The auction for Nortel Network's optical networking and carrier ethernet business went into a second day on Saturday, after Ciena called for a break in the auction late on Friday, two sources said.

Last month Nortel Networks Corp, the bankrupt Canadian telecommunications equipment maker, said that Ciena's cash-and-stock bid, worth some $526 million, would be the stalking horse offer for these assets.

Earlier this week another source familiar with the sale told Reuters that Nokia Siemens Networks and private equity firm One Equity Partners had also bid for the assets.

(Reporting by Anupreeta Das; Editing by Jon Boyle)