Cisco Systems Inc., the world's biggest maker of networking equipment, said its data-center chief, Jayshree Ullal will leave the company.

John McCool, one of Ullal's deputies, will take over her job, said Cisco spokeswoman Elizabeth McNichols.Ullal's is the third top official to leave in about 15 months.

Ullal joined Cisco with the acquisition of Crescendo Communications Inc. in 1993. She went on to become one of Chief Executive Officer John Chambers's top managers, running a business that brought in more than $12 billion in sales last year.

Ullal, 47, was a member of the nine-person development team that reports to Chambers. McCool will take her spot in that group.

Ullal's departure follows the December resignation of Chief Development Officer Charles Giancarlo, who quit to join private- equity firm Silver Lake. Mike Volpi, a senior vice president who left in February 2007, became CEO of Internet television provider Joost in June.

Cisco fell 21 cents to $25.49 today on the Nasdaq Stock Market. The shares have dropped 5.8 percent this year.

Cisco Systems