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Fiber-Optic Communications

Fiber-Optic Communications. James N. Downing. Chapter 8. Optical Signals and Networks. 8.1 Optical Signal Characteristics. Electrical-to-Optical Signal Conversion The electron is converted to a photo—preserving information that is coded Optical source LED Laser Diode

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Fiber-Optic Communications

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  1. Fiber-Optic Communications James N. Downing

  2. Chapter 8 Optical Signals and Networks

  3. 8.1 Optical Signal Characteristics • Electrical-to-Optical Signal Conversion • The electron is converted to a photo—preserving information that is coded • Optical source • LED • Laser Diode • Regenerated and retimed by clock recovery circuit

  4. 8.1 Optical Signal Characteristics • Optical Signal Formats • OOK • Uses two signal levels—one and zero • Two line codes—return-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

  5. 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.

  6. 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

  7. 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

  8. 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

  9. 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 storage—8 times faster than ESCON

  10. 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

  11. 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

  12. 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)

  13. 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.

  14. 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

  15. 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

  16. 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)

  17. 8.4 SONET • Next Generation SONET (NG-SONET) • Generic Framing Procedure (GFP) • Virtual Concatenation (VC) • Link Capacity Adjustment Scheme (LCAS) • Smart DWDM

  18. 8.4 SONET • Alternative and Hybrid Transport Systems • Carrier Class Ethernet • LAN PHY • WAN PHY • RPR

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