Last year, Charter was punished by the Federal Communications Commission because it had spent two years preventing customers from using their own modems. As a result, the nation’s second-biggest cable company must now follow a shortened testing procedure to verify third-party modems and file compliance reports every six months detailing its efforts to let customers attach their own modems to its network. The company also had to pay a $640,000 fine.

The FCC's rules are clear: cable companies must let customers use their own equipment (including modems) unless it isn’t compatible with the network or unless it would cause some kind of harm or was designed to let customers obtain services they didn't pay for. But if you’re a customer of a company that simply refuses to let you use a third-party modem, getting what you want is not easy.

Elbert Davis of Crown City, Ohio, is a customer of Armstrong, a much smaller cable company with about 800,000 subscribers. He owns a Motorola/Arris Surfboard SB 6121 modem that he'd like to use instead of the Arris CM820 supplied by Armstrong. But the cable company won't allow it, despite offering no proof that it would harm the network or is incompatible. (The Surfboard is a DOCSIS 3.0 device certified by CableLabs, the cable industry's equipment testing body.)

Davis complained to the FCC about the modem issue and data caps months ago, without making any progress, and more recently contacted Ars.

"The market should decide which modems will be used, not the monopoly ISP," Davis told Ars.

Unlike some other cable companies, Armstrong doesn't charge a modem rental fee. One could argue that this means customers get the necessary equipment without paying extra. But you could also argue that the policy prevents customers from saving money by using their own equipment. (Davis previously used his Surfboard modem with Suddenlink, another ISP, allowing him to save $5 per month. He switched to Armstrong when he moved to Crown City in August 2015.)

"I think Armstrong should charge consumers less for not using Armstrong equipment," Davis said. "I believe by claiming it's free, even though consumers are charged if the modem is not returned, and not billing separately for the rental, Armstrong is trying to circumvent the FCC rule permitting consumers to use their own modems, and minimize FCC complaints." (Armstrong does permit use of third-party wireless routers, and Davis uses his own router in order to avoid a $5-per-month router rental fee.)

Armstrong's advertised broadband prices range from $30 to $150 a month for download/upload speeds ranging from 4Mbps/1Mbps to 300Mbps/20Mbps.

Armstrong imposes a 200GB monthly data cap on Internet-only customers who subscribe to lower speed tiers and charges $10 for each additional 50GB allotment. This is much more restrictive than the 1TB cap used by Comcast and some other providers. Armstrong imposes its lowest data caps on Internet customers who don't also subscribe to TV service, making it harder to replace cable TV with online streaming.

Davis' family uses online streaming services instead of cable TV but watches video judiciously to avoid overage charges. "We’ve disabled any streaming service on our children’s TVs," and on tablets used by the kids, Davis said. "We watch both Netflix and Hulu in the lowest possible [quality] settings" in order to use less data.

Armstrong declines to answer questions

Armstrong has certified only three modems for residential use and doesn't allow customers to connect any others to its network. We sent Armstrong a list of questions about its modem-testing process and asked the company to explain why its policy does not violate the FCC rule that compatible third-party modems must be allowed unless they cause electronic or physical harm to the network or could be used for unauthorized receipt of service.

One of the questions we asked Armstrong includes why it can't support any modem that uses the same version of DOCSIS as its cable system. RCN, for example, gives customers instructions on how to avoid monthly rental charges. Instead of only allowing a few specific routers, RCN tells customers to get just about any modem supporting the DOCSIS 3.0 standard. We also asked why Davis' specific modem model isn't allowed.

Armstrong declined to answer any of our questions and instead provided a general statement:

"As a regional, privately-held provider, Armstrong as a matter of policy does not comment in the press regarding either customer issues or company regulatory policy," Armstrong VP of Cable Marketing David Wittmann told Ars. "As a general statement, Armstrong is immensely proud of our 50-year track record of providing excellent, award-winning customer care and our unflinching compliance with all federal, state and local regulations... With respect to our customer, we look forward to addressing his needs directly with him, should he choose to contact us regarding this or any other broadband-related matter."

Davis did contact Armstrong about this issue. He provided Ars with screenshots from his chat with a customer service representative. The rep told Davis, "We normally discourage customers from purchasing their own modems, since many of them are not compatible with our network."

