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Cuda 12000 IP Access Switch CLI-based Administration Guide
Packet Over SONET (POS) Interface Administration 117
Packet Over SONET (POS) Interface Administration
Packet over Synchronous Optical Network (SONET) allows for high-speed
transport of IP data packets over a SONET network. The OC-3 and OC-12
POS modules contain a single physical interface that supports connection to
STS networks and supports transmission speeds of up to 155 Mbps.
A SONET frame is 810 bytes represented as a grid of 9 rows by 90 columns.
The frame consists of hierarchal layers, each providing services for the layer
above it. Figure 6-2 shows the logical representation of the SONET layers.
Figure 6-2 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 frame, which it then passes to the photonic
layer.
Section
Line
Photonic
Path