It is a part of the MAP protocol, e.g. MAP V3 / V4.
The message is used to query a HLR / HSS for customer location and status information. Having the Location and the status (e.g. IMSI attached, detached, etc..) of the customer a CAMEL application (gsmSCF) can decide on what actions can be taken.
For CAMEL you will need a minimum of CAP V2 and MAP V3.