in functions of layer 1 include RF processing, modulation/demodulation of the physical channels, multiplexing/demultiplexing of the physical channels, error detection and correction, rate matching, power control, synchronisation, etc. Layer 2 is the link layer. It is required because of the need to allocate minimum resources for a constantly changing data rate. It has two main sub-layers within itself: RLC and MAC. 3G RADIO NETWORK PLANNING AND OPTIMISATION There are two other layers - called the 'packet-data convergence protocol' (PDCP) and 'broadcast - multicast control' (BMC) - but they exist only in the user plane. The MAC (medium access control) layer in an entity that is responsible for the mapping of the logical channels to the transport channels. It provides data transfer services on the logical channels. As it is an interface between L1 and L3, it also provides functions like multiplexing and demultiplexing of packet data units to/from the physical layer. The MAC layer is also responsible for measurements related to traffic volume on the logical channels and further reporting to layer 3. Functions like segmentation and reassembly of the variable-length packet data into smaller payload units is done by the RLC (radio link control) layer, a sub-layer of layer 2. Another important function of this sub-layer is error correction by re-transmission in an ac- knowledged data transfer mode. Other functions include controlling the rate of information flow, concatenation, ciphering, and preservation of the higher-order PDUs. There are three modes of configuring an RLC by layer 3: transparent mode (no proto- col overhead added), unacknowledged mode (no re-transmission protocol in used, SO data delivery is not guaranteed), and acknowledged mode (a re-transmission protocol is used and data delivery is guaranteed). PDCP and BMC protocols exist only in the user place. PDCP is only for packet data, with its major function being compression of the PDUs at the transmitting end and decompression at the receiving end in all