final seminar report sunil[1] · b) Synchronous Digital Hierarchy: It can provide data rate from...

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DWDM 1. INTRODUCTION Communication has always been an important aspect of human life from stone age to

this modern era. However the mode of communication gradually changed with the passage of

time. Telecommunication came into existence about 150 year ago. Initially only voice

communication was part of telecommunication. Systems were designed keeping in view the

voice transmission. It was low capacity, short distance, and purely frequency based analog

system. This was know as FIRST generation system. Use of data on this voice network

started in SECOND generation systems. Internet, private data transfer, Tele printer, Fax, 9.6

kbps data for defence, were application supported by second generation voice network. This

system was designed for voice communication but data was also supported by it. Now in this

modern era we had THIRD generation system which is design for Data communication and

also support voice on it. It support high speed data communication such as Broad band,

Teleconferencing, Video conference, Internet, GPRS, Edge, Core networking and so on.

To meet demand of very high BANDWIDTH due to exponential increase in

telephone, mobile, and Data networks, Time Division Multiplexing (TDM) switching

technique was used in Telecom Networks .Media such as coaxial cable and microwave were

having their limitation such as limited capacity, disturbance due to atmospheric effect, cost

and maintenance problem. OPTICAL FIBER cable were having capabilities to over come

these limitations and has been proved as the best replacement. Use of optical fiber resulted in

a revolution in telecommunication transmission.

In analog carrier communication system, the frequency division multiplexing (FDM)

method is often adopted to make full use of bandwidth resources of cables and enhance the

transmission capacity of the system. It involves transmitting several channels of signal

simultaneously in a single cable and, at the receiver end, utilizing band pass filter to filter the

signal on each channel according to the frequency difference among the carriers. But this

TDM/FDM was not utilizing the complete Bandwidth of optical fibers. This resulted in

optical fiber frequency division multiplexing (OFDM) [5]. This method can also be used to

enhance the transmission capacity of the system .In fact this multiplexing method is very

effective in optical communication. Unlike the frequency division multiplexing in analog

carrier communication system, optical fiber communication utilizes optical wavelength as

single carrier. It divides the low attenuation window of optical fiber (Appendix A) into

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several channels according to the frequency difference of each wavelength channel. Further,

it implements multiplexed transmission of multi channel optical signals in a single fiber.

Since some optical components (such as narrow-bandwidth optical filter and coherent laser)

are currently not mature, it is difficult to implement ultra dense optical frequency division

multiplexing of optical channel [7] . However, alternate channel optical frequency division

multiplexing can be implemented based on current component technical level [3]. Usually,

multiplexing with larger channel spacing (even indifferent windows of optical fibers) is

called optical wavelength division multiplexing(WDM) and WDM in the same windows

(within a band (C,L…)) with smaller channel spacing is called as dense wave division

multiplexing(DWDM) (Appendix B) With the advancement in optical technologies,

nanometer level multiplexing can be implemented. Multiplexing of 8,16,32 or more

wavelengths with smaller wavelength spacing is called DWDM (Figure1). DWDM

technology make efficient utilization of bandwidth and low attenuation characteristics of

single mode optical fibers and uses multiple wavelength as carriers and allow them to

transmit in the fiber simultaneously. When compared to common single channel system,

dense wave division multiplexing greatly increase the network capacity and make efficient

use of the bandwidth resource of optical fibers. Moreover DWDM has many advantages such

as simple capacity, expansion and reliable performance. Especially it can access various

types of services and this gives it a bright prospective of applications.

DW

DM

MU

LTIP

LEXE

R SINGLE FIBRE

SDH OPTICAL SIGNALS

Fig 1: A overview of DWDM Technique

A typical DWDM system structure and optical spectrum is shown in figure 1.At the transmit

end, optical transmitter outputs signal of different wavelength whose accuracy and stability

meet certain requirement. The signals are multiplexed via an optical wavelength multiplexer

and send to an Erbium Doped optical fiber power amplifier (EDFA). After amplification, this

multi channel optical signal is sent to optical fiber for transmitting. In the midways optical


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line amplifier may be installed or not according to practical conditions. At receiver ends, the

signals are amplified by the optical pre amplifier and send to the optical wavelength de

multiplexer which separates them into original multi channel optical signals.

