The concept of a light-tree is introduced in a wavelength-routed optical network. A light-tree is a point-to-multipoint generalization of a lightpath. A lightpath is a point-to-point all-optical wavelength channel connecting a transmitter at a source node to a receiver at a destination node. Lightpath communication can significantly reduce the number of hops (or lightpaths) a packet has to traverse; and this reduction can, in turn, significantly improve the network’s throughput. We extend the lightpath concept by incorporating an optical multicasting capability at the routing nodes in order to increase the logical connectivity of the network and further decrease its hop distance. We refer to such a point-to-multipoint extension as a light-tree.

1. Shree Sant Gajanan Maharaj College of Engineering,
Shegaon – 444203
(2019 - 20)
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SEMINAR ON
“ LIGHT TREES ”
Presented By :
Mr. Prashant Chaudhari
Final Year C.S.E
Roll no. : 66
Group no. : G 19
Seminar Guide :
Prof. M. G. Ingle

2. CONTENTS
• Introduction
• Physical Topologies
• WDM and its types
• Comparisons of CWDM and DWDM
• Light Path
• Light Tree
• Multicast Switch Architecture of Light Tree
• Optical Layer
• Unicast, Broadcast & Multicast Traffic
• Applications
• Advantages and Disadvantages
• Conclusion
• References
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3. INTRODUCTION
• The concept of light tree is introduced in a wavelength routed
optical network
• Employs wavelength division multiplexing(WDM)
• Point to point multipoint
• Enables single hop communication
• Increases network throughput
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4. PHYSICAL TOPOLOGIES
• First generation
Copper based or microwave technology
Eg: Ethernet
• Second generation
Optical fiber for data transmission
Switching is performed in electronic domain
Eg: FDDI
• Third generation
Optical fiber are used for both transmission & switching
Eg: WDM
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5. WAVELENGTH DIVISION MULTIPLEXING
• Technology which multiplexes a number of optical carrier signals
onto a single optical fiber by using different wavelengths (i.e.,
colors) of laser light.
• Technique to carry different wavelengths through a single optic
fiber
• 2 types :
a) Coarse Wavelength Division Multiplexing (CWDM)
b) Dense Wavelength Division Multiplexing (DWDM)
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6. Coarse Division Multiplexing
• Used to save fiber resources
• Suitable for the application in short distance, high bandwidth
and areas with dense access point
• Low cost
Fig 2.2.1 Coarse Wavelength Division Multiplexing
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7. DENSE DIVISION MULTIPLEXING
• Support up to 80 channels
• Suitable for long distances
• High cost
• High Wavelength capacity
Fig 2.2.2 Dense Wavelength Division Multiplexing
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8. Comparison of CWDM and DWDM
Feature CWDM DWDM
Wavelength 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
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9. LIGHT PATH
• It is an all optical channel
• Used to carry circuit switched traffic
• It may span multiple fiber links
• Can create logical(or virtual) neighbours out of nodes that may be
geographically far apart from each other
• The 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
no. of transmitters and receivers
• Each light path operates on a point-to-point basis
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10. LIGHT TREES
• Light tree as a point to multipoint extension of light path
• A point to point multipoint all optical channel
• Multicasting applications
• Single-hop communication
• Increases network throughput
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11. MULTICAST SWITCH ARCHITECTURE
Fig Linear Divider Combiner
• Acts as a generalized optical switch with the added functions of multicasting
(signal dividing) and multiplexing (signal combining).
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12. OPTICAL LAYER
• Topology of a wavelength routing network may be an arbitrary
mesh
• Mesh consists of several fiber links
• The network provides light paths between pairs of network nodes
• A light path is simply a high bandwidth pipe carrying data up to
several gigabytes per second
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13. FEATURES OF OPTICAL LAYER
• Transparency
• Wavelength reuse
• Reliability
• Virtual topology
• Circuit switching
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14. TRANSMISSION TYPES IN LIGHT TREE
• There are three types of transmissions used in light trees:
1. Unicast traffic
2. Broadcast traffic
3. Multicast traffic
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15. UNICAST TRAFFIC
• Single source to single destination
• Do not scale for streaming media
• Web surfing, file transfer
• Sending private information
Fig Unicast transmission
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16. BROADCAST TRAFFIC
• Single source to all destination in a network.
• One packet received by everyone.
• Uses a special IP address typically ends in 255 (eg. 192.0.2.255 or
255.255.255.255)
• Examples are television, radio, etc.
Fig Broadcast transmission
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17. MULTICAST TRAFFIC
• Delivery of information only to the interested systems
• Difficult to scale across large networks
• Multimedia delivery
• The user can choose whether to receive the data
Fig Multicast transmission
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18. COMBINING UNICAST & MULTICAST TRAFFIC
Fig Combination of unicast and multicast
• Combination is used when routers in a network are not capable of
handling multicast traffic
• IP/TV can use unicast transmissions to send multimedia content across the
non-multicast enabled router
• Small casting 18

19. ADVANTAGES OF LIGHT TREES
• Data security
• Ease of installation
• Eliminating spark hazards
• High bandwidth over long distances
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20. DISADVANTAGES OF LIGHT TREES
• Price
• Fragility
• Opaqueness
• Requires special skills
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21. APPLICATIONS OF LIGHT TREES
• Teleconferencing
• Videoconferencing
• Internet news distribution
• Internet television
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22. CONCLUSION
• WDM WAN based on light trees is capable of supporting broadcasting and
multicasting over a wide area network
• Employ a minimum number of opto-electronic devices
• Provide a very high bandwidth optical layer
• Efficiently routes unicast, broadcast and multicast packet-switch traffic
• Enable single hop count
• Maximizes the throughput
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23. REFERENCES
1) R. Lin, M. Zukerman, G. Shen and W. Zhong, "Design of light-tree based optical inter-
datacenter networks," in IEEE/OSA Journal of Optical Communications and Networking,
vol. 5, no. 12, pp. 1443-1455, Dec. 2013.
2) B. Mukherjee,” Optical Communication Networks”, New York:McGraw-Hill, 1997.
3) I. Chlamtac, A. Ganz, G. Karmi, "Lightpath communications: An approach to
highbandwidth optical WAN's", IEEE Trans. Commun., vol. 40, pp. 1171-1182, July
1992.
4) L. H. Sahasrabuddhe, B. Mukherjee, “Light-trees: Exploiting optical multicasting to
improve the performance of unicast and broadcast traffic in wavelength-routed optical
networks”, Aug. 1998.
5) R. M. Krishnaswamy, and K. N. Sivarajan, “Design of Logical Topologies: A Linear
Formulation for Wavelength-Routed Optical Networks with No Wavelength Changers,”
IEEE/ACM Trans. Networking, vol. 9, no. 2, Apr. 2001, pp. 186-198.
6) L. H. Sahasrabuddhe and B. Mukherjee, “Light-Trees: Optical Multicasting for Improved
Performance in Wavelength-Routed Networks,” IEEE Commun. Mag., Feb. 2009, pp. 67-
731790.
7) https://koovik.com/en/2018/09/21/iptv-broadcast-multicast-unicast-streaming/
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24. THANK YOU !
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