SDH/SONET:Maintenance and Performance Events

We know SDH/SONET is older technology now but just have a glimpse for the revision of basic FM process:

SDH SONET MAINTENANCE

SDH and SONET transmission systems are robust and reliable; however they are vulnerable to several effects that may cause malfunction. These effects can be clas- sified as follows:

• Natural causes: This include thermal noise, always present in regeneration systems; solar radiation; humidity and Raleigh fading in radio systems; hardware aging; degraded lasers; degradation of electric connections; and electrostatic discharge.
• A network design pitfall: Bit errors due to bad synchronization in SDH. Timing loops may collapse a transmission network partially, or even completely.
• Human intervention: This includes fiber cuts, electrostatic discharges, power failure, and topology modifications.

Anomalies and defects management. (In regular characters for SDH; in italic for SONET.)

All these may produce changes in performance, and eventually collapse transmission services.

SDH/SONET Events

SDH/SONET events are classified as anomalies, defects, damage, failures, and alarms depending on how they affect the service:

• Anomaly: This is the smallest disagreement that can be observed between mea- sured and expected characteristics. It could for instance be a bit error. If a single anomaly occurs, the service will not be interrupted. Anomalies are used to monitor performance and detect defects.

Defect: A defect level is reached when the density of anomalies is high enough to interrupt a function. Defects are used as input for performance monitoring, to con- trol consequent actions, and to determine fault causes.

• Damage or fault: This is produced when a function cannot finish a requested action. This situation does not comprise incapacities caused by preventive maintenance.
• Failure: Here, the fault cause has persisted long enough so that the ability of an item to perform a required function may be terminated. Protection mechanisms can now be activated.
• Alarm: This is a human-observable indication that draws attention to a failure (detected fault), usually giving an indication of the depth of the damage. For example, a light emitting diode (LED), a siren, or an e-mail.
• Indication: Here events are notified upstream to the peer layer for performance monitoring and eventually to request an action or a human intervention that can fix the situation .