Fiber-Optic Communications

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Fiber-Optic Communications

• James N. Downing

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Chapter 8

• Optical Signals and Networks

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8.1 Optical Signal Characteristics

• Electrical-to-Optical Signal Conversion
• The electron is converted to a photopreserving
  information that is coded
• Optical source
• LED
• Laser Diode
• Regenerated and retimed by clock recovery circuit

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8.1 Optical Signal Characteristics

• Optical Signal Formats
• OOK
• Uses two signal levelsone and zero
• Two line codesreturn-to-zero and
  non-return-to-zero
• Return to zero code has twice the bandwidth but
  less dispersion
• Non-return-to-zero code more commonly used
  because of the simplicity but clock recovery is
  more difficult

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8.2 Wavelength Division Multiplexing

• WDM assigns a unique wavelength to each channel
  and allows more than one wavelength to be
  transmitted in the same fiber.

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8.2 Wavelength Division Multiplexing

• Dense Wavelength Division Multiplexing
• Developed for the C and L bands
• Consist of 100 channels from 186 THz to 195.9 THz
• Somewhat expensive
• Practical for long-haul high capacity applications

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8.2 Wavelength Division Multiplexing

• Coarse Wavelength Division Multiplexing
• Allows multiplexing with wider wavelength spacing
• Lower cost
• Easier installation
• Requires no precision laser diodes
• Requires no sophisticated filters
• Choice for metro markets

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8.3 Optical Networks

• Fiber in the Network
• Characteristics are optimized over the long,
  straight runs with few interruptions
• Optical Network Transport Protocols
• Fiber Distributed Data Interface (FDDI)
• Provides dual counter rotational ring for CAN and
  MAN
• Primarily used for storage

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8.3 Optical Networks

• Optical Network Transport Protocols
• Fibre Channel
• Used for connections of servers to shared storage
  devices over short distances
• Enterprise system connector ESCON
• Interconnects the S/390 mainframe to storage
• FICON
• Connects mainframe to storage8 times faster than
  ESCON

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8.4 SONET

• Synchronous Optical Network
• What is SONET?
• Provides a standard optical transport
• Operates at the physical layer for framing and
  transporting data over fiber optics
• Four layers path, line, section, and photonic
  layer

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8.4 SONET

• What is SONET?
• Path layer Defines and controls the end-to-end
  communications on the network
• Line layer Synchronization and automatic
  protection switching (APS)
• Section layer Details procedures between optical
  repeaters such as framing, scrambling, and error
  monitoring
• Photonic layer Controls the optical-to-electronic
  conversion

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8.4 SONET

• The STS-1 Frame and Data Formats
• 9 by 90 matrix of 810 bytes
• Transport Overhead
• Contains the section and path overheads for a
  total of 27 bytes
• Synchronous Payload Envelope
• Contains the matrix of information to be
  transmitted (783 bytes)

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8.4 SONET

• The STS-1 Frame and Data Formats
• 4 of available payload is used for operations,
  administration and management.
• First two bytes of the line overhead are
  pointers, which specify the offset to the first
  SPE byte that is allowed to float inside the
  allotted space.
• Timing is via a precise stratum 3 reference.

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8.4 SONET

• Advantages
• Standardization and synchronization
• More efficient multiplexing and depmultiplexing
• More reliable, flexible, and expandable
• Less equipment is required
• Reconfigurable network with centralized
  management
• Ring type topologies

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8.4 SONET

• Disadvantages
• Rigid rate hierarchy and convergence requirements
• Inefficient use of bandwidths
• Current rate hierarchy is not suitable for
  Ethernet transport
• Limited node network management functions
• Lack of storage area network

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8.4 SONET

• Evolving Network Transport Services
• Packet over SONNET (PoS)
• Link Access Procedure (LAPS)
• IP over LAPS
• Ethernet over LAPS
• Generic Multi-Protocol Label Switching (GMPLS)
• Resilient Packet Rings (RPR)
• Multiservice Provisioning Platforms (MSPP)

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8.4 SONET

• Next Generation SONET (NG-SONET)
• Generic Framing Procedure (GFP)
• Virtual Concatenation (VC)
• Link Capacity Adjustment Scheme (LCAS)
• Smart DWDM

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8.4 SONET

• Alternative and Hybrid Transport Systems
• Carrier Class Ethernet
• LAN PHY
• WAN PHY
• RPR