I admit it, I'm a heavy internet user. I've been a heavy internet user since before the term was coined. I'm the guy you always talk to when you want to find out what you're going to be doing with technology in the next two years. Yes, I'm THAT guy – I download, game, stream, use VoIP and more over my internet connection. With that in mind, I was more than a bit alarmed when AT&T recently announced that they were going to cap usage on all DSL lines.

AT&T claimed I used 33% more data than was actually sent and received in January.

I had followed the UBB controversy in Canada, and knew that many of the Canadian ISPs were having trouble getting reliable usage numbers from their equipment. It was with that foreknowledge that I logged into AT&T's DSL usage meter (found here, account required) and was shocked.

AT&T said that I had used 361GB in a single month! Surely this couldn't be right. I'm a heavy user, but every time I even so much as glanced at my usage stats they've always been in the 200GB range. Surely something was amiss, so I decided to dig deeper.


It's an old habit, but the first thing I do when I suspect something is wrong with any bill is enter all the line items into a spreadsheet and add them up myself. It sounds like busywork, but sometimes you'll catch unlisted charges that have been phantomly added to your bill, or occasionally an outright math error. I couldn't believe what I found. AT&T's usage meter results insist I had used 341.39GB down, and 20.18GB up. But when I added all the daily detail entries (the DSL equivalent of a call log), only 332.8GB down and 0.72GB up are accounted for.

AT&T is claiming that I used 361.57GB of data, but according to their own daily data I only used 333.52GB, an 8.5% overcharge.


After finding that AT&T can't add its own stats correctly, I decided that more in-depth checking was warranted. Luckily, my DD-WRT router is the last stop before my DSL modem, and it automatically keeps upload and download usage meters. I already had everything necessary to fact-check AT&T's usage numbers. When I compared the daily AT&T usage data vs DD-WRT's usage data, I was in for a shock. It appears as though AT&T's data is entirely corrupt. Not only was I being wildly overcharged on some days (to the tune of a 15GB overcharge in a single day), but I was also being undercharged on other days.

The errors become glaringly obvious when the AT&T reported data minus the DD-WRT reported data is graphed. Points above the axis are overcharges, points below the axis are undercharges:

The corresponding upload usage graphs aren't any more pretty, and clearly demonstrate that there is a problem:


This appears to be a smoking gun, demonstrating the unreliability of AT&T's data usage collection on their DSL lines. In January AT&T claimed I used a total of 64 Gigs more data than DD-WRT recorded (a 20% overcharge), and in February AT&T claimed I used an additional 34.5 Gigs (a 17% overcharge). When you compound those overcharges with the additional 10% overcharge from AT&T's simple math mistakes, the net effect is that AT&T claimed I used 33% more data than was actually sent and received in January.

Finally, I wanted to know if I was simply an unfortunate soul, or if I had stumbled across a systematic problem in AT&T's usage meter. I started a thread in the forums here at Broadband Reports and found quite a number of other people experiencing similar issues with AT&T overbilling their data usage. Though their data collection methods vary, the consistent theme is the same: AT&T's usage meter is wildly inaccurate.


It's not hard to maintain independent usage statistics to double-check AT&T's numbers. If you have a DD-WRT compatible router, it will keep your upload and download history automatically. If you don't have a compatible router, you can still run WallWatcher or MRTG to get the total bandwidth used by your router. Finally, if your computer is connected directly to your DSL modem without a router, you can run software like Net Meter to track your internet usage.

Using any or all of these tools, you'll be able to monitor your total bandwidth usage and compare it to AT&T's. Enough people have reported problems that it's worth your time and effort to set up independent monitoring before AT&T's usage caps start May 2nd.


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