SONET

INTRODUCTIONDigital transmission standards for fiber-optic cable

Independently developed in USA & EuropeSONET (Synchronous Optical Network) by ANSISDH (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

SONET was originally designed for the public telephone network.

A bit-way implementation providing end-to-end transport of bit streams.

Multiplexing done by byte interleaving.

SONET commonly transmits data at speeds between 155 megabits per second (Mbps) and 2.5 gigabits per second (Gbps).

One of SONET’s most interesting characteristics is its support for a ring topology .

Very flexible to carry other transmission systems (DS-0, DS-1, etc)

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

Path

Termination

Path

Termination

Line

Termination

Line

Termination

Section

Termination

path

line line line

ADM ADMregenerator

section section sectionsection

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)

Devices: STS Multiplexer/ Demultiplexer, Regenerator, Add/Drop Multiplexer and Terminals

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 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

• 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

SONET NETWORKS

1. Point-to-point network :

2. Multipoint network :

Ring Network: UPSR

Unidirectional Path Switching Ring (UPSR)

Ring Network: BLSR

Bidirectional Line Switching Ring (BLSR)

Mesh Network

Ring network has the lack of scalabilityMesh network has better performance

SONET Advantages

Reduced network complexity and cost

Allows transportation of all forms of traffic

Efficient management of bandwidth at physical layer

Standard optical interface

De-multiplexing is easy.

SONET Disadvantages

Strict synchronization schemes required

Complex and costly equipment as compared to cheaper Ethernet

SYNCHRONOUS DIGITAL HIERARCHY (SDh)

INTRODUCTION

Standard for interfacing optical networks

Simple multiplexing process

SDH is basically the international version of SONNET

SONNET is NORTH AMERICAN version of SDH

SDH frame structure

• STM-1 frame is the basic transmission format for SDH

• Frame lasts for 125 microseconds • It consists of overhead plus a virtual container capacity

SDH network elements

Regenerator (Reg.)

Terminal Multiplexer (TM)

Add/Drop Multiplexer (ADM)

Digital Cross Connect (DXC)

REGENERATORSTM-NSTM-N STM-NSTM-N

RegeneratorRegenerator

It mainly performs 3R function:

1R – Reamplification

2R – Retiming

3R – Reshaping

It regenerates the clock and amplifies the incoming distorted and attenuated signal. It derive the clock signal from the incoming data stream.

Terminal Multiplexer (TM)

Terminal Terminal MultiplexerMultiplexer

STM-NSTM-NPDHPDH

SDHSDH

It combines the Plesionchronous and synchronous

input signals into higher bit rate STM-N Signal.

Add/Drop Multiplexer (ADM)

STM-NSTM-NSTM-NSTM-N

PDHPDH SDHSDH

Add / Drop Add / Drop MultiplexerMultiplexer

Digital Cross Connect (DXC)

STM-16STM-4STM-1

140 Mbit/s34 Mbit/s2 Mbit/s

STM-16STM-4STM-1

140 Mbit/s34 Mbit/s2 Mbit/s

Cross - Connect

TYPICAL LAYOUT OF SDH LAYER

General view of Path Section designations

SDHSDHmultiplexermultiplexer

SDHSDH RegeneratorRegenerator

##Cross-Cross-

connectconnect

SDHSDHmultiplexermultiplexerSDH SDH SDH

PDHATMIP

Regenerator Section

Regenerator Section

Multiplex Section Multiplex Section

Path

Network Configurations

Point to Point

Point to Multipoint

Mesh Architecture

Ring Architecture

SDH Advantages

Allows multi-network internetworking

SDH is synchronous

Allows single stage multiplexing and de-multiplexing

DENSE WAVELENGTH DIVISION MULTIPLEXING

THE GENERAL STRUCTURE OF THE DWDM SYSTEM

Multiple channels of information carried over the same fibre, each using an individual wavelength

Dense WDM is WDM utilising closely spaced channels

Channel spacing reduced to 1.6 nm and less

Cost effective way of increasing capacity without replacing fibre

Allows new optical network topologies, for example high speed metropolitian rings

Wavelength Division

Multiplexer

Wavelength Division

Demultiplexer1

A2

3B

C

1X

2

3Y

Z1 2 + 3

Fibre

ITU Recommendation is G.692 "Optical interfaces for multichannel systems with optical amplifiers"

G.692 includes a number of DWDM channel plans

Channel separation set at:

50, 100 and 200 GHz

equivalent to approximate wavelength spacings of 0.4, 0.8 and 1.6 nm

Channels lie in the range 1530.3 nm to 1567.1 nm (so-called C-Band)

Newer "L-Band" exists from about 1570 nm to 1620 nm

Supervisory channel also specified at 1510 nm to handle alarms and monitoring

Optical Spectral Bands

Transmitters

DWDM Multiplexer

Power Amp

Line Amp

Line Amp

Optical fibre

Receive Preamp

DWDM DeMultiplexer

Receivers

Each wavelength behaves as if it has it own "virtual fibre"

Optical amplifiers needed to overcome losses in mux/demux and long fibre spans

•THE ERBIUM DOPED FIBER AMPLIFIERS (EDFA)•MULTIPLEXERS•DEMULTIPLEXERS •ADD/DROP MULTIPLEXER•OPTICAL SWITCH.

DWDM AdvantagesGreater fibre capacity

Easier network expansion No new fibre needed

Just add a new wavelength

Incremental cost for a new channel is low

No need to replace many components such as optical amplifiers

DWDM systems capable of longer span lengths TDM approach using STM-64 is more costly and more susceptible to chromatic and

polarization mode dispersion

Can move to STM-64 when economics improve

DWDM DisadvantagesNot cost-effective for low channel numbers

Fixed cost of mux/demux, transponder, other system components

Introduces another element, the frequency domain, to network design and management

SONET/SDH network management systems not well equipped to handle DWDM topologies

DWDM performance monitoring and protection methodologies developing