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Wavelength Routing Testbeds

Presented By, Bibi Mohanan

M.Tech, OEC Roll No :7

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platform for experimentation of large development projects

allow for rigorous, transparent, and replicable testing of scientific theories, computational tools, and new technologies.

Testbed

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Wavelength Routing Testbeds

All Optical Network Consortium (AON) NTT Ring Optical Network Technology

Consortium(ONTC) MONET

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AON

End node

End node

End node

End node

End node

Bypass filter

Bypass filter

AWG

End node

End node

DEC

MIT Campus

Combiner

Splitter

Combiner

Splitter

Level 1

Level 0

Level 0

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(a)AON

All Optical Network Consortium Static WRT 2 level hierarchy-Level 0 & Level 1 Level 0- LAN Level 1- MAN Deployed in Boston Area

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AON continued……

20 wavelengths,50 Ghz(0.4 nm) apart Odd no: level 0,even no: level 1 End node:-Tunable Transmitter &Receiver 3 types of service

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AON continued…..

A-Service: Provide circuit switched light paths Set up by tuning Transmitters or receivers at the

end nodes Receiver uses tunable fiber fabry-perot filter(10 ms

tuning time b/w channels) Demonstrated at 2.5Gbps & 10 Gbps

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B- Service: Circuit switched service Pre assigned time slots on a light path Also support packet switching & datagram services Uses a coherent optical receiver:-local

oscillator ,photodetector

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Switching time b/w wavelengths = laser tuning time + time to acquire bit clock (200ns)

Require the sychronisation off all nodes Demonstrated at 1Gbps

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C-Service Datagram service Out of band at 1310 nm Set up & takedown A-&B-service connections Level -1 & level-0 n/w has a centralized sheduler

connected via C-service to each other & the end nodes

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(b)NTT Ring

Unidirectional ring:- 1 working fiber & 1 protection fiber N/w has 1 hub node(center node) & many access

nodes(remote nodes) Hub node sends out signals at N different wavelengths, all

MUXed in to working fiber N access nodes Hub node communicates with access node i on wavelength

i,& access node i communicates with hub node also on wavelength i

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NTT Ring

Access node 2Access node 1

Hub node

λ2 λ2 λ1 λ1

λ 1 λ2 λ3 λ4λ4 λ3 λ2 λ1

Protection fiber

Working fiber

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Node architecture in NTT testbed

OADM

OADM

Transmitters

Switch

EDFA EDFA

EDFA EDFA

LoopbackReceivers

Loopback

Switch Switch

CouplerCouplerProtection fiber

Working fiber

Level equalizer

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Protection against link failures

Two mechanisms Only one method at a time1. Linear protection Protection fiber does not carry any traffic

normally In the event of a fiber cut, restoration is

accomplished by looping the traffic on the working fiber on to the protection fiber around the ring

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2. 1+1 path protection Same traffic is sent on both working fiber &

protection fiber in opposite directions Receiver in the access node selects one of them

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NTT Ring continued… Have 6 wavelengths, spaced 100 GHz apart Running over DSF with a distance of 40 km b/w nodes at

622 Mbps 1 hub node & 2 access nodes Each access node include1. Optical amplifiers Compensate for losses2. Multi channel power equalizer Equalize the channel variations due to different component losses at different wavelengths and due to non flatness of

the amplifiers

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Test bed distance was limited by four-wave mixing To reduce four-wave mixing:- At each node, after DeMUXing the wavelengths, each

wavelength was delayed by a different value This randomizes the phase relationship b/w the different

wavelengths at each node FWM powers at each transmission stage b/w the nodes are

summed, rather than the electric fields being summed in phase

Major accomplishments:- Demonstration of WDM transmission over DSF Demonstration of different protection mechanisms

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(c) ONTC Optical Network Technology Consortium Reconfigurable wavelength routing architecture Consists of two interconnected unidirectional rings Each ring has two nodes with one additional common mode Has four wavelengths, spaced 4 nm apart Running over standard SM fiber,distance of 150 km at

155Mbps Carries ATM traffic One of the wavelengths also used to carry four analog

subcarrier MUXed video channels Uses an EDFA after each optical node to compensate for

fiber & component losses

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ONTC

OADM

OADM

Access node

Access node

OXC

Access node

Access node

OADM

OADM

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ONTC continued…

Wavelength crossconnects & add/drop MUXes are made by combining wavelength MUX/DeMUXes with optical switches

The MUX/DeMUX units are made with dielectric thin film –based filters

Switches are relay activated mechanical switches Each end node has a four-wavelength DFB laser

array as a transmitter & a four –wavelentgh integrated receiver

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Switches within the nodes are controlled by a central controller

Central controller communicate to the controllers within the nodes via in-band ATM connections

Each node has a 10-dB coupler at its output A small portion of the power is tapped off, and the

wavelength and power of each channel were monitored by a wavelength/power meter

Major emphasis was to develop commercial-quality acousto optic filters (AOTFs) for wavelength routers

But the AOTFs showed excessive crosstalk

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An OADM and an access node in ONTC

Switch

Switch

Switch

Switch

Receiver Array

TransmitterArray

ATM Switch

λ1 λ2 λ3 λ4

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ONTC continued….

ONTC demonstrated several key technologies Demonstrated , ATM virtual topology over the optical layer Trasparency aspect of WDM by transmitting

several forms of data over different light paths concurrently

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(d)MONET To develop field-hardened testbeds of wavelength-routed

networks to bring them closer to commercial deployment Field trial consists of a local ring n/w with OADMs

interconnected to a long-distance n/w via an OXC Uses 8 wavelengths spaced 200 GHz apart Data transmitted at 2.5 Gbps per wavelength Over 2000km of dispersion- managed fiber(std. single

mode fiber along with dispersion compensating fiber at appropriate intervals)

Also includes a local ring n/w with several OADMs & a 4×4 OXC to interconnect the local ring n/w to the long- distance testbed

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MONETBellcore local-exchange testbed

AT &T/Lucent long –distance testbed

OADM OADM

OADM OADM

OADM OADM

OADM OADM

OXC

Transmitters

Receivers

Amplifiers2080 km fiber

OADM

OADM

OADM

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Advances:- Handling monitoring and management Robust against outages Developing field-ready optical components

such as LiNbO3 -based optical crossconnects

Understanding the economics of WDM n/w versus other alternatives

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Summary All-optical testbed demonstrations were mostly

transmission oriented and concerned with the physical layer issues

Also demonstrated the use of specific types of switches,MUX/DeMUXes, filters &amplifiers

Dielectric thin film-based filters:- Good MUX/DeMUXes Have flat passbands Low loss Polarization insensitive

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Optomechanical switches:- Have slow switching times(10s of ms) Low loss Very low crosstalk AOTF:- Can simultaneously switch many channels High crosstalk and loss

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LiNbO3 & semiconductor amplifier-based switches:-

Faster than optomechanical switches(µs to ns) More amenable to integration Simultaneously switch many channels High crosstalk and loss OXC and OADM nodes suffer from large losses(10

dB) Need EDFA to compensate losses

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REFERENCE

Optical Networks:A practical Persepective

Rajiv Ramaswamy,Kumar.N.Sivarajan