01-01 Generation of Alarms and Performance Events

OptiX OSN 9500 Alarms and Performance Events Reference Contents

Issue 01 (2007-12-31) Huawei Technologies Proprietary i

Contents

1 Generation of Alarms and Performance Events...................................................................1-1 1.1 Overview.......................................................................................................................................................1-2

1.1.1 Signal Flow Directions and Levels ......................................................................................................1-4 1.1.2 Two Common Alarms ..........................................................................................................................1-4 1.1.3 Alarm Management..............................................................................................................................1-5

1.2 Generation and Detection of Alarmsand Performance Events in the SDH Higher Order Signal Flow.........1-6 1.2.1 Downstream Signal Flow.....................................................................................................................1-7 1.2.2 Upstream Signal Flow........................................................................................................................1-10

1.3 Suppression Relations Among SDH Alarms ...............................................................................................1-11 1.4 Generation and Detection of the SDH Performance Event .........................................................................1-12

1.4.1 Bit Error .............................................................................................................................................1-12 1.4.2 Pointer Justification ...........................................................................................................................1-15

1.5 Application of Fault Locating Based on the Signal Flow............................................................................1-18 1.5.1 Bit Error .............................................................................................................................................1-18 1.5.2 Alarm .................................................................................................................................................1-19 1.5.3 Summary............................................................................................................................................1-21

Figures OptiX OSN 9500

Alarms and Performance Events Reference

ii Huawei Technologies Proprietary Issue 01 (2007-12-31)

Figures

Figure 1-1 SDH alarm signal flow .....................................................................................................................1-3

Figure 1-2 Flowchart of alarm signals generated between the SDH interface and the cross-connect unit.........1-7

Figure 1-3 Suppression relation of main alarms...............................................................................................1-12

Figure 1-4 Error detection relation and location...............................................................................................1-13

Figure 1-5 AU pointer location and content .....................................................................................................1-16

Figure 1-6 Networking diagram of error analysis ............................................................................................1-18

Figure 1-7 Networking diagram of alarm analysis ...........................................................................................1-20

OptiX OSN 9500 Alarms and Performance Events Reference Tables

Issue 01 (2007-12-31) Huawei Technologies Proprietary iii

Tables

Table 1-1 Bit error terms...................................................................................................................................1-14

Table 1-2 Positions of performance events and alarms.....................................................................................1-15

Table 1-3 Pointer justification state ..................................................................................................................1-17

OptiX OSN 9500 Alarms and Performance Events Reference

1 Generation of Alarms andPerformance Events

Issue 01 (2007-12-31) Huawei Technologies Proprietary 1-1

1 Generation of Alarms and Performance Events

About This Chapter

The following table lists the contents of this chapter.

Section Describes

1.1 Overview Describes the overview of SDH alarms and performance events.

1.2 Generation and Detection of Alarmsand Performance Events in the SDH Higher Order Signal Flow

Describes the generation and detection of alarms and performance events in signal flow of higher order part.

1.3 Suppression Relations Among SDH Alarms

Describes the alarm suppression.

1.4 Generation and Detection of the SDH Performance Event

Describes the generation and detection of SDH performance events.

1.5 Application of Fault Locating Based on the Signal Flow

Describes the application of fault locating based on the signal flow.


OptiX OSN 9500Alarms and Performance Events Reference

1-2 Huawei Technologies Proprietary Issue 01 (2007-12-31)

1.1 Overview There are sufficient overhead bytes in the SDH frame, including the regenerator section overheads, multiplex section overheads and path overheads. These overhead bytes carry alarm and performance information, which enables the SDH system to perform in-service monitoring of alarms and bit errors. With an understanding of the alarm generation and detection principles, you can quickly locate faults.

Figure 1-1 shows the SDH alarm signal flow.




Figure 1-1 SDH alarm signal flow

T1512780-93/d02

SPI RST (Note 1) MST MSA HPOM HUG HPC HPT HPA LPOM LUG LPC LPT LPA

PhysicalSection

RegeneratorSection Multiplex Section Higher Order Path Lower Order Path

NOTES1 This column represents the degenerate connection function present in a regenerator.2 The insertion of all-ones (AIS) and FERF on certain defects may be optional.This figure shows these options as dashed lines. See Recommendation G.783.

FIGURE 2-2/G.782SDH maintenance signal interaction

UnusedLPC output/LP-UNEQ

LOFRS-BIP

Error (B1)Regenerated signal

passed through

HP-UNEQHP-TIM

HP-SLMHP-BIP Error (B3)

HP-FEBEHP-FERFHP-FERFHP-FEBE

LOS

MS-AISMS-Exc. Error (B2)MS-BIP Error (B2)

MS-FERFMS-FERF

AU-AISAU-LOP

HP-LOM/TU-LOP

LP-UNEQLP-TIM

LP-SLMLP-BIP Error (B3/V5)

LP-FEBELP-FERFLP-FERFLP-FEBE

AU-AIS

TU-AIS

TU-AIS

HO Path signal passed throughHOVC with POH and unspeci fied payloadHO unequipped signal

LO Path signal passed throughLOVC with POH and unspecified payloadLO unequipped signal

UnusedHPC output/HP-UNEQ

«1»

«1»

«1»

«1»

«1»

«1»

«1»

«1»

«1»

DetectionGenerationInsertion of all-ones (AIS) signalAlarm Indication SignalFar End Block ErrorFar End Receive FailureLoss Of FrameLoss Of MultiframeLoss Of PointerLoss Of SignalSignal Label MismatchTrace Identifier MismatchUnequipped signal per Recommendation G.709

«1»AISFEBEFERFLOFLOMLOPLOSSLMTIMUNEQ




1.1.1 Signal Flow Directions and Levels This section describes the basic concepts, including the upstream signal flow, downstream signal flow, higher order path, and lower order path, which are involved in the signal analysis.

