Nortel Networks i2021 Series manual Point-to-Point Circuits, Passive-Bus or Multipoint

i2021 ISDN Teleset

Point-to-Point Circuits

A point-to-point application typically has the Terminating Resistors “On” at both ends of the interface.

Fig. 5: Terminating Resistor Range

Passive-Bus or Multipoint

These may be new terms to you, so we will define them so you can better understand their meaning. Passive Bus means that you can connect several devices to the same Basic Rate Interface (ISDN line). Improperly set Terminating Resistors account for many of the problems with ISDN service. The “short version” of this explanation is that both ends of a bus or circuit must be terminated.

Your choices of terminating resistance are two: none or 100 Ohms. The idea is to terminate both ends of the bus. Set the resistors to ON at both ends of the bus.

The best advice is to follow the instructions given by the NT1 manufacturer and those of your terminating devices.

In the following configuration, the Terminating Resistors are “On” at both ends of the interface. The resistors are on at the NT1 and “On” at the farthest i2021 from the NT1.

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