SONET
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