Term Refers to Figure

Downstream signal flow

A signal direction: high-rate SDH interface → cross-connect unit→ low-rate SDH interface or Ethernet interface.

high-rateSDH

interfacecross-connect

unit

Downstreamsignal flow

high-rateSDH

interface

low-rateSDH

interface

Upstream signal flow

A signal direction: low-rate SDH interface or Ethernet interface→ cross-connect unit→high-rate SDH interface.

Upstreamsignal flow

high-rateSDH

interface

high-rateSDH

interfacecross-connect

unit

low-rateSDH

interface

Higher order path The path between the high-rate SDH interface and the cross-connect unit.

高速SDH接口

Higherorder path

high-rateSDH

interface

high-rateSDH

interface

low-rateSDH

interface

cross-connectunit

Lower order path

The path between the cross-connect board and the low-rate SDH interface or Ethernet interface.

Lower orderpath

high-rateSDH

interface

high-rateSDH

interface

low-rateSDH

interface

cross-connectunit

1.1.2 Two Common Alarms This section describes two types of common alarms: AIS and RDI.

The AIS alarm or all "1"s alarm inserts the all "1"s signals into the lower level circuits, which indicates that the signal is unavailable. Common AIS alarms include the multiplex section alarm indication signal (MS_AIS) and the administrative unit alarm indication signal (AU_AIS).




The RDI alarm indicates the alarm transferred back to the local NE from the opposite NE after the opposite NE has detected alarms such as LOS (loss of signal), AIS and TIM (trace identifier mismatch). Common RDI alarms include MS_RDI and HP_RDI.

If an alarm is generated on an NE, it may not be a faulty NE. The alarm can be generated due to a fault at the opposite NE or due to other factors. For example, the R_LOS alarm is generated due to a fiber cut, and the HP_LOM alarm at the local NE is generated due to the failure of the cross-connect board at the opposite NE.

1.1.3 Alarm Management This section describes the alarm reporting process.

Alarms can be reported in the following ways:

The boards report the detected alarms to the NE software. The NE software reports the alarms to the T2000 server. The users query the alarms on the T2000 server through the T2000 client.

In the entire process, alarms are saved on the T2000 after three levels of filtering.

The three levels of filtering are as follows:

Alarm suppression Alarm auto-report Alarm filter

In addition, alarm reversion affects alarm reporting.

Alarm Suppression The suppression function can be enabled for all alarms on an NE or a board of an NE. In case of alarm suppression, the corresponding NE or board does not monitor the alarm.

Alarm Auto-Report After this function is enabled on an NE, the alarms on the NE are reported to the iManager T2000 subnet level management system (T2000) immediately after the alarm occurs. An alarm panel is displayed on the T2000 for users to check the alarm information.

Users can also disable this function for certain alarms. This reduces the impact of a large number of alarms on the T2000 performance.

Alarm Filter When the alarm filter function is enabled on the T2000, it does not affect the alarms on the NE. The T2000 accepts or discards the reported alarms based on the alarm filter function setting.




This function is set at the NE level. If the function is enabled, the T2000 discards the alarms, and the alarms are not saved into the alarm database. If the function is disabled, the T2000 saves them into the alarm database.

Alarm Reversion There are two levels of alarm reversion: the NE level and the port level.

At the NE level, there are three modes of alarm reversion: non-revertive, auto-revertive and manual-revertive.

Non-revertive: This is the default value. In this mode, the alarm reversion function of a port cannot be enabled.

Auto-revertive: In this mode, the alarm reversion function of a port can be enabled only when alarms actually occur at the port. If the alarms are cleared, the alarm reversion function of the port is automatically disabled. If you disable the alarm reversion function of a port in this mode, the reported alarm status of the port returns to the actual state of the alarm regardless of the status of the current alarm at the port.

Manual-revertive: In this mode, if you enable the alarm reversion function of a port, the reported alarm status at the port immediately reverses the status of the alarm regardless of the status of the current alarm at the port. If you disable the alarm reversion function of a port in this mode, the reported alarm status at the port immediately turns into the actual state of the alarm regardless of the status of the current alarm at the port.

The precautions to be taken when you set the alarm reversion function are as follows:

If the alarm status of the boards (including the alarm indicators) does not change, it indicates the actual running state of the equipment.

The alarm reversion function is realized on the NE software. The data on the NE software and the data on the T2000 is the same. That is, the alarm statuses are reversed after the alarms are generated.

1.2 Generation and Detection of Alarmsand Performance Events in the SDH Higher Order Signal Flow

The fault locating principle is "line first, then tributary; high level first, then low level". The alarm and performance data generated in the higher order part can trigger the report of lower order alarms and performance events. Thus, first focus on the alarm, performance information generated between the SDH interface and the cross-connect board during maintenance.

