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Avaya officials earlier this week confirmed that the networking vendor’s President and CEO Lou D’Ambrosio will step down for medical reasons.

"Lou has been a guiding force at Avaya during his six-year tenure, the last two as CEO," said Dave Roux, co-founder of technology investment firm Silver Lake and non-executive chairman of Avaya, in a statement. "He has shaped a compelling strategy, built a strong team, and led the company through important technology transitions to market share leadership. We know he will attack this personal challenge with the same winning spirit and determination he has brought to the toughest business challenges."

While the company searches for a new chief executive, D’Ambrosio’s post will be filled by Silver Lake executive Charles Giancarlo, the former Chief Development Officer at Cisco and a popular personality among networking channel resellers. Giancarlo had been widely  considered the heir apparent to Cisco CEO John Chambers before resigning in Dec. 2007 to join Silver Lake.

"It has been a true privilege to serve the customers and team of Avaya,"  D’Ambrosio said in the statement. "I have been blessed to lead a company that has clear technological leadership, a wonderful customer franchise, and the most dedicated team in the industry. I will be passionately rooting for Avaya and proudly watching the company thrive."

Giancarlo will assume the Avaya CEO and president role full time and will remain in that role until a successor is named. D’Ambrosio will maintain an advisory role to the company, according to Avaya officials.