FiberOptic Communications James N Downing Chapter 8 Optical

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 – Regenerated and retimed by clock recovery circuit

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

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.

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

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. 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

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

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

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

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)

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.

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

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

8. 4 SONET • Evolving Network Transport Services – – – – Packet over SONNET (Po. S) Link Access Procedure (LAPS) IP over LAPS Ethernet over LAPS Generic Multi-Protocol Label Switching (GMPLS) Resilient Packet Rings (RPR) Multiservice Provisioning Platforms (MSPP)

8. 4 SONET • Next Generation SONET (NG-SONET) – – Generic Framing Procedure (GFP) Virtual Concatenation (VC) Link Capacity Adjustment Scheme (LCAS) Smart DWDM

8. 4 SONET • Alternative and Hybrid Transport Systems – Carrier Class Ethernet • LAN PHY • WAN PHY – RPR