Question: In an MBMS (Multimedia Broadcast/Multicast Service) context, what does the 'Initial_Buffering_Duration' metric primarily measure, and in which unit is it expressed?
Option 1: Time from receiving the last RTP packet to playing completion, expressed in milliseconds.
Option 2: Time from receiving the first RTP packet until playing starts, expressed in seconds (potentially as a fractional value).
Option 3: Total session duration from start to end of playback, expressed in minutes.
Option 4: Data transfer rate during the initial buffering phase, expressed in kilobits per second.
Explanation: The 'Initial_Buffering_Duration' metric measures the elapsed time from when the MBMS client receives the first RTP packet until playback commences. This duration is quantified in seconds, allowing for precision by accommodating fractional values, crucial for assessing initial latency and perceived quality of service.