Marconi OMS 1200
Technical Product Description
221 02-ZAP 701 25/1 Rev C 2006-08-04
© Ericsson AB 2006
03PHB00004AAV-CUA
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7.4.4.1
Bi-directional Revertive Mode
In this mode, traffic in both directions of transmission is switched automatically to the
protection channel in case of failure of the working channel (even if the failure is in
only one direction of transmission). To ensure that both multiplexers at each end of
the section always switch to the same channel, signalling via the K1, K2 bytes of the
SOH is performed.
In Revertive mode, for 1+1 protection, one of the two identical STM-n channels,
designated working channel 1 (Worker Channel 1), is the preferred path for the traffic.
The other channel is designated protection and is used for traffic only when the
working channel fails. Consequently, traffic on the protection channel is automatically
switched back (revert) to the working channel upon recovery of the latter.
If a mode mismatch is detected in this mode, the SMA stays in Revertive mode.
7.4.4.2 Bi-directional Non-Revertive Mode
Switching for this mode is in both directions in an identical manner to bi-directional
Revertive mode. However, in bi-directional non-revertive mode, traffic on the
protection channel is not switched back to the working channel upon recovery of the
latter. Instead, traffic remains on the protection channel until the protection channel
itself fails (or manual switching is performed). Non-revertive mode of operation is
designed to prevent unnecessary disturbances to traffic, which occur when a revertive
mechanism switches back.
Note:
Although the aim is to make protection switching of channels in an SMA
hitless, this may not always be guaranteed.
For 1+1 protection, there is no conceptual distinction between the channels in
non-revertive mode and traffic switching between them takes place in an essentially
symmetrical manner (i.e. there is no preferred channel). However, the two channels
are still termed Working Channel 1 and Protection Channel, including the identification
of the channels to an operator via the NMI
7.4.4.3 Unidirectional Revertive Mode
Unidirectional mode means that the transmit and receive directions do not relate to the
same worker. The switching decision is based solely on local traffic performance
indications received on the incoming STM-n channels (or locally generated manual
switch commands). The local receive two-way selector switch therefore operates to
select the protection channel when the working channel fails.
Revertive operation means that the switch operates to select the working channel
upon its recovery, as for bi-directional Revertive mode, although, in unidirectional
mode, the SMA only considers the local working channel recovery conditions.
Signalling between the two SMAs at each end of a multiplexer section is not required
in unidirectional mode. However, K1 and K2 bytes are still exchanged to provide
indications of local actions to the remote end (rather than requests for action).
It is possible to use Unidirectional Revertive mode on all 1+1 protected SMA
equipment using the ITU-T/ETSI standard protocol.
