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Reliability Systems: A Maintenance Aid
Page 6-1General
6
DEFINITY Enterprise Communications Server Release 5
Maintenance and Test for R5vs/si
555-230-123
Issue 1
April 1997
6
6
Reliability Systems: A Maintenance
Aid
General
A high or critical reliability system provides highly-available call processing
because single points-of-failure in the system that result in loss of call processing
are minimized. Such a system uses the existing duplicated TDM buses, provides
the SPE, translation card, and Tone-Clock circuit pack duplication, and it uses
packet bus redundancy. These components are each single points of failure in a
standard reliability system.
The SPE is fully duplicated. The two SPEs are mounted in separate carriers and
powered by different carrier power supplies. As a result, a high or critical
reliability system has two control carriers: the A control cabinet and the B control
cabinet.
Since the circuit packs in the two SPEs are the same, the SPEs have identical
capabilities. Either SPE can act as the active SPE. However, only one of the SPEs
can be the active SPE at any given time. The active SPE performs the same
operations that the single SPE performs in a standard system; that is, all call
processing, administration, and maintenance activities being performed by the
switch. All memory writes performed on the active SPE are copied to the other
SPE. The other SPE is known as the standby SPE. Its role is to take over as the
active SPE if the current active SPE fails. If the active SPE (or a component of the
active SPE) fails, the system automatically switches to the standby SPE.
Under normal conditions, the system operates using both TDM Buses. If the
system detects transmission problems on one of the buses, it takes that bus
out-of-service and operates with only one bus. This action results in a reduction
in capacity. However, if the system detects a problem with one of the Tone-Clock
circuit packs, it is able to take that circuit pack out-of-service without any impact
on system capacity or performance.