Verilink DIU 2130 (880-503297-001) Product Manual - Manual (Page 51)

T1 Dial Backup Option Overview
Verilink 5-3
How dial backup
works
The T1 Dial Backup Option allows a Verilink DIU 2130/DBU to
automatically connect both nodes of a circuit to a dial-up circuit
and switch the Data Terminal Equipment (DTE) data to the dial-up
circuit.
Events that indicate a circuit failure at the near-end are:
• Loss of frame (LOF) on the T1 signal
• DDS ASC within the channelized data
Either node can initiate dial backup mode. The far-end monitors the
incoming calls and responds automatically to complete the circuit.
When both sides are connected, the DIU 2130/DBU(s) switch the
Data Terminal Equipment (DTE) data to the dial backup circuit.
The dedicated T1 portion of the circuit remains intact for
troubleshooting. The DIU 2130/DBUs route the DTE data over the
backup circuit until the dedicated circuit can be restored.
When the T1 circuit comes back up, the system automatically
switches back to the T1 circuit. (See the Caution in the section
Managing Alarms and Testing, on page 510.) The operator can use
AM2000 to manually override the automatic mode setting at any
time.
AM2000 also tracks the status of the switching and the associated
alarms and sends test patterns.
Each DIU 2130/DBU supports one dial backup circuit. (Both Port 1
and Port 2 are dedicated to the option.) Port 2 of the DIU 2130/DBU
is always the backup circuit. Figure 2 diagrams the switched and
unswitched modes internal to the DIU 2130/DBU.
Figure 2 Internal State of the DIU 2130/DBU in Normal and Backup Modes of Operation
The DTR control lead of the DCE attached to Port 2 of the
DIU 2130/DBU is used to initiate the call to the dial backup circuit.
The handshake lead Carrier Detect (CD) is monitored in the answer
mode at the central site. Backup mode initiates when:
1. Loss of Frame is declared for the T1 line. LOF is defined as 2.5
seconds ( ± 0.5 seconds) of Out of Frame (OOF) integrated
(therefore applying a leaky bucket algorithm for an
intermittent T1 circuit).
DTE Connection
DIU 2130/DBU
Backplane
Bus
DIU 2130/DBU
Backplane
Bus
Port 1
Port 1
Port 2
Port 2
NORMAL MODE BACKUP MODE
LOF
SW 56 DSU