nt apparatus, and is subjectively the more access, and calls set up over the PSTN with the modem. important of the two. In PABXs which have digital transmission two types of data Most modern PABXs and key systems are digital in nature and facility can be provided. 64kbit/s switched connections, where the therefore inherently capable of providing both voice and data ser- data circuit is normally of a slower speed and is rate adapted by a vices. Cordless business systems must be capable of supporting the terminal adaptor using either an ECMA or proprietary rate adaption same range of voice and non-voice services. High integrity authen- technique, which converts the data terminal output into the 64kbit/s tication procedures and mechanisms are required in order to provide bit stream. D channel packet switching is available on some ISDN secure access to the cordless system and provide confidentiality of PABXs, particularly French designs, where low speed data in packet the information transmitted over the cordless link. format is supported on all basic rate ISDN lines and makes a very A major feature of cordless systems is the provision of mobility simple and cheap way to access packet network services. both within a system and between systems, and specific mechan- isms and protocols must be defined to support this important fea- ture. Cordless PABX and key systems Wide area coverage systems such as cellular radio require central control and allocation of the channels available to each transmitter, A cordless PABX (or key system) may be simplistically regarded as to optimise channel re-use in order to maximise spectrum usage. a PABX (or key system) where some or all of the terminals are This central control is not possible in the cordless business system connected to the central switching system by cordless means instead area where a multiplicity of unrelated systems installed by of by hard wiring. Such a definition encompasses the situation numerous service providers must coexist. Cordless business sys- where individ