TELE-X - a Satellite System for TV and Data Communication ...

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BJORN LENGQUIST
PER AKE WIBERG
Ericsson Information Systems AB
Functional separation
A network supervision system has to continuously
collect and present information regarding
the operation of the network. It must also be
able to detect faults and advise on how to clear
these, fig. A.
The supervision system includes an administrative
function in order to facilitate the operation
and maintenance of the network equipment.
The data transmission network, which provides
the circuits between the data terminal equipments,
consists of modems, multiplexers and
lines. The modems convert the digital data flow
to signals that can be transmitted over long
distances via telecommunication lines. The
multiplexers exploit the transmission capacity
of a line so that it can be used for several different
purposes simultaneously.
The data terminal equipments, DTE, can be of
different types. In a large network some terminals,
for example communication and host
computers, take a bigger load than others.
Other terminals are of the work station type
(visual display units, personal computers).
The supervision of the terminals is usually separated
from the network supervision. However, it
is not advisable to separate these functions entirely.
With integrated supervision it must be
possible to check the function of a whole system
from a single point.
Supervisory functions
Monitoring, fig.B, means that the system collects
data continuously from the supervised devices
and compares the values with values
stored in a memory. If the data deviate from the
expected values, an alarm is sent to the operator.
With the aid of a number of test functions he
can then trace the cause of the fault. The operator
can eliminate the fault temporarily by making
reconnections in the network. He can also
connect in standby equipment if available.
The monitoring requires a signalling channel
between the supervision centre and each device
in the system. This channel, designated the
diagnostic channel, is used to transmit values
from the devices to the supervision terminal,
and to send commands to the parts that carry
out tests and functional checks.
The diagnostic channel can be designed in different
ways, as a separate channel or a secondary
channel. If it is built as a secondary channel,
it is possible to utilize the frequency band on the
line between the two modems. If the transmission
equipment does not permit a secondary
channel, as in the case of baseband modems, a
separate channel is set up. This means that either
a separate line is installed or a temporary
circuit is connected up.
The central equipment controls the communication
with the monitoring and test devices. It
also holds information regarding the current
state of the system, since all changes are recorded.
The operator's work station includes a
visual display unit, a printer and a keyboard.
Administrative functions
One of the major problems in large communication
networks is how to get access to information
concerning all the supervised devices in
the system. The system must be able to distinguish
between the various devices as regards
type, function, supplier, when it was
bought, service contract and history. Moreover
the system must also be able to maintain a register
of fault reports and the actions to be taken
when an alarm is obtained.
The administrative functions in a supervision
system should include aids for analyzing the
large amounts of data collected, for example as
regards the intensity of a certain type of fault
during a specific period.
The system should also include a program that
measures (and outputs) the load on a specific
component in the network, e. g. the number of
characters of commercial traffic per unit on a
transmission route. Such a function would be of
great assistance to the administrator, since it
would give the amount of traffic at different
times.
Graphic presentation contributes to efficient interworking
between the operator and the supervision
system. The display shows the position of
every device in the network, its function and
place in the system. All deviations from the normal,
as well as the actions taken, are shown on
the screen in different colours or with different
intensity.
The development of aids for administrative
functions is based on products from Ericsson
Information Systems.
Fig. B
Monitoring is carried out with the aid of units
placed at the modems and other supervised
devices. The central control equipment is connected
to the monitoring units via a signalling
channel, and informs the operator about the
current state of the system via a visual display
unit or printer