Introduction to Optical Networks

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Introduction to Optical Networks
Ajmal Muhammad, Robert Forchheimer Information
Coding Group ISY Department
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Communication Systems

• Basic Blocks

• Coverage and Topology

• Three basic components
• Source and Transmitter
• Destinations and Receiver
• Communication channel (medium)
• Communication channel
• Wired
• Wireless
• Glass
• Water and or materials

• Coverage (public network)
• LAN
• MAN
• WAN
• Topology
• Bus
• Ring
• Mesh
• Star

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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

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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

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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
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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

Triple Play
The Information Revolution would not have
happened without the Optical Fiber
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Network Architecture
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Elements of a Fiber Optic Link
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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

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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

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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

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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 (?)

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Optical Networks
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Transmission Window
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Transmission Bands Capacities
Shannon theorem
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WDM Grids ITU-T G.694.1
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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.

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Optical Amplifier and EDFA
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Inside an EDFA
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Layered Model for Todays Networks
Current protocol stacks
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Current Multiple Protocol Stacks
22 bandwidth used for protocol overhead
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Towards a two Layer Network Architecture
A perfect combination
Flexibility Capacity
Less latency Higher bandwidth utilization
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The Optical Layer
The optical layer provides lightpath service to
its client layers Lightpath optical
connection An optical channel trail between two
nodes that carries the entire traffic within a
wavelength
Client layers
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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

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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

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Simplified view of an Optical Connection
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