"Armstrong is not able to support your brand of modem," the rep also said, while noting that Armstrong supports a few other DOCSIS 3.0 modems from Arris and Hitron.

“Customers must use Armstrong's modem”

Davis also provided us Armstrong's official responses to his FCC complaints, from back in April and June of 2016.

"Mr. Davis mentions in his complaint that Armstrong refused to install his combination modem/router when connecting service. Armstrong's policy permits its customers to use their own router, however, customers must use Armstrong's modem which is provided free of charge," Armstrong's complaints response team wrote to the FCC and Davis in the April letter. That is not totally correct, since Armstrong does allow three models of modems that customers can purchase on their own.

The next letter from Armstrong in June says that an Armstrong executive told Davis that he "may indeed install non-harmful retail cable modem hardware, consistent with FCC rules," but provided no evidence that Davis' modem would harm the network. The letter said that "Armstrong believes the complaint has been resolved."

On the data cap issue, Armstrong pointed to FCC official statements calling data caps a reasonable bandwidth management tool and noted that it is following a practice used by larger ISPs. "Many of the largest Internet service providers in the country have established such limits in the last few years and such policies are rapidly becoming industry standard," Armstrong wrote.

An FCC spokesperson declined to comment on whether Armstrong is violating any rules.

Modem makers pay cable companies for testing

Charter's punishment by the FCC came in response to a complaint from modem maker Zoom Telephonics. Davis recently contacted Zoom CEO Frank Manning about Armstrong, and Manning told Davis that he'd try to help and would forward the information to the appropriate FCC officials.

Blocking customer modems is "very much against the intent of Section 629 [of the Communications Act], which was to encourage an open retail market. In my view, barring customers from using suitably certified customer-supplied modems violates section 629," Manning told Ars.

Former FCC Chairman Tom Wheeler cited Section 629 requirements when he tried to impose rules making it easier for cable TV customers to avoid set-top box rental fees. But he wasn't able to get the controversial idea passed before the presidential election, and new Chairman Ajit Pai, a Republican, took the plan off the table.

While Zoom put significant resources into fighting Charter over modem attachments, it isn't planning a similar battle against Armstrong. Manning believes that small cable companies should be expected to follow the rules, just like big companies. But there's a greater "return on investment" from fighting a big cable company like Charter than a much smaller one like Armstrong, he said. "I think it’s a question of whether it’s worth the energy to fight Armstrong," he said.

Zoom still believes that Charter should charge a separate modem fee so that customers can save money by using their own equipment. (The FCC considered making this a requirement last year, but decided not to.)

"We’ve spent a lot of money in opposing Charter to get where we are now, and some of the things we asked for we still don’t have," Manning said.

While individual consumers like Davis can file an FCC complaint, Manning said it's "tough" for a single person to get a major issue resolved at the commission. He fears that enforcement may become more lax under the new Republican administration. (An FCC spokesperson told Ars that consumer complaints can trigger investigations.)

The testing that some cable companies do to make sure that modems are compatible with their networks is "quite extensive," and Zoom pays CableLabs, Comcast, and other cable companies to go through their testing, Manning said.

Zoom clashed with Comcast over modem attachments years ago, but the companies agreed to a settlement in 2011. Comcast has been great to work with ever since then, Manning said.

"We very much like the way they [Comcast] approach the market, and Time Warner Cable was similar before Charter bought them," Manning said.

“Service providers need to follow the law”

Comcast provides customers with instructions on selecting a third-party modem and activating the device. It's not only giant cable companies that do this. RCN encourages third-party modems, as we mentioned earlier, and a small cable company called Blue Ridge tells its customers that "most DOCSIS 2.0 and 3.0 cable modems and routers should function" on its network.

Manning hasn't studied the Armstrong case closely but noted that some cable companies simply allow just about any CableLabs-approved modem. The CableLabs certification involves "very expensive and extensive testing that typically takes months," he said.

"We think it's an important issue," Manning said. "Service providers need to follow the law and the FCC needs to enforce it."

Disclosure: The Advance/Newhouse Partnership, which owns about 13 percent of Charter, is part of Advance Publications. Advance Publications owns Condé Nast, which owns Ars Technica.