Optical Networking

Outline
Introduction
First Generation Optical Networks

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Fiber Distributed Data Interface (FDDI)

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Synchronous Optical Network/Synchronous Digital
Hierarchy (SONET/SDH)

Second Generation Optical Networks

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Wavelength Division Multiplexing (WDM)
Optical Networking Components
Wavelength Routing Networks
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Introduction(1)
Advantages of Optical Transmission

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Large bandwidth permits high data transmission, which also supports the aggregation of voice, video, and data
Technological improvements are occurring rapidly, often permitting increased capacity over existing optical fiber
Immunity to electromagnetic interference reduces bit error rate and eliminates the need for shielding within or outside a building
Glass fiber has low attenuation, which permits extended cable transmission distance
Light as a transmission medium provides the ability for the use of optical fiber in dangerous environments
Optical fiber is difficult to tap, thus providing a higher degree of security than possible with copper wire
Light weight and small diameter of fiber permit high capacity through existing conduits

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Introduction(2)
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Disadvantages of Optical Transmission
 Cable splicing:
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Welding or fusing: you must clean each fiber end, then align and carefully fuse the ends using an electric arc.
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Gluing
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Time consuming
Least amount of signal loss between joined elements.
Bonding material that matches the refractive index of the core of the fiber.
Time consuming
Higher loss of signal power than fusing.

mechanical connectors
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Considerably facilitate the joining of fibers,
More signal loss than do the other two methods
Can reduce the span of the fiber to a smaller distance.
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Introduction(3)
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Fiber cost:
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On a (bit/s)/km basis, the fiber cost will always be less than that for copper cable.

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Some organizations may require only a fraction of the capacity of the optical fiber.
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It is often difficult to justify fiber to the desktop and similar applications where the cost of copper cable may be half or less than the cost of fiber.

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Introduction(4)
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The big picture

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Fiber Distributed Data Interface (FDDI)

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Dates back to the early 1980s
FDDI uses token-passing scheme
Uses two fiber pairs, each operating at 100 Mbits/s.
Data rates approaching 90% of its 100 MB/s operating rate
FDDI was, and in some locations still is, commonly used at the Internet Service Provider (ISP) peering points that provide interconnections between ISPs.
Relatively expensive

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FDDI Position in the OSI Reference Model

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FDDI is defined as the two bottom layers of the seven-layer OSI reference model It provides a transport facility for higher-level protocols such as TCP/IP
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Physical layer is subdivided into:
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FDDI 4B/5B Coding
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The selection of the 4B/5B coding was based on the need to reduce the signaling level from 200 MHz to a 125-MHz rate (cost reduction)
Each bit is encoded using non-returnto-zero-inversion (NRZI) transmission Because 4 bits are encoded into 5 bits, this means there are 16, 4bit patterns.
Those patterns were selected to ensure that a transition is present at least twice for each 5-bit code.
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DC balance: important for thresholding at receiver
For some input data sequences the worst case DC unbalance is 10%

Because 5-bit codes are used, the remaining symbols provide special meanings or represent invalid symbols.
Special symbols
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I symbol is used to exchange handshaking between neighboring stations,
J and K symbols are used to form the Start Delimiter for a packet, 

which functions as an alert to a