ADTRAN 1200063L1, Manual

Page: 19 / 137

Chapter 1. Introduction
61200063L1-20 DSU III TDM User Manual 1-3
DIAL BACKUP OPERATION
The DSU III TDM may be configured with optional dial backup cards.
This allows the TDM to back up the DDS circuit in the event of an inter-
ruption. The TDM supports dial backup operation over 4-wire Switched
56, 2-Wire Switched 56, 1B+D ISDN, or analog (V.32 bis) public service
telephone network (PSTN) when equipped with the appropriate dial
backup module.
Contact your local telco provider to determine which services are avail-
able for your location.
The DSU III TDM equipped with a Switched 56 or ISDN module can auto-
matically or manually back up all four ports in the event of a DDS circuit
failure. Upon restoration of the DDS circuit, the DSU III TDM can be au-
tomatically or manually returned to dedicated operation.
When using analog V.32 bis backup, only port 1 is backed up.
When operating at a DDS loop rate of 64 kbps, the TDM is capable of back-
ing up all four ports over the Switched 56 service if no more than 52.8 kbps
of bandwidth has been allocated to the ports.
If more than 52.8 kbps of bandwidth has been allocated to the four ports,
the TDM turns off ports during dial backup until the 52.8 kbps limit is not
exceeded. Ports are turned off in the sequence 4, 3, and 2. For example, in
Figure 1-1 on page 1-2, ports 3 and 4 would be turned off during dial back-
up.
Overview of Dial Backup Options
4-Wire Switched 56 Backup Option
This 4-Wire Switched 56 Service allows customers to pay for data connec-
tion only for the time the unit is active. The regional operating companies
provide the 4-wire local loop service to SW56 customers.