ZyXEL Communications IES-1248-51A, User Manual

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IES-1248-51V User’s Guide
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H A P T E R
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VoIP
This chapter shows you how to configure the Voice over Internet Protocol (VoIP)
features on your IES-1248-51V.
45.1 VoIP Overview
VoIP (Voice over IP) is the sending of voice signals over the Internet Protocol. This
allows you to make phone calls and send faxes over the Internet at a fraction of
the cost of using the traditional circuit-switched telephone network. You can also
use servers to run telephone service applications like PBX services and voice mail.
Internet Telephony Service Provider (ITSP) companies provide VoIP service.
Circuit-switched telephone networks require 64 kilobits per second (kbps) in each
direction to handle a telephone call. VoIP can use advanced voice coding
techniques with compression to reduce the required bandwidth.
The IES-1248-51V connects POTS (Plain Old Telephone System) end-user
telephone subscribers to the IP network by converting the analog voice signal into
data packets and transmitting them over the network.
45.1.1 Introduction to H.248
The H.248 protocol, also known as MEGACO (MEdia GAteway COntrol) or the
Gateway Control Protocol, defines a VoIP network in which basic functions (such
as voice coding and decoding) are performed by one device, and higher functions
(such as setting up and managing calls) are performed by another.
The H.248 protocol was developed jointly by the IETF (Internet Engineering Task
Force) and the ITU (International Telecommunication Union). It is defined by the
IETF in RFC 3525, and by the ITU in ITU-T H.248-1.
An H.248 VoIP network has a single intelligent control unit, which manages a
network of dumb endpoint devices.
An H.248 VoIP network consists of one or more media gateways and a media
gateway controller.