Glossary

G

G.711 a law, G.711 µ law

Standard for a Codec.

G.711 delivers a very good voice quality 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 standard 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 bandwidth 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 telephone 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 ProviderSee SIP provider.Global IP AddressSee 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 connected to the handset by a cable.

HTTP Proxy

Sever via which the Network subscribers 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 standards 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.

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