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I'm tryin to set up a number of IP cameras (D-link DCS-920 and DCS-930L) to send images by FTP to a server (Ubuntu server (10.04 I think)). The images are about 15KB each and currently I have 6 cameras sending images at 1FPS each.

The cameras are connected to an 8 port unmanaged 10/100 Ethernet switch. The switch is connected to an WiFi bridge (Ubiquiti Nanostation 2) that connects to an access point (Ubiquiti Nanostation 2) connected to the server via a Gigabit switch. Below is a simple diagram of it:

Camera--->10/100switch--->WiFi Bridge--->WiFi Access Point--->Gb switch--->Server

Ideally at 1FPS I should get 3600 images per hour per camera. But the amount of images I get drops dramatically if I keep the whole setup running for over a week. Then it drops to around 1000-1500 per hour.

When I check IP address transmission rate from the cameras using iftop on the server, I see the transmission rate from the camera IPs randomly drop to 0. I tested just having one camera connected to the server directly and was able to consistently get 3600 images per hour. So I think the cameras are working ok. I added external antennas (the whole setup is outdoor) to both the bridge and access point, I also made sure that it was not transmitting on channels that overlap with channels used by nearby WiFi networks. Doing both, I got the signal to be about -30Dbm and the problem persists.

I'm looking for some ideas on what's going wrong with this set up and where to check/fix to get the image FTP rate to not drop. Any suggestions on fixing this problem would be greatly appreciated.

One specific idea I'm thinking of is if it makes sense at all that the amount of traffic is somehow causing the switches to drop packets and if using a different switch would solve the problem.

share|improve this question
That makes 90KiB/s total, which is around 900kbps. That isn't exactly lots of traffic, unless your WiFi setup is truly archeological (or there is lots of other traffic). It is very unlikely that the network is to blame. Are the images sometimes much bigger? Is there any pattern to the speed loss? Install sysstat, leave it running a few days and check for any other activity on the system. Try to look for other WiFi activity (or perhaps electromagnetic interference?) when it goes slow. Measure network traffic, perhaps something else is swamping the net? – vonbrand Apr 29 '13 at 19:23
Thank you for helping me with this problem. The image size does fluctuates a little, but the highest it ever got was about 17KB. I didn't notice any particular patterns with the speed drops. The network is specifically used for the cameras, nothing else is connected to it, but I'll double check on that. The whole thing is set up next to an airport, I'd imagine that'd be a source of EM interference, but wouldn't that be fairly consistent from day to day? As I understand, FTP is based on TCP & should offers reliable transport. So if there's packet loss, shouldn't it resend? – EricB Apr 30 '13 at 12:38
Yes, FTP is based on TCP; yes, it does resend. Very strange... See if there is perhaps heavy use of the channel when speed drops (near airposrt means the usage pattern might change a lot). – vonbrand Apr 30 '13 at 13:12

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