Digital Enhanced Cordless Telecommunications

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DECT or Digital Enhanced (former European) Cordless Telecommunications is an ETSI standard for portable phones, commonly used for domestic or corporate use. DECT can also be used for wireless data transfers.

DECT is (like GSM) a cellular system. A major difference between the systems is the cell radius, DECT cells have a radius of 25 to 100 meters while GSM cells are 2 to 10 km.

British Telecom DECT cordless telephone (base unit and handset are shown)

Some another DECT properties:

net bit rate: 32 kbits/s
frequency: 1900 Mhz
carriers: 10 (1880..1900 Mhz)
timeslots: 2 x 12 (up and down stream)
channel alocation: dynamic
traffic density: 10000 Erlangss/kmÃÂÃÂ²

DECT physical layer use:

Frequency division multiple access (FDMA),
Time division multiple access (TDMA) and
Time division duplex (TDD)

This means that the radio spectrum is divided into physical channels into two dimensions: frequency and time.

DECT media access control layer is the layer which controls the physical layer and provides connection oriented, connectionless and broadcast services to the higher layers. It also provides encryption services.

DECT data link layer uses a variant of the ISDN data link protocol called LAPC. They are based on HDLC.

DECT network layer contains various protocol entities:

Call Control (CC)
Call Independent Supplementary Services (CISS)
Connection Oriented Message Service (COMS)
Connectionless Message Service (CLMS)
Mobility Management (MM)

All these communicate through a Link Control Entity (LCE).

The call control protocol is derived from ISDN DSS1, which is a Q.931 derived protocol. Many DECT specific changes have been made.

Three application areas:

Domestic DECTs are connected to a base (radio fixed parts) connected to the PSTN. A base can accept more DECT handsets.
Business DECTs connected to PBX. Such a case, many radio fixed parts. The DECT handset dynamically connect to these (hand over feature)
Public DECT connected to the PSTN (very rare). An high density alternative to GSM.
Local loop (very rare). In this case, a DECT radio link replaces the normally wired connection between the final PSTN distribution point to the subscriber.

DECT GAP is an interoperability profile for DECT. The intent is that two different products from different manufacturers that both conform not only to the DECT standard, but also to the GAP profile defined within the DECT standard, should interoperate for basic call functionality.