SONET/SDH

SONET/SDH

17.1 Architecture
17.2 SONET Layers
17.3 SONET Frames
17.4 STS Multiplexing
17.5 SONET Networks
17.6 Virtual Tributaries



Digital transmission standards for fiber-optic cable
Independently developed in USA & Europe
SONET(Synchronous Optical Network) by ANSI
SDH(Synchronous Digital Hierarchy) by ITU-T
Synchronous network using synchronous TDM multiplexing
All clocks in the system are locked to a master clock
It contains the standards for fiber-optic equipments
Very flexible to carry other transmission systems (DS-0, DS-1, etc)

SONET/SDH Architecture

Architecture of a SONET system: signals, devices, and connections
Signals: SONET(SDH) defines a hierarchy of electrical signaling levels called STSs(Synchronous Transport Signals, (STMs)). Corresponding optical signals are called OCs(Optical Carriers)

SONET/SDH Architecture

SONET devices: STS multiplexer/demultiplexer, regenerator, add/drop multiplexer, terminals

SONET/SDH Architecture

Connections: SONET devices are connected using sections, lines, and paths
Section: optical link connecting two neighbor devices: mux to mux, mux to regenerator, or regenerator to regenerator
Lines: portion of network between two multiplexers
Paths: end-to-end portion of the network between two STS multiplexers

SONET Layers

SONET defines four layers: path, line, section, and photonic
Path layer is responsible for the movement of a signal from its optical source to its optical destination
Line layers is for the movement of a signal across a physical line
Section layer is for the movement of a signal across a physical section, handling framing, scrambling, and error control
Photonic layer corresponds to the physical layer of OSI model

SONET Layers



SONET Frames

Each synchronous transfer signal STS-n is composed of 8000 frames. Each frame is a two-dimensional matrix of bytes with 9 rows by 90 × n columns.

A SONET STS-n signal is transmitted at 8000 frames per second
Each byte in a SONET frame can carry a digitized voice channel
774 voice channels are supported by STS 1 signaling simultaneously.
Prove that STS-1 has data rate of 51.84 Mbps.

SONET Frames

In SONET, the data rate of an STS-n signal is n times the data rate of an STS-1 signal
In SONET, the duration of any frame is 125 μs

Concatenated Signal

The suffix c (for concatenated) means that the STS-n is not considered as n STS-1 signals. So, it cannot be demultiplexed into n STS-1 signals
An STS-3c signal can carry 44 ATM cells as its SPE
SPE of an STS-3c can carry 9 x 260 = 2340 which can accommodate approximately 44 ATM cells, each of 53 bytes

Add/Drop Multiplexer

Only remove the corresponding bytes and replace them with the new bytes including the bytes in the section and line overhead