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Department of Electrical EngineeringIndian Institute of Technology Kanpur
1Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Introduction to Optical Networks
Yatindra Nath Singh
Assistant Professor
Electrical Engineering Department
Indian Institute of Technology, Kanpur
Email: [email protected]
http://home.iitk.ac.in/~ynsingh
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
2Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
What are optical network?
Telecomm Networks build using various communication
media
- Twisted pair copper wire
- Coaxial cable
- Wireless (Radio, microwave, satellite, infrared)
- Optical fiber
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
3Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Optical fiber uses - carrier frequency of the order of 1015Hz.
- Bandwidth generally a smaller fraction of carrier frequency
Large BW is available (of the order of 40 THz)
Optical fiber has low loss in 1.3 m and 1.55 m bands
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
4Copyright Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Advantages of fiber
- Large Bandwidth-distance product.
- immunity to noise and intereference- very low cost per unit bandwidth
- easy upgradability using WDM technology
- Tapping of signal from fiber without being detected - difficult.
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
5Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Due to all these advantages
- Optical fiber Networks have high capacity
- Can be used for providing the high bandwidth services
- Even in wireless, infrared means high bandwidth connectivity.
All the networks using optical fiber as transmission medium -
optical networks
When - transmitted signal remains in optical form till its arrival at
destination -All-optical network
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
6Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Degradation of signal in optical fiber
- Dispersion
Minimum dispersion at 1.3m
- Attenuation
Minimum attenuation at 1.55m
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
7Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Telecommunication Networks
Access Networks Access Networks
Essentially consists of two portions
Backbone network
A
B
Router/Switch
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
8Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
A and B communicate with each other via switch/router
(exchange in conventional terminalogy)
These are Switched Networks.
When the links are optical fiber - optical network
But the signal might go through E/O and O/E conversion
many times before reaching destination
Commonly deployed networks with fiber as point-to-point link
FDDI, DQDB, SONET/SDH, ATM, IEEE802.3
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
9Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
All-optical networks
- Broadcast
transmitted optical signal - received by everyone.
- Switched
transmitted optical signal - switched through a specific
path and received by the designated receiver.
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
10Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Broadcast optical networks
4x4
Star
Coupler
Tx Rx
Star topology network
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
11Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Folded Bus
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
12Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Tree-net topology
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
13Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
In Broadcast networks
Bandwidth of single channel - shared by all the users.
Media access using media access control protocolsMAC protocols need to consider
- The network is high speed
High speed network - packet transmission timecomparable to packet propagation time
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
14Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
To use the available bandwidth
- Wavelength division multiple access (WDMA)
- Time division multiple access (TDMA)
- Code division multiple access (CDMA)
O/E and E/O interfaces cannot operate above few tens of Gbit/s
WDMA - currently implementable technology.
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
15Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Optical TDMA, CDMA implementations
- need very short pulses (can be generated by mode locked
lasers).
- Time division multiplexers/ demultiplexer requires very tight
tolerance of fiber length (due to tight timing requirments)
- Encoder and decoders will require again very tight tolerance
in fiber length used for delay lines.
- Dispersion - need to be taken care of.
WDMA
- Existing available devices can be used.
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
16Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Media access control protocols for multiple channels
Classification based on tunability
- Fixed transmitter fixed receivers (FTFR)
- Tunable transmitter fixed receivers (TTFR)- Fixed transmitter tunable receiver (FTTR)
- Tunable transmitter tunable receiver (TTTR)
Tunability makes the devices costly.
- FTFR based multihop networks.
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
17Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Strong similarity with switching networks
Virtual topology is built over broadcast medium
1
2
3
4
5
6
7
8
1
2
3
4
- All the links seen here
are on differentwavelength
- Each node has two fixed
transmitter and two fixed
receiver
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
18Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Some other Multihop topologies investigated in litrature
- Hypercube
- Manhattan street network (Torus)
- Dual bus
- Ring
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
19Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
For MAC protocols with tunable component proposed solutions
generally use
- Schedulling - a schedule for transmission and reception on the
basis of stastistics is computed periodically by centralised or
distributed algorithms and used for coordination.
- pretransmission coordination using dedicated channel
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
20Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Switched Network
- uses optical switches
classified as circuit switched or packet switched. Commercially
emphasis on circuit switched all-optical networks.
- due to near term feasibility.
- also knows as wavelength routed networks
These network can be used to provide virtual topology to be usedby SDH, ATM or directly by IP layer.
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
21Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
IP
ATM
SDH
Optical Layer
IP
ATM
Optical Layer
IP
Optical Layer
As time progresses IP over WDM will take over
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
22Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
A
B
CD
E
Physicaltopology
with
wavelength
routes
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
23Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
A
B
CD
E
Virtual topology
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
24Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
In IP over WDM
- possibility of reconfigurable topology means continous
optimisation of topology depending on traffic condition can
be done.
Issues
- Estimation of condition when the reconfiguration is needed
(will be done by IP layer)
- Management algorithms for optical layer to work with limited
wavelength.
- Fault management in optical layer.
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
25Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
Other exciting things in optical networks
- Switching techniques and architectures.
- Network architectures using devices and phenomenon based onoptical nonlinearty
- Multiwavelength soliton networks.
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
26Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
What we have been doing in IIT Kanpur in the area of optical
networks
- Studies in all-optical packet switched architecture.
- Investigation on all-optical subscriber access network
- Routing and management problems in IP over WDM
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
27Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
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Department of Electrical EngineeringIndian Institute of Technology Kanpur
28Copyright 2000 Dr.Y.N.Singh, IIT Kanpur Introduction to Optical Networks
What future will have
- All-optical packet switched WANs as backbone networks
having huge capacities.
- All-optical subscriber access networks (will be quite limited)
Most of the access network is expected to be dominated by
wireless. Infrared will have its share in it.