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Dense wavelength division multiplexing (Download Full Seminar Report)
Post: #1

Dense wavelength division multiplexing (DWDM) is a fiber-optic transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial-by-character.

The role of scalable DWDM systems in enabling service providers to accommodate consumer demand for ever-increasing amounts of bandwidth is important. DWDM is discussed as a crucial component of optical networks that allows the transmission of e-mail, video, multimedia, data, and voice”carried in Internet protocol (IP), asynchronous transfer mode (ATM), and synchronous optical network/synchronous digital hierarchy (SONET/SDH), respectively, over the optical layer.

Post: #2

The technology of combining a number of optical wavelengths and then transmitting the same through a single fibre is called wavelength division multiplexing (WDM). Conceptually, the technology is similar to that of frequency division multiplexing (FDM) used in analogue transmission. Dense wavelength division multiplexing (DWDM) is anew born multiplexing technology in the fibre optic transmission, bringing about a revolution in the bit rate carrying capacity over a single fibre. The emergent of DWDM system is one of the important phenomena in development of optic fibre transmission. This article gives introduction of DWDM technology.

.doc  report.doc (Size: 97 KB / Downloads: 266)

There has always been a technological talent to fulfill the constant need to extent the capacity of communication channel and DWDM (Dense Wavelength Division Multiplexing) has dramatically brought about an explosive enlargement of the capacity of fiber network, solving the problem of increasing traffic demand most economically.

DWDM is a technique that makes possible transmission of multiple discrete wavelengths carrying data rate as high as fiber plant allows over a single fiber unidirectionally or bidirectionally.

It is an advanced type of WDM in which the optical channels are more closely spaced than WDM.


In normal optical link there is one optical source at transmitting end and one photo detector at receiving end. Signals from different light sources use separate and unique assigned fiber for transmission of signal. As the spectral bandwidth of the laser source is very narrow, this type of transmission makes use of only a small portion of the entire optical band and remaining portion of the band is not used. In DWDM technology, the different light sources are first converted to pre-assigned wavelength according to the DWDM standards and then combined in such a manner that they occupy different portion of the available optical band. In between the two optical signals suitable guard band is also left, so that there is no interference from adjacent channels. Thus DWDM technology makes use of the entire optical bandwidth.


The system performs the following main functions.

Generating the signal: The source, the solid state laser, must provide stable light within the specific, narrow band width that carries the digital data, modulated as an analog signal.

Combining the signals: Modern DWDM systems employ multiplexers to combine the signal. There is some inherent loss associated with multiplexing and demultiplexing. These loss is dependent upon the number of challenge but can be mitigated with optical amplifiers, which boost all the wavelengths at once with out electrical conversion.

Transmitting the signals: The effect s of cross talk and optical signal degradation or loss must be reckoned with in fiber optic transmission. These affects can be minimized by controlling variables such as channel spacings, wavelength tolerance, and laser power levels. Over a transmission link, the signal may need to be optically amplified.

Separating the signals: At the receiving end, the multiplexed signals must be separated out. Although this task would appear to be simply the opposite of combining the signals.

Receiving the signals: The demultiplexed signals is received by photo detectors.


The general architectural forms that have been most commonly used in WDM networks are wavelength routing network and broadcast “ and “ select network.


Wavelength routing networks are composed of one or more wavelength selective elements and have the property that the signals takes through the network is uniquely determined by the wavelength of the signal and port through which it enters the network.

So, for example, in figure (3 ) an n×n network is shown in which n receivers through a network consist of several WDM elements by tuning to a selected wavelength the signal from a given laser can be rated as a selected output port on the network. Since there are n inputs and n output one might expect n² wavelength would be required to form a complete interconnection. It turn out, how ever, that it can always be arranged so that with only n wavelengths, n inputs can be interconnected with n output in a completely non interfering way.


In figure ( 4 ) the wavelength to go from input S¹ to output port R3 is λ2. it is possible to address each output port uniquely by choice of wavelength and no out port can receive any given wave length from more than one input. This is extendible to any size network with n wavelengths but it does require n² interconnection fibers between the WDM stages.


The second major architectural type is the broadcast - and “ select network illustrated in figure (5 ). In this network, all inputs are combined in a star coupler and broadcast to all output. Several different possibilities exist depending on whether the input laser, the output receivers, or both are made tunable. If the input lasers are tunable and output receivers are tuned to fixed wavelength, the architecture is basically a space-division switch in function. The properties of this network are that it uses wavelength addressing of the output port, but that with only a single wavelength selectable at each output, only point to point connection are possible and multicast connection can not be achieved.

If the output receivers are made tunable but the input lasers are tuned to fixed unique wavelength, this architecture supports multicast connection. This is achieved by arranging to have more than one receivers tuned the same source wavelength at the same time. Output port exists in this mode and is exacerbated by multicast function. If both the transmitters and receivers are made tunable ,the possibility exists for reducing the number of wavelength required but the result that there are not enough wavelength available to support simultaneous n×n interconnection.


