DECT or Digital Enhanced Cordless Telecommunications (formerly Digital European Cordless Telephone) is an ETSI standard for digital portable phones (cordless home telephones), commonly ud for domestic or corporate purpos. DECT can also be ud for wireless broadband data transfers. DECT is recognid by the ITU as fulfilling the IMT-2000 requirements and thus qualifies as a 3G system. Within the IMT-2000 group of technologies, DECT is referred to as IMT-FT (Frequency Time).
DECT was developed by ETSI but has since been adopted by many countries all over the world. The original DECT frequency band (1880 MHz–1900 MHz) is ud in all countries in Europe. Outside Europe, it is ud in most of Asia, Australia and South America. In the United States, the Federal Communications Commission in 2005 changed channelization and licensing costs in a nearby band (1920 MHz–1930 MHz, or 1.9 GHz), known as Unlicend Personal Communications Services (UPCS), allowing DECT devices to be sold in the U.S. with only minimal changes. The channels are rerved exclusively for voice communication applications and therefore are less likely to experience interference from other wireless devices such as baby monitors and wireless networks. DECT devices made for u in the U.S. u the brand DECT 6.0to distinguish them from both DECT devices ud elwhere and U.S. cordless equipment operating in the 900 MHz, 2.4 GHz and 5.8 GHz ISM bands. T
he "DECT 6.0" term was coined by Rick Krupka, Director of Cordless Products at Siemens, when he was driving the acceptance of DECT in the US with the FCC. This was a marketing term not a spectrum band reference; the term "6.0 GHz" for DECT 6.0 phones is incorrect, since it operates at 1.9 GHz. Calling it DECT 1.9 would have confud the market place in expecting the bigger the number the better the product. In fact, however, at 1.9 GHz cordless phones can operate over a greater distance than 2.4 GHz or 5.8 GHz can.
Contents
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∙ 1 Application
∙ 2 Features广场文化
∙ 3 Technical details
∙ 4 DECT for Data Networks
o 4.1 Radio links
∙ 5 See also
∙ 6 References
∙7 External links
[edit] Application加拿大绿卡条件
The DECT standard fully specifies a means for a portable unit such as a cordless telephone to access a fixed telecoms network via radio, but unlike the GSM standards does not specify any internal aspects of the fixed network itlf. Connectivity to the fixed network (which may be of many different kinds) is done through a ba station or "Radio Fixed Part" to terminate the radio link, and a gateway to connect calls to the fixed network. In most cas the ba station connection is to the public switched telephone network or telephone jack, although connectivity with newer technologies such as Voice over IP has become available. There are also other devices such as some baby monitors utilising DECT, and in the devices there is no gateway functionality.
The DECT standard originally envisaged three major areas of application:
∙domestic cordless telephony, using a single ba station to connect one or more handts to the pu
blic telecoms network, which is now available
∙enterpri premis cordless PABXs and wireless LANS, using many ba stations for coverage. Calls continue as urs move between different coverage cells, through a
mechanism called handover. Traffic both within the system and to the public telecoms
network
∙public access, using large numbers of ba stations to provide building or urban area coverage as part of a public telecoms network.
Of the, the domestic application (cordless home telephones) has been extremely successful. The enterpri PABX market had some success, and all the major PABX vendors have offered DECT access options. The public access application has not succeeded, since public cellular networks have fulfilled the need better. The one major application of DECT for public access, the Telecom Italia's FIDO network covering major cities in Italy, lasted about a year and was shut in 1997.
DECT has also been ud for Fixed Wireless Access as a substitute for copper pairs in the "last mile" in countries such as India and South Africa. By using directional antenna and sacrificing some t
raffic capacity, cell coverage could extend to over 10 km. In Europe, the power limit laid down for u of the DECT spectrum (250 mW peak) was expresd in ERP, rather than the more commonly-ud EIRP, thus permitting the u of powerful directional antenna to produce much higher EIRP and hence long ranges.
