DECT protocol architecture

Date: 2015-10-07; view: 500.

The DECT protocol (ETSI. 1992b) is based on the principles of the OSI model. The complete common interface relevant to public access applications is defined in terms of the three lowest layers modified to account for the specific requirements of radio transmission and in-call handover. The structure is shown in Figure 49.9 where four DECT layers are identified. The OSI layers are indicated for reference. The Physical Layer (PHL) has the task of modulation and demodulation, acquire bit and burst synchronisation, control synchronisation and independent burst collision detection and measure the received signal strengths.

The Medium Access Control Layer (MAC) performs two main functions:

1. It selects the radio channels and then establishes and releases the communication link.

2. It multiplexes and demultiplexes all information into burst packages.

These two functions are used to create three services; a broadcast service, a connection orientated service (e. g. for telephony) and a connectionless service (e. g. for packet-like transmission).

The broadcast service is always transmitted from every base in a reserved data field (A field) on at least one physical channel. This beacon transmission allows portable parts (PP) to quickly identify and lock on to any suitable base (fixed part, FP) without requiring PP transmissions. The Data Link Control Layer (DLC) is largely responsible for providing very reliable data links to the network layer. This layer has two operational planes. The C-plane is con­cerned mainly with the fully error controlled transmission of inter­nal control and signalling information. The U-plane offers a similar function in support of the specific requirements of the services being conveyed. For example the transparent unprotected service used for speech transmission.

Finally the Network Layer (NWK) is the main signalling layer of the protocol. It functions by exchanging messages between peer entities in support of, for example, establishment, maintenance and release of calls. Many additional messages support a range of independent capabilities and services. One group contains the necessary procedures that support cordless mobility which includes FP and PP authentication and location registration.

The lower layer management entity is concerned with procedures that involve more than one layer and yet are often only of local significance. Consequently they are only defined in general terms.