Basically, there were three aspects of dub that influenced dubstep. The most important was playing the instrumental versions of vocal garage tracks, which was a little like what dub was to reggae - the instrumental of a full vocal.The second was dub as a methodology, which, for me, is apparent in all dance music: manipulating sound to create impossible sonic spaces using reverb, echo and such. The third is the influence of the genre called dub. (It became a cliché actually, through sampling old Jamaican films and soundtracks, and adding vocal samples.)