ling information. The U-plane offers a similar this process the area to be served is covered by a number of base function in support of the specific requirements of the services being stations, each of which provides radio coverage over a limited conveyed. For example the transparent unprotected service used for radius. This radius is typically of the order 20-50 metres depending speech transmission. partly on the construction nature of the building being served but Finally the Network Layer (NWK) is the main signalling layer of more likely on the density of telecommunications traffic to be the protocol. It functions by exchanging messages between peer catered for. In this latter case each small cell is able to offer a certain Lower Layer Management Entity C Plane U Plane Network Layer Layer 3 (NWK) Data Link Control Data Link Control Layer (DLC) Layer (DLC) Layer 2 Medium Access Control Layer (MAC) Physical Layer Layer 1 (PHL) Figure 49.9 DECT structure in relation to the OSI model DECT digital specification 49/11 station Handset Figure 49.10 DECT system. Each one of 10 carriers can serve up to 12 handsets or terminals number of radio channels and the smaller the cell the shorter the 2. Ability to offer variable bit rate channels to data and ISDN distance away the same channels can be re-used with acceptable options. co-channel interference ratio. This is the classical cellular frequency 3. Ability to cater for the traffic requirements of high capacity re-use concept that gives very high orders of spectrum efficiency, business communications systems. expressed in terms of Erlangs per MHz per sq. km. Frequency distribution is achieved by segmenting the available The result of putting all these requirements into practice, includ- band into ten carrier frequencies from 1881.792MHz to ing those of Section 49.2, produced an FDMA/TDMA/TDD system 1897.344MHz and separated by 1728kHz. having ten carriers each conveying 12 time division duplex 32kbit/s Time distribution has been achieved by employing time division channe