Question: In an MBMS User Service with multiple PLMN areas, what is the primary purpose of the 'alternative-tmgi' attribute at the session level?
Option 1: To replace the default TMGI in the MBMS bearer mode declaration attribute for all UEs.
Option 2: To list alternative TMGIs, enabling UEs to determine service availability based on their current PLMN-ID location.
Option 3: To specify a unique TMGI for each MBMS bearer service instance within a single PLMN area.
Option 4: To indicate the absence of an MBMS User Service in all PLMN areas.
Explanation: The 'alternative-tmgi' attribute facilitates UEs in identifying if a service is available at their current location by matching the TMGI derived from their PLMN-ID with either the default TMGI or one of the alternative TMGIs listed, ensuring seamless service accessibility across different PLMN areas.