S.CON1M TX/FX Managed Converter
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12 – Fault Propagation ( FP) mechanism
The main purpose of fault propagation mechanism implemented in media converters is
to allow real-time notification of any link failure to upper hierarchy devices (e.g.
switches/routers with redundant links), consequently activating an alternate path to
communicate with a mission critical site. However, such mechanisms implemented in
other vendors’ products, may suffer from an inherent drawback. These are typical bi-
directional mechanisms: fault propagates both from fiber to TP port and from TP to the
fiber port. When such devices are connected to modern devices implementing FEF
(Far End Fault) it may become a lethal combination: while propagating the fault as
intended, when fault (original link break) is repaired (i.e. original link is restored), such
systems will hang and can be restored only by manual intervention.
The powerful fault-propagation mechanism implemented in the S.CON1M prevents
such deadlock. The fault propagation is bi-directional,
(F >T, and/or T >F).
When
S.CON1M senses loss of its UTP link, it deliberately cuts its F/O link (T > F) and if the
F/O link is disrupted, the SCON1M will cut its UTP link (F > T).
The S.CON1M utilizes a unique bidirectional FP mechanism. When turned on, both FP
directions are at their “stand by” state, hence, F>T or T>F can be activated. However,
only one FP direction can be activated at any time. When a FP direction has been
activated due to a link down signal, the other direction FP is blocked and cannot be
active for as long as the first direction FP holds. This powerful mechanism allows free
operation of the S.CON1M with all types of FP or FEF enabled devices.
When a Master Unit at the central node (router/switch) becomes aware that its TP port
is disrupted (to which a remote end device is connected), it may trigger a back-up
mechanism (if equipped with such feature and a redundant link is needed to the
remote site) and/or alert the network manager.
The FP mechanism is enabled/disabled by means of the DIP switch S5, whereas the
F>T and T>F are under control of the SNMP agent management module.
The FP mechanism should be disabled while installing or maintaining the network.
Normally while installing a F/O network, it is common to establish first a F/O link and
only afterwards to connect the network devices to the converters.
The
Link Test
mode is for diagnostic purposes.
The Link Test in the S.CON1M unit is enabled through the DIP switch S5 (UP position)
disabling the FP mechanism.
In this mode each of the link segments (typically 3: TP, F/O, TP) provides separate
and true indication of its integrity therefore the defective link can be identified and
consequently repaired (following the FP activity due a link failure). After repairing (or
completing installation), set the DIP switch S5 to Down position to resume the Fault
Propagation mechanism.
While in TEST mode, the S.CON1M provides full functionality and run normal data
traffic, except the fault propagation is disabled. In other words, if one or both
converters forming the link are – by mistake or negligence left in this mode, it will not
obstruct the normal data traffic.
When interconnecting some legacy devices, you may experience linking-up problems.
In such case, it is recommended to disable momentarily the Fault Propagation feature
(remain in Test Mode). If however, the FP is needed, make sure that all the links (F/O
and UTP) are operative in the network, and only afterwards re-enable the FP
mechanism.
