user manual

DEFINITY Enterprise Communications Server Release 5
Maintenance and Test for R5vs/si
555-230-123
Issue 1
April 1997
Packet Bus Fault Isolation and Correction
Page 9-7Maintenance of the Packet Bus
9
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.
Maintenance of the Packet Bus
The following topics are discussed:
■ Comparison between the Packet Bus and the TDM Bus
■ Packet Bus Maintenance Software
■ Overview of Fault Correction Procedures
Packet Bus and TDM Bus: a Comparison
Although the Packet Bus is similar to the TDM Bus in many ways, there are some
important differences. For example, there are two physical TDM Busses in the
switch (refer to the TDM-BUS section in Chapter 10, ‘‘
Maintenance Object Repair
Procedures’’, for more information), and one of these busses can fail without
affecting the other (although half of the call-carrying capacity is lost in this case).
On the other hand, there is only a single Packet Bus in the switch, and a failure of
that bus can disrupt all traffic on the Packet Bus.
In High or Critical Reliability systems, the Maintenance/Test circuit pack provides
Packet Bus reconfiguration capabilities. This allows the Packet Bus to remain in
service with up to three lead failures. There is no corresponding facility on the
TDM Bus, where the second physical TDM Bus continues to carry traffic until
repairs are completed.
In addition, the system response varies according to the type of bus failure.
Specifically, a catastrophic TDM Bus failure (one that affects both TDM Buses)
disables ALL traffic in the system, while a catastrophic Packet Bus failure affects
only Packet traffic. This means that all TDM traffic is unaffected, while all BRI and
ASAI traffic does not work. The significance of this distinction depends on the
customer’s application. (For example, a customer whose primary application
requires ASAI would consider the switch to be out of service, while a customer