How do you know if your broadband meter is accurate?

When happens when your ISP says you’re going over your broadband cap, but your own self-installed usage meter still says you have plenty of gigabytes left? That’s what Ken Stox is about to find out, as he takes on his ISP to try to figure out why his own usage numbers are 20 percent to 30 percent lower than those provided by AT&T (s t).

Stox, a Chicago-area resident, posted his tale Wednesday morning on Slashdot after AT&T notified him that he was approaching his broadband cap. This is exactly how AT&T’s cap is supposed to work: When a user gets to 60 percent of the monthly allotment consumed, followed by the 95 percent and the 100 percent mark, AT&T sends an email. But in this case, the user was tracking his data consumption and saw AT&T’s totals didn’t match his own records.

From his Slashdot post:

When this was implemented, I started getting emails letting me know my usage as likely to exceed the cap. After consulting their Internet Usage web page, I felt the numbers just weren’t right. With the help of Tomato on my router, I started measuring my usage, and ended up with numbers substantially below what AT&T was reporting on a day-to-day basis. Typically around 20-30% less. By the way, this usage is the sum of inbound and outbound.

He then detailed how AT&T gave him the runaround when he asked about the discrepancy. He was told that AT&T’s measurement of data was “proprietary,” and that if he wanted to dispute it, he would need to write a letter. He ended his post asking if there were any regulatory agencies that monitor the accuracy of ISPs’ meters. So far, there aren’t, something I’ve called on the FCC to address, especially given that more than six in 10 U.S. broadband subscribers have some kind of data cap.

I’ve emailed the FCC to see if the agency is aware of Stox’s issue and if it had reached out to either Stox or AT&T for more information. I also reached out to AT&T with a list of questions, and will update the story if I hear back from either party.

I did speak with Stox this afternoon to find out a bit more about his situation. He says that he’s a customer of AT&T’s DSL service because he cannot get access to U-Verse in his home. (Maybe AT&T’s planned investment in expanding U-verse will help him out on this front). For now, as a DSL customer, he has a 150 GB per month cap. Once he goes over that amount he would have to pay $10 for another 50 gigabytes.

Stox said that he has received several notices from AT&T since the ISP started enforcing its bandwidth cap, so he started tracking his data consumption by using Tomato, a Linux program installed on his router that allows him to write programs to track his data and customize his router settings. He said he couldn’t send me charts of his data because he had mistakenly erased them, but as an example he said his measurements showed the he consumed 5.1 GB on November 8 while AT&T’s usage meter showed he had consumed 8.1 GB. Stox is one of the lucky AT&T customers that actually has a meter he can check.

Now, there are a couple of things that might account for this discrepancy. Stox said that AT&T might be tracking a gigabyte in the more commercial sense as 1 billion bytes, as opposed to the more technical method that would result in a number that would be roughly 7 percent higher (1,073,741,824 bytes). Stox also noted that packet headings and other information that AT&T sends to route his traffic might also account for some overage — those are bytes his router wouldn’t necessarily count. He also mentioned that his timing might not match up with AT&T’s version (for example if AT&T’s daily totals ended at 12 ET while his ended at 12 CT).

For him, the problem is that AT&T won’t share any of its methodology with him. “What’s their definition of a byte?” he asked. “What’s their version of a day? I just want to know,” he said.

AT&T offers the following from its Frequently Asked Questions section:

What is included in my usage?
Usage includes all of the data you have received (downloaded) or sent (uploaded). In addition, we take into account the standard network protocols (such as Ethernet and IP activity) that are used to transmit content via the Internet.

But that doesn’t answer all of Stox’s questions. To him AT&T’s ability to charge him $10 for more Internet access just because he’s hit some cap that’s defined by AT&T and overseen by AT&T without any required disclosure seems anti-consumer. So far, he hasn’t filed a complaint with the FCC, or with the Illinois Commerce Commission, but he did say he had been contacted by Public Knowledge and he might wait for their advice before making any formal complaint. Already the advocacy organization is using the case as an example of why the FCC needs to get more involved in monitoring and asking questions data caps.