Question: Under what condition(s) is a cell considered 'known' by the User Equipment (UE) for determining the UE Re-establishment delay requirement?
Option 1: The cell has been previously camped on by the UE during network attachment.
Option 2: * a) The UE had radio links connected to the cell in the previous active set, * b) The cell was measured by the UE during the last 5 seconds.
Option 3: The cell is broadcasting the strongest reference signal power in the area.
Option 4: The cell is the UE's current serving cell before radio link failure.
Explanation: A cell is considered 'known' by the UE if either or both of two conditions are met: (a) the UE had an established radio link with the cell in its previous active set, or (b) the UE measured the cell within the last 5 seconds. This impacts the UE Re-establishment delay requirement after a radio link failure.