OTU

OTU

OMU

BA LAOMU

PA

OTU

OTU

OSC OSCOSC

Optical TX Optical RxOptical line Amplifier

Tx RxMUX DEMUX

OFA WDM

WDM

λ2....

λ1

λ16

TRANSPONDERS

OPTICALSIGNALS.STM-1STM-4

STM-16ATM

IP

Fig. 2: Block schematic of DWDM System

OTU: Optical Transponder Unit BA: Booster Amplifiers OMU: Optical Multiplexing Unit LA: Line Amplifiers ODU: Optical De Multiplexing Unit PA: PRE Amplifiers OSC: Optical Supervisory Unit OFA: Optical Fiber Amplifiers The following steps describe the system shown in Fig 2:

1. The transponder accept input in the form of standard single mode laser. The input can

come from different physical media and different protocols and traffics types.

2. The wavelength of each input signal is mapped to a DWDM wave length.

3. DWDM wave length from the transponders are multiplexed into single optical signal

and launched into fiber

4. A post amplifier boosts the strength of the optical signal as it leave the system

5. Optical amplifier are used along the fiber span as needed

6. A pre amplifier boosts the signal before it enter the end system

7. The incoming signal is de multiplexed and fed to respective receiver

8. From receiver they are transmitted to different system according to requirement

1.1 Versatility of DWDM:

DWDM is a fiber optic transmission technique that employs light wavelength to

transmit data parallel by bit or serial by character. It is the optical network that allows the


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transmission of e-mail, video, multimedia data voice carried in Internet protocol (IP),

asynchronous transfer mode (ATM) and synchronous optical networks (SDH). DWDM

increases the capacity of embedded fiber by first assigning incoming optical signal to specific

frequencies within a designated frequency band and multiplexing the resulting signal out onto

one fiber[7].

Fig. 3: Versatility of DWDM


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2. Evolution of DWDM Developments in fiber optics are closely tied to the use of the specific region on the optical

spectrum where optical attenuation is low. The regions, called windows, lie between areas of high

absorption. The earliest system were developed to operates around 850n, the first window in silica

based optical fiber. A second windows (S BAND at 1310 nm, soon proved to be superior because of

its low attenuation followed by a third windows (C-BAND) at 1550nm with even lower optical loss.

Now a days, a fourth window (L- BAND) near 1625 nm is under development. (Appendix A)

Early WDM, in late 1980s [4], were using the two widely spaced wavelength in the

1310 nm and 1550 nm regions. The early 1990s saw a second generation of WDM in which

two to eight channel were used. These channel were now spaced at an interval at about

400GHZ in the 1550 nm window .By the mid-1990s DWDM system emerged with 16 to 40

channels and spacing from 100 to 200 GHZ. By late 1990s DWDM system had evolved to

the point where they were capable of 64 to 160 parallel channels, densely packed at 50 or

even 25 GHZ interval.

Late1990’s

64-160 channels25-50 GHZ spacing

Mid1990’s

16-40 channels 100-200 GHz spacingDense WDM, integrated systems withNetwork Management, add-drop functions.

Early1990’s

2-8 channels passive WDM 200-400 GHz spacing WDM components/parts

Late1980’s

2 channels WidebandWDM 1310 nm, 1550 nm

Fig.4: Evolution of DWDM 2.1 Present Scenario Applications such as Broad Band, Telemedicine ,Video Conferencing Broadcast

Television, Networking, MPLS VPN and rapid demands in telecom has resulted in


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spontaneous increase in the demand of BANDWIDTH in telecom domain. The hurdles to

meet this demand was the limitation of existing Optical fiber cables. The existing optical

fiber G652 was facing challenges such as Attenuation, Chromatic dispersion and Non

linearity. Due to this, maximum data rates carried by G652 was STM-16 (2.5 Gbps).The one

of the solutions to meet current demand was to lay new Optical fiber cable on existing route,

which was economically impractical. The solution adopted was to establish new systems for

new demand on same route, but it led to the exhausting of fibers. Increase in the capacity of

existing network without expensive re-cabling resulted in evolution of DWDM (Dense Wave