The signal flow of this route is illustrated in Figure 1-2.




Figure 1-2 Flowchart of alarm signals generated between the SDH interface and the cross-connect unit

"1"LOSSTM-Nopticalinterface

B1BI Err.

K2

AIS

MS-AIS

K2MS-RDI

B2

M1

Frame synchroniser andRS overhead processor

MS overheadprocessor

C2

AU-AISAU-LOP

J1 HP-UNEQHP-TIM

B3B3 Err.

G1G1

HP-REI

HP-RDI

MS-REI

H4

C2HP-LOM

HP-SLM

B2-Err.

Downlink signal flow

Pointer processor and HPoverhead processor

AIS

A1, A2LOF

Signal transfer point Alarm termination point(Report to SCC unit)(Insert down all "1"s signal)

H1,H2H1,H2

"1"

"1"

Alarm report or return

(RST) (MST) (MSA, HPT)

Cross-connectunit

Based on the processing positions of various overhead bytes in the STM-N frame structure, the overhead bytes are divided into three modules:

regenerator section overhead multiplex section overhead higher order path overhead

If the first two modules are faulty, all the higher order paths are affected. If a fault occurs in the overhead bytes of the last module, only a certain higher order path is affected. Therefore, the areas that are affected can be easily located and a test can thus be performed in the related paths.

The following describes the signal flow and the processing of each overhead byte module by module.

1.2.1 Downstream Signal Flow In the higher order downstream signal flow, overhead bytes are extracted and terminated.

Frame Synchronizer and Regenerator Section Overhead Processor Regenerator section overheads related to alarms and performances handled in this section are: framing bytes (A1, A2), regenerator section trace byte (J0), error checking byte (B1).

The alarm signal flow is as follows:

In the receive direction When the STM-N optical signal from the optical line enters the optical receive module, it is first changed into an electrical signal after optical/electrical conversion (O/E conversion) and then sent to the frame synchronizer and scrambler for processing. In this process, the O/E converter module detects this signal. If there is no input signal, or if the optical power is too low or too high or if the code of the input signal is of a wrong type, an R_LOS alarm is reported.




If the fiber is broken, or if the optical transmit module at the opposite NE or the optical receive module at the local NE fails, there is no signal. The optical power can be extremely low if the fiber is too much attenuated or if the optical joint is in poor contact. The received power overload indicates the optical power is over high. If the optical power overload occurs, check whether the optical attenuator is damaged, or whether the transmission distance of the optical interface board is proper. A mismatch in the code type occurs usually when the signal rates between the upstream NE and the downstream NE are not the same, or when the failed JSTG board at the upstream NE causes a disorder in data transmission. In this case, check whether the optical interface board at the upstream NE is normal or whether the JSTG and the cross-connect & timing boards operates normally. The R_LOS alarm is only related to the quality of the input signal but not to the overhead bytes.

If the R_LOS alarm occurs, the SDH equipment can enter the normal state only when the optical receive module at the local NE has continuously detected two correct code patterns and when new R_LOS alarms are not detected.

If the R_LOS alarm occurs, the system can insert all "1"s signal to the lower level circuits.

Detecting the A1, A2 and J0 bytes After the frame synchronizer has received an STM-N signal from the optical/electrical conversion module, it captures the A1, A2 framing bytes in the signal. Meanwhile, it extracts the line reference synchronous timing source from the signal and sends it to the JSTG board for clock locking. Normally, the A1 value is 0xF6, and the A2 value is 0x28. If the A1 value is not 0xF6 or the A2 value is not 0x28 for five consecutive frames, an R_OOF alarm is reported. If the R_OOF alarm lasts more than 3ms, an R_LOF alarm is reported and the all "1"s signal is inserted. In case of an R_LOF alarm, if the frame alignment state lasts more than 1ms, the equipment has returned to normal. The J0 byte is used to confirm that both ends of the regenerator section are in continuous connection. The J0 byte at the receive end is required to match the one at the transmit end. If a mismatch is detected, the equipment reports a trace identifier mismatch (J0_MM) alarm. An unscrambler is mainly used to unscramble all the bytes except A1, A2, J0, and the two bytes that follow the J0 bytes in the STM-N signals.

Detecting the B1 byte The regenerator section overhead processor extracts and processes other regenerator section overhead bytes in the STM-N signal. The B1 byte is the key byte. If the B1 byte recovered from the STM-N signal is not the same as the BIP-8 computing result of the preceding STM-N frame, the B1 error is reported. If the B1 bit error exceeds the threshold 10-6, a B1_SD alarm is reported. If the number of B1 bit errors exceeds the threshold 10-3, a B1_EXC alarm is reported. When ten severely errored seconds (SESs) in regenerator section appear consecutively, (or the ratio of the errored blocks reaches 30% in one second), a regenerator section unavailable time event (RSUATEVENT) occurs.

The F1, D1–D3 and E1 bytes in this section, which are unrelated to the alarm and performance event, are sent to the SCC module and the overhead module.




