ion unit (TRU). This unit interacts with the Abis and Ater interfaces. It also reallocates the traffic and the signalling channels to the correct transceiver (TRX). The TRU may be capable of making cross-connections at the 2 Mbps level and drop-and-insert functionalities at the 8 kbps level. Transmission units are capable of holding branching tables. These tables guide the transmission units on what to do with the traffic coming in from the PCM lines; e.g. should it just let it pass to the next BTS, or should it drop some traffic meant for its own TRX, etc. Base Station Controller The base station controller (BSC) is capable of many functions. Radio channel manage- ment is an integral function of the BSC and includes tasks such as channel management and release. It is responsible for the handover management function that is based on an assessment of signal power, signal quality at the MS in both the uplink and downlink di- rections, and adjustments related to the minimisation of interference in the radio network. It is also responsible for measurements related to the implementation of frequency hop- ping (FH) within the network. Other important functions include interaction with the base station and MSC on either side, encryption management such as storing the encryption pa- rameters and forwarding the same to the base stations, traffic and channel management, etc. Also, the BSC-BTS signalling, which includes the LAPD, transceiver signalling (TRXSIG) and BSC-MSC signalling which is CCS7, is handled by the BSC itself. The BSC is also responsible for carrying the O&M information to the BTS. Apart from these functions, the BSC also performs one more function of concern to transmission planners, which is traffic concentration between itself and the BTS. This means TRANSMISSION NETWORK PLANNING PROCESS that even if there were a channel available on the air- and Abis interface, the subscriber would not be able to make a call because of the blocking on the Aten interface. Transcoder and Sub-multiplexer (TCSM) Transcoder