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ISDN BRI Interface 129
equipment complying with relevant ISDN standard of ITU-T able to access ISDN
easily.
User-network interface specification of ISDN:
In ITU-T I.411 recommendations, reference configurations for ISDN user-network
interfaces are given according to concepts of function group (a group of functions
required by users to access ISDN) and reference point (a point used to distinguish
function groups), as shown in the following diagram.
Figure 47 Reference configuration of ISDN user-network interface
The function group includes:
■ Network terminal 1 (NT1): It mainly fulfills functions of OSI layer 1 including the
subscriber line transmission function, loop test and D channel contention.
■ Network terminal 2 (NT2): Also called intelligent network terminal, including
layer 1-layer 3 of OSI.
■ Type-1 terminal equipment (TE1): Also called ISDN standard terminal, which is
user equipment conforming to ISDN interface standard (such as digital phone
set).
■ Type-2 terminal equipment (TE2): Also called non-ISDN standard terminal,
which is user equipment not conforming to ISDN interface standard.
■ Terminal adapter (TA): It implements adaptation function, making TE2 to access
ISDN standard interface.
The reference point includes:
■ R reference point: It is between non-ISDN equipment and TA
■ S reference point: It is between user terminal and NT2.
■ T reference point: It is between NT1 and NT2.
■ U reference point: It is between NT1 and line terminal.
Preparations before Configuration
Be clear about the following items before the configuration:
TE2 TA
TE1
S
SR
2345
NT2 NT1
UT
1