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Sdh alarm presentation
1. Defect and Failure
1. A defect is a detection of an alarm such as loss of signals, loss
of frames, AIS and Excessive Errors
2. A failure is a defect that persists beyond a maximum time
allocated. It is used to access to integrate Automatic
Protection Switching ( APS ).
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2. LOS : Loss of Signal
1. This alarm is raised when the STM-N level drops below the
threshold at which a BER of 10-3 or worse is detected
2. It could be due to cut cable, excessive attenuation of the signal or
an equipment fault
3. The LOS state will clear when 2 consecutive framing patterns are
received and no LOS condition is detected
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3. OOF : Out of frame
1. This situation occurs when 5 consecutive SDH frames are
received with invalid framing patterns(A1 and A2 bytes)
2. The maximum time to detect OOF is therefore 625µSec
3. The OOF clears when consecutive SDH frames are received with
valid framing patterns
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4. LOF : loss of frame
1. The LOF occurs when the OOF state exists for a 3 mSec.
2. If OOFs are intermittent, the timer is not reset to zero until an “in
frame” state persists continuously for specified time in msecs
3. As the framing bytes are there in Regenerator section overhead
(RSOH), this alarm is sometimes known as RS-LOF
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5. LOP : loss of Pointer
1. The LOP state occurs when ‘n’ consecutive invalid pointers are
received or ‘n’ New Data Flags (NDF) are received (other than in a
concatenation indicator), where n >8
2. The LOP state is cleared when 3 equal valid pointers or 3
consecutive AIS indications are received.
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7. W
P
W
P
W
W
P
1 + 1 Protection scheme
1 : 1 Protection scheme
1 : N Protection scheme
Network Protection
Linear Protection (G.783)
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8. Protection : RING SYSTEM
Ring System
Unidirectional
Ring / Switch
Bidirectional
Ring / Switch
PPS
LPS
PPS
LPS
2-fiber
2-fiber
2-fiber
4-fiber
2-fiber
Subnetwork Connection Protection Ring (SNCP-ring)
(2F-UPSR)
MS Dedicated Protection Ring
(2F-ULSR) (for further study, G.841)
Subnetwork Connection Protection Ring (SNCP-ring)
(2F-BPSR) (for further study, G.841)
4F MS Shared Protection Ring (MS-SP ring)
(4F-BLSR)
2F MS Shared Protection Ring (MS-SP ring)
(2F-BLSR)
LPS: Line Protection Switch (MS protection)
PPS: Path Protection Switch (VC trail protection)
MS: Multiplex Section
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9. Unidirectional and Bidirectional Rings
ADM
ADM
ADM
A
ADM B
Traffic A B
Traffic B A
Unidirectional Ring
• traffic between A-B
• uses the entire length of ring
B -> A
Bidirectional Ring
A
B
longer
path
ADM
ADM
ADM
ADM
• use the shorter or longer path
• increase number of paths
• short path traffic
• long path protection
Traffic A B
Traffic B A
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Editor's Notes
Ring systems are classified into five types based on employed switching method combination (unidirectional or bidirectional switch and path or line switch),
(and fiber number (2 or 4 fibers).
Theoretically any combination between switching and routing direction is possible. But in the ring system, above uni-uni and bi-bi combination is used.
SNCP-ring (Unidirectional)
3.1 Also called 2-fiber Unidirectional Path Protection Switch Ring (2F-UPSR)
3.2 No switching protocol is required. This is a simple and fast switching scheme.
MS Dedicated Protection Ring
4.1 2-fiber Unidirectional Line protection Switch Ring (2F-ULSR)
4.2 Protocol by K1 and K2 in MSOH is required and it is not standardized yet by ITU-T.
SNCP-ring (Bidirectional)
5.1 2-fiber Bidirectional Path protection Switch Ring (2F-BPSR)
5.2 Ring must be controlled at a path level and protocol by K3 or K4 in POH is required. It is not standardized yet by ITU-T.
4F MS-SP ring
6.1 4-fiber Bidirectional Line protection Switch Ring (4F-BLSR)
6.2 Protocol by K1 and K2 in MSOH is required.
2F MS-SP ring
7.1 2-fiber Bidirectional Line protection Switch Ring (2F-BLSR)
7.2 Protocol by K1 and K2 in MSOH is required.
There are two different algorithm in 4/2F MS-SP ring, the terrestrial application and the transoceanic application.
