Digital Enhanced Cordless Telecommunications

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DECT or Digital Enhanced (former European) Cordless Telecommunications is an ETSI standard for digital portable phones, commonly used for domestic or corporate purposes. 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.

Image:Cordless.phone.750pix.jpg

Some other DECT properties:

net bit rate: 32 kbit/s
frequency: 1900 MHz
carriers: 10 (1880..1900 MHz)
timeslots: 2 x 12 (up and down stream)
channel allocation: dynamic
traffic density: 10000 Erlangs/km²

DECT physical layer uses:

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 in two dimensions: frequency and time.

The power emitted from portable part as well as base stations when sending is 100mW.

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 with the DSC Cipher (DECT Standard Cipher).

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.

Four 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 handsets 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, are able to interoperate for basic calling. In other words, any phone that supports the GAP can be registered with any base station that also supports it, and be used to make and receive calls. They will not necessarily be able to access advanced features of the base station, such as remote operation of an answering machine built into the base. Most consumer-level DECT phones and base stations support the GAP profile, even ones that do not publicise this feature, and thus can be used together.

DECT was developed by ETSI but has since been adopted by many countries all over the world. DECT is used in all countries in Europe, outside Europe it is used in most of Asia, Australia and South-America. So far North-America has been off-limits for DECT, but that looks set to change in the near future.

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