MSBR Series 55 MSBR Series
Hardware Installation Manual 5. Cabling the Device
5.5.2 Connecting the PSTN Fallback for BRI Lines
The device supports PSTN Fallback for BRI lines. If the device loses power, for example,
due to a power outage or the unplugging of its power cable, it automatically routes calls
from the Tel side to the PSTN (instead of to the IP network).
PSTN Fallback is supported if the device houses one or more BRI modules, where each
BRI module provides two or four spans.
In the event of a PSTN fallback, the BRI module's metallic relay switch automatically
connects line Port 1 to Port 2 of the BRI module.
For example, if a PBX trunk is connected to Port 1 and the PSTN network is connected to
Port 2, when PSTN Fallback is activated, calls from the PBX are routed directly to the
PSTN through Port 2.
To connect the BRI line interfaces for 1+1 PSTN Fallback:
1. Connect Port 1 to a PBX.
2. On the same BRI module, connect Port 2 to the PSTN.
Figure 5-32: Cabling BRI PSTN Fallback – Mediant 800B MSBR
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