Connection problems - local web-server, wireless router, sixty smart phones

grantgz · Mar 23, 2015

I have set up a LAMP web server and plugged it in to a router. In a room I want up to sixty students to connect through wireless to this local web server.
Today I found many phones could not connect and a reconnection from my phone also failed. The web-server was still responsive and top didn't show any CPU or memory problems. My phone reconnection showed an authentication problem so it was not the phones.
I suspect the two routers I tried could not handle more than 20 connections.

Does this sound like the likeliest cause?
What can I do to get this running?

bill001g · Mar 23, 2015

Some have artificial limits to protect you from doing dumb stuff.

You have 2 limits the first is the pure number of session the router is designed to keep track of. This is a memory limitation but memory is cheap so I would suspect it is pretty high now. I know years ago some commerical cisco ones were limited to 15.

The more important limit is bandwidth. Wireless sharing is completely uncontrolled. All the end units are responsible to not transmit over each other. It does not work all that well when you have lots of active clients. The number of devices greatly depends how much data they are sending as well as how often they attempt. Sending small amounts of data but doing it a lot is as bad as sending large amounts of data.

This is almost a impossible calculation to make. Most commercial installation say to not put more than 10 clients per AP but it is pretty easy for 2-3 devices streaming video to completely make it unusable for all the other devices.

I would say with 60 devices you first try 3 AP running on channels 1,6,11 on the 2.4g channels and force them to 20mhz. If that is not good enough you are going to have to use 5g channels also or put in more AP on channels 1,6,11 but turn the power way down to avoid interference.

grantgz · Apr 7, 2015

bill001g :

Some have artificial limits to protect you from doing dumb stuff.

You have 2 limits the first is the pure number of session the router is designed to keep track of. This is a memory limitation but memory is cheap so I would suspect it is pretty high now. I know years ago some commerical cisco ones were limited to 15.

The more important limit is bandwidth. Wireless sharing is completely uncontrolled. All the end units are responsible to not transmit over each other. It does not work all that well when you have lots of active clients. The number of devices greatly depends how much data they are sending as well as how often they attempt. Sending small amounts of data but doing it a lot is as bad as sending large amounts of data.

This is almost a impossible calculation to make. Most commercial installation say to not put more than 10 clients per AP but it is pretty easy for 2-3 devices streaming video to completely make it unusable for all the other devices.

I would say with 60 devices you first try 3 AP running on channels 1,6,11 on the 2.4g channels and force them to 20mhz. If that is not good enough you are going to have to use 5g channels also or put in more AP on channels 1,6,11 but turn the power way down to avoid interference.

grantgz · Apr 7, 2015

Thanks Bill

Everything is running off one laptop which is the webserver and it is wired to the router. Other devices can be plugged into the router using cable.
If I understand you correctly, I could connect another wireless router to the first and run both on different channels?
I suspect my connection problems are not due to bandwidth as the pages delivered are tiny and the students only have access to a very small number of files on the laptop. Daisychaining routers may not help if the first router will only accept a limited number of connection

bill001g · Apr 8, 2015

There is some limit into the maximum number of things you can plug into a router but it is in the many thousands. There are other limits like the DHCP pool size but that is something you can easily change.

You want to cable as many devices as you possible can. The problem with wireless is there is huge amounts of wasted bandwidth. Devices transmit over the top of each other all the time since it is a shared media. Whenever this happens the data is destroyed and must be retransmitted. You get too many devices and they spend most there time correcting for transmitting over the top of each other.

Running multiple routers/AP really is the only solution and this is how it is done in large enterprise installations.

As to why you would see a 20 device limit that is hard to say. There really is no actual limit in the basic technology it just doesn't work real well above certain levels. You would have to dig though the documentation of the device to see.

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Connection problems - local web-server, wireless router, sixty smart phones

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