Clarence J. Chandran, chief operating officer (COO) for Nortel Networks Corp and likely successor to president and CEO John Roth, is taking a six-to-12 month medical leave of absence. Chandran has recently undergone surgery to deal with complications arising from a serious stabbing attack he suffered in Singapore in 1997. Roth will assume Chandran's duties in his absence. Based in Boston, Chandran is responsible for day-to-day operations with the Carrier, Service Provider and Enterprise Customers division, including sales, marketing, R&D and customer care. He joined Nortel Networks in 1985 from Bell Canada where he began his telecommunications career in 1973. Chandran was appointed COO in June 2000....