Bit errors refer to the differences between the actual and expected characteristics of a performance monitoring entity. Bit errors may affect the functions of performance monitoring entities.
Bit errors indicate that transmit signals are damaged because some bits of digital signal code streams during signal transmission have errors (for example, a bit that should be bit 0 changes to bit 1.)
Bit errors can be generated by internal or external interference.
l Internal interference refers to intersymbol interference (ISI) caused by component noise or dispersion. Bit errors generated by internal interference are distributed at random.
l External interference includes external electromagnetic and electrostatic interference. Bit errors generated by external interference are distributed in burst mode.
Table 1-3 describes the impact of bit error distribution modes on services.
Table 1-3 Impact of bit error distribution modes on services
Service | Impact |
Voice service | Bit errors that are distributed at random have a small impact on voice services. This type of bit errors may affect the quality of voice services. Service interruption may occur only when there are a lot of bit errors. |
Data service | Bit errors that are distributed in burst mode have a small impact on data services because data services have the retransmission capability upon errors. |
Table 1-4 Bit error performance defined in ITU-T
Bit Error Performance | Definition | Reference |
Errored Block (EB) | A block in which one or more bits are in error. | G.8201 |
A block in which one or more bits are in error. | G.826 | |
Background Block Error (BBE) | An errored block not occurring as part of an SES. | G.8201 |
An errored block not occurring as part of an SES. | G.826 | |
Background Block Error Ratio (BBER) | The ratio of BBE in available time to total blocks in available time during a fixed measurement interval. The count of total blocks excludes all blocks during SESs. | G.8201 |
The ratio of Background Block Errors (BBE) to total blocks in available time during a fixed measurement interval. The count of total blocks excludes all blocks during SESs. | G.826 | |
errored second (ES) | A one second interval with at least one errored block. | G.8201 |
A one-second period with one or more errored blocks or at least one defect. | G.826 | |
Severely Errored Second (SES) | A one-second period which contains ³ 15% errored blocks or at least one defect. | G.8201 |
A one-second period which contains ³30% errored blocks or at least one defect. SES is a subset of ES. | G.826 | |
Severely Errored Second Ratio (SESR) | The ratio of SES in available time to total seconds in available time during a fixed measurement interval. | G.8201 |
The ratio of SES to total seconds in available time during a fixed measurement interval. | G.826 |
G.8201- Error performance parameters and objectives for multi-operator international paths within the Optical Transport Network (OTN)
G.826- End-to-end error performance parameters and objectives for international, constant bit-rate digital paths and connections
According to ITU-T recommendations, a period of unavailable time begins at the onset of ten consecutive SES events. These ten SESs are considered to be part of unavailable time. A new period of available time begins at the onset of 10 consecutive non-SES events. These ten seconds without SESs are considered to be part of available time. Figure 1-3 describes the statistics principles of unavailable seconds (UAS) defined in ITU-T G.8201/G.826.
Figure 1-3 UAS statistics principles
Figure 1-4 ES/SES statistics process defined in G.8201
ES/SES statistics process defined in G.826
