Question: In a UTRAN Iu interface, when a Relocation to GERAN Iu-mode fails for CS (Circuit Switching) due to incompatible RAB (Radio Access Bearer), what information does the Target BSC include in the RELOCATION FAILURE message besides the cause value "GERAN Iu-mode Failure"?
Option 1: UE: User Equipment Identity
Option 2: GERAN Classmark IE (Integrity Protection Information Element)
Option 3: Source RNC (Radio Network Controller) ID
Option 4: Failed RAB Configuration Details
Explanation: When a Relocation to GERAN Iu-mode fails for CS due to the Target BSC's inability to provide an appropriate RAB matching the GERAN BSC Container IE, the Target BSC reports this failure with specific details. Including the GERAN Classmark IE in the RELOCATION FAILURE message provides crucial information about the UE's (User Equipment) capabilities, aiding in diagnosing or handling the relocation failure, which is essential for efficient network operation and potential retries or alternative routing decisions.