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I have a project where I would like to connect ~200 devices to a single AP.

Each of these devices will be offset in their communication so that there will only be approximately 10 devices relaying TCP packets to a server at any given time.

I would like all devices to stay connect to the server through open sockets at all time and just space out data sending in the way described above.

My first concern is the DTIM beacon messages that the AP will have to send to all of the devices. Will a reasonable priced (less than $500) router be capable of this?

Also if anyone else can think of additional problems that may occur that would be a huge help!

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    200 concurrent tcp connections doesn't seem to be that much. Every Pi could likely handle that. – Helmar Mar 5 '17 at 9:30
  • Plenty of commercial routers seem to have major issues with performance after several days of uptime - with only 10s of connected devices. Remember the underlying hardware is similar to a Pi already. – Sean Houlihane Mar 5 '17 at 12:22
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    I'm not concerned about the number of tcp connections to the server, just the ability of the router hardware to handle servicing 200 devices. I believe that as far as message traffic from the devices to router I should be okay as I am allocating fixed time slots to disperse communication... But I am concerned about the ability of the router to service all DTIM beacons for that many devices. Looking for advice from anyone who has experience or better understanding of these beacon messages – Wolfgang_Horton Mar 5 '17 at 19:07
  • Keeping sounds open sounds tempting - set it & forget it; no need to worry about tearing down and setting up connections. BUT, of course, with permanent connections, we still have to handle unexpected closure and open them again. If you are concerned about the routers ability to handle so many connections, then perhaps you ought to set them up & tear them down as needed. Of course, you probably need to find a way to synch their clocks at power on. – Mawg says reinstate Monica Mar 6 '17 at 8:16
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From the sounds of what you're trying to do I think you'll be fine, and obviously the outcome will depend on the router you get. (I'm going to use Ubiquiti as an example)

According to a Ubiquiti employee the hard-coded limit on concurrent connections is set to 50 million:

https://community.ubnt.com/t5/EdgeMAX/Maximum-number-of-Connections-Sessions/m-p/1153434/highlight/true#M53514

However Ubiquiti does have their own (practical) recommendations:

http://dl.ubnt.com/UBNT-inter-ops-5g_2.pdf

http://dl.ubnt.com/UBNT_inter-ops-2.4g_2.pdf

As far as IoT is concerned, from my personal experience I used a $35 Ubiquiti Air Router for a Arduino Training session with 20 wifi modules connected to it.

For the exercise we all played a 20-player asteroids game where all 20 modules made a request every 20 milliseconds. So that would be about 1000 requests every second. The router performed perfectly with default settings.

for $35 I'd say it's worth a try

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