Division Multiplexing) in present day Telecom world. DWDM can be viewed as a parallel set

of optical channels each using a slightly different light wavelength, but sharing single

transmission medium. DWDM is third generation transmission system working in third

window of optical networks(1550nm) and having capabilities of carrying 32channel of STM-

16 (80Gbps) and distance of 640 km. Due to its unique characteristic such as Open system

Smooth upgradeability, Add-Drop of wavelength , FEC(Forward Error Correction), long and

very long haul application NMS (Network Management System), 32optical channel on same

fiber, 80 Gbps data rate. DWDM has emerged as one of the most important phenomena in the

development of fiber optic transmission technology.

Evolution of PDH , SDH and finally DWDM was to meet requirement s such as long

distance transmission, high bit rate and large number of wave length in optical fiber

networks. DWDM is a mile stone of optical fiber transmission in telecommunication.

2.2 Challenges For The Existing Telecommunication Networks:

Earlier, the forecast of the amount of bandwidth capacity needed for networks were

calculated on presumption that a given individual would use only networks bandwidth for a

maximum of six-minutes/ hour. This formula did not fit well in the amount of traffic

generated by internet access (300 per cent growth rate per year), Faxes, multiple phone lines,

modems, teleconferencing and data and video transmission .Enormous amount of bandwidth

capacity is required to provide the service demanded by consumer. Many service providers

are coping with fiber exhaust in their networks.[5](Fig.5)


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ADVANTAGES OF DWDM

2.3 Resolving the Capacity Crisis

One way to alleviate fiber exhaust is to lay more fibers, but it is not economical. A

second choice is to increase the bit rate using time division multiplexing (TDM) (Fig 5 ) in

the following way: a) Plesiochronous Digital Hierarchy :

It can provide data rate from 8Mbps to 140 Mbps on existing fiber(Fig.6)

b) Synchronous Digital Hierarchy :

It can provide data rate from 155Mbps to 2.5Gbps on existing fiber.(Fig.7)

The third choice for service is DWDM , which increases the capacity of embedded fiber

by first assigning incoming optical signals to specific frequency ( wavelength) within a

designated frequency band and then multiplexing the result signal out onto one fiber

.DWDM can provide data rate from 2.5 Gbps to 80 Gbps on existing fiber

EXCHA

MUX &

OLTE

MUX &

OLTE

EXCHBLIGHT (OFC)

4 to 64 PCM 4 to 64 PCM

PDH

Fig. 5. Peliosynchronous Digital Hierarchy

Fig. 5: Challenges For The Existing Telecommunication Networks

Fig.5: PDH Multiplexing Technique


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EXCHA

MUX &

OLTE

MUX &

OLTE

EXCHBLIGHT (OFC)

63 TO 1008 PCMSTM-1 TO STM-16

63 TO 1008 PCMSTM-1 TO STM-16

SDH

Fig. 6. Synchronous Digital Hierarchy

As shown in fig. 6 the loss in fiber cable is less at 1400-1600 nm. DWDM take advantage of

this properties of fiber and it operate in 1500nm band (Appendix B).Thus DWDM can work

up to distance of 640km which is much greater then PDH/ SDH system .DWDM works in

C Bands. Fig 8. shows four optical windows at different wave length ( 800 nm ,1300 nm ,

1500 nm ,1600 nm).It is clear that losses are less at higher wave length but it requires very

low attenuation fiber on route and high quality of laser is used to generate higher wave length

Fig. 7: SDH Multiplexing Technique

Fig. 8 : Wavelength Vs Losses (Ref: “Introduction to DWDM Tech”, Cisco System Inc. pg 34)


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3. Overview of DWDM NETWORK Architecture In this section, an overview of the design of a typical DWDM network is undertaken []

The details of the various blocks/components as shown in Fig. 2 is given in detail so as to

have better understanding.

