608
14 Basic Measurement and Monitoring Techniques
enables maintenance and operation of optical channels. This information includes
maintenance signals, path monitoring, tandem connection monitoring, automatic
protection switching, and designation of fault type and location.
Optical channel transport unit The optical channel transport unit (OTU) contains
the ODU frame structure, the OTU overhead, and appended forward error correction
(FEC). The OTU changes the digital format of the ODU into a light signal for transport
over an optical channel. It also provides error detection and correction and section
layer connection monitoring functions.
14.7.3 Fundamental OPM Function
The fundamental function of optical performance monitoring is to examine the
temporal behavior of performance factors that may affect the health of an optical
signal. This process involves checking the operational status of elements in the physical layer and assessing the quality of the optical signals in each WDM channel.
OPM can be viewed by means of the following three layers.
Transport-layer monitoring deals with optical-domain characteristics that relate to
WDM channel management. This involves real-time examinations of factors such as
the presence of a channel, whether the wavelength has been registered by the system,
and the optical power level, spectral content, and OSNR of each WDM channel.
Optical signal monitoring examines the quality of each WDM channel. This
measurement function examines the signal quality features of an individual channel.
These features include the Q factor, the electronic SNR, and various eye-diagram
statistics such as openness and distortions resulting from dispersion or nonlinear
effects.
Protocol performance monitoring deals with digital measurements such as the BER.
The main factors that OPM is watching for are component faults and signal impairments. Component faults can result from malfunctions or degradations of elements,
improperly installed or configured equipment, or damage to a network (such as a
backhoe digging up a cable or a storm destroying a fiber line). Signal impairments
can arise from many diverse factors. Among these are noises and transients from
optical amplifiers, chromatic and polarization-mode dispersions, nonlinear effects,
and timing jitter.
All these factors taken together present a big challenge to devising a comprehensive OPM system. However, a single OPM system does not need to check all possible
degradation mechanisms. In fact, cost constraints prevent the deployment of such a
super-sophisticated performance monitoring procedure. In a practical network, the
simplest OPM system might monitor only the optical power levels of each channel at
a particular point in a WDM network. Advanced OPM systems will include using a
miniaturized spectrometer to control the outputs of devices such as optical amplifiers
14 Basic Measurement and Monitoring Techniques
enables maintenance and operation of optical channels. This information includes
maintenance signals, path monitoring, tandem connection monitoring, automatic
protection switching, and designation of fault type and location.
Optical channel transport unit The optical channel transport unit (OTU) contains
the ODU frame structure, the OTU overhead, and appended forward error correction
(FEC). The OTU changes the digital format of the ODU into a light signal for transport
over an optical channel. It also provides error detection and correction and section
layer connection monitoring functions.
14.7.3 Fundamental OPM Function
The fundamental function of optical performance monitoring is to examine the
temporal behavior of performance factors that may affect the health of an optical
signal. This process involves checking the operational status of elements in the physical layer and assessing the quality of the optical signals in each WDM channel.
OPM can be viewed by means of the following three layers.
Transport-layer monitoring deals with optical-domain characteristics that relate to
WDM channel management. This involves real-time examinations of factors such as
the presence of a channel, whether the wavelength has been registered by the system,
and the optical power level, spectral content, and OSNR of each WDM channel.
Optical signal monitoring examines the quality of each WDM channel. This
measurement function examines the signal quality features of an individual channel.
These features include the Q factor, the electronic SNR, and various eye-diagram
statistics such as openness and distortions resulting from dispersion or nonlinear
effects.
Protocol performance monitoring deals with digital measurements such as the BER.
The main factors that OPM is watching for are component faults and signal impairments. Component faults can result from malfunctions or degradations of elements,
improperly installed or configured equipment, or damage to a network (such as a
backhoe digging up a cable or a storm destroying a fiber line). Signal impairments
can arise from many diverse factors. Among these are noises and transients from
optical amplifiers, chromatic and polarization-mode dispersions, nonlinear effects,
and timing jitter.
All these factors taken together present a big challenge to devising a comprehensive OPM system. However, a single OPM system does not need to check all possible
degradation mechanisms. In fact, cost constraints prevent the deployment of such a
super-sophisticated performance monitoring procedure. In a practical network, the
simplest OPM system might monitor only the optical power levels of each channel at
a particular point in a WDM network. Advanced OPM systems will include using a
miniaturized spectrometer to control the outputs of devices such as optical amplifiers