MSBR Series 45 Mediant 500 MSBR
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 the IP network).
In the event of a PSTN fallback, the BRI module's metallic relay switch automatically
connects line Port 1 to Port 2. 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 BRI line 1 (Port #1) to a PBX.
2. Connect BRI line 2 (Port #2) to the ISDN network (PSTN).
Figure 5-13: Cabling (Ports 1 and 2) BRI PSTN Fallback
Note: This PSTN Fallback feature has no relation to the PSTN Fallback Software
Upgrade Key.
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