Question: In a GPRS network, a Mobile Station (MS) in STANDBY or PMM-IDLE state, switching from A/Gb mode to Iu mode (or vice versa), wants to send uplink signalling. What procedure must the MS perform before sending this signalling?
Option 1: Immediately send an LLC PDU to establish a connection.
Option 2: Perform a Location Area Update (LAU) procedure for network registration.
Option 3: Send a Service Request message without any prior update.
Option 4: Execute a Routing Area (RA) update procedure before sending signalling.
Explanation: When the MS changes mode and needs to send uplink signalling while in STANDBY or PMM-IDLE state, it must first update its routing area to ensure the network is aware of its current location and mode for efficient signalling and data transmission. This step is crucial for maintaining connectivity and facilitating communication between the MS and the network, ensuring correct routing of messages.