3.1 Optical Transponder Unit (OTU):

The major function of the OTU board are to employ the Optical /electrical/ optical

conversion made to realize wave length conversion. OTU includes transmission OTU and

receiver OTU.

Fig.7 :TRANSPONDER / TRANSLATOR / WAVELENGTH CONVERTOR

O/E E/OElectrical REGENERATION

OPTIONAL

REGENERATOR

3.2 Optical Multiplexers and De-multiplexers Unit (OMU & ODU):

As DWDM system send signal from several source over a single fiber, they must

include some means to combine the in coming signal. This is done with multiplexers, which

take optical wavelength from multiple fiber and converge them into one beam At the

receiving end the system must be able to separate out the components of the light so that they

can be discreetly detected de multiplexers perform this function by separating the received

beam into its wave length components and coupling then to individual fiber. De

multiplexing must be done before the light detected, because photo detector are inherently

broadband device that cannot selectively detect a single wave length Multiplexer can be

passive or active design. Passive designs are based on prisms, direction grating or filter, while

active designs combines passive devices with tunable filter. The primary challenges for these

devices is to minimized cross talk and maximize channel separation.

Fig.9: Optical Transponder Unit


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Fig 7:Multiplexing And De multiplexing Using Prism And Lens

Fig 8:Multiplexing And De multiplexing Using Waveguide Grating Diffraction

Fig.10:Multiplexing ,De multiplexing And Add DropUsing mirror

Multi WavelengthFilter

Simple multiplexing and de multiplexing can be done with prism (Fig 10) .A parallel beam

of polychromatic light impinges on prism surface, each components wavelength is refracted

differently. This is the RAINBOW effect. In the output light , each wavelength is separated

from the next by an angle. A lens then focus each wave length to the point where it need to

enter a fiber. The same components can be used in reveres to multiplex different wave length

onto one fiber. Another technology is based on the principle of diffraction and of optical

interface (Fig.11). When a polychromatic light source impinges on a diffraction grating each

wave length is diffracted a different angle and there fore two different point in space. Using a

lens there wavelength can be focused onto individual fiber. Arrayed Waveguide Grating

(AWG’S) are based on diffraction principle (Fig.12).An AWG device some time called an

optical waveguide router grating router, consists of an array of curved-channel waveguide

Fig.12: Multiplexing And De multiplexing Using Array of Wave Guide

Fig:10: Multiplexing And De multiplexing Using Prism And Lens

Fig.13: Multiplexing , De multiplexing And Add Drop Using mirror


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with a fixed difference in the path between adjacent channel .The wave guide are connected

to cavities at the input and output. When the light enters input cavity , it is diffracted and

enter the wave guide array .There the optical length difference of each wave guide introduces

phase delays in the output cavity ,where an array of fiber is coupled .The process results in

different wave length having maximal interference at difference, which correspond to the

output pots. Another technology is based on the principle of multilayer interference

filters(Fig.13). By positioning filter, consist of the films, in optical path, wave length can be

sorted out. The property of each filter is such that it transmits one wave length while

reflecting others. By cascading these devices many wave length can be de multiplexed.

1 2

3

DROP

Fig.11:Add Drop Using Circulator & Fiber Grating Diffraction

COUPLER

D M

Fig.12:Add Drop Using Circulator And coupler

3.3 Optical Add Drop Multiplexers (OADM) :

This is the area in which multiple wave length exist .It is often desirable to be able to

remove or insert one or more wavelength at some point along this spans. An OADM

performs this function. Rather then combining and separating all wave length, the OADM

can remove some while passing others. In this add drop is at optical stage and no optical

/electrical/optical conversion take place It is made by circulator and tunable fiber grating

(Fig 14 & 15 )

Fig.15: Add Drop Using Circulator And Coupler

Fig.14: Add Drop Using Circulator &Fiber Grating Diffraction


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3.4 Optical Fiber Amplifier (OBA, OLA, OPA):

Optical amplifiers also can be used to boost signal power after multiplexing or before

de multiplexing By making it possible to carry large loads that DWDM is capable of

transmitting over long distance, the EDFA(Erbium Doped Fiber Amplifier) was key enabling

technology. Erbium is a rare elements that, when excited, emits light around 1.54 micrometer

– the low loss wave length for optical fiber is used in DWDM. A weak signal enters the

Erbium doped fiber , into which light at 980 nm or 1480 nm is injected using a pump laser.

