3.3. Importance of the impedance matching adapters (ISDN Adapter)

When ISDN-BRI ports (e.g. BRI-HFC4, BRI-HFC8) are used, a line termination resistor (ISDN Adapter or impedance matching adapter) must be used to avoid signal reflections. One adapter per port must be used.

The Telecom NT1 Network-termination units and most of the PBX (switchboards) usually have already a line termination resistor. The Abilis BRI port doesn't have any.

Differences between a Point-to-Point connection and a Point-to-multiPoint connection:

Figure 3.4. ISDN Adapter

ISDN Adapter

[Warning]Warning

The impedance matching adapter MUST be connected near the ISDN port of the Abilis (you can use the 10 cm cable provided with the Abilis).

[Warning]Warning

The Improper connection of line terminations may cause disturbances like noisy conversations, data loss, line drops, and in general a poor and unstable service.

[Tip]Tip

Interesting chapters: Section 75.1, “How to configure ISDN ports to connect PBX or ISDN lines”.