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INTRODUCTION TO OPTICAL NETWORKS

RAJEEV DIXIT(PGDCSA)DAYAL BAGH EDUCATIONAL INSTITUTE

What I hope you will learn

What is optical communication. Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures

Circuit, Packet and Burst

15/11/2010DAYAL BAGH EDUCATIONAL INSTITUTE 2

Optical communication is any form of telecommunication that uses light as the transmission medium.

An optical communication system consists of a transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the message from the received optical signal.

15/11/2010DAYAL BAGH EDUCATIONAL INSTITUTE3

Optical communication

http://en.wikipedia.org/wiki/Telecommunication

http://en.wikipedia.org/wiki/Light

http://en.wikipedia.org/wiki/Transmission_medium

http://en.wikipedia.org/wiki/Communication_system

http://en.wikipedia.org/wiki/Transmitter

http://en.wikipedia.org/wiki/Signal_(information_theory)

http://en.wikipedia.org/wiki/Channel_(communications)

A Lot of features it has

Having a very high bandwidth i,e > 100 mHz.

Very low attenuation.

Also avoid interferences.

Loss is negligible .

High information carrying capacity.DAYAL BAGH EDUCATIONAL INSTITUTE4

Other advantages

Transparent to bit rates and modulation schemes

Low bit error rates 10-9 as compared to 10-5 for copper wires

High speed transmission To make this possible, we need:

All-Optical reconfigurable (within seconds) networks

Definitely a difficult taskDAYAL BAGH EDUCATIONAL INSTITUTE

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What a path will look like

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* All-optical Switch with wavelength converters and optical buffers

All-OpticalSwitch*

All-OpticalSwitch*

All-OpticalSwitch*

Optical Amplifier

Lasers generate the signal Optical receivers

Optical fiber

Fiber & Lasers Fiber

Larger transmission band Reduced dispersion, non linearity and

attenuation loss Lasers

Upto 40Gbps Tunability emerging Reduced noise (both phase and

intensity) Made from semiconductor or fiber


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Optical Amplifiers

As opposed to regenerators Make possible long distance transmissions Transparent to bit rate and signal format Have large gain bandwidths (useful in WDM

systems) Expensive (~$50K)


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Then:Regenerators

Now:Optical Amps

MEMS Switches


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2-D Optical Switches Crossbar architecture Simple Digital Control of mirrors Complexity O(N²) for full non

blocking architecture Current port count limited to 32

x 32.

3D MEMS Switch Architecture


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3-D Optical Switches Analog Control of Mirrors. Long beam paths (~1m) require

collimators. Complexity O(N) (Only 2N

mirrors required for a full non blocking NxN switch)

Lucent Lambda Router : Port 256 x 256; each channel

supports upto 320 Gbps.

Wavelength Converters

Improve utilization of available wavelengths on links

All-optical WCs being developed Greatly reduce blocking probabilities


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No converters

1

2 3

New request 1 3

1

2 3

New request 1 3

With converters

WC

Optical Buffers

Fiber delay lines are used To get a delay of 1msec:

Speed of Light = 3*108 m/sec Length of Fiber = 3*108 *10-3 m

= 300 km


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Generation I

Point-to-point optical links used simply as a transmission medium

Fiber connected by Electronic routers/switches with O-E-O conversion

Regenerators used for long haul


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E-OSwitch

O-E-OSwitch

O-ESwitch

Regenerators

Electronic data as the signal

Signal receivedas electronic

Generation II

Static paths in the core of the network

All-Optical Switches (may not be intelligent)

Circuit-switched Configurable (but in the order of

minutes/hours) Soft of here


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Gen II: IP-over-Optical


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IP Router NetworkIP Router Network

IP Router NetworkOptical Subnet

Optical Subnet

Optical Subnet

Light Path

End-to-end path

Peer Model IP and optical networks are treated as a

single integrated network OXCs are treated as IP routers with

assigned IP addresses Single routing protocol instance runs

over both domains Topology and link state info maintained

by both IP and optical routers is identical


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Overlay Model

IP network routing and signaling protocols are independent of the corresponding optical networking protocols

IP Client & Optical network Server Static/Signaled overlay versions Similar to IP-over-ATM


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Generation III

An All-Optical network Optical switches reconfigurable in milli-

seconds Intelligent and dynamic wavelength

asignment, path calculation, protection built into the network

Possibly packet-switched Dream of the Optical WorldDAYAL BAGH EDUCATIONAL INSTITUTE

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Generation III (contd.)

