The Maintenance/Test Circuit Pack (TN771D)
Issue 4 May 2002
9-11 555-233-123
The yellow LED on the TN771D Maintenance/Test circuit pack provides a visual
indication of the state of the packet bus, as follows:
■ Blinking at a rate of 1 per sec — the Maintenance/Test Packet Bus port
cannot swap leads to correct a Packet Bus fault (that is, there are too many
faults). The Packet Bus may be unusable. If the failures detected by the
Maintenance/Test Packet Bus port are open lead failures, the Packet Bus
may still be operating.
■ On steady — the Maintenance/Test Packet Bus port has swapped leads
on the Packet Bus. The Packet Bus is still operating.
NOTE:
Because the yellow LED on the Maintenance/Test circuit pack can
also be on steady when the other ports on the circuit pack are in use,
the ports on the Maintenance/Test circuit pack used for ISDN-PRI
trunk testing must be busied out before the Maintenance/Test circuit
pack is used to help resolve Packet Bus faults. This is done via the
busyout port PCSS02 and busyout port PCSS03 commands. Also,
be sure to release these ports when the process is completed.
■ Off — there is no Packet Bus fault present.
NOTE:
It takes 5 to 10 seconds for the LED to respond to a change in the
state of the Packet Bus.
In normal switch operation, the Maintenance/Test provides the visual feedback of
the Packet Bus state. When standalone mode (described in the next section) is in
effect, these visual indications are still provided; however, the Packet Bus is never
reconfigured, and, as a result, the yellow LED either blinks or is off.
Standalone Mode
The TN771D Maintenance/Test provides a standalone mode for detecting Packet
Bus faults. In the standalone mode, a terminal is connected to the
Maintenance/Test circuit pack via the Amphenol
™ connector on the back of the
cabinet. This setup allows the System Technician to determine the state of the
Packet Bus without having to access the Manager I terminal to provide these
functions, even if the switch is not in service. Note that the Maintenance/Test does
not reconfigure the Packet Bus when it is operating in standalone mode.
Standalone mode is used in the Packet Bus Fault Correction procedures. As a
result, a TN771 and a corresponding terminal must be available to the
technician who is to perform such procedures. A High or Critical Reliability
system has a TN771 in each port network. However, the customer of a system
that does not have High or Critical Reliability may have purchased a TN771 for
ISDN-PRI trunk testing, or to increase the system’s ability to detect Packet Bus
failures.
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