This injection light simulates the erbium atoms to release their stored energy as additional

1550 nm light .As this process continues down the fiber, the signal grows stronger .The

spontaneous emission in the EDFA also add noise to the signal .EDFA is capable of gains

of 30 dB or more and out put power of +17db or more. The target parameter when selecting

n EDFA are low noise and flat gain .Gain should be flat because all signal should be

amplified simultaneously EDFA is available in C band and L band.

Erbium fiberErbium fiber

Signal inSignal in1550 nm1550 nm

IsolatorIsolatorSignal outSignal out

WavelengthWavelength--selectiveselectivecouplercouplerPump Residual pumpResidual pump

Fig.13 Erbium Doped Fiber Amplifier (EDFA)

The optical fiber amplifiers can be of many types depends on application. It can be used at

transmitting end or at receiving end or at route. EDFA can be used in all application by

changing direction of pumping signal. It is classified in three following types:

Fig.16: Erbium Doped Fiber Amplifier (EDFA)


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Optical Fiber Amplifiers

OBA OPA OLA

(Optical Booster Amplifier) (Optical PRE Amplifier) (Optical Line Amplifier)

- High optical output power - High receiving sensitivity - Compensate the loss of Tx

- Used in Transmitter side - Used in Receiver side - Used as Regenerator

.

3.5 Optical Supervisory Channel (OSC):

It is used for supervision of DWDM networks and its components .It works on wave

length of 1510 nm and speed of 2.048 Mb/s .It is use in Network Monitoring System. (Fig 17)

Line Terminal Equipment In-line Amplifier

Tx λ1

Tx λ2

Tx λ3

Tx λ4

Tx λ5

Tx λ6

Tx λ7

Tx λ8

DAT

A IN

λ1

λ2

λ3

λ4

λ5

λ6

λ7

λ8

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

λ1

λ2

λ3

λ4

λ5

λ6

λ7

λ8

Line Terminal Equipment

Σ λ + λ sup erv isory

Tx λsup

System ControlProcessor

Rx Tx

OSC

Network Management Network Management

System ControlProcessor

Rx λsup

Fig.14 Optical Supervision Channel

Fig.17: Optical Supervision Channel


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4. Salient Features of DWDM: Apart from having better Bandwidth characteristics DWDM system are more adaptable

under faulty conditions as it can be used in Rings. In case of optical fiber cable cut, the ring

goes in protection mode and thus avoids any failure. This fault tolerant capability is described

below

4.1 DWDM In Ring:

The DWDM system only provides “virtual” optical fiber. The protection for each

wavelength on SDH layer is independent to the protection mode of other wave length .This

ring can be two fiber or 4 fiber. To employ OADM with the add/ drop multiplexing capability

to form rings is another application mode of DWDM technology in ring networks. At present

network formed by OADM s can be classified into two mode.

Fig.18: DWDM RING

One is wave length path protection based on single wave length protection. ie. 1+1 protection

of single wave length which is similar to path protection of SDH system. The other is line

protection ring which protect the single of multiplexed wave length. when fiber is cut off, the

“ loop back” function can be implemented in two nodes near the fiber cut off. Thus all the

services are protected .This is similar to MSP of SDH. From the aspect of specific forms, the

line protection ring can be divided into two fiber bi directional ring and two fiber

unidirectional ring, half of the wave length operate as working and other as protection wave

length. Figure19 shows protection after optical fiber cable cut.

