2.4Ghz / 20Mhz client capacity? (720p clients)

[Pericynthion]

So I hope this is the right forum for this question - I'm struggling to wrap my head around something.

I have an ASUS RT-AC66U running fine for the majority of clients - I have 5Ghz laptops and mobile clients (even an 802.11ac media bridge) all connected without issues.

On my 2.4Ghz side, I think I'm hitting a limit.

I have 5 of the Dropcam HD devices (using the Atheros AR6103G, 1x1:1 embedded adapters) - which can stream up to 720p (although I am running them at a lower resolution for now).

When I connect up to 2 or 3 cameras, the 2.4Ghz network is fine - I can connect clients (even the 5Ghz that drop onto it at distance) and everything is fine. Thanks to the AC-66U I get great through put without having to crack up the TX power.

However as I add additional Dropcam clients onto the 2.4Ghz network, all the clients on that radio die. The TX rates reported by some clients (normally reporting 130Mb/s) drop to zero on occasion, and the radio becomes unusable. Reduce the camera count and everything is back to normal.

Now my initial gut was it was a faulty client / wireless profile, but it seems to not be device specific. It also has zero effect on the 5Ghz and wired client performance - as if nothing was there. I don't have any bandwidth issues and the traffic meter for the 2.4Ghz isn't shooting off the charts. So I'm pretty sure this isn't a Wireless<->LAN issue, but a Wireless<->router issue.

So I'm thinking that I am exhausting the 20Mhz channel streams from the router (3 with the AC66U) with these 2.4Ghz cameras. These aren't typical clients because they are permanently connected and sending data.

So my simple questions are;

1) Is there a way I can calculate what the limit / capacity is of the 20Mhz channel? Is it just as simple that on a 3 stream router, 3 permanently connected clients will occupy all the available stream.
2) Is there anything I can do to mitigate it (other than setting up a separate router / AP dedicated for them to use)
2) If I upgrade these to 5Ghz capable ones (Dropcam HD pro), am I just moving the problem into the other band - and again how will I know when I am at capacity of the radio (i.e. #streams = #supported cameras).

Thanks in advance - I'm going round in mind-circles trying to figure out exactly what is going on ;-)

 

[thiggins]

The problem is not related to the number of antennas. Single stream clients do not attach to individual antennas.

 

[Pericynthion]

Ok - thanks. So what is the capacity of a 2.4ghz 20mhz channel (frequency not bandwidth) - is it possible I'm just saturating the spectrum by having so many streaming clients (I guess it's like 5 people all watching Netflix at once - but uploading rather than downloading.

 

[Pericynthion]

Ps. I also replicated the issue using an old Apple Time Capsule as an AP, so I'm pretty sure it's not router specific and is something generic to do with the single 20mhz channel.

 

[thiggins]

It's unlikely you are hitting channel capacity. I found Dropcam HD's used about 500 kbps worst case when I tested them.

1x1 802.11n should be good for at least 20 Mbps.

You can check channel capacity for yourself. Use one of the network speed measurement tools with a wireless notebook and wired client.
Or just download a large file and use one of the NetMeters to monitor bandwidth use.

Since you are seeing the problem with multiple routers it is more likely something with the Dropcams.

 

[Pericynthion]

Yeah that's what I figured. As I say it doesn't seem to affect the overall upload /download speed of 5Ghz/wired clients so I'm pretty confident it is the Dropcam devices themselves - finding on what it is of course is a different issue ;-)

Thanks again for the info!

 

[theoak]

It really depends on your camera's settings.

My FOSCAM 720P I have set to send 720P at around 900 to 1000 kbps - both audio and video being measured ... 15 frames per second at a bit rate of 1M.

If I crank up the settinga to a bit rate of 4M and 30 frames per second, I get just under 3000 kbps.

With 5 on your network though, I think you would be fine too. Do you watch all 5 at the same time?

You could connect all your cameras to the Apple AP and have that AP as your "camera" AP, freeing your Asus up for your other devices.

 

[Pericynthion]

So I sort of got back to looking into this - obviously the separate AP plan works, but I also found that segregating the dropcams onto their own guest SSID (alongside the main SSID, still 2.4Ghz, on the primary router) seems to equally solve the issue.

Sort of goes back to my original thought that this is the dropcams doing something nasty at the WPA2/AES level rather than it being a physical issue.


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[Pericynthion]

Further update (should anyone struggling find themselves here) , the dropcam HD's seem to have an issue handling 'WPA2 Personal' AP's.

If I set the AP (or in my example the guest SSID) to use 'WPA-Auto-Personal', they seem to be connecting fine as WPA2, with AES. Oddly enough if I set the AP's to TKIP+AES they still connect with WPA2/AES but with no impact to the other 2.4Ghz devices on the radio.

I would love to explain why this fixes it but it does.

I still stand by my theory the embedded client in the dropcam's is having a hard time detecting/negotiating a pure WPA2 Personal connection (remember I replicated this on both the Apple and ASUS routers) - so even though the WPA-auto and TKIP+AES options give it a less secure option, it still ends up at WPA2/AES anyway.

One for the 'what the hell' file I think..