PEMBROKE, Bermuda, March 6 -- Undersea fiber optic cable network supplier TyCom Ltd. said it plans to buy back up to $500 million of its stock. TyCom, a unit of Tyco International, has 520.4 million shares outstanding, of which 14 percent, or about 73 million, are publicly traded. TyCom said the timing and amount of the stock repurchases, intended to enhance shareholder value, would be subject to market conditions and other factors. Earlier, the company said it entered into a $1.25 billion deal with India's DishnetDSL Ltd. to build an undersea fiber optic network between India and Guam that will connect to the United States, providing broadband communications.