Abstract :
The concept of light tree is introduced in a wavelength routed optical network, which
employs wavelength -division multiplexing (WDM). Depending on the underlying
physical topology networks can be classified into three generations:
First Generation: these networks do not employ
fiber optic technology;
instead they employ copper-based or
microwave technology. E.g. Ethernet.
Second Generation: these networks use optical
fibers for data transmission but switching is performed in electronic domain.
E.g. FDDI.
Third Generation: in these networks both data
transmission and switching is performed in optical domain. E.g. WDM.
WDM wide area networks employ tunable
lasers and filters at access nodes and optical/electronic switches at routing
nodes. An access node may transmit signals on different wavelengths, which are coupled
into the fiber using wavelength multiplexers. An optical signal passing through
an optical wavelength-routing switch (WRS) may be routed from an output fiber
without undergoing opto-electronic conversion.
A light path is an all-optical channel,
which may be used to carry circuit switched traffic, and it may span multiple
fiber links. Assigning a particular wavelength to it sets these up. In the
absence of wavelength converters, a light path would occupy the same wavelength continuity constraint.
A light path can create logical (or
virtual) neighbors out of nodes that may be geographically far apart from each
other. A light path carries not only the direct traffic between
the nodes it interconnects, but also the traffic from nodes upstream of the source to
nodes upstream of the destination. A major objective of light path
communication is to reduce the number of hops a packet has to traverse.
Under light path communication, the
network employs an equal number of transmitters and receivers because each light
path operates on a point-to-point basis. However this approach is not able to
fully utilize all of the wavelengths on all of the fiber links in the network,
also it is not able to fully exploit all the switching capability of eachWRS.
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