Fiber-Optic Communications James N. Downing

Optical Signals and Networks 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 (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)

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