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DEFINITY Enterprise Communications Server Release 6
Maintenance for R6vs/si
555-230-127
Issue 1
August 1997
Packet Bus Fault Isolation and Correction
Page 9-4Packet Bus
9
the packet bus in its neighbor. The TN771 Maintenance/Test Circuit Pack
(discussed in detail later) provides packet bus maintenance testing and
reconfiguration capabilities.
Packet Bus Faults
Two types of packet bus failures can occur:
■ Shorts. A short occurs when leads on the packet bus become connected
together. Such a connection can occur due to component failures on the
packet bus interface of a circuit pack, a failure of the cables between
carriers or the TDM/LAN terminators, or by pins being bent together on the
backplane. Usually, a failure that occurs during normal operation is
caused by a circuit pack failure. However, if the system configuration is
being modified (for example, circuit packs are being moved), the cause of
a subsequent packet bus failure is probably bent pins.
■ Opens. An open occurs when there is a break on the packet bus such that
the electrical path to the termination resistors is broken. Usually, this break
is caused by a failed TDM/LAN cable or by a failed TDM/LAN terminator.
The break can also be caused by a failure in the backplane of a carrier,
although this is unlikely.
Shorts on the packet bus occur much more often than do opens. This is because
the incorrect insertion of a circuit pack can cause leads to be shorted together. It
is possible for a circuit pack to be the cause of a packet bus fault but still exhibit
trouble-free operation. For example, the insertion of a TDM-only circuit pack
(TN754B Digital Line) could bend the packet bus pins on the backplane.
However, since the circuit pack does not communicate on the packet bus, the
pack is not affected by the problem.
Packet bus faults do not necessarily cause service interruptions. However, most
packet bus shorts do cause these interruptions. Depending on what leads are
defective, the system may be able to recover and continue to communicate. This
can be detrimental because it makes isolating the fault difficult. The
Maintenance/Test circuit pack provides the capability to detect, and, in some
cases, correct packet bus faults.
Packet Bus Connectivity
Various circuit packs communicate on the packet bus (see next section).
For details on ISDN-BRI and ASAI connectivity, refer to “BRI-PORT” and
“BRI-SET/ASAI-ADJ” in Chapter 10, ‘‘
Maintenance Object Repair Procedures’’.
For details on Expansion Interface connectivity, refer to “EXP-INTF”.