Multiplex Section Overhead Processor Multiplex section overhead bytes, which are related to the alarm and performance event handled in this part, include the following bytes:

Automatic protection switching channel bytes (K1, K2) Multiplex section error monitoring byte (B2)

The signal flow is as follows:

Detecting the K1 and the K2 bytes The functions of the multiplex section overhead (MSOH) processor are as follows: − Extracts and processes the MS overhead bytes in the STM-N signal. − Detects the SF and the SD. − Sends the D4–D12 bytes, and the E2 byte to the SCC and the overhead units. − Realizes the multiplex section protection (MSP) function by using the K1 and K2

bytes, the SCC unit, and the cross-connect unit. If the code of the bits 6–8 of the K2 byte is "111", an MS_AIS alarm is generated and an all "1"s signal is inserted. If the code of the bits 6–8 of the K2 byte is "110", an MS_RDI alarm is generated.

Detecting the B2 byte If the B2 byte recovered from the STM-N signal is not consistent with the BIP-24 computing result of the preceding STM-N frame (all bits expect for the RSOH), B2 bit errors occur. The M1 byte is used to check if an MS_REI alarm is reported. The M1 byte carries the error count of the interleaved bit blocks that the B2 byte has detected. If B2 bit errors exceed the threshold 10-6 (default), a B2_SD alarm is generated, and if they exceed the threshold -3 (default), a B2_EXC alarm is generated. In the multiplex section protection mode, the B2_EXC and the B2_SD (if enabled) alarms can trigger the MSP switching. If the B2 byte detects SES for 10 consecutive seconds, the multiplex section unavailable time (MSUAT) event occurs.

Pointer Processor and Higher Order Path Overhead Processor This part handles the pointer justification and higher order path overhead. Bytes related to pointer justification are H1, H2 and H3, and those related to the alarm and bit error are J1, C2, B3, G1, and H4.

Their alarm flows are as follows:

Detecting the H1 and H2 bytes The pointer processor interprets and justifies the pointer based on the H1 and H2 bytes of each AU-4, completes frequency and phase alignment and tolerates phase jitter and wander in the network. At the same time, the pointer processor locates each VC-4 and sends it to related higher order path overhead processor. If the H1 and H2 bytes of the AU pointer are detected to be all "1"s, an AU_AIS alarm is reported and all "1"s signal is inserted. If the pointer values of H1 and H2 are illegal (not in the normal range of 0–782) and illegal pointers are received consecutively in eight frames, the administrative unit loss of pointer (AU_LOP) alarm is reported and all "1"s signal is inserted.




If the AU pointer positive justification occurs, the number of the PJCHIGH of the MSA increases by 1. If the AU pointer negative justification occurs, the number of the PJCLOW of MSA increases by 1.

Detecting the J1, C2, B3 and G1 bytes The higher order path overhead processor processes the higher order path overhead (HPOH) bytes in the received VC-4s. The processing mode for each byte is as follows. If the J1 byte value detected is not the same as the preset one, an HP_TIM alarm is reported and all "1"s signal is inserted. If the C2 byte is detected to be 0x00, a higher order path unequipped (HP_UNEQ) alarm is reported and all "1"s signal is inserted. When the C2 byte detected is different from the preset value, a higher order path signal label mismatch (HP_SLM) alarm is reported and all "1"s signal is inserted. If the B3 byte recovered from the POH is not the same as the BIP-8 computing result of the VC-4 signal, the B3 bit error is reported. In the STM-N (N≤4) lower order SDH interface board, to extract the TU-12 signal from VC-4, the H4 byte should indicate which frame of the current multiframe the current TU-12 is. When the H4 byte is detected to be illegal, a higher order path loss of multiframe (HP_LOM) alarm is reported, and the all "1"s signal and normal H4 byte are inserted. If the G1 (bit 5) byte is detected to be 1, an HP_RDI alarm is reported. The value of G1 (bits 1–4) determines whether an HP_REI alarm is reported. If G1 (bits1–4) is 1 to 8, an HP_REI alarm is reported. When ten consecutive seconds are detected as SES (or the ratio of the errored block reaches 30% in one second) by monitoring the B3 byte, a higher order virtual container unavailable time event (HVCUATEVENT) is reported.

Other overhead bytes F3, K3, N1 are reserved for future use.

Finally, the N x STM-1 payloads are sent to the cross-connect unit for the cross connection of the higher order path and the lower order path.

1.2.2 Upstream Signal Flow The generation of the initial value of overhead byte and the return of the alarm signal to the opposite NE are completed in the Upstream signal flow of the higher order part.

Pointer Processor and Higher Order Path Overhead Processor The payload signals from the cross-connect board is sent to the higher order path

overhead processor. The higher order path overhead processor generates the higher order path overhead bytes

that are sent to the pointer processor together with the N payloads. Along the Upstream direction, the higher order path overhead bytes such as J1, C2, B3, G1, F2, F3, and N1 are set.

If the AU_AIS, AU_LOP, HP_UNEQ or HP_LOM (HP_TIM and HP_SLM optional) alarm is detected in the downstream signal flow, the processor sets the G1 (bit5) byte to 1 to returns the HP_RDI alarm to the remote end.

If B3 bit errors are detected in the downstream signal, the processor sets the G1 (bits1–4) byte to a corresponding bit error value (ranging from 1 to 8) as per the error value detected, and returns an HP_REI alarm to the remote end.

