Question: What happens to the GTP-U PDU sequence numbers when a PDU is transferred over multiple GTP tunnels between GGSN, SGSN, and SRNS/SBSS in a GPRS network?
Option 1: The SGSN generates new sequence numbers for each tunnel on both downlink and uplink.
Option 2: The original GTP-U PDU sequence numbers allocated by the GGSN (downlink) and SRNS/SBSS (uplink) are kept unchanged across all tunnels.
Option 3: Sequence numbers are incremented by each network element (GGSN, SGSN, SRNS/SBSS) for every tunnel transition.
Option 4: The use of sequence numbers is discontinued when a PDU crosses from one tunnel to another.
Explanation: Maintaining consistent sequence numbering across multiple tunnels ensures orderly delivery and prevents packet misordering, which is crucial for reliable data transfer in GPRS networks. This approach simplifies network operations by avoiding the need for resequencing at each hop, thus preserving the original sequence allocated by the source (GGSN for downlink, SRNS/SBSS for uplink), even in scenarios involving relocation or inter-system changes.