It is a fundamental principle of Internet libertarianism that carriers should not discriminate in how they treat packets based on the content of those packets. This "net neutrality" principle is easier to describe than to formalize, however.
In the US we have had what might be called telegraph neutrality and telephone neutrality rules. There have been laws preventing the telephone company from, for example, dropping calls from the DNC headquarters but not the RNC headquarters. It's an old story, and the whining about a "government takeover of the Internet" is just nonsense. (See p. 314 of Blown to Bits for more on this.)
Today the FCC passed some neutrality rules, after a long delay. It's not everything that everyone could have wanted, and Public Knowledge has already sent me an email grieving the loss of an opportunity. I'm not so disappointed. In fact, I am mainly worried that even these rules will be challenged in court, by telcos and cable companies who will insist that they own the damned wires and should be allowed to decide what goes through them. The real problem is that it will be hard to get the new Congress to give the FCC the authority it needs to make rules like these. And that will in the long run be bad for new businesses, while good for the existing near-monopoly players in the communications world.