ed to one RLC entity at the receiving end to its peer RLC entity at RNC varies depending on the implementation and de- the transmitting end by means of status reports. ployment, but up to a few hundred NodeBs per RNC is The Medium Access Control (MAC) layer offers ser- not uncommon. The RNC is, among other things, in vices to the RLC in the form of so-called Logical Chan- charge of call setup, quality-of-service handling, and nels. The MAC layer can multiplex data from multiple management of the radio resources in the cells for which logical channels. It is also responsible for determining the it is responsible. The ARQ protocol, handling retrans- Transport Format of the data sent to the next layer, the missions of erroneous data, is also located in the RNC. physical layer. In essence, the transport format is Thus, in Release 99, most of the 'intelligence' in the the instantaneous data rate used over the radio link and is radio-access network resides in the RNC, while the better understood once the interface between the MAC NodeBs mainly act as modems. and physical layer has been described. This interface is WCDMA evolution: HSPA and MBMS CHAPTER 4.6 Internet Core network To other NodeBs To other NodeBs Dedicated channels NodeB Figure 4.6-2 WCDMA radio-access network architecture. To core network Control plane User plane Layer 3 Signaling Radio channels access bearers Layer 2 RLC Logical channels Layer 2 MAC Transport channels Physical Layer Layer 1 NodeB Figure 4.6-3 WCDMA protocol architecture. CHAPTER 4.6 WCDMA evolution: HSPA and MBMS specified through so-called Transport Channels over detects an error, the RLC protocol in the receiver is in- which data in the form of transport blocks are trans- formed and requests a retransmission. After CRC at- ferred. There are several transport channels defined in tachment, the data are encoded using a rate-1/3 Turbo WCDMA. coder (convolutional coding is also supported by In each Transmission Time Interval (TTI) one or sev- WCDMA, but typically not used for packet-data se