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Transcript
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 (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