OADM

OADM

OADM


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Fig.19: Fault tolerant capability of DWDM Networks

4.2 Other main feature supported by DWDM are as follows:

DWDM networks is smooth upgradeable network

DWDM network is Combination of Integrated and open system

Channel equalization technology is used for better performance

Main channel and supervisory channel are independent

Forward error correction (FEC) technology is used in DWDM

DWDM network has Automatic level control (ALC) function

DWDM has gradable optical ADD/DROP multiplexing technology

Unified and intelligent Network Management

DWDM can be used up to 640 Km

4.3 Physical characteristic effecting DWDM System

Fiber physical characteristics impact per : Wavelength , km, Data rates.

Environmental issues affect performance (bending, splices, vibration, temp, etc)

Attenuation of optical pulse.

OADM

OADM OADM

OADM


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5. Research Issues & Future Directions in DWDM 5.1 Transmission Impairment : Developing network-layer solutions to counter physical-layer impairments, such as laser

shift, dispersion in fiber, and also impairment that affects optical components such as

amplifiers, switches, and wavelength converters, is another important issue. A signal

degrades in quality due to physical-layer impairment as it travels through switches (picking

up crosstalk) and EDFAs (picking up noise). This may cause a high bit error rate (BER) at the

receiving end of a light path. The work is going for estimates the online BER on candidate

routes and wavelengths before establishing a connection between a source–destination pair.

One approach is to establish a connection with minimum BER. Another is to establish a

connection with BER lower than a certain threshold if no such connection is found, the

connection request is rejected.[1] Another networking study which considers physical-layer

device characteristics while attempting to solve a network-layer problem is amplifier

placement in WDM optical networks.[2 ]

5.2 Optimization of Location for Amplifier Placements:

In wavelength routed networks, optical amplification is required to combat various power

losses such as fiber attenuation and coupling loss in wavelength routers .Since optical

amplifiers are costly, their total number in the network should be minimized ,apart from

determining their exact placements in the network. However, optical amplifiers have

constraints on the maximum gain and the maximum output power they can supply. When

optical signals on different wavelengths originating at various nodes at locations separated by

large distances arrive at an amplifier, their power levels may be very different. This

phenomenon, known as near–far effect, can limit the amount of amplification available since

the higher-powered wave lengths could saturate the amplifier and limit the gain seen by the

lower-powered wave lengths .The amplifier placement problem considering the limitations of

the devices(for example, maximum power of a transmitter, fiber attenuation, minimum power

required on a wavelength for detection [this represents both the receiver sensitivity level and

the amplifier sensitivity level], maximum power available from an amplifier, and maximum

[small-signal] amplifier gain . The general problem of minimizing the total amplifier count is

a mixed-integer nonlinear optimization problem.[10]


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5.3 Virtual Private Networks over WDM Optical Networks: A virtual private network (VPN) is a communication network between two or more machines

or networks, built for the private use of an organization, over a shared public infrastructure

such as the Internet. In other words, a VPN turns the public network (Internet) into a

simulated WAN by letting an organization securely extend its network services to remote

users, branch offices, and partner companies. VPNs require strong security protocols, such as

IP Sec (IP Security), to be used for data transfer, as they consist of several machines not

under the control of the organization—IP routers and the Internet that carries the traffic

.VPNs can make use of the concept of a light path offered by WDM, to create secure

tunnels(channels) of bandwidth across the WDM backbone network.[9]

5.4 NEXT-GENERATION Optical Internet Networks

WDM-based optical networks are becoming the right choice for the next-generation Internet

networks to transport high-speed IP traffic. In the first phase, light path based circuit

switching WDM networks are deployed as a means of carrying IP traffic. SONET and ATM

networks have been widely deployed in the transport networks. SONET systems have several

attractive features such as high-speed transmission and network survivability. ATM networks

have several attractive features such as flexible bandwidth allocation and QoS support.

