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Definition
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: a).First
Generation: these networks do not employ fiber optic technology; instead they
employ copper-based or microwave technology. E.g. Ethernet.
b).Second Generation:
these networks use optical fibers for data transmission but switching is performed
in electronic domain. E.g. FDDI.
c).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 each WRS.
A light tree is a point to point multipoint all optical
channel, which may span multiple fiber links. Hence, a light tree enables single-hop
communication between a source node and a set of destination nodes. Thus, a light
tree based virtual topology can significantly reduce the hop distance, thereby
increasing the network throughput.
Requirements:
1. Multicast -capable wavelength routing switches (MWRS) at every node in the
netwok.
2. More optical amplifiers in the network.
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