What is DECT?
DECT stands for:
Digital
It is all digital. This means that all communications on the air-interface
is digital and therefore free of the interference as can be heard on analogue
cordless telephones. Also all control signalling between the system and
portable is outside of the users speech path, so no interference is
experienced from that. Besides this the modern integrated circuitry
incorporated in these systems make it possible to perform all kinds of
sophisticated operations on these communications, of which high quality
encryption is the probably the most important.
Enhanced
Added to standard speech communication all kinds of supplementary services
are provided. Services found in the Integrated Services Digital Network
(ISDN) can be found on DECT systems as well. Examples are Calling Line
Identification Presentation (CLIP), Three Party Calls (3PTY), Multiple
Subscriber Number (MSN) etc. Besides standard digitized speech
communication, all kinds of data communications is possible. Think about
messaging (effectively replacing paging), cordless computer network
connections etc.
Cordless
Cordless means portable or locally mobile. It has to be seen as a
replacement of the cable that connects the handset/computer/... to the
telephone/network/... infrastructure. The main advantage is that the user
can use and be reached on his/her telephone whatever there location in the
coverage of the system. And that for the cost of normal wired telephones.
This does not imply that there is a limit to the size of the system. A
domestic system might cover one house, a business system might cover one or
more buildings and factories, while even complete cities may be covered for
public access.
Telecommunications
Speech is the main means of interpersonal communication and therefore the
main application of DECT. But other applications are possible. E.g. local
paging will be completely replaced by DECT, while laptops create the need
for a seamless, no hassle, company computer network connection. Another area
of appplication is in the local loop, the connection between the telephone
network and users premises, especially where a copper cable is not
available.
But what about GAP?
To answer this we have to look at the emergence of DECT in the early 90's.
Different European manufacturers of telecommunication systems came together
in the Radio Equipment and Systems (RES) Technical Committee of the European
Telecommunications Standards Institute
(ETSI) to discuss the development
of a standard for cordless telephony. The results of these discussions were
a collection of standards (European Telecommunication Standard (ETS) 300 175)
based on the combined works of these manufacturers.
Since the standards are a compromise from the developments of all
participating manufacturers there was a wide variety of implementations of
this standard resulting in poorly compatible products. To counter this
situation the Generic Access Profile (GAP) was created, stating the
mandatory elements of the DECT standard for telephony applications. Systems
and handsets which are GAP compliant work together even if they are from
different manufacturers.
But things are moving ahead. With more and more private and public systems
and operators coming on-line every day there has to be standards for
interworking between these systems. For that purpose the Cordless Terminal
Mobility (CTM) Access Profile (CAP) has been defined. They provide the
handset user with seamless integration of systems it has subscriptions on.
Where can I find DECT?
Since DECT is an access technology it can front-end just about any
network. Current implementations can be found in the domestic and SOHO
environment in the form of a base station which is wired to a normal
telephone line (either ISDN or analogue) and containing all functions to
support multiple DECT handsets.
Since DECT is a scaleable technology a system can be expanded to cover a
larger area and support a higher traffic load; situations that can be found
in a business environment. A DECT system can be the front end of a private
branch exchange (PBX).
Even the public domain is a possible application for DECT. Due to it's use
of high frequencies, dynamic channel selection and short range it is ideally
suited for noisy radio environments with high traffic load, as the modern
cities are today.
But developments don't stop there. Cordless data communication networks with
flexible bandwidth allocation are being developed as well as telecommunications
through the cable-TV networks and that is not the end to it.
Geographic spreading
DECT is a development of the European Telecommunications Standards Institute
(ETSI) and therefore primarily introduced in the European countries. But since
then other parts of the world have allocated frequencies to be used with DECT.
The Far East is the prime example as well as Africa and South-America. In
the later for example the 1910-1930 MHz band is allocted for systems such
as DECT systems to operate as fixed wireless access systems.
In North-America a similair standard is in use, called ISM which stands for
'Industrial, Scientific and Medical'. It works in the 902 to 928 MHz band,
20 channels, uses low power transmission and is FCC license free. In Japan a
similar system was in use, called PHS, but that seems to be phased out quickly.
Written by my own two hands and an ASCII editor.
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Last updated July 5, 1999
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