UPDATE 1-Ciena takes Nortel unit auction to 2nd day -sources

* Optical networking, carrier ethernet unit sale continues

* Nokia Siemens/One Equity Partners also bidding -source

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NEW YORK, Nov 21 (Reuters) - The auction for Nortel Network's optical networking and carrier ethernet business went into a second day on Saturday, after Ciena (CIEN.O) 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 $522 million, would be the stalking horse offer for these assets. [ID:nN07462090]

Earlier this week another source familiar with the sale told Reuters that Nokia Siemens Networks and private equity firm One Equity Partners had also jointly bid for the assets. [ID:nN18125510]

Ciena's stock fell sharply after it revealed the proposed deal last month, with analysts saying the rising price and possible equity side of the deal would weigh on investors minds.

Ciena's offer consisted of $390 million cash and 10 million Ciena shares.

Analysts and investors have been concerned about Ciena's offer because the U.S. networking gear maker would have to take significant pains to integrate the Nortel assets.

Although the assets are a good fit for Ciena's portfolio, the deal would weigh down operations, they said.

Nortel, once North America's biggest telecoms equipment maker, filed for bankruptcy protection in January. It is selling off its assets rather than trying to restructure.

One Equity manages $8 billion for JPMorgan (JPM.N) in private equity investments.

Nokia Siemens is a 50-50 venture of Nokia (NOK1V.HE) and Siemens (SIEGn.DE). (Reporting by Anupreeta Das; Editing by Jon Boyle)