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The Network layer of the DECT standard (EN 300 175-5) defines messages and procedures used for the high-level control of the call made through the DECT system. Since the DECT system is an access system the Network layer in the base system usually interacts with an 'Interworking Unit (IWU)' which interfaces the DECT system to a telephone line, trunk line, PABX or Local Area Network. In the portable it communicates with the user through some sort of user interface, either a simple keypad/LCD dislay for telephones or complete computer programs for data applications.
There are a lot of messages defined in the standard. Each message contains its own set of 'Information Elements' (IE's) which provides the parameters belonging to the message, e.g the calling party number in a setup message. Not all messages and information elements have to be supported by all implementations and in all situations. A small subset of these is mandatory. Additional 'profiles' exist which define the mandatory subset for certain applications. The 'Generic Access Profile (GAP)' is one which was created to make sure equipment from different manufacturers can work together for voice applications. Note that the GAP not only covers the Network layer, but DLC, MAC and PHL as well.
The Network layer messages can be devided into five distinct groups:
| CC | Call Control |
| MM | Mobility Management |
| COMS | Connection Oriented Message Service |
| CLMS | Connectionless Message Service |
| SS | Supplementary Service |
The Call Control group has everything to do with the setup and release of calls. For an example see DLC. The Mobility Management group of messages concern the identities of the various parties as well as encryption information which is partly based on the identities. The Connection Oriented Message Service has to do with all kinds of additional information related to the call, e.g. cost information. The Connectionless Message Service is also a message service, but has no relation to a specific call. This service is used to page a portable to setup a connection so a incoming call from the network can be put through to the user. Supplementary Service contain messages for all kinds of addtional featues.
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