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We've got a Draytek 2829VN Wifi router and I'm wondering how many concurrent connections I should expect a router of this kind to cope with? We are looking to connect 60 iPads!

I'd also be interested in knowing what might happen when it starts to reach capacity?

Not looking for details specifically for this model, but in general.

Thanks!

UPDATE

Thanks for everyone's help!

We ended up going with 3 wired Cisco AP's, sharing a single SSID across 3 channels. The venue already has WiFi running across channels 1,6 & 11 (the default it seems) so we've opted for channels 3, 8, and 13 which seems to be working very well, with around 20 iPads per AP.

The iPads then picked up the signal almost immediately, something they were taking in excess of 2 minutes to do when running on channels 1,6,11 due to interference.

Lesson learned : don't assume that setting up WiFi for large numbers of people is easy!

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Usually if you're asking this question it's not a good sign...how many are you trying to push through it? –  Bart Silverstrim Oct 20 '10 at 11:22
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ahem....60 iPads? –  user57675 Oct 20 '10 at 11:29
    
Um....well...depending on the data you're pushing,... –  Bart Silverstrim Oct 20 '10 at 11:41
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@jay 60 clients? Forget it. You'll be lucky if they're all able to associate simultaneous, let alone transfer real data. We see a nominal max clients just around 25 for our 2.4Ghz stuff. The 5Ghz doesn't seem to bear many more clients, but it seems less susceptible to interference. These numbers are totally anecdotal. –  jscott Oct 20 '10 at 11:49
    
SOHO routers can do a dozen semi-efficiently. Good business class can double that number. And you can double those if you're willing to accept very degraded performance. That still isn't close to 60. –  Chris S Oct 20 '10 at 12:57

4 Answers 4

up vote 11 down vote accepted

While Oneiroi's answer starts to get you there. There are a few flaws that deserved more than a comment on his answer.

First, the bandwidth you are actually contending for isn't the back end ethernet link, but the wireless link speed. So on a 54 mbps router you would be contending for that 54 mbps. At 60 clients that would be about 900kbps each, not counting TCP overhead, counting TCP overhead you are already down to ~720kbps.

Secondly, you still have to deal with signal strength issues, which depending on your location could greatly effect throughput.

Thirdly, you have to deal with interference between those 60 radios all trying to broadcast. Years ago when I was working on planning an 802.11b wireless network the engineer we talked to said the rule of thumb was about 10-12 clients per AP for best performance, you can probably move that up to 20-25 (pure off the cuff number)with today's newer technologies. But that still doesn't get you to 60.

I would suggest that you take a look at some pure Wireless APs (not routers) and do a site survey to find the optimal placements for them.

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Concurrent connections are dictated by 2 things, bandwidth & resource,

On the resource front it would be best to ask the vendor, the cpu & memory of he hardware could be a limiting factor in the supported concurrent connections.

Bandwidth is the major limiting factor, whilst you may connect @ 54mb/s remember if you users are contenting with 50 others all over the 100mb/s Ethernet attached to the access point their actual available bandwidth becomes 2mb/s.

As you start to reach capacity you will find:

Bandwidth: The Ethernet connection is always transferring the maximum available for the connections (i.e. 100mb.s)

Resource: assuming someone isn't attempting to crack your network by spamming de-auth packets you will see a lot of "broadcasts" from the AP, as it tries to reconnect with dropped clients.

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As Bart hinted, we already have a situation where 60+ wifi devices are attempting to connect to a single wifi router. What we are seeing is devices losing their connections and malformed HTML responses/requests. –  user57675 Oct 20 '10 at 11:31
    
Can you get SNMP data from the AP? it would be worth graphing this over time, and keeping a time sheet of reported incidents to match up against the graphs (Checking for CPU and memory usage especially). –  Oneiroi Nov 10 '10 at 10:38
    
On another note, should cpu + memory + bandwidth be fine, chances are you have some interference occurring, try stepping through the available wifi channels, if you have not already –  Oneiroi Nov 10 '10 at 10:39

I don't see that model specifically, but similar model lines look like they're a SOHO class routers. The price on those models makes them look like a step above home routers, but I'd be wary of their limits.

If you're pushing 60+ devices through a wireless system simultaneously, I'd really strongly consider getting a dedicated access point and a separate router. Combo router/switch/wireless AP's in my experience tend to get glitchy and have issues with maintaining connections or having a subcomponent die and require a reboot, killing everything until it restarts.

They also tend to have limits in their routing tables that start giving odd behavior for things like web browsing or computers that get booted off the network.

If I had to guess, you're overpushing that router. Suggest getting separate, higher-end systems.

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As others have said, you're probably "oversubscribing" the wifi router. Wifi is a shared medium so all 60 clients are sharing and contending for the 54Mbps (assumed) bandwidth available through the wifi link. That's somewhat analogous to connecting 60 wired clients to a hub and uplinking that via a single 10, 100, or 1000Mbps link to your core switch, but in addition you've also got signal quality and potential interference issues to deal with as well.

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