Comcast, Charter discuss possible sale of TWC assets

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Cable companies Comcast and Charter are working on a deal for Comcast to purchase Time Warner Cable assets in key markets in New York, North Carolina and New England, sources tell CNBC.

The potential deal, and any deal Comcast and Charter might agree to, is entirely contingent on the success of Charter's proposed acquisition of Time Warner Cable, sources say.

And while Comcast and Charter are close to agreeing to terms, Charter and Time Warner Cable are still far from a deal, sources tell CNBC.

(Read more: Comcast has first video customer growth in 6 years in Q4: CEO)

Both Comcast and Charter declined to comment.

A lot has to happen before Charter would be able to sell Comcast those cable assets. So why are they negotiating now?