Microsoft Corp has filed a lawsuit in a patent fight involving Lucent Technologies Inc., Gateway Inc. and Dell Computer Corp., after being asked to intervene because the products involved use its own technology.

Lucent filed a claim against Gateway in the U.S. District Court for the Eastern District of Virginia in June last year, claiming that some Gateway products incorporating Microsoft technology infringed Lucent-owned patents. Lucent also targeted Dell, in the District Court of Delaware, with a similar patent suit last year, according to court documents.

In October, the Gateway case was moved to California, according to court documents available on the District Court's Web site.

Several of the products involved use Microsoft technology, and in February Microsoft was ordered by Judge Barry Moskowitz, of the Southern District of California, to intervene as a defendant and counterclaimant.

On Tuesday Microsoft filed a lawsuit requesting that the District Court declare invalid 13 patents that Lucent claims to hold. The patents cover audio and video coding as well as position-sensed stylus and touch-screen form-entry technology, according to court documents.

These patents, Microsoft said in its filing, are "not infringed and are invalid, and ... some are unenforceable."

Lucent responded on Wednesday with a request for a jury trial, according to further court documents.

"When we spoke to Microsoft about this, we said that we were asking for a fair return on our technology," Lucent spokeswoman Mary Lou Ambrus said Friday. "Since the beginning of Lucent, we have always tried to maximize the value of our intellectual property."

Ambrus refused to comment further on the case, saying she would not speculate on what would happen next in the legal battle.

Microsoft was not immediately able to comment.