Holmes claims that he obtained a copyright for his song “Dazed and Confused” in 1967, two years before Led Zeppelin recorded their own “Dazed and Confused.”
The Yardbirds, Page's previous band before Zeppelin used to perform a slightly different version as "I'm Confused", which Page adapted for the version included on 'Led Zeppelin', the band's first album in 1969. In 1967 Holmes opened up for The Yardbirds in New York, where Page heard the song.
Led Zeppelin have been sued before over claims of plagiarism, primarily by blues artists such as Willie Dixon, or their record labels. If Holmes’ federal lawsuit is successful, he can only sue Page for damages from the past three years, due to the statue of limitations.
To compare the two songs, first here's Holmes' version, from his 1967 debut album ' "The Above Ground Sound" Of Jake Holmes'.
Led Zeppelin's classic version from 'Led Zeppelin' 1969