The H4 byte is not processed in the Upstream direction.




The pointer processor generates N AU-4 pointers, adapts VC-4 into AU-4, and the AU-4 pointers are represented by the H1 and H2 bytes.The multiplexing processor then multiplexes N AU-4s into a STM-N signal and sends it to the multiplex section overhead processor.

Multiplex Section Overhead Processor The multiplex section overhead processor sets the MSOH bytes such as K1, K2, D4-D12, S1, M1, E2 and B2 for the received STM-N signal.

If an R_LOS, R_LOF or MS_AIS alarm is detected in the downstream signal flow, the processor sets K2 (bits 6–8) to 110 and returns an MS_RDI alarm to the remote end.

If B2 bit errors are detected in the downstream signal flow, the processor returns an MS_REI alarm to the remote end through the M1 byte.

Frame Synchronizer and Regenerator Section Overhead Processor The regenerator section overhead processor sets the overhead bytes in regenerator

section such as A1, A2, J0, E1, F1, D1-D3 and B1, and sends a complete STM-N electrical signal to the frame synchronizer and scrambler.

The frame synchronizer and scrambler scramble STM-N electrical signals, and then the E/O module converts the STM-N electrical signal into the STM-N optical signal and sends it to the optical interface.

1.3 Suppression Relations Among SDH Alarms The alarms are associated with one another. Some of the alarms trigger other alarms. In particular, higher order alarms often trigger lower order alarms.

Example:

If an R_LOS occurs on the optical interface board due to loss of signal, an AIS is inserted into the downstream circuit. As a result, all the overhead bytes are all "1"s, and alarms such as R_LOF, R_OOF, and MS_AIS are triggered.

The occurrence of these alarms is natural. However, these alarms are not helpful to the maintenance staff. If the upstream node fails, the maintenance of the downstream nodes is unnecessary.

In addition, if these alarms are reported on all the NEs at the same time, the data reported may be too large in size and the workload of the T2000 and the SCC board may be too heavy. As a result, the operator cannot solve the problem because too much information floods in.

To avoid this situation, alarm suppression is introduced to suppress the report of unnecessary alarms.

Figure 1-3 shows the suppression relation of the main alarms.




Figure 1-3 Suppression relation of main alarms

R-LOS R-LOF

B2-EXC MS-AIS

AU-LOP AU-AIS HP-UNEQ HP-TIM HP-SLM

TU-AIS

The higher level alarms above the arrow can suppress the lower level alarms below the arrow. Thus, pay attention to higher level alarms when locating faults.

Though alarms at different levels can be suppressed, performance events at different levels cannot. For example, B1 bit errors do not trigger B2 bit errors. The data on B2 bit errors is collected by counting the bit errors within the area monitored by the B2 byte.

1.4 Generation and Detection of the SDH Performance Event

The performance events of an SDH network includes the bit errors, jitter, wander, and availability. They are key factors that influence the transmission quality of the SDH network.

1.4.1 Bit Error Bit errors are detected through the parity check of the B1, B2, B3 and V5 bytes.

Generation Mechanism The SDH system adopts bit interleaved parity (BIP) to detect bit errors. The BIP is done on the BIP matrix of the regenerator section, multiplex section, higher order path, and lower order path with the B1, B2, B3 and V5 bytes.

The B1 byte is used for error monitoring of the regenerator section. This function shall be a bit interleaved parity 8 (BIP-8) code using even parity. The working mechanism of the B1 byte is as follows:

At the transmit end, the BIP-8 is computed for all bytes of the current frame after scrambling and the result is placed in the B1 byte of the next frame before scrambling.

At the receive end, the BIP-8 is computed for all bits of the current frame before descrambling and the result is compared with the value of the B1 byte of the next frame after descrambling.

If the two values are different, conduct exclusive-OR operation on them. The number of "1"s in the result is the number of errored blocks in the frame during the transmission.




The B2 byte is used for error monitoring of the multiplex section and the working mechanism is similar to that of the B1 byte. The B1 byte monitors the errors occurring in the whole STM-N frame during the transmission. One STM-N frame has only one B1 byte. The B2 byte monitors the errors occurring in every STM-1 frame of the STM-N frame. There are N % 3 B2 bytes in an STM-N frame. For example, there are three B2 bytes for one STM-1 frame.

The working mechanism of the B2 bytes is as follows:

At the transmit end, the BIP-24 is computed for all bits of the previous STM-1 frame except for the RSOH (if B1 checks the whole STM-N frame, RSOH is included) and the result is placed in the B2 bytes of the current frame before scrambling.

At the receive end, the BIP-24 is computed for all bits of the currentSTM-1 frame after descrambling except for the RSOH and exclusive-OR operation is conducted between the parity result and the B2 bytes in the next STM-1 frame after descrambling.

The number of "1"s in the result of the exclusive-OR operation is the number of errored blocks occurring in this STM-1 frame within the STM-N frame during the transmission. A maximum of 24 errored blocks can be detected.

The B3 byte is used for monitoring of the bit errors of the VC-4 within the STM-N frame during the transmission, and for monitoring of the errors of the 140Mbit/s signal within the STM-N frame. The monitoring mechanism is similar to that of the B1 and B2 bytes; however, the B3 byte is used to perform the BIP-8 parity for the VC-4 frame.

