The acronym for Custom Local Area Signalling Service. This is the SS7 service that allows automatic call return (*69) and repeat dialing (*66). For *69 the person recieving the call does not answer. The recipiant then picks up the phone and dials *69. The SSP serving them initiates a query on the last number to call the line to an SCP. The SCP does a lookup to find out where the calling number resides and launches a query to the SCP responsible for that area. This SCP then determines the end SSP and notifies it of the request to initiate a call to the originating number. The SSP then sends a response to the SSP that originated the CLASS query and a normal ISUP call is started.