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Chapter: Optical Communication and Networking : Optical Networks

Wavelength Routed Networks

1. Optical Cross Connect 2. Performance Evaluation of Wavelemgth Conversion

Wavelength Routed Networks

·           Two problems arise in broadcast and select networks,

·           More wavelengths are needs as the number of nodes in the network grows.

·           Without the widespread are use of optical booster amplifier, due to this splitting losses is high.

·           Wavelength routed networks overcome these limitations through wavelength reuse, wavelength conversion, and optical switching.

·           The physical topology of a wavelength routed network consists of optical wavelength routers interconnected by pair of point-to-point fiber link in an arbitrary mesh configuration.

·           Each link can carry a certain number off wavelength which can be directed independently to differently output paths at a node.

·           Each node may have logical connections with several other nodes in the network, where each connection uses a particular wavelength.

·           The paths taken by any two connections do not overlap, they can use the same wavelength.


1. Optical Cross Connect


·           The concept of an optical cross connect architecture is the physical path structure, have a high degree of path modularity, capacity scaling, and flexibility in adding or dropping channels at a user site can be achieved.

·           The physical path structure is called as path layer.

·           These cross connects (OXCs) operate in the optical domain and can route very high capacity WDM data streams over a network of interconnected optical paths.

·           OXC architecture uses space switching without wavelength conversion.

·           The space switching can be constructed of a cascade of electronically controlled optical directional-coupler elements or semiconductor-optical-ampliier switching gates.

·           Each of the input fiber carries a M wavelengths.

·           The input, arriving aggregate if signal wavelength is amplified and divided into N streams by a power splitter.

·           Tunable filter then select individual wavelengths, which are directed to an optical space switching matrix.

·           A waveguide grating demultiplexer could be used to divide the incoming aggregate stream into individual wavelength channels.

·           The switch matrix directs the channels either output lines, or to a particular receiver attached to the OXC at outputs ports 9 through 12.

·           Signals that are generated locally by a user get connected electrically via the digital cross connect matrix (DXC) to an optical transmitter.

·           They enter the switch matrix, which directs them to the appropriate output line.

·           The M output lines, each carrying separate wavelength, are fed into a wavelength multiplexer (‘mux’ and a demultiplexer is ‘demux’) to form a single aggregate output stream.

·           An optical amplifier to boost the signal level for transmission over the trunk fiber.


2. Performance Evaluation of Wavelemgth Conversion

·           These effects are

(1) Probability models

(2) Deterministic algorithms

·           The benefits are greater in a mesh network than in a ring or fully connected network.


The Effect of Wavelength Conversion

·           Simple model, circuit switched networks is used.

·           The probability that a wavelength is blocked along a path.

·           It provides insight into the network performance improvement using wavelength conversion.

·           Assume H links (or hops) between two nodes A and B.

·           The expected number of busy wavelength on any link is ρF, where ρ is a measure of the fiber utilization along the path and F is the number of a available wavelengths per fiber link.

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