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D.Mynbaev TCET4102,Module10,Spring2008 1

NEW YORK CITY COLLEGE of TECHNOLOGYTHE CITY UNIVERSITY OF NEW YORK

DEPARTMENT OF ELECTRICAL AND TELECOMMUNICATIONS

ENGINEERING TECHNOLOGY

Course : TCET 4102 Fiber-optic communicationsModule 10: DWDM and CDWM

Prepared by: Professor Djafar K. MynbaevSpring 2008


• Components for optical networks –review

• Evolution of optical networks

• Wavelength-division multiplexing (WDM)

• Dense wavelength-division multiplexing (DWDM)

• Coarse wavelength-division multiplexing (CWDM)

• Comparison of DWDM and CWDM

Textbook: Djafar K. Mynbaev and Lowell L. Scheiner, Fiber-Optic Communications Technology, Prentice Hall, 2001, ISBN 0-13-962069-9.

Notes:

The figure numbers in these modules are the same as in the textbook. New figures are not numbered.

Always see examples in the textbook.

Key words

• Optical networks

• Wavelength-division multiplexing (WDM)

• Dense wavelength-division multiplexing (DWDM)

• Coarse wavelength-division multiplexing (CWDM)

• Channel spacing

• WDM bit rate

Module 10: DWDM and CWDM


• Fiber-optic communications systems start with a simple point-to-point link.

• As the transmission length increases, the need for boosting an optical signal arises; thus, an O/E/O regenerator is introduced.

• Based on this simple configuration, massive deployment of long-distance and regional telephone networks began in the late 1980s.

Overview of optical networks

Evolution of optical networks


Tx

Info Info

Electrical Optical

Optical fiber

RxTx

Rx

Electrical

O/E/OREG

Tx-Transmitter

Rx-Receiver

REG-

Regenerator

Block diagrams of a fiber-optic link


Evolution: From point-to-point link to WDM networks

Basic point-to-point fiber-optic link

Link with regenerator


• In the middle of the 1990s, network

operators started to experience a lack

of fiber capacity (―fiber exhaust‖).

WDM has become the solution to this

problem.




1

3

4

1

2

3

4

MUXDE-

MUX

Basic wavelength-division multiplexing (WDM) link

MUX-WDM Multiplexer

DEMUX-WDM Demultiplxer


Evolution: WDM concept

WDM concept





Evolution: WDM spectral view

WDM link: spectral viewComputer simulation of a WDM system using LinkSim (RSoft Inc.)




• WDM became the practical technique for

increasing channel capacity only after

optical amplifiers (OAs) had been

developed.

• Erbium-doped fiber amplifier (EDFA) was

the first -- and still is the most -- ubiquitous

type of optical amplifier.


Evolution: introduction of OA (EDFA)



WDM link: introduction of OA (EDFA)


Figure 4: WDM link with OAOverview of fiber-optic networks

Evolution of fiber-optic networks

Overview of fiber-optic networks


1

2

3

4

1

2

3

4

MUXDE-

MUX

WDM link with optical amplifier (OA) increasing link

capacity and distance first generation of optical networks.

-

OA




Evolution: WDM link with OA




• Introducing optical add/drop multiplexer

(OADM) has allowed the network operator

to add/drop a wavelength (channel) at a

specific point in the transmission link.

• An OADM is a switch with only two (input

and output) ports.


Evolution: introduction of OADM

WDM: Introduction of OADM




Figure 5: WDM with OADMOverview of fiber-optic networks

Evolution of fiber-optic networks (Figure 3)

1

2

3

4

1

2

3

4

MUXDE-

MUX

OADM OA

WDM link with optical add/drop multiplexer (OADM)




Evolution: WDM link with OADM





Evolution: drop a channel—spectral view

Computer simulation of a WDM system using LinkSim (RSoft Inc.)




• Development of optical cross-connects (OXCs)

has enabled the network operator to switch

wavelengths (channels) among different links

creating WDM fiber-optic communications

networks.

• WDM network’s logical configuration can be

modified independently of its physical topology

by routing individual wavelengths rather than

switching entire light beams among optical fibers.


Evolution: introduction of OXC



WDM: Introduction of OXC


1

2

3

4

1

2

3

4

MUXDE-

MUX

OADM

OXC

OA

WDM network with optical cross-connect (OXC)


Evolution: WDM link with OXC

OXC/OADM switches λs logical topology can be changed independent of

physical topology.



