I wasn't responding to you or anything you said crutschow. On/off shift keying is the most basic form of ASK, which is what the original poster was asking about. I simply mentioned that on/off keying was prone to noise and that as you call it multi level keying is more reliable, two/multi level ASK becomes on/off shift keying when the 'low' level is lower than the level of detection of the receiver, they're essentially the same thing, with different practical uses.
Due to advances in both analog and digital transceivers, on/off shift keying is effectively obsolete. Not necessarily useless, but still obsolete.
Roff. I fail to see why you mention frequency shift keying when the poster wants to know about amplitude shift keying?