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G
G.711 a law, G.711 µ law
Standard for a Codec.
G.711 delivers a very good voice qual-
ity that corresponds to that in the ISDN
fixed network. As there is little com-
pression, the necessary bandwidth is
around 64 Kbit/s per voice connection,
but the delay caused by coding/decod-
ing is only 0.125 ms.
"a law" describes the European stand-
ard and "µ law" describes the North
American/Japanese equivalent.
G.726
Standard for a Codec.
G.726 delivers a good voice quality. It is
inferior to the quality with codec G.711
but better than with G.729.
G.729A/B
Standard for a Codec.
The voice quality is rather less with
G.729A/B. As a result of the high level
of compression, the necessary band-
width is only around 8 Kbit/s per voice
connection, but the delay is around
15 ms.
Gateway
Connects two different Networks,
e.g. a router as an Internet gateway.
For phone calls from VoIP to the tele-
phone network, a gateway has to be
connected to the IP network and the
telephone network (gateway/VoIP pro-
vider). It forwards calls from VoIP to the
telephone network as required.
Gateway Provider
See SIP provider.
Global IP Address
See IP address.
GSM
Global System for Mobile Communication
Originally, European standard for
mobile networks. GSM can now be
described as a worldwide standard. In
the USA and Japan national standards
are now more frequently supported
than in the past.
H
Headset
Combination of microphone and head-
phone. A headset makes handsfree
talking more comfortable. There are
headsets available which are con-
nected to the handset by a cable.
HTTP Proxy
Sever via which the Network subscrib-
ers can process their Internet traffic.
Hub
Uses one Infrastructure network to
connect several Network subscribers.
All data sent to the hub by one network
subscriber is forwarded to all network
subscribers.
See also: Gateway, Router.
I
IEEE
Institute of Electrical and Electronics Engineers
International body that defines stand-
ards in electronics and electrotechnol-
ogy, concerned in particular with the
standardisation of LAN technology,
transmission protocols, data transfer
rate and wiring.
Infrastructure network
Network with central structure: all
Network subscribers communicate
via a central Router.
Instant messaging
(German: immediate exchange of messages)
Service that uses a client program to
allow chatting in real time, i.e. to send
brief messages to other subscribers on
the Internet.
Glossary
117
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