Reference:Configuration/BRI/Physical

The basic settings of the ISDN Basic Rate interfaces (TEL, PPP, BRI) can be made here.

NT Mode:	The interface is operated in TE (Terminal Equipment) mode as standard. It behaves like a normal ISDN terminal and synchronises itself to the network clock (clock slave). A checked check box operates the interface in NT (Network Termination) mode. It behaves like an ISDN network termination (NTBA) and provides the clock (clock master).
Do not use for synchronisation:	TE Mode interfaces are by default used to obtain the clock for the internal PCM bus. With this checkmark the interface can be excluded as clock source. This can be checked to control where the device gets its clock from. (For a direct cable from one ISDN interface to another ISDN interface of the same box, this checkmark has to be set on the TE interface for such a connection, because synchronization does not work). Only visible if 'NT Mode' is unchecked.
Swap tx/rx:	Swap the transmit/receive.
100 Ohm Termination:	Turns on 100 Ohm bus termination.
Supply Inline Power:	A checked check box turns on the power supply for the relevant interface.
µ-law:	This check box must be checked if the device is located in a country that uses the ISDN µ-law standard. This includes the North America and Asian region, for example.
Permanent Activation:	Activates the line permanently. Only in TE mode.
Loopback:	A checked check box enables the loopback function. This is only necessary for conformance test purposes.

Pinout of the BRI connector

RX and TX can be swapped for NT operation with software configuration so that no crossover cable is needed.

TE Mode

Pin	Function
3	TX+
4	RX+
5	RX-
6	TX-

NT Mode

Pin	Function
3	RX+
4	TX+
5	TX-
6	RX-