Modes Of Operation For Sncp - Ericsson Marconi OMS 1200 Product Description

7.5.2

Modes of Operation for SNCP

There are four modes of operation for SNCP, which are operator configurable options
via the NMI. The default mode is Unidirectional Non-Revertive.
Bi-directional switching modes of operation only apply to bi-directional traffic SNCs
and the Operator is prevented from attempting to configure bi-directional switching
modes of operation for unidirectional traffic SNCs.
7.5.2.1 Unidirectional Revertive Mode
In revertive mode, there is a preferred channel for receiving the VC. The preferred
channel is denoted the working channel and the channel used for protection purposes
is denoted the protection channel.
When there are no failure conditions or active operator entered commands, the
receive selector selects traffic from the designated working channel. If there is a failure
on the working channel the switching mechanism, under normal circumstances,
automatically causes a changeover to select traffic from the protection channel.
Upon recovery of the working channel, the selector is automatically switched to select
this channel in preference to the protection channel (after the expiry of any Wait to
Restore period). Only the recovery conditions of the local working channel are
considered.
7.5.2.2 Unidirectional Non-Revertive Mode
This mode of operation is identical to unidirectional revertive mode except that traffic is
not switched back to the working channel from the protection channel when the former
recovers from a failure condition. This prevents the disturbance to traffic which
otherwise occurs when the selector is operated (switching of VCs is non-hitless).
Automatic protection switching is therefore symmetrical between the two channels in
non-revertive mode. However, the two channels are still designated Working and
Protection. The SMA selects traffic from the designated working channel as a default
when first configured for SNC protection or on power-up of the SMA.
7.5.2.3 Bi-directional Revertive or Non-Revertive Mode
If SNCP is applied across the complete end-to-end VC-trail then the two SMAs
involved can operate in bi-directional switching mode. Otherwise, only unidirectional
mode is possible.
In this mode, also named dual ended switching, traffic is switched automatically to the
same (working or protection) channel at each end of the path. In order to ensure that
both multiplexers at each end of the path always switch to the same channel,
signalling via nominated VC POH bits is performed.
Revertive operation means that the switch is operated to select the working channel
upon its recovery and after expiry of any wait to restore time-out.
Non-revertive operation means that the traffic is not switched to the working channel
when the latter recovers.
In bi-directional mode of operation, to avoid multiple switching actions after a WTR
timer expires, the SNCP controller in the local node signals a RR use worker channel
but does not immediately action a switch back to the worker channel.
221 02-ZAP 701 25/1 Rev C 2006-08-04
03PHB00004AAV-CUA
Marconi OMS 1200
Technical Product Description
© Ericsson AB 2006
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