Nortel i2021 Series User Manual

Nortel i2021 Series User Manual Manual pdf 13 page image

i2021 ISDN Teleset7Point-to-Point CircuitsA point-to-point application typically has the Terminating Resistors “On” atboth ends of the interface.Fig. 5: Terminating Resistor RangePassive-Bus or MultipointThese may be new terms to you, so we will define them so you can betterunderstand their meaning. Passive Bus means that you can connectseveral devices to the same Basic Rate Interface (ISDN line). Improperlyset Terminating Resistors account for many of the problems with ISDNservice. The “short version” of this explanation is that both ends of a busor circuit must be terminated.Your choices of terminating resistance are two: none or 100 Ohms. Theidea is to terminate both ends of the bus. Set the resistors to ON at bothends of the bus.The best advice is to follow the instructions given by the NT1 manufacturerand those of your terminating devices.In the following configuration, the Terminating Resistors are “On” at bothends of the interface. The resistors are on at the NT1 and “On” at thefarthest i2021 from the NT1.