WDM link with OADM and OXC


1

2

N

1

2

N

MUXDE-

MUX

OADM

OXC

OA


Evolution: WDM optical network

•••

•••

J-L J-L

OA

OA

OA

WDM network with OA, OADM,

and OXC reconfiguration of

lightpaths second-generation

optical networks.






OADM

OADM

OADM

OADM

OADM

OADM

OXCOXC

WDM ring network with OADMs and OXCs.






OXC

OXC

OXC

OXCOXC

Advanced WDM mesh-like network with OXCs supported by

commercially available equipment.




WDM network

Circuit

switching

WDM network

Burst

switching

WDM network

Packet

switching

Time


Evolution: From point-to-point link to WDM

networks




networks

WDM networks’ switching evolution: Circuit switching in

ring and mesh networks (second generation), burst switching in ring

and mesh networks (R&D stage), and packet switching (R&D

stage) with optical label switching supporting all transfer modes

(next generation). (After [8[,[9]).

Today we have time, wavelength, and spatial (fiber-fiber)

switching. The finer granularity will be achieved with optical burst

switching. The finest granularity will be achieved with optical

packet switching.




networks

Three generations of optical networks (after [9]).

Point-to-point link

Goal: Increase capacity

Technology: DWDM

WDM networks

Goal: Optical circuit switching

Technology: Reconfigurable OXC

All-optical intelligent networks

Goal: Optical packet switching

Technology: Burst, label and packet

switches


• Types of WDM– DWDM

– CWDM

• Transporting flexibility– Every wavelength is a huge transporting vehicle theoretically can carry

any information in any format

– Granularity at wavelength and subwavelength levels bandwidth on demand with fixed network physical topology

– Wavelength provides Layer 1 optical functionality, while channel provides a Layer 2 link that is mapped onto a wavelength separation the physical and logical aspects

• Switching flexible logical topology over fixed physical topology

– Broadcast and select

– Wavelength routing

• WDM technology


Evolution: main features of WDM networks




Wavelength-division

multiplexing

Dense wavelength-division

multiplexing (DWDM)

Coarse wavelength-division

Multiplexing (CWDM)

Ultra-dense wavelength-division

multiplexing (U-DWDM)




DWDM: ITU-T Recommendation G.694.1 (06/2002) specifies the frequency grid anchored to

193.1 THz (1552.52 nm). This grid starts from 196.1 THz (1528.77 nm) and

supports a variety of channel spacings ranging from 12.5 GHz (~0.1 nm) to 100 GHz

(~0.8 nm) and wider. The pictures below show wavelength comb and its detail on an

oscilloscope screen.




DWDM occupies wavelengths from ~1530 nm to ~1610 nm. This range is subdivided

in two subsections: C-band and L-band, where C and L stand for conventional and long

bands, respectively.

1250 1350 1450 1550 1650

Wavelength (nm)

0.2

0.4

0.6

Att

enuat

ion (

dB

/km

)

Original

1270-1350

Extended

1350-1470

Short

1470-

1530

Con-

ven-

Tio-

nal

1530-

1562

Long

1570-

1610

EO S C L U

Ultra-

Long

1625-

1530 1610




•It is a gift of nature that EDFAs operate in the range (1530

nm to 1600 nm), where standard singlemode fiber (SMF)

exhibits minimum attenuation. Thus, EDFAs can be used to

compensate for transmission losses.This fortunate

coincidence has triggered the wide use of DWDM

technology.

•DWDM technology increases network transmission capacity

but it is a costly solution because cooled lasers and other

expensive components are required Applications: long-

haul and ultra-long-haul networks.




Put more bandwidth on fiberTask:

Solutions:Ultra-dense WDM

(U-DWDM)

25 GHz and 12.5 GHz

Increase TDM

data rate

10 Gbit/s and 40 Gbit/s

ProsConsPros Cons

U-DWDM vs. high-speed TDM




U-DWDM vs. high-speed TDM (continued)

U-DWDM - 25 GHz and less

PROS (after [4]):

•Electronics is available at low cost

•Simplifies TDM

•Allows for the use of slower data rates;

e.g., 10 Gbit/s and 2.5 Gbit/s

•Alleviates dispersion (both chromatic

and polarization-mode) problems

CONS (after [3] and [4]):

•Requires rigid stability from lasers,

multiplexers, and other optical

components high cost

•Requires developing new optical

components, e.g., a super-continuum

source

•Requires more channels to deliver high-

volume traffic to utilize the advantage of

slower channel bit rate more

components, especially TX and Rx


PROS (after [3]):

•Reduces cost of transmission

(increasing data rate by factor of

four reduces transmission cost by 40%)

•Better supports 40 Gbit/s services

•Can be overlaid on existing 10 Gbit/s

networks

•All key components are available (with

the exception of 40 Gbit/s FEC devices)

•Reduces number of components per

channel.



