Basic Node
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.
3.9.2 Network layer protection
3.9.2.1 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 R3 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.
The 1+1 E1 SNCP function is independent of the 1+1 radio protection and
the MSP 1+1.
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4/1555-CSH 109 32/1-V1 Uen B 2007-09-14
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