The telecommunications company presented arguments at the US Court of Appeals for the Federal Circuit, asking for a $1.52 judgment against Microsoft to be reinstated.

A San Diego court found the Redmond company liable in February 2007 of infringing on two patents related to MP3 technologies. That judgment came out of a case that was originally filed against Gateway and Dell in 2003, for using MP3 playing software in their computers.

However, this case is not as straightforward. Last August, a district court found that the award was unnecessary after it ruled it wasn't in violation of one of the patents, and that it held a valid license for the other.

That license was valid because Microsoft had signed an agreement with Germany's Fraunhofer Institute, which jointly filed the patent with AT&T. In arguments Monday, Microsoft lawyers cited this agreement, saying it should still be valid.

AT&T spun off Lucent in 1996. Ownership of most of the company's patent portfolio went to Lucent, and Alcatel then acquired Lucent ten years later.

It does not seem as if Alcatel-Lucent is necessarily arguing that Microsoft does not hold that license. What it is disputing is the "new work" added to the patent, which Redmond is apparently using in its Windows Media Player.

Neither company has yet provided comment on Monday's developments.