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VoIP (voice over IP)
is a term used in IP telephony for a set of
facilities for managing the delivery of
voice information using the Internet
Protocol (IP). Also known as Voice over
Internet Protocol (VoIP) which is refers to
a technology that allows you to make
telephone calls using a broadband Internet
connection instead of a regular (or analog)
phone line.
In general, this means sending voice information in digital
form in discrete packets rather than in the
traditional circuit-committed protocols of
the public switched telephone network (PSTN).
In addition to IP, VoIP uses the real-time
protocol (RTP) to help ensure that packets
get delivered in a timely way. Using public
networks, it is currently difficult to
guarantee Quality of Service (QoS).
Better service is possible with private
networks managed by an enterprise or by an
Internet telephony service provider (ITSP).
Using VoIP, an enterprise positions a "VoIP device" at a
gateway. The gateway receives packetized
voice transmissions from users within the
company and then routes them to other parts
of its intranet (local area or wide area
network) or, using a T-carrier system or
E-carrier interface, sends them over the
public switched telephone network.
Typically there are three styles of Voice
over IP calls. It can be either from PC to
PC, or it could be from a PC to phone or
from phone to phone. The key components here
are the gateways, which adapt traditional
telephony to the Internet. A call goes over
the local public switched telephone network
(PSTN) to the nearest gateway server, which
digitizes the analog voice signal using
pulse code modulation, compresses it into IP
packets, and moves it onto the Internet for
transport to a gateway at the receiving end.
Some services using VoIP may only allow you to call other
people using the same service, but others
may allow you to call anyone who has a
telephone number - including local, long
distance, mobile, and international numbers.
Also, while some services only work over
your computer or a special VoIP phone, other
services allow you to use a traditional
phone through an adaptor.
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