Question: What is the primary purpose of the STR command in the context of DIAMETER sessions between the GGSN and BM-SC?
Option 1: To establish a new DIAMETER session for an MBMS bearer service.
Option 2: To terminate a DIAMETER session, indicating that the GGSN would like to be deleted from the distribution tree of a particular MBMS bearer service.
Option 3: To activate a Trace Session in the BM-SC and initiate the associated Diameter Session.
Option 4: To modify the QoS parameters for an existing MBMS bearer service.
Explanation: The STR command is used to terminate a DIAMETER session, which informs the BM-SC that the GGSN would like to be deleted from the distribution tree of a particular MBMS bearer service. This is typically done when the last MBMS UE context for the MBMS bearer service is deleted or when an individual UE requests to leave the MBMS bearer service.