Technical information

Cuda 12000 IP Access Switch CudaView Administration Guide
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Figure 10-2 SONET Network Structure
The layers that comprise a SONET frame include:
■ Path Layer — Maps the payload into the synchronous payload
envelope (SPE) of the SONET frame and creates the STS-1 synchronous
payload envelope (SPE). In POS transmission, the payload contained in
the SPE is the PPP encapsulated IP datagram. It then passes the
resulting STS-1 SPE to the Line layer.
■ Line Layer — Combines 3 STS-1 SPEs and adds the appropriate line
overhead. This multiplexing of 3 STS-1 SPEs is also referred to as
concatenation. It then passes the concatenated SPE to the section
layer.
■ Section Layer — Adds section overhead, performs scrambling, and
creates the actual STS-3c and STS-12c frames, which it then passes to
the photonic layer.
■ Photonic Layer — Converts the electrical STS signals to an optical
signal, referred to as Optical Carrier (OC). This OC signal is then
transmitted over the circuit.
Each layer consists of its own overhead bytes. This overhead provides the
powerful management and fault-tolerance capabilities inherent in a SONET
network.
SONET overhead also provides for various alarms and error
messages—known as defects—to be reported. Alarms allow for the
reporting of network failures; error messages report incomplete failures that
may compromise data transmission.
Section
Line
Photonic
Path