Technical data

98 Theoretical and general applications www.westermo.com
ISDN components/interface
ISDN components include terminals, Terminal Adapters TA, Network-Termination
devices NT, Line Termination equipment LT, and Exchange-Termination equipment
CLA. Two terminal types are used in ISDN. Specialised ISDN-terminals with an ISDN-
interface, Terminal equipment type 1 TE1, and terminals with an interface other than
ISDN, units with a V.24 interface. These are referred to as Terminal Equipment type 2
TE2. TE1 is connected to ISDN with a 4-wire interface “twisted-pair” digital link, while
TE2 is connected to the ISDN network via a TA. The terminal adapter can either be a
freestanding device or an interface card mounted in the TE2 device. When TE2 and
TA are freestanding units, a standardised interface such as RS-232/V.24 or V11/RS-485
is usually used.
The next interface up-stream is the Network terminal, this makes up the interface
between the 4-wire interface in the customer installation and telecom operator’s con-
ventional 2-wire copper cables.
Network terminals are also available in two types, NT1 and NT2, where NT2 is a
more complex device and which makes up layers 2 and 3, protocol functions and con-
centration. NT2s can, for example, be found in office switchboards. In most countries
the network terminals belong to the telecom operator.
In the reference model for ISDN there are a number of reference points established
that make up the interface between the reference model’s devices/terminals according
to the following:
… R --- Reference point that makes up the interface between non ISDN
devices and terminal adapters TA standard RS-232/V.24.
… S --- Reference point that makes up the interface between TE/TA and NT1.
… T --- Reference point that makes up the interface between NT1 and NT2 devices.
… U --- Reference point that makes up the interface between NT and the LT line
terminal.
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