Packet Bus - Avaya Definity SI Maintenance Manual

Packet Bus Fault Isolation and Correction

Packet Bus

Each port network has its own packet bus, and, accordingly, there is one packet
bus MO in each port network. The packet bus is not duplicated, as is the TDM
Bus. However, there are several spare leads on the packet bus and, in high and
critical reliability systems, these spare leads are used to recover from some
failures on the packet bus.
Packet Bus Usage
The packet bus carries ISDN-BRI signaling information for ISDN-BRI stations and
data modules and for ASAI adjunct connections. The TN556 ISDN-BRI circuit
pack is used for these connections. The SPE interface to the packet bus is the
TN778 Packet Control (in high and critical reliability systems, there is one TN778
in each SPE). For systems with multiple port networks, the TN570 Expansion
Interface is used to pass messages from the packet bus in one port network to 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.
9-4 Issue 4 May 2002 555-233-123