Avaya MCC1 Maintenance Procedures page 249

around a small number of failed leads. The TN771D circuit pack provides a standalone mode (that
is, one that does not involve communication with the SPE) for inspecting the packet bus for faults.
This is a critical tool for the packet bus fault correction procedures, which are described later.
Effect of circuit pack failures on the packet
bus
A failure of any of the circuit packs described in the previous section can disrupt traffic on the Packet
Bus. Some failures cause actual Packet Bus failures with corresponding alarms, while others cause
service outages without alarming the Packet Bus (although the failed circuit pack(s) should be alarmed).
The following list discusses the effects on the Packet Bus of a failure on each circuit pack that uses the
Packet Bus.
• TN778 Packet Control. A failure of the Packet Control typically causes all Packet traffic in the
system to fail. As a result, ISDN-BRI sets are not able to make or receive calls, and
communication with an ASAI adjunct fails. A failure of the Packet Control may also cause a
failure of the Packet Bus itself if the failure is on the interface circuitry. Otherwise, only the
Packet Control is alarmed.
In a High or Critical Reliability system, there is one TN778 Packet Control in each SPE. If a
Packet Control failure in the active SPE causes a Packet Bus disruption, performing an SPE
interchange may restore service. In some cases, circuit pack failures may require that the circuit
pack be replaced before service is restored.
TN570 Expansion Interface. A failure of the Expansion Interface typically causes all Packet
•
traffic in the connected EPN to fail. If the failure is on the Packet Bus interface, the Packet Bus
may be alarmed as well.
In a High or Critical Reliability system, there is one EPN link in each control carrier for each
EPN. If an active Expansion Interface failure causes a Packet Bus disruption, performing an
Expansion Link switch may restore service. In some cases, circuit pack failures may require that
the circuit pack be replaced before service is restored.
• TN556 ISDN-BRI Circuit Pack. A failure of the ISDN-BRI circuit pack typically causes some
or all ISDN-BRI sets and data modules and/or an ASAI adjunct connected to the circuit pack to
fail to function. If the failure is on the Packet Bus interface, the Packet Bus may be alarmed as
well.
TN771 Maintenance/Test. A failure of the Maintenance/Test may cause an incorrect indication
•
of a packet bus failure or the inability to detect such a failure. A failure of the packet bus interface
of the circuit pack may cause the packet bus to be alarmed.
A failure of the packet bus interface on any of the circuit packs discussed can cause the packet bus to be
alarmed. This is true because such a failure may result in shorting packet bus leads together. This
typically disrupts ALL packet bus traffic in the affected port network. A failure of the packet bus in the
PPN affects packet traffic in the EPNs as well. Also, packet bus failures that do not affect all endpoints on
that packet bus may occur. Therefore, a packet bus failure should not be ruled out even if some packet
service is still present.
A circuit pack can fail in a manner such that it transmits bad data on the Packet Bus. If the Packet Control
fails in such a fashion, all Packet traffic is disrupted (because all traffic requires the Packet Control).
Likewise, such a failure on the Expansion Interface may disrupt all Packet traffic in that port network.
Maintenance Procedures
December 2003
Packet and serial bus maintenance
S8100 packet bus fault isolation and repair
249