Section: 5.1.2.3 UE - PDN GW user plane with 2G access via the S4 interface
Content: Legend: - GPRS Tunnelling Protocol for the user plane (GTP-U): This protocol tunnels user data between SGSN and the S-GW as well as between the S-GW and the P-GW in the backbone network. GTP shall encapsulate all end user IP packets. - UDP/IP: These are the backbone network protocols used for routing user data and control signalling. - Protocols on the Um and the Gb interfaces are described in TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7]. Figure 5.1.2.3-1: User Plane for A/Gb mode