VISVESVARAYA TECHNOLOGICAL UNIVERSITY BELGAUM-590010 Seminar
presentation on LIGHT TREE by NAME USN Vasanth.M 1AT07TE059 Under
The Guidance Of ATRIA INSTITUTE OF TECHNOLOGY Anandanagar,
Bangalore-560024 Mr.Ravindra Internal Guide, Lecturer, Department
of TE
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Contents Introduction Block Diagram Comparison between CWDM and
DWDM Light Path Light Tree- example Architecture of
wavelength-routed optical network Multicast Switch Architectures An
MWRS based on a splitter bank MWRS based on a drop and continue
switch. The Optical layer Unicast,Broadcast and Multicast Traffic.
Light trees problem formulations Advantages and Disadvantages
Future enhancement Conclusion References
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Introduction Today, there is a general consensus that in near
future wide area networks (WAN) will be based on Wavelength
Division Multiplexed (WDM) optical networks. Depending on the
underlying physical topology networks can be classified into three
generations: 1 st Generation : They employ copper-based or
microwave technology. eg. Ethernet. 2 nd Generation : These
networks use optical fibers for data transmission but switching is
performed in electronic domain. eg. FDDI. 3 rd Generation: These
networks both data transmission and switching is performed in
optical domain. eg. WDM.
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Block diagram Traditional Digital Fiber Optic Transport Single
Pair of Fibers Traditional Digital Fiber Optic Transport Single
Pair of Fibers Single Pair of Fibers Digital Transceiver Single
Pair of Fibers
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Digital fiber optic transport using WDM Digital Transceiver
Single Pair of Fibers WDM MUX Fiber Optic Transport using WDM
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Comparison between CWDM and DWDM Two types of WDM Coarse
wavelength division multiplexing(CWDM) Dense wavelength division
multiplexing(DWDM) Feature CWDM DWDM Wavelengths per fiber 8 16
40-80 Wavelength spacing 2500GHz (20nm) 100 GHz (0.8nm) Wavelength
capacity Up to 2.5 Gbps Up to 10 Gbps Aggregate Fiber capacity 20
40 Gbps 100 1000 Gbps Overall cost Low Medium Applications
Enterprise, metro-access metro-core, regional
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Light Path A light path is an all-optical channel which may be
used to carry circuit switched traffic and it may span multiple
fiber links. A light path can create logical (or virtual)
neighbors. A light path carries direct traffic between nodes it
interconnects. Major Objective of light path communication is to
reduce the number of hops. Under light path communication the
network employs an equal number of transmitters and receivers
because light path operates on point to point basis.
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Light Tree A light tree is a point to point multipoint all
optical channel which may span multiple fiber links. It enables
single-hop communication between a source node and a set of
destination nodes. A light tree based virtual topology can reduce
the hop distance, thereby increasing the network throughput.
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Light tree example Figure : Architecture of a wavelength-routed
optical network and its layered graph
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Light tree example Contd We refer light tree as a point to
multi point extension of light path. Many multicasting applications
exist such as teleconferencing, software/file distribution
including file replication on mirrored sites, distributed games,
Internet news distribution-mail mailing lists. In future as
multicast applications become more popular and bandwidth
intensive.
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Architecture of Wavelength-Routed Optical Network NSFNET
backbone topology
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Virtual links induced by the light tree consisting of source UT
and destination nodes TX,NE and IL. Architecture of
Wavelength-Routed Optical Network contd
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A WDM control network may require efficient delivery of
broadcast traffic. which may be modelled as a layered graph in
which each layer represents a wavelength and each physical fibre
has a corresponding link on each wavelength layer. The switching
state of each wavelength-routing switch (WRS) is managed by a
controller. A light tree based broadcast layer may provide an
efficient transport mechanism for such multicast applications.
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Multicast Switch Architectures Linear divider combiner
(LDC)
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Multicast Switch Architectures contd linear divider combiner
with two input fibers (the Pis), two output fibers (the Pos) two
dividers and four control signals (the js). The LDC acts as a
generalized optical switch with added functions of multicasting and
multiplexing. Formula Derivation: The values of 1, 2, 3, 4 control
the proportion of the input power that can be sent to the output
links. Let Pi1 and Pi2 be the power on the input links, and let Po1
and P02 be the output powers. Then, Po1= (1-1) (1-3) Pi1+ (1-2)
3Pi2 and Po2= 1 (1-4) Pi1+14Pi2
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An MWRS based on a splitter bank A multi-cast capable
wavelength routing switch
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An MWRS based on a splitter bank contd An optical splitter
splits the input signal into multiple identical output signals.
