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Circuit Packs That Use the Packet Bus
Issue 4 May 2002 9-7 555-233-123
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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.
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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.
However, if an ISDN-BRI circuit pack fails such that it transmits bad data, all
devices connected to the circuit pack fail to function. This failure may also disrupt
the entire Packet Bus whenever the circuit pack tries to transmit data. Such a
disruption may be indicated by Packet Bus alarms that occur and go away,
intermittent failures of other Packet circuit packs, and/or interference with other
connected endpoints. The failures mentioned are difficult to isolate because of
their intermittent nature. In most cases, the failed circuit pack is usually alarmed,
and all connected endpoints on the circuit pack are out of service until the circuit
pack is replaced. These symptoms help in isolating the fault.