only way to retain a stable connection is to reduce the line speed.

A few things that can temporarily drive down signal strength:

• Polarization (relative orientation of the base station, the client, and their respective antennas)
• Solid objects in the way (people, walls, furniture)
• Interference from other devices operating on or emitting noise in the same spectrum, like other routers, bluetooth devices, microwaves, vacuum cleaners, etc.
• Distance
• Power saving settings on the device preventing it from transmitting at a power beyond a certain threshold
• Network congestion (lots of clients doing a lot of stuff at the same time with the same access point)

Bottom line is, just let the router and client negotiate a sane speed at any given moment, by keeping it on auto. That said, you could theoretically eliminate 802.11b/g, because 802.11n completely supercedes 802.11b/g, and contains all the speeds that 802.11b/g advertised. So you can take advantage of the improved protocol features of 802.11n but still allow the router and client to step down to lower speeds if they need to.

What you actually want to do is to disable the older protocols, which is a completely separate issue than setting the minimum speed to connect to the network. Your router's configuration page may or may not have a setting to explicitly disable b/g/a; if it doesn't have this setting, then just don't worry about it.

Answer 2

The above suggestions are all fine and good considerations, and maybe my experience described below, if not a direct answer to the question, can help add to the discussion in some way --

My personal experience has shown that in my 16 client wireless network over a 3 mile valley here in my Colorado neighborhood, that there has been one situation where having the ability to set a fixed data rate on a router box was necessary, in fact a life saver. I have 16 routers spread across a 3 mile valley. One day I had to replace a router because it was getting ready to die, or so I thought. Replacing the box I thought was bad with a brand new one did NOT seem to fix things...

The new one was a different brand router that apparently had the SAME PROBLEM or so it seemed. After much hair-pulling and hours of diagnosing, I discovered that the old and new boxes did not like the 2 - antenna setup (external panel and yagi stick antennas) that this client has. When loaded down with heavy activity it got slower and slower until it reached the point where I could reproduce it reliably by running a speed tester which sent a big burst of data and then the speed would slow down little by little to 1 Mbps AND STAY THERE even after my speed test was done. (i.e it bonked) WORST OF ALL, whenever that would happen, ALL of the other 15 client routers were dragged down to 1 Mbps too!! 16 different users calling me all day asking when the system will be back up!

The only fix I could find that WORKED was to change the data rate on that node to a FIXED value. Because our auto-negotiated speed capability is typically from 100 to 180 Mbps, and has never been observed going below 80 or so (when things are running right), plus the fact that our maximum data rate from the source is about 40 Mbps. SO... I was able to safely change the new router from auto, to a fixed rate of 54 Mbps. AND IT WORKED. That is probably the issue with your clients dropping when you set a fixed rate- your real-world speeds are occasionally dropping down below your fixed rate you set.

In my situation setting it to fixed worked great, but only because my set speed exceeds my minimum worse-case real-world speed AND exceeds my source-available speed. If anything, the overall network has been noticeable FASTER since the change, like the old box was having problems auto-negotiating for some reason, and bogging down the network with excessive packet re-tries or something. The auto algorithm just didn't seem to be able to handle this particular situation.

Maybe I don't really know what the heck I'm talking about :-), but I do know what worked for me. I guess they have the ability to set them to fixed for a reason, maybe? I was sure glad after many hours of frustration. Maybe I can save someone else the same headaches I had. JD in Colorado