Event structure: native BERT

 Event Structure What is a BERT event ?...

native BERT display by using Clarinet Event-Editor without any filter ...

BERT decoding by using Clarinet Event-Editor with a filter ...

Standards
  • ITU G821 recommendation
  • FT/CNET/LAB/208 application note, 3rd edition (transmission of data of the Pseudo Random Sequences type (PRS) and their control)

BERT event

The BERT (Bit Error Rate Test) events are generated during the BERT simulation with generation/reception of a test sequence looped back on the DL link.

Test sequence

The test sequence is a pseudo-random sequence complying with ITU recommendations:

  • V52 recommendation for transfer-rates of 50 to 4800 bit/s: degree 9 polynomial, 511 bit sequence, 1 + X 5 + X 9.
  • O152 recommendation for 64000 bit/s transfer-rates: degree 11 polynomial, 2047-bit sequence, 1 + X 9 + X 11.
  • O151 recommendation for higher transfer-rates: degree 15 polynomial, 32767 bit sequence, 1 + X 14 + X 15.

BERT measure results

The reported events are of several types:

  • events generated in real time reporting the detection error:
    • Errored Second (ERR-SEC).
    • Severely Errored Second (SEV-SEC).
    • Counters of errored bits and errored blocks.
  • intermediate results events:
    • Elementary period measurement (EPM).
    • G821 report.
  • final result event:
    • G821 report.

More details about BERT in Clarinet Slides.(see Native events/BERT)

The binary event structure is defined in the Clarinet-API.

Clarinet Event-Editor: native BERT display

The edition of the BERT events without any decoding/formatting allows to display the contents of the differents fields:

bert_native.gif (13212 octets)

 Event information Date Date of the event (end of BOP frame) in the format: hh:mm:ss/xxx.y  
N The interface number which identifies the Clarinet-interface connected to the host.

Event types Measure_info Relating to the control of the BERT measure.
Real_time Relating to real time events.
Available_time Relating to periodic results of the BERT measure during the available time.
Measure_result Relating to the results of the BERT measure.

BERT syntax
Word Item type Designation
BE Bit Error
BE-num Number of Bit Errors within a block.
BE-numb Number of Bit Errors within an errored second.
BER Bit Error Rate
BL Block (511, 2047 Bits)
BL-count BLock number
BLE event BLock Error
BLE-count Number of BLock Errors
BLER BLock Error Rate
ERR-SEC event Errored Second
ERF-SEC Error Free Second
SEV-SEC event Severely Errored Second (BER > 10-3)
DEG-SEC Degraded Second (10-3 > BER > 10-6)
DEG-MIN Degraded Minute
DM Degraded Minute
UNAV Unavailability
FLT-IND Fault Indication
AV-BER Average BER (on the error bits)
AO-BER Average Overall BER
AR-BER Average Residual BER
EPM event Elementary Period Measurement
 

Measure information events

  • decoding of the Measure info event in the following format:

    Beginning of BERT measure

Real time events

  • decoding of FLT-IND event in the following format:

Beginning of Fault Indication
End of Fault Indication

  • decoding of SEC event in the following format:

    TYPE BE-num= xxxxxx BER >10ee-y FLT-IND: X UNAV: X

    The field significance is as follows:

    • TYPE: ERR-SEC or SEV-SEC.
    • BE-numb= xxxxxx: number of errored bits.
    • BER >10ee-y: error rate value between 1 and 9 10-y.

      example: BER>10ee-5 => 1.10-5 < BER < 9.10-5.

    • FLT-IND: X: Fault Indication (Y/N).
    • UNAV: X: Unavailability (Y/N).
  • decoding of PRS event (BERT+ event) in the following format:

    BLE BE-num= xxxxxx BL-count= xxxxxx BLE-count= xxxxxx

The field significance is as follows:

  • BLE: error on block (511, 2047...bits).
  • BE-num= xxxxxx: value of number of errored bits in the block.
  • BL-count= xxxxxx: value of received block counter (since measurement beginning).
  • BLE-count= xxxxxx: value of errored received block counter (since measurement beginning).

Available time event

The representation of an EPM event is supplied by a line including the degraded minute indication (DM:X, X being YES/NO) and the error rate during the EPM.

In order for the information contained in the intermediate reports to be valid, there is a delay of 9 seconds between the end of period date to which the report refers and the date when the report is generated. The date displayed is the report generation date.