U-DWDM vs. high-speed TDM (continued)

TDM - 40 Gbit/s

CONS (after [3] and [4]):

•Magnitude of chromatic dispersion

increases with the square of the bit rate;

e.g., a rise from 2.5 Gbit/s to 10 Gbit/s

increases Δtchro 16 times

•Polarization-mode dispersion (PMD)

becomes the major hurdle at L > 1000

km

•Must use FEC and more sophisticated

modulation formats to improve OSNR

•Better work with new improved fibers

problems with installed plant.




U-DWDM vs. high-speed TDM – summary

•There are no decisive arguments in favor of or against each approach

•40-Gbit/s technology is ready to be deployed (though FEC devices

are not yet available)

•25-GHz channel spacing has been demonstrated at the commercial

level; 2.5 Gbit/s data rate at 6.25-GHz spacing has been demonstrated

•Both technologies allows us to reach the same level of spectral

efficiency

•There is no crucial need for deployment of either technology

market will decide




ITU-T Recommendation G.694.2 (approved in December 2003) specifies the

frequency grid for CWDM: It must range from 1271 nm to 1611 nm with 20-nm

channel spacing.

Coarse wavelength-division multiplexing (CWDM)

1271 1351 1451 1551 1611Wavelength (nm)

0.2

0.4

0.6

Att

enuat

ion (

dB

/km

)

EO S C L U

••• ••• ••• •••

From specified

18 λs, the most

popular are

eight λs,

occupying the

range from 1471

to 1611 nm.




CWDM became a feasible technology only after enhanced singlemode fiber (E-

SMF) was developed.

CWDM (continued)

1250 1350 1450 1550 1650

Wavelength (nm)

0.2

0.4

0.6

Att

enuat

ion

(d

B/k

m) EO S C L U

S-SMF (standard SMF)

E-SMF:

Enhanced SMF, also called zero-water-peak SMF (ZWP)

CWDM bandwidth1271 1611




Advantages:

•CWDM offers a cost-effective solution to the ―fiber-exhaust‖ problem since

inexpensive components can be used. The most saving comes form the use of un-

cooled lasers, which results in small-form-factor pluggable transceivers.

Disadvantages:

•Inexpensive components can support only relatively low-rate signals (maximum

2.5 Gbit/s per wavelength).

•EDFAs do not cover the entire CWDM spectrum; therefore, transmission

distance is limited to 20 km. (Transmission up to 80 km distance has been

demonstrated.) Partial solution: SOAs that cover the range from 1300 to 1600

nm.




DWDM vs. CWDM:

DWDM CWDM

Dense channel spacing

more bandwidth more expensive

Wide channel spacing

less bandwidth less expensive

Long-haul networksHybrid

networks

Metro core and access

networks




DWDM vs. CWDM (continued):

•DWDM and CWDM are complementary rather than competitive

approaches;

•In metro core networks, both technologies are applicable; the use of

both CWDM and DWDM makes the overall network more cost-

effective;

•Hybrid CWDM/DWDM systems that transport both CWDM and

DWDM signals are commercially available (Nortel, Meriton, and

ADVA). [Source: Lightwave, February 2004, pp.15-20.] Main problem: Large

dispersion of E-SMF fiber. Solution: the use of negative dispersion

fiber [5].






DWDM vs. CWDM (continued):

Example of hybrid DWDM/CWDM transmission. Source: www.rbni.com.




Logical topology:

•Switching at the wavelength level allows for overlaying

flexible logical topology on fixed network physical

topology.

•We distinguish between two types of WDM networks by

their approaches to delivering information (logical

topology):

–Broadcast-and-select

–Wavelength-routing


Main

Tx

Tx

Rx3

ONU

Tx

Tx

Rx2

Rx1

Rx4

Tx

λ1 λ2 λ3 λ4

Broadcast-and-select network

with bus topology.

