Nortel Networks OPTera Metro 3500 - Manual (Page 49)

Operation, administration, and maintenance (OAM) features 2-11
Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
A BLSR offers a network-level protection capability, and differs from a UPSR
in that the nodes in a BLSR are aware of the larger configuration. In a BLSR,
switching nodes communicate to each other through K-bytes. A UPSR node
has no network knowledge and does not rely upon any APS communication
with other nodes.
Protection
Protection in a BLSR is provided by using a time slot select function. The
network elements adjacent to the protected span bridges the working time slots
in the failed direction to the preassigned protection time slots in the direction
away from the failure. The network element where the signal is dropped from
the ring receives (selects) from the protection time slots on the side away from
the failure.
A BLSR bridge request can be initiated either by an operator or autonomously.
Note: All user-initiated protection switching commands are signaled on
the APS channels (K1 and K2 bytes).
User-initiated BLSR switching commands
• Forced switch
— This command performs the ring switch from the working to the
protection channels for the span between the node at which the
command is initiated and the adjacent node to which the command is
destined. This switch occurs regardless of the state of the protection
channels, unless the protection channels are satisfying a higher priority
request.
• Manual switch
— This command performs the ring switch from the working to the
protection channels for the span between the node at which the
command was initiated and the node to which the command was
destined. This occurs if the protection channels to be used are operating
at a BER better than the signal degrade threshold and are not satisfying
an equal or higher priority request (including failure of the protection
channels).
• Lockout of working/protection
— These command performs a lockout (working or protection) which
prevents the working line from switching to the protection line. When
you perform a lockout, you prevent traffic from switching to the
protection line. If traffic is on the protection line, it returns to the
working line regardless of the condition of the working line. After you
initiate a lockout request, the lockout request remains active until you
release it. The lockout command has the highest priority.