Question: In which of the following security contexts is the function used for retrieving the Short Term Key (VSTK) for establishing group calls, utilizing authentication data specific to that context?
Option 1: EPS Security Context, leveraging EPS authentication vectors (RAND, XRES, CK, IK, AUTN)
Option 2: VGCS/VBS Security Context, using VGCS/VBS authentication data
Option 3: GSM Security Context, with GSM authentication data for non-3G capable networks
Option 4: MBMS Security Context, during the MSK Update Mode procedure
Explanation: The correct answer is Option 2 because the function is specifically used in the VGCS/VBS security context for retrieving the VGCS/VBS Short Term Key (VSTK), essential for establishing VGCS/VBS calls, distinct from EPS, GSM, or MBMS contexts serving different telecom network purposes.