λ2

λ3λ4

λ1

λ2λ3λ4

λ1 λ1

λ2

λ4

λ3

λ2

λ3λ4

λ1

λ2

λ3λ4

λ1






Tx1/Rx1

Tx3/Rx3

Tx2/Rx2

TxN/RxN

λ1

λ2

λ1

λ3

λ1

Wavelength conversion

Wavelength reuse

λ2

λ2

λ2

λ1

λ1

λ1

λ1

Network establishes temporary path called lightpath for transmission a specific

channel (wavelength). For example, channel λ1 is transmitted from Tx1 to RxN.

Wavelength-routing network




• Both types of networks may be static (when

configuration is predetermined) and dynamic

(when networks reconfigure in response to current

demands).

• Examples of broadcast-and-select networks

include CATV and PON networks. WDM

networks with reconfigurable OADMs and OXCs

are examples of wavelength-routing networks.

• Wavelength routing is a separate topic that is

outside the scope of this tutorial.




WDM technology: Components and subsystems (after [6])

Components

•Couplers

•Filters

•Multiplexers and

demultiplexers

•Wavelength converters

•Equalizers and

attenuators

•Isolators and circulators

Subsystems

•Transmitters and receivers space and

power dissipation problems arrays of laser

diodes and photodiodes (e.g., [7])

•OXCs and OADMs

•Optical amplifiers and optical regenerators

•Dispersion compensators

WDM technology: Testing new testing technology




By this stage of WDM network evolution,

the main stress has been placed on the

physical aspect of development of

optical networks.


References from Module 9:

1. John R. Vacca, Optical Networking Best Practices Handbook, Hoboken, N.J.: Wiley – Interscience, 2007.

4. Djafar K. Mynbaev, The physical layer of the optical networks: Devices and subsystems, IEEE Communications Society, online tutorial, 2006.

5. Djafar K. Mynbaev and Lowell L. Scheiner, Fiber-Optic Communications Technology, Prentice Hall, 2001.

6. Djafar K. Mynbaev, ―Next-generation optical networks from network layer and physical layer perspectives,‖ Tutorial presented at the 11th International Conference on Telecommunications, Fortaleza, Brazil, August 2004.

7. Manasi Deval et al, ―Distributed Control Plane Architecture for Network Elements,‖ Intel Technology Journal, November 14, 2003, pp.51-63.

8. Uyless Black, Optical Networks, Prentice Hall, 2002.

9. Yinghua Ye and Sudhir Dixit, ―Surviavibility in IP-over-WDM Networks,‖ in IP over WDM edited by Sudhir Dixit, Hoboken, N.J.: Wiley – Interscience, 2003.

10. Rajiv Ramaswami and Kumar N. Sivarajan, Optical Networks – A Practical Perspective, 2nd ed., San Francisco: Morgan Kaufmann, 2002.

11. Vivek Alwayn, Optical Network Design and Implementation, San Jose, CA: Cisco Press, 2004.

12. Arun K. Somani, Survivability and Traffic Grooming in WDM optical Networks, New York: Cambridge University Press, 2006.


References for Module 10:1. Djafar K. Mynbaev and Lowell L. Scheiner, Fiber-Optic Communications Technology,

Upper Saddle River, N.J.: Prentice Hall, 2001.

2. Benyuan Zhu, ―Ultra high density and long haul transmissions,‖ OFC’04, ThE1.

3. B. Mikkelsen et al, ―Deployment of 40 Gb/s systems: Technical and cost issues,‖ OFC’04, ThE6.

4. Jeff Hecht, ―Speeding up transmission rates with slower signals,‖ Laser Focus World, November 2002, pp. 91-96.

5. H.S. Chung, Y.G. Jang, and Y.C. Chung, ―Directly modulated CWDM/DWDM System using Negative Dispersion Fiber for Metro Network Application,‖ OFC’04, WG5.

6. Stamatis Kartalopoulos, ―The Flexibility of DWDM in Handling Continually Increasing Bandwidth Demands for Future Optical-Fiber Communication Networks,‖ IEEE LEOS Newsletter, April 2002, pp 15-19.

7. John Ceske et al, ―CWDM vertical-cavity surface-emitting laser array spanning 140 nm of the C, S, and L fiber transmission bands,‖ OFC’04, TuE7.

