Section: 5.1.2.4 UE - PDN GW user plane with 3G access via the S12 interface
Content: Legend: - GPRS Tunnelling Protocol for the user plane (GTP-U): This protocol tunnels user data between UTRAN 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 Uu interface are described in TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7]. - SGSN controls the user plane tunnel establishment and establish a Direct Tunnel between UTRAN and S-GW as shown in Figure 5.1.2.4-1. Figure 5.1.2.4-1: User Plane for UTRAN mode and Direct Tunnel on S12