The V5 byte performs the functions of error monitoring, signal label and VC-12 path status. Bits 1–2 are used to perform the BIP-2 monitoring of bit errors in the VC-12 within the STM-N frame. If the receive end detects errored blocks, the number of such blocks are displayed in the performance events at the local end. At the same time, bit b3 of the V5 byte reports the lower order path remote error indication (LP_REI) to the transmit end, and the corresponding number of errored blocks are displayed in the performance events at the transmit end.

Error Detection and Report Figure 1-4 shows the error detection relation and location.

Figure 1-4 Error detection relation and location

V5

B1

B2

B3

RSTMST RST MST HPTHPTLPT LPT

In Figure 1-4, RST is regenerator section terminal, MST is multiplex section terminal, HPT is higher order path terminal, and LPT is lower order terminal. The B1, B2, B3 and V5 errors are detected respectively among these terminals.




Figure 1-4 shows that errors occurring in the lower order path are not detected in the higher order path, multiplex section and regenerator section. If errors occur in the regenerator section, they occur in the multiplex section, higher order path and lower order path as well.

Generally, higher order bit errors can trigger lower order errors. If the B1 error occurs, the B2, B3 and V5 errors are generated. On the contrary, if the V5 bit error occurs, B3, B2 and B1 bit errors are not necessarily generated.

When the SDH system detects errors, it reports the error performance events or alarms and notifies the remote end of error detection through overhead bytes.

Terms Table 1-1 lists the terms.

Table 1-1 Bit error terms

Term Description

BE Block error. It indicates that one or more bits have errors.

BBE Background block error. It indicates an errored block occurring outside the period of UAT and SES.

FEBBE Far end background block error. It indicates that a BBE event is detected at the far end.

ES Errored second. It indicates a certain second that is detected with one or more errored blocks.

FEES Far end errored second. It indicates that an ES event is detected at the far end.

SES Severely errored second. It indicates a certain second, which contains more than 30% errored blocks or at least one serious disturbance period (SDP). The SDP is a period of at least four consecutive blocks or 1 ms (taking the longer one) where the error ratios of all the consecutive blocks are more than or equal to 10-2 or a loss of signal occurs.

FESES Far end severely errored second. It indicates an SES event that is detected at the far end.

CSES Consecutive severely errored second. It indicates the SES events that occur consecutively, but last less than 10 seconds.

FECSES Far end consecutive severely errored second. It indicates a CSES event that is detected at the far end.

UAS Unavailable second. A period of 10 consecutive seconds during which the bit error ratio per second of the digital signal in either of the transmission directions of a transmission system is inferior to 10-3. These ten seconds are considered to be part of the unavailable time.

Relationship with Alarms When the local end of the SDH system detects errors, it reports error performance events or alarms and notifies the remote end of error detection through the overhead bytes.




Based on these performance events and alarms from the local NE and the remote NE, locate the faulty section of the path or locate the direction where errors occur.

Table 1-2 lists the positions of the performance events and alarms.

Table 1-2 Positions of performance events and alarms

Performance event Alarm Item

Bit errors detected at and reported by the local NE

Bit errors detected at the remote NE, but reported by the local NE

Bit error threshold-crossing detected at and reported by the local NE

Bit errors detected at the remote NE but reported by the local NE

Regenerator section

RSBBE - B1_EXC -

Multiplex section

MSBBE MSFEBBE B2_EXC MS_REI

Higher order path

HPBBE HPFEBBE HP_CROSSTR HP_REI

Lower order path

LPBBE LPFEBBE LP_CROSSTR LP_REI

If the B1 byte recovered from the STM-N signal is not the same as the BIP-8 computing result of the previous STM-N frame, the B1 bit error is reported.

If the B2 byte recovered from the STM-N signal is not the same as the result of BIP-24 computing for all bits except for the regenerator section overhead in the previous STM-N frame, the B2 bit error is reported.

If the B3 byte recovered from the HPOH is not the same as the BIP-8 computing result of the VC-4 signal of the previous frame, the B3 bit error is reported.

If B1, B2 and B3 bit errors exceed 10-6, alarms such as B1_SD, B2_SD, B3_SD occur. If B1, B2 and B3 bit errors exceed 10-3, alarms such as B1_EXC, B2_EXC and B3_EXC occur.

When ten SES events in the regenerator section occur consecutively (or the ratio of the errored blocks reaches 30% in one second), a regenerator section unavailable second (RSUAS) performance event is reported.

When ten consecutive seconds are detected as SES (or the ratio of the errored block reaches 30% in one second) by monitoring the B2 byte, a multiplex section unavailable second (MSUAS) performance event is reported.

When ten consecutive seconds are detected as SES (or the ratio of errored block reaches 30% in one second) by monitoring the B3 byte, a higher order path unavailable second (HPUAS) performance event is reported.

1.4.2 Pointer Justification Pointer justification is a phenomenon especially for the SDH network. If pointer justification occurs, the clocks of some of the NEs in the SDH network are not synchronous.




Payload pointer in the SDH can be classified into administrative unit pointer (AU_PTR) and tributary unit pointer (TU_PTR). Pointer justification falls into administrative unit pointer justification and tributary unit pointer justification.