8. Ken-ichi Sato, ―Key Enabling Technologies for Future Networks,‖ Optics & Photonics News, May 2004, pp. 34-39.


References (continued):

9. Fei Xue and S.J. Ben Yoo, ―High-Capacity Multiservice Optical Label Switching for the Next-Generation Internet.,‖ IEEE Communications Magazine, May 2004,ppS16-S22.

10. S.J. Ben Yoo, ―Optical-label switching, MPLS, MPLambdaS, and GMPLS,‖ Optical Network, May/June 2003, pp. 17-31.

11. Botaro Hirosaki et al, ―Next-generation Optical Networks as a Value Creation Platform,‖ IEEE Communications Magazine, September 2003, pp. 65-71.

12. Ken-Ichi Kitayama and Masayuki Murata, ―Versatile Optical Code-Based MPLS for Circuit, Burst, and Packet Switchings,‖ Journal of Lightwave Technology, November 2003, pp. 2753-2764. 1.

13. Nasir Ghani, Sudhir Dixit and Ti-Shiang Wang, ―On IP-WDM Integration: A Retrospective,‖ IEEE Communications Magazine, September 2003, pp. 42-45.

14. Monir Hamdi and Chumming Qiao, ―Engineering the Next-Generation Optical Internet,‖ Optical Networks, November/December 2003, pp. 5-6.

15. Uyless Black, Optical Networks, Prentice Hall, 2002.

16. Angela L. Chiu andJohn Strand, ―Control plane considerations for all-optical and multi-domain networks and their status in OIF and IETF‖ Optical Networks, January/February 2003, pp.26-35.



17. Chinsheng Xin et al, ―On an IP-Centric Control Plane,‖ IEEE Communications Magazine, September 2001, pp. 88-93.

18. Alan McGuire, Shehzad Mirza, and Dareen Freeland, ―Application of Control Plane Technology to Dynamic Configuration Management,‖ IEEE Communications Magazine, September 2001, pp. 94-99.

19. Manasi Deval et al, ―Distributed Control Plane Architecture for Network Elements,‖ Intel Technology Journal, November 14, 2003, pp.51-63.

20. ―Driving Optical Network Evolution,‖ www.iec.org/online/tutorial/drive_opt/index/html.

21. ―OIF UNI/NNI Interoperability Demo,‖ www.oiforum.com/public/downloads/UNI-NNI.ppt.

22. Jim Jones, “User-Network Interface (UNI) 1.0,” Optical Networks, March/April 2003, 2003, pp. 85-93.

23. Daryl Eigen, Shibin Jiang, and Ike Song, ―Metro Amplifiers Provide Gain Without Pain,‖ Optical Networks, March/April 2003, pp. 95-97.

24. Peter Tomsu and Christian Schmultzer, Next Generation Optical Networks, Prentice Hall PTR, 2002.

http://www.iec.org/online/tutorial/drive_opt/index/html

http://www.oiforum.com/public/downloads/UNI-NNI.ppt





25 Josep Sole-Pareta et al, ―Some Open Issues in the Optical Networks Control Plane,‖http://pcsostres.ac.upc.es/doctorat/papers/200306-172/icton2003-xmasip.pdf.

26 Sergio Sanchez-Lopez et al, ―PNNI-based Ciontrol Plane for Automatically Switched Optical Networks,‖ Journal of Lightwave Technology, November 2003, pp. 2673-2681.

27 Lu Shen and Byrav Ramamurthy, ―Provisioning and restoration in the next-generation optical core,‖ Optical Networks, March/April 2003, pp. 32-45.

28 Soo-Hyuan Choi et al, ―Standardization efforts in optical networking focused on architecture and signaling issues,‖ Optical Networks, May/June 2003, pp. 32-48.

29 Wesam Alangar, ―Optical networking evolution in ITU-T and IETF – A reality check,‖ OFC’04, FH1.

30 Nic Larkein, ―ASON and GMPLS – The Battle of the Optical Control Plane,‖ Data Connection Limited, Enfield, UK, August 2002.

31 Thomas DiMicelli, ―Emerging Control Plane Standards and the Impact on Optical Layer Services,‖ www.oiforum.com/public/downloads/DiMicelli2.ppt

32 Djafar Mynbaev, ―PON performance improves with multiplexing,‖ WDM Solutions, January 2003, pp.18-20.

http://www.oiforum.com/public/downloads/DiMicelli2.ppt

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