This MIB module defines the managed objects for physical layer characteristics of optical interfaces and performance statistics objects for protocol specific counters in optical devices. Performance monitoring (PM) parameters are used by service providers to gather, store, set thresholds for and report performance data for early detection of problems. Thresholds are used to set error levels for each PM parameter. During the accumulation cycle, if the current value of a performance monitoring parameter reaches or exceeds its corresponding threshold value, a threshold crossing alarm (TCA) is generated. The TCAs provide early detection of performance degradation. Glossary: LBC : Laser Bias Current TX : Transmit RX : Receive PMD : Polarization Mode Dispersion OSNR : Optical Signal to Noise Ratio DGD : Differential Group Delay CD : Chromatic Dispersion rad/s : radian per second dB : decibel dBm : decibel-milliwatt ps : picosecond nm : nanometer.