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SONET Port Configuration 4-77
Bridging
These errors can occur in any of the four optical layers of a SONET network,
which are (in order from lowest to highest layer in the hierarchy) the physical
Medium, Section, Line, and Path layers.
¥ The Medium layer is the Photonic layer that physically converts electrical
signals to optical signals.
¥ The Section layer deals with the transport of frames across the optical
medium, including framing and scrambling data for transmission, the error
monitoring and maintenance between section-layer elements (such as signal
regenerators/repeaters), and orderwire (provisioning channels).
¥ The Line layer is responsible for reliably transporting the higher-level Path
layer payload and overhead across the physical medium. It is responsible for
synchronizing (clocking) the data transmission, multiplexing signals into a
single channel, error monitoring and maintenance between line-layer
elements (such as Add/Drop Multiplexers), and switching to secondary data
paths should the primary path experience failure.
¥ The Path layer transports services between path-terminating equipment.
It maps signals into a format required by the line layer, and reads, interprets,
and modiÞes path overhead for performance monitoring and automatic
protection switching.
Error reporting occurs at the Section, Line, and Path layers, and is carried within
the corresponding SONET overhead. In terms of the SONET protocol stack, the
three layers with overhead are mapped to the SONET link as shown in the
following diagram.
The statistics and errors indicators provided in the SONET/SDH statistics
window are taken from both the end-to-end Path layer, and from the Section layer
between the FE100-Sx or APIM-2x and the Add/Drop Multiplexer to which it is
connected. They reßect errors that may be occurring on your customer premises
equipment, as well as errors that may be occurring at the Line or Section layers
within the SONET MAN/WAN ring itself.
Path-
Terminating
Equipment—
(FE100-Sx
or APIM-2x)
OC-3c
link
Line-
Terminating
Equipment—
Telco/SP ADM
(Add/Drop
Multiplexer)
Regenerators
Line-
Terminating
Equipment—
Telco/SP ADM
(Add/Drop
Multiplexer)
Path-
Terminating
Equipment—
(FE100-Sx
or APIM-2x)
OC-3c
link
Path
Line
Section