What has to be considered when operating the ISDN S0 bus 2 as TE?



The internal S0 Bus2 of a LANCOM 1723/1823 VoIP is to be operated in TE mode at a PBX or NTBA.


These two LANCOM router models supply a voltage of 40 volts on the internal S0 bus for a phantom power supply of ISDN terminal equipment. This allows ISDN terminal equipment to be operated without its own power supply, even if there is no ISDN exchange line to supply power to the ISDN-1 connection. A total of up to two ISDN telephones can be operated without their own separate power supply.

A consequence of this enhancement is that the second S0 bus CANNOT be operated at an NTBA, even if the 40V power supply has been disabled with the DIP switches. You can, for example, use the internal S0 bus at a PBX system in TE mode if you are certain that the PBX system does not form a through-connection to an NTBA.

Check to be sure that this cannot occur by means of the PBX-system's internal lifeline relay in the case of failure of the PBX. These PBX buses may only be connected to the ISDN-1 port. This limitation does not apply to the LANCOM internal lifeline relay.

If the second S0 bus is operated in TE mode, it is essential to shut off the 40V supply by means of the DIP switch to prevent damage to the equipment.