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Technical Specifications
Issue 1 December 1997 10-39
pack and fan shelf failure rates is shown in Table 10-22 and Table 10-23,
respectively.
Operation System Interface Availability 10
The Bellcore objective states that the OS outage should be less than 28 minutes
per year (50 percent hardware, 50 percent software).
*
Therefore, the objective
applies to the TL1/X.25 interface. This objective applies to circuitry needed to
maintain communication from the DDM-2000 OC-12 Multiplexer to the central
office's OS. Since the OS interface is used in the central office, the reliability
model assumes the mean time to repair is 2 hours and the environmental factor is
1.0. Table 10-21 lists the predicted outages for the TL1/X.25 interface.
Optical Module Maintenance Objective 10
According to Bellcore, the objective for mean time between failure (MTBF) of a
one-way regenerator is a minimum of 4 years. A regenerator is defined as any
circuit packs that perform the electrical-to-optical and optical-to-electrical
conversion. The failure rate of the 23G/23G-U OLIU is 11400 FITS according to
the RPP method. This translates to a MTBF of 10 years, which meets the
objective.
Infant Mortality 10
Bellcore requires that the number of circuit pack failures in the first year of
operation should not exceed 2.5 times the number of failures per year beyond the
first year. The ratio of first year failures to failures in subsequent years is known as
the infant mortality factor (IMF). The requirement is to have an IMF of less than
2.5.
†
DDM-2000 OC-12 Multiplexer circuit packs are subjected to an environmental
stress testing (EST) program. The purpose of the program is to eliminate early life
failures, conduct failure mode analysis on defective circuit packs, and use
corrective action to make the product more reliable. All new circuit pack codes in
manufacturing are subjected to EST. However, based on field return data, when
the early life failures for any circuit pack codes have been minimal and the infant
mortality factor is below 2.5, these circuit pack codes may be subjected only to
sampling EST.
* TA-NWT-000418, Issue 3, November 1991, p. 36.
† TA-NWT-000418, Issue 3, November 1991, p. 40.
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