LNP stands for Local Number Portability. This is the SS7 TCAP service that allows you to take you phone number with you, especially when changing local phone companies. The process is very similar to the other TCAP services. The SSP of the person originating the call checks to see if the NPANXX of the number dialed is a portable range. If so a query is launched to an SCP to get the LRN of the number. The SCP returns this information and the ISUP call is setup based on this.