Technical Description
Network layer and physical link layer protection share the following
characteristics:
Permanently Bridged
Identical traffic is transmitted on the active and the
passive physical link/connection.
Uni-directional
Only the affected direction is switched to
protection. The equipment terminating the physical
link/connection in either end will select which line to
be active independently.
Non-revertive
No switch back to the original link/connection
is performed after recovery from failure. The
original active link/connection is used as passive
link/connection after the protection is re-established.
1+1
One active link/connection and one passive
(standby) link/connection.
Automatic/Manual
switching mode
In automatic mode, the switching is done based
on signal failure or signal degradation. Switching
can also be initiated from the management system
provided that the passive link/connection is free
from alarms.
In manual mode, the switching is only initiated from
the management system, regardless of the state
of the links/connections.
3.10.2 Network layer protection
3.10.2.1 1+1 E1 SNCP
1+1 E1 Sub-Network Connection Protection (1+1 E1 SNCP) is a protection
mechanism used for network protection on E1 level, between two MINI-LINK
TN R4 NEs. It is based on the simple principle that one E1 is transmitted on
two separate E1 connections.
The switching is performed at the receiving end where the two connections are
terminated. It switches automatically between the two incoming E1s in order
to use the better of the two. The decision to switch is based on signal failure
of the signal received (LOS or AIS).
At each end of the protected E1 connection, two E1 connections must be
configured to form a 1+1 E1 SNCP group.
An operator may also control the switch manually.
The connections may pass through other equipment in between, provided
that AIS is propagated end-to-end.
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