Field Trial of Optical Fibre Cable-TV System Optical Fibre System for ...

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Fig. 2
Automatic testing of multiplexing equipment after
manufacture
Reliability predictions of failure occurrence
as a function of time provide information
regarding the future behaviour
of the equipment and the system. The
result is also used as a basis for the planning
of maintenance and for calculating
the operating costs during the life of the
equipment, life cycle costs (LCC).
The reliability of complex systems and
networks depends on their design and
construction. The calculations are
based on the predicted reliability of the
equipment used.
The purpose of the telecommunication
network is to offer the customer good
services. The service quality in the network
is a function of such factors as the
availability of the network.
In order to meet technically and economically
feasible availability requirements
and to increase the probability of
transmission paths surviving catastrophes
it is sometimes necessary to introduce
redundancy at relevant points in
the network. The views on the use of
redundancy expressed here are based
on Ericsson's experience of the operation
of equipment with high built-in reliability.
They may be of assistance when
deciding on the requirements and design
of redundancy in systems, links or
networks.
Reliability is one of the basic design parameters
in Ericsson's transmission
equipments. High built-in reliability has
been achieved by
- using selected components of high
quality 1
- limiting the stress by reducing the
power (derating)
- reducing the power consumption in
order to keep the temperature low
- careful checking of components and
manufacture
- improving the design on the basis of
operational experience (follow-up).
It is certainly economically justifiable to
have high reliability built into the equipment
right from the start. Loss of income
and the cost of maintenance work and
spares in connection with failures can
warrant the expenditure of up to 40%
more for equipment with higher built-in
reliability 6 .
If a decision-maker is to be able to assess
and trust the data supplied by the
manufacturer the prediction method
must be known and its trustworthiness
verified. Prediction results must be presented
in a suitable form and a clear
manner and should be easily understandable
even by non-specialists, i.e.
anybody with a normal technical training.
The panel "Terminology and Definitions"
explains concepts and termsina
somewhat simplified form.
It is a difficult task, and one of considerable
responsibility, to express oneself
in a simple and easily understandable
way in a discipline that uses such complicated
mathematical tools as those
used for reliability calculations. The
price that has to be paid for simplicity is
reduced mathematical accuracy, limited
terminology, simplified models and
last but not least, some loss of the author's
technical prestige.
Reliability prediction and its
trustworthiness
Prediction method
The prediction is carried out by mean
of special computer programs, using
the parts count method, i.e. the fa""