Cablevision is biggest loser in FCC broadband speed report

Update. The FCC released its first-ever “Measuring Broadband America” report (PDF) on Tuesday, offering consumers a detailed look at the performance of the 13 biggest ISPs. The good news is that most ISPs actually deliver their bits within 80 percent of the advertised speed. Even during peak hours, when America is busy streaming movies from Netflix, (s NFLX) most customers won’t notice much of a difference. But there’s bad news for Cablevision (s CVC) customers: Your ISP fared much worse than any of the other major broadband provider.

Just take a look at this chart depicting the sustained download speeds to see how bad things really are in Cablevision households:

Looks like the only time of day Cablevision customers really get what they paid for is during the morning hours. Or in the more diplomatic words of the FCC: “Results differ significantly among different ISPs.”

To be fair, Cablevision wasn’t the only ISP that wasn’t quite able to deliver what it promised. AT&T (s T) also scored below advertised performance, with customers on average only getting around 80 percent of what they signed up for. However, AT&T’s performance was much more reliable throughout the day, with peak speeds only differing slightly from 24-hour sustained download speeds:

The good news for Cablevision customers, as well as broadband users in general, is that upload speeds tend to oftentimes exceed advertised speeds:

The FCC’s report is based on data gathered by special routers sent to 9000 consumers in March 2011. The agency notes that the speeds mentioned in the report are national averages, and do not reflect specific speeds in any given market. One should also keep in mind that advertised speeds differ by access technology and broadband tier, meaning that someone with a slow DSL line may still be worse off than someone with a top of the line Cablevision package.

Update: A Cablevision spokesperson disputed the findings in an emailed statement: “Cablevision delivers some of the fastest Internet connections in the country, on our basic tier, two higher levels of service and our WiFi network and this report simply does not reflect the experience of our nearly 3 million broadband customers. Our high-speed Internet product leads the nation in consumer adoption and has consistently won top ratings in much broader and more extensive consumer surveys conducted by J.D. Power & Associates, PC Magazine and others.”

Update 2: The FCC’s final report features a slightly tweaked chart depicting the sustained download speeds over a 24 hour period. We updated the article with the new chart. For reference, the original chart can be found here.