Optical “routers” perform L3 routing No differentiation between optical and

electrical IP domains Routing decision for each packet made

at each hop Statistical sharing of link bandwidth Complete utilization of link resources


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State of the World Today


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Electronic Network

Electronic Network

Electronic Network

Electronic Network

O/E/O

O/E/O

O/E/OO/E/O

O/E/O

O/E/O

Optical Core

E/O

E/O E/O

E/O

View of a E/O node


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Electrical Optical

Input Port 1

Input Port 4

Input Port 3

Input Port 2

Optical Link 1

Optical Link 2

Optical Link 3

Input Port 1

Input Port 4

Input Port 3

Input Port 2

O P 1

O P 2

O P 3

O P 4

O P N-1

O P NPhysical View

Logical View

Optical Circuit Switching


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Electronic Network

Electronic Network

Electronic Network

Electronic Network

O/E/O

O/E/O

O/E/OO/E/O

O/E/O

O/E/O

Optical Core

E/O

E/O E/O

E/OOS

OS

OSOS

OS

OS

O/E/O

O/E/O

O/E/OO/E/O

O/E/O

O/E/O



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Electronic Network

Electronic Network

Electronic Network

Electronic Network

O/E/O

O/E/O

O/E/OO/E/O

O/E/O

O/E/O

Optical Core

E/O

E/O E/O

E/OOS

OS

OSOS

OS

OS

WC


A circuit or ‘lightpath’ is set up through a network of optical switches

Path setup takes at least one RTT Need not do O/E/O conversion at every

node No optical buffers since path is pre-set Need to choose path Need to assign wavelengths to paths Hope for easy and efficient

reconfigurationDAYAL BAGH EDUCATIONAL INSTITUTE

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Optical Packet Switching

Internet works with packets Data transmitted as packets

(fixed/variable length) Routing decision for each packet made

at each hop by the router/switch Statistical sharing of link bandwidth

leads to better link utilization Traffic grooming at the edges? Optical

header?


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OXCs and LSRs

Electrical Network – Label Switched Routers (LSR)

Optical Network – Optical Cross Connects

Both electrical and optical nodes are IP addressable

Distinctions No merging No push and pop No packet-level processing in data plane


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Optical Burst Switching

Lies in-between Circuit and Packet Switching One-way notification of burst (not reservation) –

can have collisions and lost packets Header (control packet) is transmitted on a

wavelength different from that of the payload The control packet is processed at each node

electronically for resource allocation Variable length packets (bursts) do not undergo

O/E/O conversions The burst is not buffered within the ON


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Comparison


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Hierarchical Optical Network


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Optical MAN

Optical MANOptical MAN

Optical MAN

Optical Core

All O

All O All O

All O

E/O

E/O

E/OE/O

E/O

E/OE/O

E/O

E/OE/O

E/O

E/O

E/O

E/O

E/O E/O

OS

OS

OS

OS

OS

WC

Hierarchical Optical Network Optical MAN may be

Packet Switched (feasible since lower speeds)

Burst Switched Sub- circuit switching by wavelength

merging Interfaces boxes are All-Optical and

merge multiple MAN streams into destination-specific core stream

Relatively static Optical Core Control distributed to intelligent edge

boxes DAYAL BAGH EDUCATIONAL INSTITUTE

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Types of Protection

Path protection Dedicated (1+1) –

send traffic on both paths

Dedicated (1:1) – use backup only at failure

Shared (N:1) – many normal paths share common backup

Link Protection Dedicated (each is

also reserved on backup link)

Shared (a on backup link is shared between many)


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Conclusion

Optical is here to stay Enormous gains in going optical O/E/O will soon be the bottleneck Looking for ingenious solutions

Optical Packet Switching Flavors of Circuit Switching


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THANK YOU

DAYAL BAGH EDUCATIONAL

INSTITUTE

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