Introduction to Optical Networks

Ajmal Muhammad, Robert ForchheimerInformation Coding Group

ISY Department

Communication Systems

Basic Blocks

• Three basic components – Source and Transmitter – Destinations and Receiver – Communication channel

(medium)

• Communication channel – Wired – Wireless– Glass – Water and or materials

Coverage and Topology

• Coverage (public network) – LAN – MAN – WAN

• Topology – Bus – Ring – Mesh – Star

Changing Service Landscape

• Network characteristics• Full redundancy • Fast restoration • High availability (99.999 %) • Low latency • High bandwidth • Dynamic allocation and high bandwidth efficiency • Support various services

• More providers and equipment builders (due to deregulation of the telecom industry)

• Providers are expected to provide more services at higher capacity at lower prices!

• A positive feedback business model! • Need for high capacity network • More users

Service Types Two basic service types (switching technologies)

Connection-oriented Connectionless

Connection-oriented Based on circuit switching (setup, connect, tear-down) Example: Public Switching Telephone Network (PSTN) Originally only supported voice Not good for bursty traffic

Connectionless Based on sending datagrams Examples: Packet, message, burst switching Improves bandwidth and network utilization

Optical Fiber

• Allowing transmission of information using light • Advantages

• High bandwidth • Low noise • Low interference (electromagnetic)

• Optical fiber installation• Measured in fiber sheath-km (or fiber km)• Example: we install 3 fiber cable within 10 km

long route; each fiber cable has 20 fibers we have 600 fiber km

• Currently more than 1.5 billion kilometers of optical fiber is deployed around the world [1]

• The circumference of earth is 40,000 Km!

[1] http://www.corning.com/opticalfiber/innovation/futureoffiber/index.aspx

Multimedia over Fiber Fiber carries various media

Voice (SONET/Telephony) - The largest traffic

Video (TV) over Hybrid Fiber Coaxial (HFC) or Fiber-Twisted Pair/Digital Subscriber Loops

(DSL) Data – Internet traffic

The Information Revolution would not have happened without the Optical Fiber

‘Tri

ple

Pla

y’

Network Architecture

Elements of a Fiber Optic Link

Elements of OPTICOM System

• The Fiber – that carries the light– Single Mode Fiber (only one EM mode exists), offers

the highest bit rate, most widely used– Multi Mode Fiber (multiple EM modes exist), hence

higher dispersion (due to multiple modes) cheaper than SMF, used in local area networks

– Step Index Fiber – two distinct refractive indices – Graded Index Fiber – gradual change in refractive

index

Elements of OPTICOM System

• Optical Transmitter converts the electrical information to optical format (E/O)– Light Emitting Diode (LED): cheap, robust and

used with MMF in short range applications• Surface emitting and edge emitting LED

– LASER Diode: high performance and more power, used with SMF in high speed links

• Distributed Feedback (DFB) Laser – high performance single mode laser

• Fabry-Perot (FP) lasers – low performance multimode laser

Elements of OPTICOM System

• Optical Receiver converts the optical signal into appropriate electrical format (E/O)– PIN Photo Diode: Low performance, no

internal gain, low cost, widely used– Avalanche Photo Diode (APD): High

performance with internal (avalanche) gain• Repeater: receives weak light signal, cleans-

up, amplifies and retransmits (O/E/O)• Optical Amplifier: Amplifies light in fiber

without O/E/O

Development of Optical Networks• First-generation optical networks

– Transmission in the optical domain (to provide capacity)– Example: SONET network (Synchronous Optical Network)

• Second-generation optical networks – Wavelength routed network (Optical Circuit Switching OCS)– More functionality in the optical domain (optical networking)

Some of the routing, switching and intelligence is moving into the optical domain

• Third-generation: optical networks (?)

Optical Networks

Transmission Window

Transmission Bands & Capacities

Shannon theorem

WDM Grids ITU-T G.694.1

Overview of WDM A characteristic of WDM is that the discrete wavelengths

form an orthogonal set of carriers that can be separated, routed, and switched without interfering with each other.

WDM networks require a variety of passive and active devices to combine, distribute, isolate, and amplify optical power at different wavelengths.

Optical Amplifier and EDFA

Inside an EDFA

Layered Model for Today’s Networks

Current protocol stacks

Current Multiple Protocol Stacks

22% bandwidth used for protocol overhead

Towards a two Layer Network Architecture

Flexibility

Capacity

A perfect combination

Less latencyHigher bandwidth utilization

The Optical LayerThe optical layer provides lightpath service to it’s client layers

Lightpath: optical connection An optical channel trail between two nodes that carries the entire traffic within a wavelength

Client layers

Optical Layer Service: Providing Lightpaths

• Bandwidth • Adaptation to and from client layers• Performance

Bit error rate (BER)

Optical signal quality (OSNR, impairments) Jitter Maximum delay

• Protection• Fault management

Layers within the Optical Layer

Optical Transport Network protocol layers Optical channel sublayer (OCh) Optical multiplex section (OMS) Optical transmission section (OTS) Physical media layer: fiber-type specification

Simplified view of an Optical Connection