Question: In a mobile network, when indirect data forwarding is utilized during a Tracking Area Update (TAU) or Routing Area Update (RAU) interaction with a Gn/Gp Serving GPRS Support Node (SGSN), what is the primary purpose of GTP T-PDU tunnelling between the old SGSN and the forwarding Serving Gateway (SGW)?
Option 1: To establish a new bearer for uplink (UL) data transmission from the User Equipment (UE) to the SGW.
Option 2: To facilitate direct communication between the UE and the old SGSN for seamless handover.
Option 3: To manage signaling for Quality of Service (QoS) adjustments in the forwarding SGW.
Option 4: To forward downlink (DL) data buffered in the old Gn/Gp SGSN to the UE via the forwarding SGW.
Explanation: GTP T-PDU tunnelling in this context is specifically used for indirect data forwarding, ensuring that any downlink data buffered at the old SGSN during a TAU/RAU interaction is efficiently forwarded to the UE through the new path established via the forwarding SGW. This mechanism prevents data loss and ensures continuity of service for the UE.