Question: What is the primary purpose of the Discard Timer Information Element (IE) in the UTRAN Iur interface Radio Network Subsystem Application Part (RNSAP) signalling?
Option 1: To schedule MAC-hs SDU transmissions based on priority in HSDPA Priority Queues.
Option 2: To define the time to live for a MAC-hs SDU, enabling the removal of out-of-date SDUs from HSDPA Priority Queues.
Option 3: To manage handover decisions between different Radio Network Controllers (RNCs) in UTRAN.
Option 4: To allocate resources for MAC-hs SDUs in the uplink direction.
Explanation: The Discard Timer IE indicates how long a MAC-hs SDU remains valid after arriving at an HSDPA Priority Queue, allowing efficient management of queue contents by discarding outdated SDUs, thus preventing unnecessary resource occupation or processing, directly impacting UTRAN's HSDPA service efficiency and performance.