Thursday, June 21, 2012

2Wire 2701HG-B Disconnect Problem - SOLVED

It's been eleven months since we got AT&T internet at the parsonage. At first, we ordered Comcast internet. They even sent us a modem. But there was this little problem of not actually having a cable plant out in the country where the parsonage is. They did finally quote us a price -- $5400 to install cable. No thanks.

So, we were thankful to get 6 Mbps/.5 Mbps AT&T DSL. They installed the 2Wire 2701HG-B Modem/Router/Wireless access point. This has been OK, except for one nagging problem.

Randomly, without warning, the router INTERNET indicator would go dark, the DSL indicator would go red and start blinking. Soon, the DSL indicator would turn to green blinking, then solid green, and the INTERNET indicator came back green. This takes 8-10 seconds, all the time the internet would be inaccessible. This might happen a couple of times a day, but more like twenty -- and more often, it seemed when someone was actively trying to use the internet.

This was especially bad when I was using Skype or my cell phone (my microcell is connected through the same internet connection). Or if I was using a virtual private network connection (VPN) to my work computers. That disruption would reset the VPN connection, and I'd have to go through a ten step process to reconnect. Perhaps two minutes later, I could try to work again. At least until it tries to reset.

Last weekend, I finally got tired of it. So I searched the web for information. Using some of the diagnostic pages inside the 2Wire router, I determined that the sequence of flashing lights represented a DSL Link Retrain. Those of you old enough to use analog modems will remember the distinctive sound of tones just before the modem connected. A DSL Link Retrain is much the same think -- only at 300 kHz instead of at audio frequencies.

Further searching revealed several articles by those unimpressed with 2wire products. One of the options is simply to replace the router. Being a ham, I'm not one to want to rush out and spend money I don't have to.

The AT&T Community Support forum unearthed an excellent thread: AT&T 2Wire 2701HG-B Disconnects / Drops. This had six pages of comments, and it took nearly an hour to read.

One of the suggestions was to measure the throughput of the connection using SpeedTest.Net, in order to determine that the DSL line was provisioned correctly by the phone company. When I tried this, as soon as I hit the uplink test -- DSL Link Retrain. I tried it a half-dozen more times. Every time I hit the uplink test, the router would do a DSL Link Retrain, save one. I now had a reproducible test, so I could try the various suggestions.

  1. Turn Packet Flood Attack Detection to Off - the theory is that activity on the router looks like a denial of service attack. Easy enough. Turn off the settings and try again. DSL Link Retrain.
  2. Move the Power Supply Brick to the Wall Outlet - theory here is that the 2Wire devices have marginal power supplies, and any reduction in voltage might cause a random glitch when the device draws power when doing something. Another easy test - replug and try again. DSL Link Retrain.
  3. Switch to 802.11b Wireless Networking - the theory here is that the 2wire devices can't internally handle the speed of 802.11g (54 Mbps) and the slower 802.11b (11 Mbps) allows the device to work correctly. Change the settings, re-do the wireless connection on the computer and try again. No DSL Link Retrain in five tries. 
At this point, I switched back to 802.11g, just to be sure the problem didn't just randomly go away. DSL Link Retrain. OK -- I'm not real happy about running 802.11b all the time. Not because of the internet connection, because it is only 6 Mbps/.5 Mbps anyway. No, two things bother me. First, I have other devices on the wireless network, such as iPads and iPhones, and I don't relish synching them at 11 Mbps. Second, the results from SpeedTest.NET were about 10% slower on 802.11b than on 802.11g.

I did notice that the router does have a speed limit setting for 802.11g. I switched it to a limit of 12 Mbps and tried again. No DSL Link Retrain in five tries. OK -- that works. And my 10% improvement in internet speed over 802.11b is back. Good. Try limit of 24 Mbps. DSL Link Retrain. The only other setting between them is 18 Mbps so try again. No DSL Link Retrain.

I've been running like this for most of a week and am pleased to say that I have suffered no further DSL Link Retrains logged by the router. It seems that high wireless speeds cause the router to reset the DSL connection. 

Frankly, this seems to be a product defect. It might be best to disable the wireless access point in the device and instead use a separate wireless access point connected to one of the Ethernet ports. (Unless, of course, that triggers the problem) I have not tested this.

A better solution may be to replace the 2Wire equipment with something that actually works. If anyone has suggestions, let me know. In the meantime, I'll be enjoying my slower (but working) wireless internet.

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