UMTS Architecture

UMTS Rel-5 provides the ultimate evolution of voice and data convergence. As shown in Figure 11.4, similar to GPRS architecture, UMTS consists of three main entities: Mobile Station (MS), UTRAN, and Core Network (CN). A mobile station or user equipment (UE) communicates with Node B which controls the radio channel within its coverage area or cell. Multiple Node Bs are controlled by the Radio Network Controller (RNC). UMTS's Node B is equivalent to GPRS's Base Transceiver Station (BTS), while RNC is equivalent to GPRS's Base Station Controller (BSC). RNC and associated Node B form the radio network subsystem (RNS). The RNCs are interconnected to each other through the Iur interface. RNC connects to the core network through Iu interface which supports both voice and data services.

Figure 11.4. UMTS Architecture

Figure 11.4. UMTS Architecture

Umts Architecture
UTRAN's protocol stack presented in Figure 11.5 consists of the Physical Layer (Layer 1), Data

Link layer (Layer 2), and Network layer (Layer 3). The Physical Layer (PHY) includes the radio. The Data Link includes the Media Access Control (MAC), the Radio Link Control (RLC), the Packet Data Convergence Protocol (PDCP), and the Broadcast/Multicast Control (BMC). The Network Layer includes the Radio Resource Control (RRC). The RRC and RLC are divided into Control and User planes. PDCP and BMC exist in the User plane only. The PDCP and RLC in Rel-5 are unchanged from the Rel-99 and Rel-4 architecture, whereas the MAC is changed to include a new module that supports HSDPA. Layers 1, 2, and 3 are part of UMTS's Access Stratum (AS). The higher layer that is part of UMTS's Non-Access Stratum (NAS) includes Mobility Management (MM), Call Control (CC), and Session Management (SM).

Figure 11.5. UTRAN's Protocol Stack

Figure 11.5. UTRAN's Protocol Stack

Umts Access Stratum

The transport channels which indicate how the data are transferred over the radio interface are defined by the service access point (SAP) between the MAC and PHY layers. The logical channels which indicate the contents or types of data transferred are defined by the SAP between the RLC and MAC layers. Therefore, one of the MAC's functions is to map the logical channels to the transport channels. The services provided by layer 2 are considered to be the radio bearer.

The Physical Layer, which is described in detail in the next section, provides transport services to the MAC through the transport channels. The physical layer transport channels are mapped to the physical channels by defining a number of radio mechanisms (i.e., modulation, channel coding, radio matching, multiplexing, interleaving). The MAC layer contains several MAC entities (i.e., MAC-d, MAC-c/sh) which will be described in Section 11.4. The Radio Link Control (RLC), the Packet Data Convergence Protocol (PDCP), the Broadcast/Multicast Control (BMC), and the Radio Resource Control (RRC) are introduced in Section 11.5.

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