users beyond the DECT link The Medium Access Control Layer (MAC) performs two main requires additional protocols that are outside the DECT specifica- functions: tion. Thus to interface a DECT link with, say, a GSM fixed part will require an appropriate IWU to establish proper unambiguous mess- It selects the radio channels and then establishes and releases age transfer and in the process influence the service standard to be the communication link. offered. Clearly the IWU concept will play a very important role in 2. It multiplexes and demultiplexes all information into burst the full exploitation of the DECT specification. packages. 49.4.3 Spectrum resource These two functions are used to create three services; a broadcast service, a connection orientated service (e.g. for telephony) and a Throughout Europe the band 1880MHz to 1900MHz has been set connectionless service (e.g. for packet-like transmission). aside for use by the DECT system. This 20MHz of spectrum must The broadcast service is always transmitted from every base in a however be used efficiently and flexibly if it is to meet the require- reserved data field (A field) on at least one physical channel. This ments of high capacity business systems. It is the main purpose of beacon transmission allows portable parts (PP) to quickly identify the Physical Layer to bring this about by ensuring that adequate and lock on to any suitable base (fixed part, FP) without requiring capacity radio channels are created in a manner that permits high PP transmissions. The Data Link Control Layer (DLC) is largely orders of radio channel re-use. The DECT spectrum resource has responsible for providing very reliable data links to the network been distributed in space, frequency and time. layer. This layer has two operational planes. The C-plane is con- Spatial distribution is brought about because DECT supports the cerned mainly with the fully error controlled transmission of inter- use of the well-known concept of cellular radio channel re-use. In nal control and signal