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Glossary
Glossary
Bandwidth
The bandwidth defines the size or transmission capacity of a transmission channel, or,
more precisely, the difference between the lowest and highest possible frequency on a
transmission channel. The bandwidth is specified in Hz. For digital data transmission, the
bandwidth determines the data volume that can pass through a transmission channel in
a specified period, i.e., the transmission speed (specified in bit/s).
The bandwidth used to transmit analogue voice data via a digital transmission medium,
e.g., the Internet for VoIP, determines the number of channels that can be used simulta-
neously and the quality of the voice transmission. How the available bandwidth is used to
transmit voice data is determined by the selection of a
. Codecs are available for
broadband transmission up to 64 Kbit/s (
) or narrowband transmis-
sion up to 32 Kbit/s (
£
Broadband mode
For VoIP (digital transmission medium), voice data is transmitted in broadband mode or
£
. In broadband mode, a transmission rate or
£
64 kbit/s is available.
The bandwidth used for the transmission is determined by the selection of a
.
Cell
Wireless coverage area of a base station in a multi-cell DECT network.
Cluster
Subdivision of a DECT network into groups (subnets) by a central management station
(DECT Manager). All telephones in the network use the central functions of the PABX
(VoIP configuration, directories, etc.). However, the base stations only synchronise within
a cluster, meaning that a handover of a handset from one cluster to a neighbouring clus-
ter is not possible.
Codec
Codec is a procedure that digitalises and compresses analogue voice before it is sent via
the Internet, and decodes (i.e., translates into analogue voice) digital data when voice
packets are received. There are different codecs with differing degrees of compression, for
instance.
Both parties involved in the telephone connection (caller/sender and recipient) must use
the same codec. This is negotiated between the sender and the recipient when establish-
ing a connection.
The choice of codec is a compromise between voice quality, transmission speed and the
necessary
£
. A high level of compression, for example, means that the band-
width required for each voice connection is low. However, it also means that the time
needed to compress/decompress the data is greater, which increases the execution time
for data in the network and thus impairs voice quality. The time required increases the
delay between the sender speaking and the recipient hearing what has been said.
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