Remember net neutrality?

Right, it's that brain-flexing term that refers to the idea that phone and cable companies should treat all of the traffic on their networks equally. No blocking or slowing their competitors, and no fast lanes for companies that can pay more.

In fact, the term itself was so nerdy that it's been "re-branded" as Open Internet.

You might have thought things were kind of settled with net neutrality after the Federal Communications Commission passed hotly debated rules in February that redefined its authority over Internet service providers.

But the new regulations could be undone: The cable and telecom industries have taken the FCC to court.

It's the third time in less than a decade that the FCC's attempts to regulate Internet access have been challenged in court. Three judges at the D.C. Circuit Court of Appeals will decide whether the rules get to stay. Here are a few things to know about the lawsuit:

1. The key question the court will answer is whether the FCC had proper authority to reclassify broadband Internet as a more heavily regulated telecommunications service.

This wonky reclassification approach has been the biggest point of contention in the FCC's latest take on net neutrality.

This court, early last year, threw out the FCC's earlier rules because it ruled they were effectively treating ISPs as if they were providing "telecommunications services," sort of like traditional telephone companies, even though the FCC itself had classified them in the more lightly regulated category of "information service providers."

So this time around, the FCC (with President Obama's weigh-in) decided to reclassify broadband Internet access under what's known as Title II of the Telecommunications Act — considering it like an essential public utility, like landline telephone service in the past century.

Various Internet and venture companies and public interest groups are supporting the FCC in the case, which is brought by cable, wireless and broadband industry associations alongside AT&T, CenturyLink and several smaller providers.

2. Reclassification is at the heart of the industry's legal challenge.

The ISPs say they don't oppose the specific net neutrality rules — no blocking or slowing down of websites and no payments for prioritized delivery of any traffic — but present the new regulatory regime as "arbitrary and capricious," illegal, overbearing and arcane.

One big fear is that the government would at some point decide to dictate prices. But the FCC has said it will "forebear from" this part of Title II.

3.Another part of the new rules the court will consider will be whether mobile Internet and cable Internet should be regulated the same way.

Wireless broadband in the past enjoyed some exemptions from net neutrality rules (including some anti-discrimination and no-blocking rules) to prevent congestion on their networks. The new rules regulate them much the same as their wireline rivals.

Internet content companies say that equality was long overdue, while the wireless industry argues that the FCC didn't follow proper procedure to adopt those rules and that the rules themselves threaten the industry's growth and innovation.

4. Not much has changed since the ruleswent into effect in June.

Telecom lawyers say that's because net neutrality principles were already being followed and nobody in the industry planned to violate them. Also, Netflix — a major factor in how people perceive the quality of their Internet download speeds — has settled its negotiations with several major ISPs to make sure its streaming goes smoothly.

But what about the telecom companies' worries about innovation and investment?

One critic of the rules has suggested a link between the industry's lower capital expenditures and the FCC's new rules, though his findings have been disputed by net neutrality supporters. Economists at a House hearing on the topic said it may be just too early to see any real evidence of any effect the rules may be having.

When FCC Chairman Tom Wheeler was asked about T-Mobile's new unlimited-streaming offer that doesn't count participating video services against data allowances, Wheeler praised it as innovative and competitive. But he also said he'd "continue to watch" how it complies with the new rules. An AT&T executive later said such mixed messages have forced the company to shelve some of its creative ideas.

The FCC has received complaints through its new net neutrality consumer portal, but my previous Freedom of Information requests showed that they tend to get settled without the FCC's involvement. And the FCC hasn't said that it has found any violations.

5.Whatever this court decides, net neutrality will likely end up at the Supreme Court.

Friday's oral arguments are scheduled to last more than two hours, and then the D.C. Circuit Court is expected to rule sometime in the spring.

If the ISPs lose, they're likely to take their case all the way to the U.S. Supreme Court.

If the FCC loses, the agency may do the same depending on the scope of its loss — if it loses on the margins, the commission could consider going back and tweaking the rules, but a bigger loss might lead to the high court.

NPR's Joel Rose contributed to this post.

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