Shares of Adtran ( ADTN) fell hard on Tuesday even after the networking equipment maker topped second-quarter earnings forecasts.

The Huntsville, Ala., company said late Monday that it had a net profit of $22.4 million, or 34 cents a share, in the second quarter, rising from a profit of $19.8 million, or 28 cents a share, in the year-ago quarter. Sales increased 6% from last year to $131.1 million. Analysts expected Adtran to earn 30 cents a share on revenue of $127.9 million, according to a poll by Thomson Reuters.

"Despite a slow enterprise environment and constrained spending by some carrier customers, Adtran continued to perform well in executing on existing business and securing new opportunities for future growth," said CEO Tom Stanton in a statement. Still, Adtran shares fell 5% to $23.54 early Tuesday.

Adtran added that the provision for income taxes in the second quarter of 2008 "continued to be unusually high due to delays in federal legislation required to extend research tax credits" for the year.

The company also declared a cash dividend for the second quarter of 2008 of 9 cents a share to be paid to holders of record at the close of business on July 31.

Among other networking and communications equipment makers, Nortel Networks ( NT) dropped 4.2%, Motorola ( MOT) slid 2%, and Cisco ( CSCO) dipped 1.5%. Meanwhile, Alcatel Lucent ( ALU) tacked on 0.2%.

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