Dialogic M7324 사용자 설명서

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2.  Introduction to PBXs and KTSs 
A PBX, or private branch exchange, is a telephone system that is usually 
installed in a business. It provides service among many extensions within the 
business as well as outside lines. Typically, PBXs are used when a large number 
of extensions are needed. A PBX can be thought of as a mini version of a 
telephone company's central office (CO) switch. Advantages offered by a PBX 
include: 
•  increased efficiency and cost savings because a specific number of CO 
telephone lines are shared among a large group of users 
•  special PBX features  
Grouped with PBXs are key telephone systems (KTSs). A KTS is generally a 
smaller version of a PBX that also provides direct access to outside telephone 
lines (trunks). When you press a "line" key on a KTS you immediately hear a dial 
tone from the central office. In contrast, on a PBX system, you have to dial a 
digit, usually "9", to get the dial tone from the central office. Typically, KTSs are 
used when fewer than 50 extensions are needed. Advantages offered by KTSs 
include that anyone in a supported office can answer an incoming call simply by 
pressing the correct line button, and that KTSs usually cost less than PBXs.  
Systems have been developed that combine PBX and KTS features. These hybrid 
systems typically serve up to 100 users and contain some features found only in 
PBXs (the ability to use single line phones) and features typically found in KTSs 
(hands free announcing and answerback). An example of a hybrid system is the 
NEC Electra Professional, which can connect to a maximum of 64 outside lines 
and 96 extensions. Some features include least cost routing, call forwarding, call 
hold, automated attendant, and caller ID. 
As noted above and for simplicity, throughout this manual the term PBX is 
sometimes used to denote a PBX, a KTS, or a hybrid system that combines both.  
Many PBX systems are digital. In a digital system, both the voice signals and 
control information transmitted between station sets within the PBX are sent as 
binary data. Analog voice signals received from outside the PBX (usually a CO) 
are converted to digital voice data and sent through the PBX. Digital voice data 
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