Question: In a UMTS network, when a UE (User Equipment) in idle mode initiates an LCS (Location Services) request for its own location, what is the first step it takes to communicate with the SGSN (Serving GPRS Support Node)?
Option 1: The UE sends an LCS PS-MO-LR Location Services invoke message directly to the SGSN.
Option 2: The UE requests a PS (Packet Switched) signalling connection and sends a Service Request indicating signalling to the SGSN via the RAN (Radio Access Network).
Option 3: The UE establishes a voice call to initiate the location services request.
Option 4: The UE sends a Location Update message to the RAN, which then forwards it to the SGSN.
Explanation: In UMTS, for a UE in idle mode to initiate any packet switched service (including LCS), it first needs to establish a signalling connection. This is done by requesting a PS signalling connection and sending a Service Request to the SGSN via the RAN, as specified for idle to active state transitions in packet switched domain operations. Only after this connection is established can the UE proceed with specific service requests, such as LCS.