Question: What is the primary purpose of the T3-TUNNEL timer in the GPRS Tunnelling Protocol (GTP) across the Gn and Gp interface?
Option 1: To regulate the transmission rate of PDUs between SGSNs for congestion control.
Option 2: To determine the maximum wait time for a response to a request message.
Option 3: To schedule periodic checks for active PDP contexts in an SGSN.
Option 4: To specify the duration after which PDUs are forwarded from the old SGSN to the new SGSN during a context transfer.
Explanation: The T3-TUNNEL timer manages the handover process between SGSNs, ensuring that Packet Data Units (PDUs) are properly redirected to the new SGSN after a certain period following the initiation of the context transfer. This timer's expiration triggers the forwarding of PDUs from the old SGSN to the new one, maintaining continuity of service for active PDP contexts.