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Fig. 5.10 Mixed multiplexing and direct calls for network management data

The NMS allows several different classes of user, and the class is associated
with the logon identification of the user. This allows a network manager
to access the system from any point in the network, and to retain the full
privileges enjoyed when using a terminal directly attached to the NMS.

The normal management of the network is carried out by users classed
as operators. When an operator logs on to the NMS, a menu giving
access to eight sub-systems is presented, all of which are related by a
database at the heart of the NMS.

The following sections show the features of these sub-systems.
Testing sub-system The testing sub-system allows the operator to request
components in the network to perform loopback tests, to determine the
quality of modems and physical circuits. The components use the V.54
controls described in Chapter 3.

The operator is able to specify which loopback test to perform, and
the duration of the test. The results can be examined when the test is
complete, and partial results can be examined as the test is running. The
results are stored in the database, allowing the operator to monitor
degradation in performance at leisure.

Control sub-system The control sub-system gives access to the individual
physical ports of each component in the network, and allows the operator
to start, stop, or close activity on the port. These terms were described in
Chapter 2.

The operator is also able to control the Network Management Protocol
on a link, without affecting other calls. This may be useful if a component
that was multiplexing a number of calls goes down and has to be replaced.
The Network Management Calls then need to be re-established. The
sub-system also allows the operator to restart units where more gentle
techniques of problem solving have not been successful.

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