Since an optical splitter is a passive device the power from at
least one output signal of an n-way optical splitter is less than
or equal to 1/n times the input power.
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MWRS based on a drop and continue switch In a drop and continue
switch a light path can be terminated at a node and simultaneously
an identical copy of the light path can be allowed to continue to
another node in the network. Technique: It is the special case of
light tree, By employing a drop and continue switch we can
construct a chain of nodes which are connected by a drop and
continue light path. All nodes on the chain will receive
transmissions on a drop and continue light path where light is
dropped.
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The Optical Layer Definition: The optical layer provides light
paths to the higher layers. In addition to the pass through
capability provided by the optical layer other features include
are: Transparency Wavelength reuse Reliability Virtual topology
Circuit switching.
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Unicast, Broadcast and Multicast Traffic Unicast Traffic: IP/TV
on Demand use unicast traffic. Each user can request the program at
a different time. with the number of simultaneous users limited by
the available bandwidth Unicast traffic is sent from a single
source to a single destination IP address.
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Unicast traffic Contd Example of Single Unicast TrafficExample
of Multiple-Stream Unicast Traffic
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Broadcast Traffic: Broadcast traffic uses a special IP address
to send a single stream of data to all of the machines on the local
network. A broadcast address typically ends in 255. (for example,
192.0.2.255) or has 255 in all four fields (255.255.255.255).
Example of Broadcast Traffic
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Multicast Traffic: Unlike unicast addresses, when a data stream
is sent to one of these addresses potential recipients of the data
can decide whether or not to receive the data. If the user wants
the data the user's machine receives the data stream if not the
user's machine can ignore it. Example of multicast traffic
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Combining Unicast and Multicast Traffic: Example of Combined
Multicast and Unicast Traffic
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Combining Unicast and Multicast Traffic contd If the routers in
a network are not capable of handling multicast IP/TV can use
unicast transmissions to send the multimedia content across the non
multicast - enabled router. A server on the other side of the
router can then use multicast transmission to deliver the content
to its local users.
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Light trees: problem formulations Here, we state the problem of
unicast traffic. We are given the following inputs to the problem:
A physical topology Gp = (V, Ep) consisting of a weighted
undirected graph. The number of wavelength channels carried by each
fibre =W. An NxN traffic matrix, where N is the number of network
nodes and the (i, j) th element is the average rate of traffic flow
from node i to node j. The number of wavelength tunable lasers (Ti)
and wavelength tunable filters (Ri) at each node.
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Advantages and Disadvantages: Advantages: Single hop
communication. Increased Bandwidth. Broadcasting and Multicasting.
Disadvantages: Difficulties arising from limited number of
transceivers per node. Difficulties arising from limited number of
wavelengths.
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Future enhancement Wavelength assignment algorithm should be
explored in future research. To Minimize wavelength cost.
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Conclusion A novel WDM WAN architecture based on light trees
that are capable of supporting broadcasting and multicasting over a
wide-area network by employing a minimum number of optoelectronic
devices. Such WDM WAN can provide a very high bandwidth optical
layer which efficiently routes unicast, broadcast and multicast
packet-switch traffic. Preliminary results show that if we employ a
set of light trees, then significant savings can be achieved in
terms of the number of optoelectronic devices that are required in
the network.
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References 1. Laxman H. Sahasrabudhe and Biswanth mikhergee,
Light trees : Optical Multicasting For Improved Performance in
Wavelength-Routed networks. 2. Biswanth Mukhergee, Dhritiman
Banergee, S.Ramamurthy And Amarnath Mukhergee,The Principles for
Designing a wide-area WDM Optical Network,IEEE/ACM
Trans.Networking. 3. Laxman H. Sahasrabudhe, Light trees: An
Optical Layer for Tomorrows IP Networks, 4. www.ucdavis.edu 5.
Rajiv Ramaswami and kumara N. Sivarajan Optical Networks. 6.
www.ieng.com/univercd/cc/td/doc/product/software