Question: What is the primary purpose of the IMSI detach in a GPRS network, and how can a non-GPRS-attached Mobile Station (MS) perform it?
Option 1: To deactivate all active PDP contexts; a non-GPRS-attached MS performs it by sending a Detach Request to the SGSN.
Option 2: To inform the network of a change in the MS's location; a non-GPRS-attached MS performs it through SMS.
Option 3: To temporarily suspend GPRS services; a non-GPRS-attached MS performs it by automatically reconnecting after a timer expires.
Option 4: To completely disconnect from SGSN-based services at the subscription level; a non-GPRS-attached MS performs it as already defined in A/Gb mode or Iu mode.
Explanation: The IMSI detach is primarily used for the Mobile Station (MS) to inform the network that it no longer wishes to access services tied to its International Mobile Subscriber Identity (IMSI), effectively disconnecting at a subscription level. For an MS not currently attached to GPRS, this procedure follows existing definitions for A/Gb mode or Iu mode, which are standard protocols for handling such detachments without requiring a GPRS attachment. This highlights the flexibility in managing network access based on the device's current state and service needs.