A VoIP phone is designed specifically for use in a voice over IP(VoIP)system by converting
standard telephone audio into a digital format that can be transmitted over the Internet, and by
converting incoming digital phone signals from the Internet to standard telephone audio. A VoIP
phone allows the user to take advantage of VoIP technology without involving a personal computer,
although an Internet connection is required. Physically, a VoIP phone set resembles a traditional
hard wired or cordless telephone set. Some VoIP phone sets offer enhanced quality audio,
comparable to that on compact disc (CD). A few VoIP phone sets allow for the transmission and
reception of image data during calls, so they can be considered video telephones.
An IP PBX is a private branch exchange (telephone switching system within an enterprise )
that switches calls between VoIP users on local lines while allowing all users to share a certain

number of external phone lines. The typical IP PBX can also switch calls between a VoIP user
and a traditional telephone user, or between two traditional telephone user in the same way that a
conventional PBX does. With a conventional PBX, separate networks are necessary for voice and
data communications. One of the main advantages of an IP PBX is the fact that it employs
converged data and voice networks. This means that Internet access, as well as VoIP
communications and traditional telephone communications, are all possible using a single line to
each user. This provide flexibility as an enterprise grows, and can also reduce long-term
operation and maintenance costs.
Ear and mouth (E&M) is a technology in voice over IP (VoIP) that uses a traditional
telephone handset with an earphone (or earpiece) for listening to incoming audio and a
microphone (or mouthpiece) for transmitting audio. Calls using an E&M interface can be made
from, received from , or disconnected by a private banch exchange (PBX) as well as from a
VoIP-capable computer.
The main advantage of E&M is the fact that it allows a PBX to reliably detect disconnect
(hang-up) signals. This eliminates problems that can otherwise occur with locked computer ports
at the terminations of calls, and thus minimizes the risk of needlessly consuming network
resources.

cordless ['kɔ:dlis]

n. 不用电线的adj. 无线的（副词cordlessly）