Therefore, ATM and/or SONET layers can be used in between the IP layer and the WDM

optical layer for transporting IP packets. A major drawback of this multilayer approach is that

it incurs increased control and management overhead. WDM technology is evolving from

circuit switching technology to burst switching and packet switching technologies. The

granularity of the basic switching entity is large in circuit switching networks, medium in

burst switching networks, and small in packet switching networks. While circuit switching

technology is mature ,the other technologies are not. In a circuit switching network, a

wavelength channel on a link is used by a circuit (light path) for a long time, until it is torn

down. In a burst (packet) switching network, a wavelength channel on a link is reserved only

for the duration of the burst (packet). The bandwidth utilization in burst and packet switching

networks is higher when compared to that in circuit switching networks. This is because, the

former networks use statistical multiplexing while the latter does not. In a burst switching

network, the basic switching entity is a burst. A number of IP packets which are destined for the same

egress router are assembled into a burst at the ingress router. The major challenges in burst

switching networks include the design of cost-effective and fast switches, burst switching

protocols, and wavelength channel scheduling. In a packet switching network, the basic


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switching entity is a packet. The major challenges in packet switching networks include the

design of cost-effective and fast switches, packet synchronization, and contention resolution.

Since optical processing is technologically and economically infeasible, the packet/burst

header is processed electronically while the payload is switched optically. Since optical

random access memory (RAM) is not available, a packet or burst cannot be buffered optically

for a long time. A possible way is to use fiber delay lines (FDLs) to buffer (delay) a packet or

burst for a short time. A multi protocol label switching (MPLS) framework has several

advantages, such as traffic engineering, explicit path routing, fast packet forwarding, and

network survivability. Due to the above advantages, future Internet networks employing

circuit/burst/packet switching are likely to use the MPLS approach[8].

5.5 Wavelength Rerouting :

Apart from wavelength conversion and space division multiplexing, there is yet another way,

called wavelength rerouting, to reduce the bandwidth loss caused by the wavelength

continuity constraint in wavelength routed networks. With wavelength converters employed

in a network, a light path need to be wavelength-continuous between two consecutive

converting nodes only. With space division multiplexing, the chance of finding a wavelength-

continuous route is enhanced, as the same wave length this available on every fiber on a link.

Wavelength rerouting creates a wavelength continuous route by migrating a few existing light

paths to new wavelengths without changing their route. However, it incurs control overhead

and, more important, the service in the rerouted light paths needs to be disrupted. Therefore,

it is imperative for any algorithm employing wavelength rerouting to migrate as few light

paths as possible.[7]

5.5 Wavelength-Convertible Networks :

One possible way to overcome the bandwidth loss caused by the wavelength continuity

constraint is to use wavelength converters at the routing nodes. A wavelength converter is an

optical device which is capable of shifting one wavelength to another wave length. The

capability of a wavelength converter is characterized by the degree of conversion. A

converter which is capable of shifting a wavelength to anyone of D wavelengths is said to

have conversion degree D. The cost of a converter grows with increasing conversion degree.

A converter is said to have full degree of conversion when the conversion degree equals the

number of wavelengths per fiber link. Otherwise, it is said to have partial or limited degree of

conversion. A WXC having one or more wavelength converters is called as a wave length


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inter change cross connect (WIXC). A node with wavelength conversion capability is called

a wavelength converting (WC) node or a wavelength interchange (WI) node. A WDM

network with WC nodes is called a wavelength-convertible network. A

node may have a maximum of Fin × W converters, where Fin is the number o fin coming

fibers at the node. When every node in a network has a sufficient number of full-degree

converters, its performance reaches the best achievable. However, such a network is

economically not feasible, as the converters are very expensive. A wavelength-convertible

network (a network with WIXCs) performs better than a wavelength-selective network (a

network without WIXCs). Wavelength converters relax the continuity constraint at a node.

Therefore, they help to reduce the bandwidth (wavelength) loss, resulting in better bandwidth

utilization.[11]


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Appendix A

ITU BAND ALLOCATION

I st Generation System works on : 850 nm (PDH System)

2nd Generation System works on: 1310 nm (SDH System)

3 rd Generation System works on: 1550 nm (DWDM System)

Optical C BAND L Band

Supervisor

Channel

1510 1520 1530 1542 1547 1560 1620

Identification Of DWDM Routes in the existing infrastructure :

1. Identification of routes with more than 60 % loaded

2. Traffic requirements-The present BW for various services and anticipated BW.

(Typically with present BW more then 2.5 Gbps)

3. Growth of BW demand in past two year .The % increase and accordingly future

anticipated growth in the traffic of network.

