Question: In which scenarios is GTP T-PDU tunnelling applicable from the old Serving and Packet Data Network Gateway (SGW) to the new or forwarding SGW, in the context of Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access?
Option 1: During a S1-based Handover procedure without SGW Relocation.
Option 2: Exclusively for inter-RAT handovers without SGW Relocation.
Option 3: During a S1-based Handover procedure with indirect forwarding, or inter-RAT handover with SGW Relocation, and also during TAU/RAU with SGW change when using indirect data forwarding.
Option 4: Only for Tracking Area Update (TAU) procedures without SGW change.
Explanation: GTP T-PDU tunnelling between old and new/forwarding SGWs is specifically applicable in scenarios involving indirect forwarding during handovers that may include a change in the serving gateway, as well as during Tracking Area Updates/Routing Area Updates with a Serving Gateway change when indirect forwarding is utilized to forward downlink data, ensuring continuity of service and efficient handling of buffered data.