MCI’s telecommunications network is expanding.

The company said it will increase its transmission capacity by more than 80% by the end of this year, partly with a new optical fiber system. The new optic lines, which will link points in the Midwest with MCI’s existing New York-Washington system, will provide “high-quality, high-speed transmission of voice, data and broadcast” traffic, the company said. MCI did not reveal the cost of the expansion but said it has purchased more than 100,000 miles of fiber.