Comcast customer discovers huge mistake in company’s data cap meter

You probably know that Comcast is hitting subscribers with overage charges of $10 when they exceed their 300GB monthly data caps. But can customers trust Comcast to measure Internet usage accurately? The nation’s largest cable company points to research it commissioned showing that its data metering is usually accurate, but one customer who contacted Ars was able to prove that he was being incorrectly accused of using excessive data.

Oleg, a programmer from Tennessee who prefers that we not publish his last name, said he got repeated warnings from Comcast that he was using too much data. But the traffic logs from his router showed that “I was not even close to Comcast’s cap,” he wrote. Oleg described his saga in a Pastebin posting, a YouTube video, and in e-mails to Ars.

Oleg received warnings in September and another in October, the latter while he was overseas for a multiple-week vacation with his wife. When they returned home on November 9^th, Comcast’s data meter was “showing I used 120 gigs of data, like, while I was gone,” he wrote. Customers can check their usage on Comcast’s website.

Calls with Comcast customer service agents didn’t clear up the problem. “I called Comcast… and was patronizingly informed that ‘it must be somebody stealing your Wi-Fi,’” he wrote. “Possible, but highly unlikely. I’m a software developer, Linux kernel contributor, and I take my home security very seriously.”

Comcast allows customers to exceed the cap in three months before they are charged overage fees. But Comcast’s incorrect metering caused Oleg’s courtesy months to be used up in September, October, and November, he said. The waived charges would have totaled $60 across the three months, and he was on the verge of being charged for real. Oleg got to work trying to prove that Comcast’s metering was inaccurate, and he says he disconnected his cable modem from his home network for six and a half days, relying on an unlimited cellular data plan and tethering for Internet access during that time. During that week, Comcast’s meter claims he used 66GB of data, he wrote.

Comcast admits: We screwed up

Oleg provided us his full name and address so we could check into his situation with Comcast. The company investigated the problem after being contacted by Ars and confirmed that its meter readings were inaccurate. “We have reached out and resolved this,” a Comcast spokesperson told Ars. “There was a technical error associated with his account, which we have since corrected.”

During the week he relied on cellular Internet, Oleg said says he used 8GB of mobile data. “That’s the ‘real’ number, as I tried not to vary the normal about of data I normally consume,” he wrote. “I am not a gamer, and I do not stream anything beyond the occasional YouTube video. In short, I’m not a high-bandwidth user.”

Comcast told Oleg that its system had him confused with another customer, he said. “It turns out their system had my modem MAC address entered incorrectly, there was an off-by-one typo that was hard to see so they were counting data from some modem who knows where,” Oleg told Ars.

Before discovering that mistake, a Comcast customer service rep had told Oleg that the company’s meter is “94.6 percent accurate.” After the truth was revealed, Comcast restored his three courtesy months. Oleg says he would switch broadband providers but Comcast is the only viable option where he lives.

No guarantee that Comcast accurately measures data use

Comcast pays an analysis company called NetForecast to report annually on the accuracy of its Internet usage meters. The latest report released in June of this year said Comcast meters had an average error rate of +0.4 percent to -4.0 percent, meaning that the meters are more likely to undercount data than overcount.

NetForecast tested at 55 homes from January 2014 to April 2015, comparing its own measurements to Comcast’s. The report says that Cable Modem Termination Systems (CMTS) in Comcast facilities count the downstream and upstream traffic for each subscriber’s cable modem, with each modem being identified by its MAC address.