Avaya Definity SI Maintenance Manual page 758

Packet Bus Fault Isolation and Correction
TN556, TN2198 and TN2208 ISDN-BRI circuit packs [BRI-BD,
BRI-PORT, ABRI-PORT, BRI-SET, BRI-DAT, ASAI-ADJ] provides
connections for ISDN-BRI station sets and data modules and for ASAI
adjuncts. The Packet Bus is used to carry signaling information for sets and
data modules. The Packet Bus passes signaling information and ASAI
messages between the SPE and the ASAI adjunct. The ISDN-BRI circuit
pack has the same fault detection capabilities as the TN570 Expansion
Interface.
TN771D (or later) Maintenance/Test circuit pack is the workhorse of
packet bus maintenance. This circuit pack can detect all packet bus
failures for the PN in which it resides. In High and Critical Reliability
systems, the circuit pack enables the reconfiguring of the packet bus
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.
9-6 Issue 4 May 2002 555-233-123