Protection Switching Criteria - Ericsson Marconi OMS 1200 Product Description

7.4.4.4 Unidirectional Non-Revertive Mode
This mode is similar to Unidirectional Revertive mode, but traffic is not switched from
the protection channel to the working channel when the latter recovers. Again, it is
only possible to use the ITU-T/ETSI standard protocol. K1 and K2 bytes are generated
to indicate the local status.
7.4.4.5 Mode Selection
Although you can configure the preferred operating mode, it is possible for the SMA to
automatically select a different mode for operation under certain specific
circumstances. There are two reasons for needing this feature.
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7.4.5

Protection Switching Criteria

MSP switching operates according to events received and detected by the SMA.
These events comprise detected STM-n section failures, operator requests for
switching and remote requests received from the multiplexer at the end of the
protected multiplexer section (via the K1/K2 byte message protocol).
The full list of events, the conditions under which they are considered active/inactive
and a brief overview of the system behaviour are described below.
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Firstly, an SMA may be connected to a remote multiplexer, which has been
inadvertently configured into a different operating mode. The SMA is capable
of detecting this condition and raising any necessary alarms. It also
automatically assumes an appropriate new operating mode to permit
continued traffic protection.
The method of detecting the remote multiplexer operating mode is via the K1,
K2 byte protocol. When a mode mismatch alarm is raised, both the alarm and
the newly assumed operating mode persist for the duration of the protection
switch. If an SMA configured mode is found to be in error, it is possible to
change and re-enter it. If Protection Section is failed, Mode Mismatch is
disabled.
Note: It is necessary to check the operating modes of the multiplexers at
both ends of the link before re-entering the mode
The second condition under which the mode can change is in response to a
locally detected failure of the protection channel. Since the signalling for bi-
directional working is carried over this channel (via the K1, K2 bytes), the
signalling mechanism is regarded to have failed when a local Signal Fail
(protection) is received. If the SMA is configured for bi-directional working, it
automatically adopts unidirectional working during the period that the Signal
Fail is active.
Under these conditions the incoming K1, K2 bytes are not monitored (they are,
in any case set to a default value by the STM-n units), although the outgoing
K1, K2 byte indications are set as for normal unidirectional mode. The mode
mismatch alarm is not set. When the Signal Fail (protection) indication clears,
full bi-directional working is automatically restored.
Marconi OMS 1200
Technical Product Description
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