49. 4 Dect digital specification

Around the mid 1980's a number of companies under the auspices of the European Conference of Telecommunications Manufacturers (ECTEL) started to define and specify a digital cordless telecommunication standard for business system use. It adopted many concepts previously exploited in European CT standards but by implementing multi-carrier time division multiple access it considerably increased the potential for cordless operation particularly in a business environment. Eventually this work led to the ETSI standard that is now know as Digital European Cordless Telecommunications, or DECT for short. (ETSI, 1992b; Ochsncr, 1990; ETSI, 1992c.) The DECT specification has two levels of standardisation.

1. The Common Interface (CI) specification that enables confor­ming equipment from different manufacturers to successfully communicate in a public access service (e. g. telepoim).

2. The coexistence interface specification that allows proprietary, non-CI, standard equipment to coexist in the common spectrum resource.

Thus DECT is able to support both public access requirements and the proprietary needs of the manufacturers, particularly those inter­ested in exploiting the considerable potential of cordlessness in the business environment. This is shown in Figure 49. 8 (ETSI, 1992b), the layers being described in the next section.

The application areas of DECT are somewhat wider than those identified in Section 49. 3. For example the system is expected to support radio access to office voice and data networks at informa­tion bit rates considerably in excess of the 32kbit/s foreseen for speech transmission. Indeed data transmission has figured signifi­cantly in the preparation of the specification. DECT, therefore, offers bearers that are well matched to the needs of teleservices.

For ISDN-based applications a continuous 144kbit/s full duplex bearer is available. Even this is not sufficient for other uses associ­ated with data transmission in real time and/or short bursts. Such requirements are indicated in Table 49.1 (ETSI, 1992b). For data applications, variable transaction times 100ms to 10 seconds are anticipated and transmission is anticipated to be predominantly one way. Fast link establishment time, under 50ms (not including Port­able Part verification) is required. Variable rate communications is required. Note that these applications demand rapid access to bearer channel and since radio channels must be released between bursts of information (to conserve spectrum for other users) then the result is a requirement for rapid radio channel acquisition algorithms capable of seizing a channel in less than 50ms.

Although the above has been written in terms of DECT as a piece of cordless terminal equipment, it was made plain during its development that the technology can also be used as an access technology to other communication networks both public and private. For example, provision has been made in the design of DECT to enable it to be developed as another access technique able to use the GSM digital cellular fixed network. This means that DECT must in due course be able to access and use the roaming and location intel­ligence built in to the GSM system. Similar provisions are being made to ensure the capability to interwork with evolving public intelligent telecommunication networks. Thus DECT is not just another cordless telephone peripheral to telephone networks, it also has the capability to become an access technology that is integrated with the network.