| 3.3. Importance of the impedance matching adapters (ISDN Adapter) | ||
|---|---|---|
 | Chapter 3. Physical connections |  |
| 3.3. Importance of the impedance matching adapters (ISDN Adapter) | ||
|---|---|---|
| | Chapter 3. Physical connections | |
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:
Point-to-Point (only one device can be connected): an impedance matching adapter is ALWAYS necessary.
Point-to-Multipoint:
If Abilis is the only device to be connected to the network-termination unit of the S0 bus or if Abilis is the farthest device from the NT unit, the impedance matching adapter MUST be inserted.
If Abilis isn't the farthest device, the impedance matching adapter MUST NOT be inserted.
![[Warning]](../images/warning.png) | 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 |
|---|---|
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]](../images/tip.png) | Tip |
|---|---|
Interesting chapters: Section 75.1, “How to configure ISDN ports to connect PBX or ISDN lines”. |
| |  | |
| 3.2. ISDN Basic Rate Interface (BRI) connection |  | 3.4. Connecting pots cards to patch panel |
