Question: In which of the following network deployment scenarios is the Idle Mode Signalling Reduction (ISR) function utilized?
Option 1: GERAN-only network deployments
Option 2: UTRAN-only network deployments
Option 3: E-UTRAN-only network deployments
Option 4: Deployments involving both 3GPP radio access technologies (e.g., between GERAN and E-UTRAN or between UTRAN and E-UTRAN)
Explanation: The Idle Mode Signalling Reduction (ISR) function reduces signalling during cell reselection in idle mode when transitioning between different types of 3GPP radio access networks, enhancing network efficiency and user experience in heterogeneous environments with multiple 3GPP radio access technologies.