Measure result event

The representation of a BERT final result event is supplied by a table with 7 lines and 3 columns.
The first line includes the measurement time value and the unavailability time value.

BERT Processing methods

Bit Error Rate calculation

The BER on a determined period is calculated by totalling the bits received and the errors, then by dividing the error total by the number of bits received.

At the end of each sequence received, the error totalizer is updated and the sequence counter is incremented. The number of bits received is calculated by multiplying the sequence length by the number of sequences. Thus, the line clock frequency does not play a role in the calculation of error rates.

Quality measurement report

Quality assessment affects only the availability time. All the information acquired during the unavailability periods is ignored.

The parameters supplied are:

  • Tmeas, Tunav, percentage of unavailability time carried over to the measurement time.
  • for SEV-SEC, ERR-SEC and DEG-MIN, total number of events and percentage of time carried over to the available time, elapsed since the beginning of the measurement period.
  • For the DEG-MIN rate, the reference time is:

Available minute = Tavail in seconds / 60

  • FLT-IND number and accumulated duration of FLT-SEC's in seconds.
  • AV-BER OVERALL and AV-BER RESID values.

EPM report

The EPM event is not real time but differs by 9 seconds in order to obtain the possible unavailability information on the last EPM second. The errored bits occurring during the 9 seconds preceding this date are not taken into account in the EPM report.

BERT Time parameters

Measurement time (Tmeas)

This is the total time elapsed between the beginning and the end of the measurement period.

Tmeas can reach 9999999 s.

Each measurement is associated with a single communication.

Elementary acquisition period (EAP)

This is a time interval of 1 second on which the acquisitions are based.

Elementary period measurement (EPM)

An EPM is a group of 60 seconds available after having excluded the SEV-SEC's and Tunav the Unavailability time.

Unavailability time (Tunav)

This is the total of basic time declared unavailable.

An unavailability period begins when the Bit Error Rate (BER) is greater than 10EE-3 during each second of a period of 10 consecutive seconds. In this case, the 10 seconds belong to the unavailability time.

An unavailability period ends when the BER is less than 10EE-3 during each second of a period of 10 consecutive seconds. In this case, the 10 seconds belong to the availability time.

Note : The FLT-SEC's are taken into account because they are compared to a second with BER > 10EE-3.

Availability Time (Tavail)

This is the difference between the measurement time and the unavailability time.

Tavail = Tmeas - Tunav.

BERT Quality parameters

Fault indication (FLT-IND)

A FLT-IND corresponds to a loss of sequence synchronization.

An FLT-IND period begins when the Bit Error Rate (BER) is greater than 10EE-1 for 3 successive sequences. In this case, the 3 successive sequences are included in the FLT-IND period.

An FLT-IND period ends when the BER is less than 10EE-1 for 3 successive sequences. In this case, the 3 successive sequences are excluded from the FLT-IND period.

Severely Errored Second (SES or SEV-SEC)

A SEV-SEC is a period of 1 second during which one of the conditions is confirmed:

  • BER >= 10EE-3.
  • a FLT-IND.

Errored Second (ERS or ERR-SEC)

An ERR-SEC is a period of 1 second during which one of the conditions is confirmed:

  • at least one error.
  • a FLT-IND.

Second With Fault Indication (FLT-SEC)

A FLT-SEC is a period of 1 second during which the condition is confirmed:

  • at least one FLT-IND.

Degraded Minute (DM or DEG-MIN)

A DEG-MIN is an EPM during which the condition is confirmed:

  • BER >= 10EE-6.

Average overall error rate (AV-BER OVERALL or AO-BER)

This is the average error rate calculated on all of the available times expressed in seconds, the accumulated duration of FLT-SEC's being excluded.

No error is counted for an FLT-SEC.

AO-BER = Serrors / [Tavail - FLT-SEC] x transfer rate

or

AO-BER = Serrors / Sbits received (Tavail - FLT-SEC)

Average Residual Error rate (AV-BER RESID or AR-BER)

This is the average error rate calculated on all of the available times expressed in seconds, the accumulated duration of the SEV-SEC's and the SEV-SEC errors being excluded.

No error is counted for an SEV-SEC.

AR-BER = Serrors - Serrors(SEV-SEC) / [Tavail - SEV-SEC] x transfer-rate

or

AR-BER = Serrors - Serrors(SEV-SEC) / Sbits received (Tavail - SEV-SEC)

 

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updated:  27-Feb-04