4. Number of system working on the route-- more than two system

5. Number of fiber used-- more than 50 %

Optical window


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Appendix B

1550.12193.41539.77194.8

1560.61192.11549.32193.51538.19194.91559.79192.21548.51193.61537.40195.0

1558.98192.31547.72193.71536.61195.11558.17192.41546.92193.81535.82195.21557.36192.51546.12193.91535.04195.3

1556.55192.61545.32194.01534.25195.41555.75192.71544.53194.11533.47195.51554.94192.81543.73194.21532.68195.6

1554.13192.91542.92194.31531.90195.71553.33193.01542.14194.41531.12195.8

1552.52193.11541.35194.51530.33195.91551.72193.21540.56194.61529.55196.01550.92193.31539.77194.71528.77196.1

Central λ(nm)

NominalCentral ∨

(THz)

Central λ(nm)

NominalCentral ∨

(THz)

Central λ(nm)

NominalCentral ∨

(THz)

ITU –T G.692 Frequency Grid


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A List Of Acronyms :

DWDM : Dense Wave Division Multiplexing

TDM : Time Division Multiplexing

FDM : Frequency Division Multiplexing

OFDM : Optical Frequency Division Multiplexing

EDFA : Erbium Doped Optical Fiber Amplifier

OSC : Optical Supervision Channel

OTU : Optical Transponder Unit

OMU : Optical Multiplexing Unit

ODU : Optical De multiplexing unit

BA : Booster Amplifier

LA : Line Amplifier

PA : PRE Amplifier

SDH : Synchrnous Digital Hierarcy

PDH : Plesiochronous Digital Hierarchy

ATM : Asynchronous Transfer Mode

IP : Internet Protocol

ADM : Add Drop Multiplexing

OADM : Optical Add Drop Multiplexing

MSP : MS –Spring

FEC : Forward Error Correction

ALC : Automatic Level Control

BER : Bit Error Rate

WIXC : Wave length Interchange Cross Connect

VPN : Virtual Private Networks

MPLS : Multiple Protocol Layer Switching


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Reference

1. “Advance Level Telecom Training Center (ALTTC)” training manual

2. Kieser , “Optical Fiber Communication”, McGarw- HLL

3. “Emerging Optical Networks” KM Sivalingam & S Subramaniunm, Kluwer

Academic Publisher , Boston.

4. R K Pankaj & R G Galler , “ Wave length Requirement of all Optical N/W” IEEE/ACM/Trng N/W VO -3 NO -3

5. “WDM N/W Economics Sensitive” in PROC NFOEC VOL-1 (APRIL 1995). 6. R K Pankaj &R G Galler ,“ Wave length Requirement of all Optical N/W” IEEE/ACM/Trng N/W VO -3 NO -3.

7. A Aggarwal ,A Bar Noy ,D Coppersmith ,R Ramaswami ,B Schieber and M Sudan,

“Efficient Routing and Scheduling Algorithm for optical Networks”, Proc. Of ACM –

SIAM symposium on Discrete Algorithms ,1994

8. J Anderson ,J S Manchester ,A. Rodriguez-Moral and M Veerranbhavan ,”Protocol

and Architectures for IP Otical Networks”Bell labs Technical JonourlaVol 4 no.1,

PP 105-124 , Jan /March 1999

9. S Chatterjee and S Pawlowski ,”All Optical Networks”,communication of ACM ,

Vol- 42,no-6,pp74-83 , June 1999

10. M W Chbat et al “Towards Widw Scale All Optical Transparent Nmetworking :The

ACTS optical pan-European NETWORKS (OPEN) Project” IEEE Journal on

selected areas in communications ,vol.16 no. 7,sept 1998

11. S Banerjee ,J Yoo AND C Chen ,”Design of wave length Routed Optical Networks

for Packet Switched Traffic”, IEEE/OSA Journal of lightwave Technology

Vol 15,no.9 pp1600-1646 ,SEPT 1997

12. Web site. http://www.zte.co.cn.

13. Web site http://iec.org.


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