Generation Mechanism of AU Pointer Justification In the AU-4 frame shown in Figure 1-5, several bytes in specific locations (the first nine bytes in the four row) are used to record the location of the starting point of data information (to represent the data information phase).

These bytes are called pointers. H1 and H2 are pointers, and three H3s are negative pointer justification opportunities.

Figure 1-5 AU pointer location and content

AU-4 PTR

9 rows

Y Byte: 1001SS11 (S Unspecified )

1*Byte: 11111111

10 270columns

1 9H1 Y Y H2 1* 1* H3H3H3

VC-4

When the network is synchronous, the pointer is used to make phase alignment among synchronous signals. If the NEs work under the same clock, the signals sent from various NEs to a certain NE have the same clock frequency. Thus, rate adaptation is not necessary. Transiently, the rate may be either a little faster or slower, so phase alignment is needed.

When the network is out of synchronization, NEs work with different frequencies, and the pointer is used for frequency justification. The pointer justification is also used to tolerate the frequency jitter and wander in the network.

If the frame rate of the VC is different from that of the AUG, information is stuffed in the H3 bytes of the AU pointer area or idle bytes stuffed with pseudo-random information are inserted to decrease or increase the frame rate of the VC.

At the same time, the pointer value is increased or decreased to raise or drop the frame rate of the VC. Thus, the positive and negative pointer justifications are necessary. Refer to Table 1-3.




Table 1-3 Pointer justification state

Byte numbering and content of the fourth row in the STM-1 frame

State

7 8 9 10 11 12

Rate relation

Pointer zero justification

H3 H3 H3 Inform- ation

Inform- ation

Inform- ation

Information rate = container rate

Pointer positive justification

H3 H3 H3 Stuffing Stuffing Stuffing Information rate < container rate

Pointer negative justification

Inform- ation

Inform- ation

Inform- ation

Inform- ation

Inform- ation

Inform- ation

Information rate > container rate

All the NEs in the SDH network are normally well synchronized, pointer justification seldom occurs. Actual performance monitoring for pointer justification of the network proves that AU pointer justification seldom occurs and neither does TU pointer justification.

However, it is difficult to guarantee all the NEs are well synchronized all the time during the long-term network running. If one or several NEs are out of synchronization, and even if this situation lasts a very short time, a great amount of pointer justifications occur. Consecutive positive or negative pointer justification adjusts the phase forward or backward to realize frequency justification.

Generation Mechanism of TU Pointer Justification The causes of TU pointer justification are as follows:

The TU pointer justification is transformed from the AU pointer justification

TU pointer justification does not occur when the E1 signal is adapted into VC-12, and synthesized into STM-1. If there is frequency deviation between the E1 signal of the switch and the SDH clock, adaptation can be performed to realize synchronization. Thus, the TU pointer justification detected on the tributary board is generally transformed from the AU pointer justification.

The TU pointer justification occurs during the demultiplexing.

If the system clock is not consistent with the received clock, TU pointer justification occurs during the demultiplexing.

When the service passes through the upstream NE which has pointer justification, TU pointer justification occurs at the local NE during the demultiplexing.

Detection and Reporting of the Pointer Justification There are two modes of detection and report of AU pointer justification: remote detection and local detection.

In the remote mode, the information about AU pointer justification generated at the local NE is transferred to the remote NE through the H1 and H2 bytes. The remote NE realizes the report of the AU pointer justification by interpreting the H1 and H2 bytes. Thus, if the remote NE reports an AU pointer justification event, the local NE has pointer justification. The remote NE refers to the downstream NE along the clock tracing direction.




In the local mode, the AU pointer justification generated at the local NE is detected and reported at the local NE. Therefore, if the local NE reports an AU pointer justification event, the local NE has pointer justification.

In the SDH system, the AU pointer justification events on a majority of optical interface boards are detected and reported through the interpretation of the H1 and H2 bytes. This is also remote detection.

As the transformation from AU pointer justification into TU pointer justification may occur at the upstream NE instead of the local NE, the local NE does not necessarily has pointer justification if the tributary board reports pointer justification events.

Generally, AU pointer justification is generated at the upstream NE, but detected and reported at the downstream NE. TU pointer justification is generated at the NE where AU pointer justification is transformed into TU pointer justification, and detected and reported at the tributary board of the NE where the service is terminated.

1.5 Application of Fault Locating Based on the Signal Flow This section describes two typical cases of troubleshooting.

1.5.1 Bit Error Networking diagram

Figure 1-6 shows a certain networking diagram.

Figure 1-6 Networking diagram of error analysis

A B C

W EW W

This is a chain network formed by three OptiX OSN 9500 NEs at the rate of 10 Gbit/s. NE A is the gateway NE. The STM-1 service is available among the NEs in the distributed service mode.

Fault phenomena

Query the monitored performance data from the T2000. At NE A, the services between NEs A and B, and those between NEs A and C are detected to have a great number of HPFEBBE events in the tributary, and a great number of HPBBE and MSBBE events on the westbound line.

At NE B, a great number of HPFEBBE and MSFEBBE events are detected on the eastbound line, and the service between NEs A and B is detected to have a great number of HPFEBBE events in the tributary, but the service between NEs B and C is normal.

