EarthLink and Time Warner Cable have extended the agreement under which EarthLink sells its broadband Internet service over TWC’s cable modem network.

The agreement was originally an outgrowth of Time Warner’s merger with AOL, as government regulators sought to protect ISP competitors, according to an EarthLink spokesman.

Since the original agreement was announced in November 2000, EarthLink has done well selling its service to Time Warner Cable customers, who now amount to one-third of its 1.7 million broadband customers, the spokesman said.

“With the Brand X decision and FCC rulings, cable companies are not required to do this,” he said. “The fact that we renewed the contract demonstrated the success of this relationship. We like to think this is the model that other companies should follow.”

Thus far, EarthLink has signed up only one other major cable MSO – Comcast – in two of its markets, Boston and Seattle.

The Brand X decision was a U.S. Supreme Court ruling that basically protected the cable industry’s refusal to provide open access on its networks to competing services.

EarthLink currently has access to Time Warner Cable networks passing 19 million homes, and that number will expand once the division of Adelphia’s cable network between Time Warner Cable and Comcast is complete.