DECT or “Digital Enhanced Cordless Telecommunications” is a technology for cordless telephones with different functions, which was previously only designed for voice communication. Will it be superseded by Voice over IP?
DECT is an ETSI standard (European Telecommunications Standards Institute) with more than 250 documents for digital voice transmission in the in-house and PABX area. For details, please click here:
DECT Historical Development
Predecessor of DECT technology was the analogue cordless telephone.
CEPT (Conférence Européenne des Administrations des Postes et des Télécommunications) specified two important standards during this period:
CEPT CT1 (Cordless Telephone): European standard with analog modulation.
The radio transmission took place over up to 40 channels. The signal transmission was specified for uplink and downlink frequencies. The uplink frequency range was 914 to 915 MHz, the downlink frequency range was in the range of 959 to 960 MHz.
CEPT CT1 +:
This standard was a further development of CEPT CT1. The radio transmission was extended to 80 channels. The uplink frequency range was between 885 and 887 MHz, the downlink frequency range was between 930 and 932 MHz.
The transmission of voice was unsecure (the calls could be intercepted). A re-assignment of the frequency bands defined at that time should be carried out in later years for GSM (Global System for Mobile Communication).
Further Developments of DECT Standards
In order to meet market requirements, ETSI expanded the standards to include data transmission services via DECT. Voice transmission via the Internet Protocol (Voice over IP) via DECT is also in use today. This is especially important as signal frequencies used for DECT are different from WLAN frequencies.
The range of radio signal transmission allows the use in a geographically restricted area (eg: within a company site or a city).
Additional standards define e.g. user interfaces or basic functions that must be implemented in compatible devices from different vendors (Generic Access Profile, GAP). This allows e.g. a simple call with a handset from one manufacturer via a base station from another manufacturer. Further advanced features (for example, call forwarding, telephone book queries, exchange of short messages) may not be supported across manufacturers.
Use of DECT Phones with a PABX or VoIP Solution
DECT Base Stations
In the professional environment, DECT base stations are connected to a PABX or a VoIP (Voice over IP) system. Thus, extensive features of the telephony solution are provided to DECT users. The DECT base station may be connected to the telecommunication system via special interfaces (and cables). Software license fees are charged for each DECT base station and cordless telephone.
DECT Phones (Handsets)
Are mobile devices that communicate via base station(s). Different designs (for office or industrial environments) are available. The devices can be operated alone with a base station or integrated into the telephone system concept of a manufacturer (also via base stations which are connected to the telephone solution directly or via local area network (LAN).
The handsets usually support the Generic Access Profile (GAP) standard.
DECT has been developed for use on small areas with high user density. The maximum movement speed was defined at 20 km per hour. The limitation is given by the applied radio technology.
DECT is a decentralized system with no specific uplink and downlink frequencies. Each of the defined 10 channels can be used for both uplink and downlink transmission.
Two operating modes are specified:
- Stand-alone with base station or operation of
- One or more base stations in combination with a telephone solution.
Special adapters allow the integration of Ethernet or V.24 devices
In Europe, the frequency range from 1880 to 1900 MHz is exclusively reserved for DECT users. 120 duplex channels are available for transferring calls. The average transmission power is 10 mW in Europe, the maximum 250 mW (24 dBm). Ask for your local requirements for the use of DECT technology in your country.
Common Interface (CI) ETSI EN 300 175
Is a common ETSI standard consisting of several parts. The cooperation between DECT and GSM or DECT and UMTS has also been specified.
DECT Packet Radio Service (DPRS)
Specifies data rates of up to 840 kbps or 5 Mbps, depending on the modulation technique.
Profiles define common functions and parameters of devices.
For example, Generic Access Profile (GAP), ETSI EN 300 444, defines the interface between the cordless telephone and the base station. It allows the operation of DECT cordless devices of different manufacturers with a common base station.
Examples of further defined profiles:
- Public Access Profile (PAP)
- Radio in the Local Loop Access Profile (RAP)
- DECT Packet Radio System (DPRS)
- DECT Multimedia Profile (DMAP)
- Multimedia in the Local Loop Access Profile (MRAP)
- Data Service Profiles (DSP)
- ISDN Interworking Profiles (IIPs)
- CTM (Cordless Telephone Mobility) Access Profiles (CAP)
- DECT/GSM (Global System for Mobile communication) Interworking Profile (GIP)
- DECT/UMTS (Universal Mobile Telecommunications System) Interworking Profile (UIP)
CAT-iq (Cordless Advanced Technology – internet and quality)
Is a set of ETSI standards for the DECT system and is intended to facilitate the interworking of ISDN and IP technology with higher voice quality (HD voice) and higher data rates.
Use of DECT or “Voice over Wireless Local Area Network”?
The question arises whether to use DECT or “Voice over Wireless Local Area Network” (VoWLAN):
Many users have built-up wireless local area network (WLAN) infrastructures in the past. They often already use “Voice over IP” (VoIP) in wired LANs and want to use the WLAN infrastructure for voice communication.
Challenge: a Wireless Local Area Network (WLAN) is in general a “Shared Media LAN” without quality of service, which would however be important for voice calls.
Solution: Modern wireless local area networks (WLANs) support prioritization (according to standard IEEE 802.11 of the Institute of Electrical and Electronics Engineers, IEEE) for voice, video or time-critical interactive traffic.
Challenge: WLANs operate most often in frequency ranges of 2.4 GHz and are disturbed by other devices in the same frequency range.
Solution: use of DECT in a separated and reserved frequency range or use of WLAN in 5 GHz range (but still at risk).
Alternatively, customers want to retain the DECT technology but transmit the digitized voice via the Internet Protocol and the DECT radio technology. Then one speaks of “Voice over IP over DECT”. Thus, the DECT advantages such as quality, reliability, protected frequencies, etc. remain. It is to be checked from case to case whether special functions such as dead man circuits or apparatus with a robust, splash-proof housing are necessary and available.
What is your suggestion? Do you believe in DECT or have you already switched to VoWLAN? What experiences have you gained? Please leave a comment! Thank you.
About the Author
Ronald Schlager is independent trainer, consultant, book author and blogger with emphasis in communications technologies and their application.
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