wlan stops working periodically

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CPCT's picture
wlan stops working periodically

A few months ago I installed dd-wrt on my new WNR3500L and I'm using it mostly as a wireless AP to access my ADSL internet connection. Everything worked fine for some time, and I was able to add USB print server support.

The issue atm is that after some time (usually in the order of half a day to max a few days), the wifi AP signal drops to a very weak signal (I have to be next to the router to pick up the SSID broadcasts) and it becomes impossible to make a connection to it.

If I then go the the administration panel (using a wired connection) and, for example, change AP name, or encryption, or txpower, etc... and press "save and apply", the AP comes back up and works fine. Then, maybe one day later, the problem returns. It seems like its happening more frequent than before.

I already have decreased txpower form the default 71mW to 30mW but to no avail. Dmesg output also does not report anything useful.

I've come to a point that I'm really fed up with it. Has anyone ever had a similar problem? Maybe someone has a suggestion? I'd appreciate any help on this.

Kong's picture
Do you transfer large amounts

Do you transfer large amounts of data through the wlan connection?
P2P etc.?

Sudipta's picture
Have you tried with different

Have you tried with different channel. It may be the case that your selected channel may conflict with neighbour.

CPCT's picture
No, I barely use the wlan for

No, I barely use the wlan for heavy traffic. Also, it could happen that I have to "reset" the wlan settings (as described) in the evening and that it has already stopped working in the morning.

I have set all wlan settings on automatic (before it was mostly on manual). Also, where I live there's only 2 neighbours that have a wifi access point. For now I have reduced the txpower even more to 25mW.

Kong's picture
It could be a broken radio

It could be a broken radio unit. I would flash the original firmware again and then check if this problem still exists, if yes-> return the router.

RobM's picture
Yes! I am having exactly

Yes! I am having exactly this problem on a dlink 615 and DD-WRT v24-sp2 (04/23/10) std

I installed dd on this router for the first time back in June, first experience with DD. Worked perfectly for until early September? when the wireless portion would stop working. The only indication was that there were some errors noted on the status/wireless/transmitted counter and there were no wireless clients connected.

I've tried various combinations of parameters. Right now I've set it so that it detects 'radar' and selects auto channel. The reason I did this is that we have new neighbours and I see a new (and very strong) wireless router, so I suspected interference.

After 3 days - wifi has not crashed. If you have this problem, make sure channel = auto and radar is on.

CPCT's picture
After reducing txpower from

After reducing txpower from 30 to 25mW, my wifi is still working! Fingers crossed.

What do you mean with the "radar" option? I searched the wireless-configuration pages but couldn't find that.

RobM's picture
The 'radar' option is called

The 'radar' option is called radar detection. It is set on the wireless/basic settings page. Note however that you shouldn't NEED to set radar detection on as it applies only to 5GHz band 802.11n I believe and I downgraded my settings to G. What I do know is that since I've turned these settings on, my wifi has not gone away in several days now. Why this should be the case is a mystery.

As I said in my earlier post, this problem started when we got new neighbours recently. (They are nice people, not their fault) Along with them came a new 'N' router that was pretty powerful. What also came along with them is a BMW 7 series that sometimes visits. I know those cars sometimes have radar based cruise control. Could the presence of those radars effect my wifi? Who knows.

Now that I have a stable configuration I'm going to watch for the arrival of the 7 series to see if it has any effect. Then I'm going to re-enable 'n' and if it remains stable I'll turn OFF radar detection and see what happens. I'm also going to try 'G' with radar off to see if the problem returns.

A search for "DD-WRT" and "radar" returned this excerpt from an Atheros document.

"Countries around the world are requiring that 5 GHz wireless LAN (WLAN) devices
support the latest Dynamic Frequency Selection (DFS) standards. DFS prevents
interference with military and civilian radars by moving WLAN transmissions out of the
channels used by the radars when radars are present. Because the affected spectrum varies
by country, WLAN chipsets must implement a highly detailed and adaptable compliance
DFS requirements are crucial for new-generation WLANs based on the IEEE 802.11n
standard. To a large extent, 802.11n was devised to provide the higher throughput capacity
needed for more robust WiFi applications, such as Voice over IP (VoIP) and multiple,
simultaneous, real-time, high-definition video streams. These high-performance, latency-
sensitive applications require reliable throughput without interruption. With many
bandwidth limitations and interference sources in the 2.4 GHz band, 5 GHz spectrum is
essential for these applications.
To accommodate wireless networking needs, most countries have opened up parts of the
spectrum once reserved for civilian and military radars-with the caveat that radar still
owns the right of way. Thus, the performance 802.11n WLANs operating in 5 GHz depends
on DFS compliance."