At NE C, the service between NEs C and A is detected to have a great number of HPFEBBE events only in the tributary.

Fault analysis

As per the principle of "NE first, board second", locate the faulty NE first.




There are bit errors between NEs A and B, and between NEs A and C, but no bit errors between NEs B and C. Thus, the fault lies between NEs A and B, because all services with errors pass this section of route. Analyze the performance data and determine whether the fault is in NE A or B or in the optical path.

First, analyze the performance data on the line as per the principle of "higher level first, lower level second, and line first, tributary second".

As is previously mentioned, there are three overhead bytes used for bit error monitoring on the line: B1, B2, and B3. The B1 byte monitors the route between the regenerator sections of two NEs. The B2 byte monitors the route between the multiplex sections of the two NEs. The B3 byte monitors only the route between the higher order paths of the two NEs.

The route monitored by the B3 byte covers those monitored by the B2 and B1 bytes, and the route monitored by the B2 byte covers that monitored by the B1 byte.

If only B2 and B3 bit errors occur, the route between the regenerator sections of the two NEs is normal, which indicates the optical path is not faulty.

If B2 bit errors occur, the route between the multiplex sections of the two NEs may fail. Check the data on bit errors. NE A has BBE, and NE B has FEBBE. It shows that the bit errors in the signal are detected at NE A, but it does not mean that the problem must be in NE A, as the bit errors are all detected in downstream signal flow.

Therefore, the bit errors detected in NE A may come either from the receive end of the local NE or from the transmit end of remote NE B. Check the NEs one by one. Self-loop the westbound optical path of NE A. If the errors of this NE disappear, the fault is not in this NE. Replace the westbound optical interface board JL64 of NE B. If the bit errors of the entire network disappear, the fault is cleared.

The relation between routes monitored by the B1, B2 and B3 bytes indicates that B1 bit errors can trigger B2 and B3 bit errors, and B2 bit errors can trigger B3 bit errors. In fact, this rule is not absolute. Though the routes monitored by the B1, B2 and B3 bytes have some relations, the areas monitored respectively by the three bytes do not always overlap. The B1 byte monitors all bytes of the STM-N frame, but the B2 byte only monitors all bytes except the regenerator section overhead, and the B3 byte only monitors all bits in VC-3 and VC-4. Hence, if bit errors occur in the overhead bytes, the relation between the three does not function. For example, bit errors detected by the B1 byte of the regenerator section cannot be detected by the B2 and B3 bytes. However, the cases for bit errors occurring only in the overhead byte are rare. Thus, the relation between the B1, B2 and B3 bytes is much helpful in locating faults.

1.5.2 Alarm Troubleshooting based on the alarms is similar to troubleshooting based on the performance parameters. The only difference is that the faults with bit errors are simple, whereas those with the alarms are rather complicated. Many types of alarms are often mixed together, which makes troubleshooting very difficult.

However, the generation mechanism of the signal flow can help a lot in solving common problems. The following is a simple example.

Networking diagram

Figure 1-7 shows the networking diagram.




Figure 1-7 Networking diagram of alarm analysis

A

B

CE

F

D

WE

W

E

E

W

W E

Six OptiX OSN 9500 NEs A, B, C, D, E and F form an STM-64 multiplex section ring. The type of centralized service is adopted. Each NE has service with NE A.

Fault phenomena

After the equipment operates for a period, abnormal switching occurs in the entire network. As a result, all services are interrupted. Specific phenomena are as follows:

Query the switching status of each NE. NEs F and B are in the eastbound and westbound switching statuses respectively, and NEs C, D and E are in the pass-through status, but NE A is always in the idle status.

When switching occurs, the eastbound and westbound optical interface boards of NE A have momentary transmit loss of signal (T_LOS) alarms. The eastbound optical interface board of NE F and the westbound optical interface board of NE B have HP_LOM alarms respectively. Except NE A, PS alarms are reported on other NEs.

Fault analysis

As per the principle of "NE first, board second", first locate the fault on a single NE.

The T_LOS alarm usually indicates that the cross-connect board sends no signal or sends a signal without frame structure to the optical interface board. This alarm is the one detected in the uplink signal flow.

The HP_LOM alarm is the one detected in the downstream signal flow. If this alarm occurs, the H4 byte becomes illegal in the route from the generation point of the opposite NE to the termination point of the local NE.

Both alarms are probably related to NE A. Hence, locate the fault on NE A.

The analysis indicates that the cause for H4 becoming illegal is the poor coordination of the cross-connect board and the optical interface board, or the failure of the optical interface board or the cross-connect board.

Generally, T_LOS alarm is related to the signal sent to the optical interface board by the cross-connect unit. Meanwhile, as the eastbound and westbound optical interface boards of NE A report T_LOS alarms at the same time, the cross-connect board is more likely to be faulty. Replace the cross-connect board.

After that, observe for some time. If the fault does not recur, it is cleared.




1.5.3 Summary The previous analysis indicates the locations of the alarms in the signal flow help to narrow down the scope of the fault. As a result, the fault can be quickly located. Therefore, maintenance staff are required to grasp the related principles of the alarm and performance signal flow.

01-01 Generation of Alarms and Performance Events

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Transcript of 01-01 Generation of Alarms and Performance Events