used in 4.6.1.1 Overall architecture WCDMA are illustrated in Figure 4.6-3 and briefly described. WCDMA is based on a hierarchical architecture with User data from the core network, for example in the the different nodes and interfaces as illustrated in form of IP packets, are first processed by the Packet Data Figure 4.6-2. A terminal, also referred to as User Equip- Convergence Protocol (PDCP) which performs (optional) ment (UE) in 3GPP terminology, communicates with one header compression. IP packets have a relatively large (or several) NodeBs. In the WCDMA architecture, the header, 40 bytes for IPv4 and 60 bytes for IPv6, and to term NodeB refers to a logical node, responsible for save radio-interface resources, header compression is physical-layer processing such as error-correcting coding, beneficial. modulation and spreading, as well as conversion from The Radio Link Protocol (RLC) is, among other things, baseband to the radio-frequency signal transmitted from responsible for segmentation of the IP packets into the antenna. A NodeB is handling transmission and re- smaller units known as RLC Protocol Data Units (RLC ception in one or several cells. Three-sector sites are PDUs). At the receiving end, the RLC performs the common, where each NodeB is handling transmissions in corresponding reassembly of the received segments. The three cells, although other arrangements of the cells be- RLC also handles the ARQ protocol. For packet-data longing to one NodeB can be thought of, for example, services, error-free delivery of data is often essential and a large number of indoor cell or several cells along a high- the RLC can therefore be configured to request retrans- way belonging to the same NodeB. Thus, a base station is missions of erroneous RLC PDUs in this case. For each a possible implementation of a NodeB. incorrectly received PDU, the RLC requests a retrans- The Radio Network Controller (RNC) controls mul- mission. The need for a retransmission is indicated by the tiple NodeBs. The number of NodeBs connect