Question: Upon receiving an SGsAP-LOCATION-UPDATE-REQUEST message with an unknown IMSI and no TMSI-based NRI container, how does a VLR (not supporting 'Intra Domain Connection of RAN Nodes to Multiple CN Nodes') typically retrieve the necessary UE context in a telecom network?
Option 1: The VLR derives the context from the provided Location Area Identifier.
Option 2: The VLR retrieves the MM (Mobility Management) context of the UE from the HSS (Home Subscriber Server).
Option 3: The VLR requests the context from the serving CS (Circuit Switched) domain operator directly.
Option 4: The VLR uses local caching to retrieve the UE's context.
Explanation: In a telecom network, when a VLR receives an update request with an unknown IMSI and lacks specific routing info, it relies on the HSS for subscriber data and mobility management context. This ensures accurate handling of the UE's location update, facilitating seamless communication services. The HSS acts as a central repository for such information, making Option 2 the correct approach in this scenario.