VoIP - IP-DECT. In business, DECT has become an esntial part of many PABX installations with manufacturer's proprietary methods of supporting PABX features over the DECT standard. Since the ont of the migration from TDM PBXs to VoIP and VoIP hybrid solutions, manufacturers such as Philips and Aastra have developed IP-DECT solutions where the backhaul from the ba station is VoIP (H323 or SIP) but the handt loop is still DECT. The solutions are sometimes restricted by the cost of the ba station and may be economic where the concentration of urs is high. PBX networking vendors such as Cisco promote the adoption of WIFI-VoIP handts as the replacement for DECT, but this impos significant overhead on the design and complexity of the WIFI network in order to provide roaming, coverage and rervation of bandwidth, not to mention QOS. The question of Voice Mobility in commercial environments is still very open. DECT is robust but needs its own radio infrastructure. WIFI is deployed as an ad-hoc network environment. The new entrant into the field will be 3G-nano Cell technology where VoIP ssions would be supported as a private connection onto a 3G handt/PDA.
[edit] Features
Typical abilities of a domestic DECT Generic Access Profile(GAP) system include:
∙Multiple handts to one ba station and one phone line socket. This allows veral cordless telephones to be placed around the hou, all operating from the same
telephone jack. Additional handts usually have a battery charger station instead of a
ba station. The additional handts do not require additional telephone sockets nor
additional transceivers
∙Interference-free wireless operation to around 100 metres outdoors. Operates clearly in common congested domestic radio traffic situations. For instance, generally immune to
interference from Wi-Fi networks or video nders, Bluetooth technology, baby monitors
and other wireless devices.
∙Ability to make internal (intercom) calls between handts.
∙An extended range between the telephone and ba (allowing greater physical distance between the two devices)
∙Extended battery talk-time, sometimes up to 24 hours
鹅掌花Many DECT systems also include additional features such as a shared phonebook, but the are not standardized and may not work across different handt types.
Some telephones also include a built-in digital answering machine and other features.
A few of the telephones also allow urs to utilize the DECT phone to retrieve wireless cellphone calls through Bluetooth technology.
Additional features to look for include: handt ringers, headt jacks, redial, a "flash" button for answering call-waiting, speaker phone, and volume controls.
One final consideration is the type of battery it us. Some telephones now utilize two rechargeable AA or AAA batteries, which are considerably less expensive than standard telephone batteries that, in some cas, can cost almost as much as purchasing a new telephone.四字成语大全集
The Consumer Reports 2008 Buying Guide offers an excellent explanation and evaluation of the various models that are currently available for sale in the United States.
[edit] Technical details
Some DECT properties:
∙Audio codec: G.726
∙Net bit rate: 32 kbit/s
∙Frequency: 1880 MHz–1900 MHz in Europe, 1920 MHz–1930 MHz in the US
∙Carriers: 10 (1,728 kHz spacing) in Europe, 5 (1,728 kHz spacing) in the US
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∙Time slots: 2 x 12 (up and down stream)
∙Channel allocation: dynamic
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∙Average transmission power: 10 mW (250 mW peak) in Europe, 4 mW (100 mW peak) in the US
The DECT physical layer us:
∙Frequency division multiple access (FDMA),
∙Time division multiple access (TDMA) and
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∙Time division duplex (TDD)
This means that the radio spectrum is divided into physical channels in two dimensions: frequency and time.
The maximum allowed power for portable equipment as well as ba stations is 250 mW. A portable device radiates an average of about 10 mW during a call as it is only using one of 24 time slots to transmit.
The DECT media access control layer is the layer which controls the physical layer and provides connection oriented, connectionless and broadcast rvices to the higher layers. It also provides encryption rvices with the DECT Standard Cipher (DSC). The encryption is fairly weak, using a 35-bit initialization vector and encrypting the voice stream with 64-bit encryption.
3月份是什么星座The DECT data link layer us LAPC (Link Access Protocol Control), a specially designed variant of the ISDN data link protocol called LAPD. They are bad on HDLC.
The DECT network layer always contains the following protocol entities:
∙Call Control (CC)
∙Mobility Management (MM)
Optionally it may also contain others:
∙Call Independent Supplementary Services (CISS)
∙Connection Oriented Message Service (COMS)
∙Connectionless Message Service (CLMS)
All the 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. The mobility management protocol includes many elements similar to the GSM protocol, but also includes elements unique to DECT.
Unlike the GSM protocol, the DECT network specifications do not define cross-linkages between the
operation of the entities (eg Mobility Management and Call Control). The architecture presumes that such linkages will be designed into the interworking unit that connects the DECT access network to whatever mobility-enabled fixed network is involved. By keeping the entities parate, the handt is capable of responding to any combination of entity traffic, and this creates great flexibility in fixed nework design without breaking full interoperability.
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. The DECT standard includes full testing suites for GAP, and GAP products on the
