Question: During an intra-LTE S1 handover with DAPS Handover applied, what is primarily transferred from the source eNB to the target eNB via the MME through the eNB Early Status Transfer procedure for each affected E-RAB?
Option 1: Entire downlink SDU packets to ensure seamless transmission
Option 2: Updated security keys for encrypted data protection
Option 3: Handover trigger conditions for more efficient handovers
Option 4: COUNT of the first downlink SDU (or for discarding already forwarded SDUs with time-based triggers)
Explanation: The eNB Early Status Transfer procedure is crucial for maintaining data integrity and preventing duplication or loss during handovers. By transferring the COUNT of the first downlink Service Data Unit (SDU) for each affected Evolved Radio Access Bearer (E-RAB), the target eNB can correctly manage the sequence of downlink data, ensuring continuity of service. In scenarios with time-based trigger conditions, this also facilitates the informed discarding of already forwarded SDUs, preventing unnecessary processing.