The US government's latest "Measuring Broadband America" report shows that many Internet customers aren't getting the speeds they pay for.

That in itself isn't a surprise, but the Federal Communications Commission report released today shows that while ISPs on average generally deliver what they promise, some are much better than others at providing advertised speeds to their entire customer base.

For example, 95 percent of Verizon FiOS (fiber-to-the-home) customers got at least 101 percent of the download speeds they paid for. (That's excluding Netflix problems caused by financial disputes—we'll get to that later.) Ninety-five percent of Cablevision customers got at least 117 percent of advertised download speeds, and 95 percent of ViaSat's satellite customers got at least 126 percent of advertised speeds. Comcast, the nation's largest broadband provider with 21 million subscribers, delivered more than its advertised speeds to 90 percent of customers and at least 98 percent of advertised speeds to 95 percent of customers.

Verizon DSL performed much worse. Fifty percent of Verizon DSL customers received at least 92 percent of their advertised speeds, and 90 percent of customers received at least 50 percent of their advertised speeds. That means 10 percent of customers got less than 50 percent of what they paid for.

DSL providers not only promise worse speeds than cable and fiber but are less likely to deliver the lower speeds they advertise. That can be seen in the numbers for Verizon's DSL services and others like Frontier, Windstream, and CenturyLink.

For AT&T, 50 percent of customers received at least 99 percent of their paid-for speeds, while 70 percent received at least 86 percent of their advertised speed. That means 30 percent of AT&T customers got less than 86 percent of their advertised speed. The numbers show that 5 percent of AT&T customers got less than 62 percent of their paid-for speed.

Unfortunately, the report does not distinguish between AT&T's DSL and its fiber-to-the-neighborhood service, the latter of which offers much higher speed guarantees. The FCC said it was unable to distinguish between AT&T's different technologies in its testing. Still, broadband providers should give all of their customers the speeds they pay for, whether that's 6Mbps or 60Mbps. AT&T's numbers on that score were generally worse than its rivals. AT&T is the country's second largest broadband provider, with 16.5 million subscribers.

Here is the full chart:

Tests were conducted in September 2013 with "Whitebox" devices that perform automated measurements and were distributed to 10,000 customers around the country. Download speed tiers ranged from 1Mbps to 75Mbps. The average advertised service tier was 21.2Mbps, up from 15.6Mbps the previous year. "Sustained download speed" is defined as "throughput in Mbps utilizing three concurrent TCP connections measured at the 25-30 second interval of a sustained data transfer."

Things look better if we only look at averages for each ISP rather than the percentile distribution:

The above chart "compares upload and download performance during peak usage periods across all ISPs," the FCC report said. "All ISPs, except for Verizon DSL, CenturyLink, Frontier DSL, and Windstream, meet 90 percent of performance or better, on average, during peak periods. Notably, these four ISPs use DSL technology."

Verizon DSL posted the biggest year-over-year decline of any service. While Verizon DSL's actual download speed was 88 percent of its advertised speed in last year's report, it fell to 83 percent this time. Across all providers, ISPs are delivering 101 percent of advertised speeds, up from 97 percent last year. The biggest jumps were CenturyLink moving from 82 percent to 95 percent, Insight going from 85 percent to 94 percent, and AT&T going from 87 percent to 94 percent.

Despite the averages, another metric helps show that many customers aren't getting advertised speeds all of the time. This one looks at what 80 percent of customers experience 80 percent of the time.

"Cablevision, for example, delivered 100 percent or better of advertised speed to 80 percent of our panelists 80 percent of the time during peak periods, and about half the ISPs delivered less than about 90 percent or better of the advertised speed for 80/80," the FCC wrote. "However about one-third of the ISPs delivered only 60 percent or better of advertised speeds 80 percent of the time to 80 percent of the consumers."

Frontier DSL, Verizon DSL, and Windstream were the worst performers in this metric, which you can see in the blue lines in this chart:

This follows a wider trend of DSL lagging behind its more modern competition. "On average, during peak periods DSL-based services delivered download speeds that were 91 percent of advertised speeds, cable-based services delivered 102 percent of advertised speeds, fiber-to-the-home services delivered 113 percent of advertised speeds, and satellite delivered 138 percent of advertised speeds," the FCC said. "These results suggest that many ISPs are meeting established engineering goals for their respective technologies."

"DSL, unlike cable and fiber technologies, is strongly dependent upon the length of the copper wire (or “loop”) from the residence to the service provider’s terminating electronic equipment, such that obtaining higher data speeds would require companies to make significant capital investments across a market area to shorten the copper loops," the FCC further noted. "On the other hand, both fiber and cable technologies intrinsically support higher bandwidths and can support even higher speeds with more incremental investments."

DSL lagged behind fiber-to-the-home and cable in terms of latency. While satellite delivered on its promised Mbps, its latency was naturally worse than Earth-based systems. "ViaSat had a measured latency of 671.1ms, approximately 19 times the terrestrial average," the FCC said.

Nearly all providers delivered lower throughput to customers during the evening, when online video watching tends to increase:

Interconnection congestion

As mentioned earlier, the reported numbers do not account for congestion at network peering points that occurs due to money disputes between ISPs and Netflix. Poor results apparently caused by interconnection congestion were treated as anomalies and not included in the report.

However, the FCC released raw data on congestion and said it will follow up with something more formal later this year. "The FCC is also taking steps to better understand the issues that presented themselves, including by analyzing network impact on video service providers such as YouTube, Hulu, and Netflix and others and requesting more information from ISPs and video providers about peering issues," the FCC said. "We are working to develop tools that measure and validate how these types of congestion issues affect the consumer experience. We expect to have instituted additional testing methodologies providing more information on network congestion and peering by winter 2014."

As we've reported, the FCC is reviewing the paid peering deals that Netflix struck with Comcast and Verizon. Although Netflix is paying both of those ISPs for direct interconnection, Verizon hasn't been able to set up enough connections to relieve its customers' Netflix problems yet. AT&T customers are also getting poor Netflix quality because AT&T and Netflix are still fighting over money.