Transition Networks
S4224 Web User Guide
33558 Rev. C
Page 551 of 669
Request State Priorities
Request / State
Priority
1111 Lockout of protection (LO)
1110 Signal fail for protection (SF-P)
Highest
1101 Forced switch (FS)
^
1011 Signal fail for working (SF)
|
1001 Signal degrade (SD) (Note)
|
0111 Manual switch (MS)
|
0110 Manual switch to working (MS-W)
|
0101 Wait to restore (WTR)
|
0100 Exercise (EXER)
|
0010 Reverse request (RR)
|
0001 Do not revert (DNR)
v
0000 No request (NR)
Lowest
Note
: SF-P (Signal fail on the protection transport entity) is a higher priority than any defect that would
cause a normal traffic signal to be selected from protection.
Protection Types
The valid protection types are:
000x 1+1
Unidirectional, no APS communication
100x 1+1
Unidirectional w/APS communication
101x 1+1
Bidirectional w/APS communication
111x 1:1
Bidirectional w/APS communication
The values are chosen such that the default value (all zeros) matches the only type of protection that can
operate without APS (1+1 unidirectional).
Note that 010x, 001x and 011x are invalid since 1:1 and bidirectional require an APS communication.
If the "B" bit mismatches, the selector is released since 1:1 and 1+1 are incompatible, resulting in a
defect.
If the "B" bit matches:
If the "A" bit mismatches, the side expecting APS will fall back to 1+1 unidirectional switching
without APS communication.
If the "D" bit mismatches, the bidirectional side will fall back to unidirectional switching.
If the "R" bit mismatches, one side will clear switches to "WTR"
Failure of Protocol Defects
The "Failure of protocol" situations for protection types requiring APS include:
Fully incompatible provisioning (the "B" bit mismatch
Working/protection configuration mismatch.
Lack of response to a bridge request (i.e., no match in sent "requested signal" and received
"requested signal") for >50ms.
Fully incompatible provisionings and working/protection configuration mismatches are detected by
receiving a single APS frame.
Detecting and clearing "failure of protocol" defects are defined in ITU-T G.8021.
Any received 'unknown request' or any 'request for an invalid signal number' is ignored.
