Network Router User Manual
1.7.1. Denitions
For the purpose of clarifying the descriptions the following denitions are used:
Failure: A failure is detected whenever a heart beat times out without receiving a monitoring
packet from both interfaces. Only the active node sends monitoring packets. e inactive node
passively listens for the monitoring packets. e inactive twin always forwards monitoring
packets. In order for an active node to receive a monitoring packet it has to complete a round trip,
such as, out IP side to twin, in IP side of twin, out 709.x side of twin, in 709.x side, or going the
other way, out 709.x side to twin, in 709.x side of twin, out IP side of twin, in IP side. A failure
may be detected on one or both interfaces.
Fault: Once a failure is detected, both twins perform a diagnostic by actively interrogating each
other on both interfaces. If the interrogation on a particular interface fails then a fault has
occurred on that interface. An alarm is generated when a fault has been determined. A fault on a
particular interface is cleared whenever a monitoring packet is received or if a diagnostic
interrogation succeeds. A cleared fault generates an alarm cleared.
Both nodes independently report failures and faults. It is possible to have a failure but not a fault.
e converse is not true. It is possible for only one twin to report a failure. For example if either
interface has failed the active node will not receive any round trip monitoring packets so it will
report a failure on both interfaces. However it will only report a fault on one. In the same event
the inactive twin will report a failure on only one interface not both. e inactive will report a
fault on one interface.
Alternatively if one interface fails and then some time later the other interface fails, the initially
active twin will not diagnose the second fault. e initially inactive twin, however, will diagnose
the second fault. erefore in order to fully characterize the failure and fault state of a redundant
pair the state of both devices must be examined. Moreover, the monitoring application is on the
LON side. In the event of an IP failure the alarm SNVT sent by the active node may not be
received by a monitor HMI on the IP side. Although the alarm is sent out both sides, the IP side
has failed so the alarm can’t propagate on the IP side and the inactive twin may not have switched
to forwarding mode in time to forward the alarm packet. Nevertheless, the inactive device will
also detect the fault and its alarm will propagate.
1.7.2. Status SNVT
e twin monitoring application has a status SNVT type 93. If bound, the status SNVT is
propagated either on a timer, or when it is updated by the monitoring application, or both, or
neither. If propagate on update is o and the update time is zero then the status SNVT will
never be scheduled for propagation. In this case the only way to read the status SNVT is to poll it.
If propagate on update is o and update time is non zero then the status SNVT will propagate
at an interval specied by the update time. If propagate on update is on and update time is non
zero then the status SNVT will propagate both on the update time interval and anytime the status
is changed. If the update time is zero and propagate on update is on then the status SNVT will
only propagate when changed or updated by the monitoring application. Typically the status is
updated when the twin mode state changes.
e elds used in the status SNVT are as follows:
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