Manufacturers (ECTEL) started to define and specify a digital cordless telecom- The basic principles of CT2/CAI operation offer significant oppor- munication standard for business system use. It adopted many tunities to minimise the inherent cost of the basic digital link. For concepts previously exploited in European CT standards but by example the 100kHz channelling does not require time dispersion implementing multi-carrier time division multiple access it consid- equalisation even when operating in a multipath environment with erably increased the potential for cordless operation particularly in no line-of-sight signal component. Furthermore there is no need for a business environment. Eventually this work led to the ETSI a radio frequency duplexer and less carrier frequency sources are standard that is now know as Digital European Cordless Telecom- R.F. pre-amp Digital demod Clock switch Burst format Synth & timing modulator O/P amp. Speech Signalling codec (keypad Dashed lines indicate etc.) N proc. possible areas for integration Control circuitry Figure 49.7 Possible integration of CT2 DECT digital specification 49/9 munications, or DECT for short. (ETSI, 1992b; Ochsner, 1990; Table 49.1 Data requirements in DECT ETSI, 1992c.) The DECT specification has two levels of standardisation. 1. The Common Interface (CI) specification that enables confor- Application Access Transaction Full rate ming equipment from different manufacturers to successfully latency duration at (without communicate in a public access service (e.g. telepoint). full rate errors) The coexistence interface specification that allows proprietary, non-CI, standard equipment to coexist in the common spectrum Remote terminal resource. 100ms 5 10 20kbit/s Thus DECT is able to support both public access requirements and the proprietary needs of the manufacturers, particularly those inter- Graphics 500ms - 10 24 128kbit/s ested in exploiting the considerable potential of cordlessness in the business environment. This is shown in Figure 49.8 (ETSI,