ELSA LANCOM Business 6000, Руководство пользователя

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Connection via 2-Mbit interface
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ELSA LANCOM Business 6000
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terminal device connection. An additional terminal adapter is thus no longer
required.
5.2.2 G.703 – simple basis for 2-Mbit connections
G.703 is an ITU (International Telecommunication Union) recommendation for
remote digital connections at speeds of 64 kbps or more. In Europe, 2-Mbit
connections in accordance with G.703 are referred to as E1 connections. The
T1 standard generally used in the USA works in the same manner as E1, but
has a bandwidth of only 1544 kbps.
G.703 is a standard on level 1 of the OSI model, i.e. at the physical level. It
defines the electrical and functional characteristics of the connections.
G.703 connections are synchronous and bit-oriented. A continuous stream of
data is transferred between the terminal points, regardless of whether it
actually contains user data.
Higher-level protocols such as G.704 are required to convert the transferred
bits into content.
5.2.3 G.704 structures the data stream
A protocol which provides additional information about the structure of the
transferred bits is required in order to use the continuous but unstructured
data stream for the transmission of content.
The ITU has thus defined a supplementary protocol to G.703: G.704. While
G.704 is not required as a protocol to structure the data stream, its use
provides a number of advantages that will become apparent later in this
chapter.
The combination of G.703 and G.704 is also known as “structured G.703”, as
opposed to the unstructured “G.703”.
Division of bandwidth into timeslots
But what is this structure exactly? G.704 divides the full G.703 bandwidth into
timeslots (timeslots). To determine the bandwidth of an individual timeslot,
the standard was oriented according to the minimal bandwidth required at
the time for voice communications. At the time that the standard was
established, 64 kbps were needed for clean voice communications. As the
timeslots are the smallest independent units for an individual connection,
they were fixed at a bandwidth of 64 kbps.