UMTS Mobile Phone Software and Operations
14.1 Introduction to UMTS Protocol Architecture
UTRAN protocol architecture consists of a set of horizontal and vertical layers. The requirements are addressed in horizontal radio network layer across different types of control and user planes. Control planes are used to control a link or for connection, whereas user planes are used for transmitting user data from higher layers. Signaling bearers are used to transmit higher layer's signaling and control information. Data bearers are the frame protocol used to transport user data. The application protocols are used to provide UMTS specific signaling and control within UTRAN, for example bearer setup in a radio network. A complete UTRAN and UE control plane architecture is shown in Figure 14.1.
The protocol architecture in the main interfaces from UE to ISP across the UMTS network for packet switched traffic is illustrated in Figure 14.2a and b. From the UE to UTRAN (RNC), the IP data packets are carried as PDCP packets. PDCP provides either an acknowledged/unacknowledged or transparent transfer service. It also performs a compression/decompression function. From the UTRAN (RNC) to SGSN IP, packets are tunneled using GTP-U. Another GTP-U tunnel then runs from the SGSN to GGSN. Using GTP-U, UMTS can carry a number of different packets, such as IPv4, IPv6, PPP, and X.25 over a common infrastructure. GTP-U packets are formed by adding a header to the underlying PDP packet and are sent using ...