Section: 5.1.2.5 UE - PDN GW user plane with 3G access via the S4 interface
Content: NOTE: Please refer to TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2] for the corresponding stack for PMIP based S5/S8. Legend: - GPRS Tunnelling Protocol for the user plane (GTP-U): This protocol tunnels user data between UTRAN and the SGSN, between SGSN and 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 and the Iu interfaces are described in TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7]. - SGSN controls the user plane tunnel establishment and establishes a tunnel between SGSN and S-GW. If Direct Tunnel is established between UTRAN and S-GW, see Figure 5.1.2.4-1. Figure 5.1.2.5-1: User Plane for Iu mode