A typical 8-channel DWDM system block is shown in the figure ( ). The main components are,

-TP (transponders)
- VOA (variable optical attenuator)
- MUX (multiplexer)

- DE MUX (de multiplexer)


-Erbium-dropped fiber optic amplifier

-Booster amplifier


-Line amplifier
- Optical add-drop multiplexer (OADM)


This unit interfacing wide pulse optical signal and MUX/DMUX equipment. It converts the wide pulse signal into a narrow wavelength of the order of 1.6nm, sending to MUX.

In the reverse direction, coloured output from DMUX is converted to wide pulse optical signal.

The transponders are of two types namely transmit transponders and receive transponders. The function of transmit transponder is to convert the incoming optical signal into pre-defined optical wavelength. The transponder (transmit) first converts the optical signal to an electrical signal and performs reshaping, retiming and retransmitting functions, also called 3R functions. The electrical signal is then used to drive the laser, which generates the optical signals having optical wavelength. The output from the all transponders (transmits) is fed to combiner in order to combine all optical channels in optical domain. In receive transponder, reverse process takes place.

Individual wavelengths are first split from the combined optical signal with the help of splitter and then fed to individual receive transponders, which convert the optical signal to electrical, thus 3R function and finally convert the signal back to the optical. Thus the individual channels are obtained. As the output of the transponder is factory set to a particular wavelength, each optical channel requires unique transponder.


This is a passive network like pre-emphasis required to adjust for uniform distribution of signal level over EDFA band so that individual channel optical output power of MUX unit remain same irrespective of the number of channels being loaded in the system.


The DWDM system transmits several optical signals over a single fiber. All the signals are combined at the transmission end and again split at receiving end. The combining is done by combiner, also called multiplexer and splitting is cone by splitter, also called demultiplexer.

The combiner and splitter can be either passive or active devices. Passive devices are based on prisms, diffraction gratings or filters, whereas the active devices are combination of passive devices and tunable filters.

Multiplexer is an optical device and converges all the colour rays to combine on one point to make a broadband pulse. Here in 8-channel systems, the 8 colour rays from 8 TPs are connected to the appropriate input ports of the MUX and the common single port is the output connected to the (Booster Amplifier).

DEMUX performs the reverse function of MUX. By this unit, the received beam is separated into its wavelength (colour) components coupling them in appropriate ports to individual fiber. This DEMUX output may be fed to TP.


In DWDM technology optical amplifiers are used instead of electrical amplifier. Thus pulse shaping and retiming functions are not done at repeater stations. The deployment of electrical amplifier in DWDM system is complex and expensive, hence optical amplifiers are used. The erbium doped fiber amplifier widely used in DWDM system. Depending upon the use of amplifier in the network it is called booster amplifier, line amplifier, preamplifiers etc.


EDFAs are widely used in DWDM system for amplification of optical signals. Erbium is a rare earth element and emits light around 1550 nm region when it is exited. Thus it is most suited for DWDM operations as DWDM also makes use of 1550nm window. The block diagram of EDFA is shown in fig(8).

1&6:tap couplers 3:wavelength coupler 7:pump laser
2&5:isolaters 4:erbium-doped fibre

It consists of doped fiber (10 to 50mlong), one or more pump lasers, a passive wavelength coupler, optical isolators and tap couplers. The tap couplers are wavelength insensitive with typical splitting ratio ranging from 99:1 to 95:5.They are generally used on both sides of the amplifier to compare the incoming signal with the amplified output. The optical isolators prevent the amplified signal from reflecting back into the device; otherwise it could increase the amplifier noise and decrease the efficiency.

The weak optical signal enters the Erbium doped fibre, into which light is injected using pump laser. The injected light stimulates the Erbium atom to release the stored energy as additional light at 1550nm.This process continues and amplification of the signal takes place. The pump power is usually injected from the same direction as that of the signal flow. This is known as co-directional pumping. It is also possible to inject the pump power in opposite of the signal flow which is known as counter-directional pumping. It is also possible to use dual pump scheme, which results doubling of the gain of amplifier. The counter-directional pumping allows higher gain where as co-directional pumping give better noise performance.

The requirement of low noise is a key factor in selecting the EDFA, because noise is also amplified along with the signal. The effect of noise is cumulative and cannot be filtered out. Therefore signal to noise ratio is an ultimate limiting factor that limits the total number of amplifiers that can be used in the concatenation
Depending upon the gain, EDFAs are classified into following three categories.
I. For long haul application.
II. For very long haul application.
III. For ultra long haul application.

For long haul applications, amplifiers are deployed after every 80kms of sections length and maximum permissible fibre lose in one section is 22dB.For very long haul applications, amplifiers are deployed after 120kms of section length and maximum permissible fibre lose in a section is 33dB.In ultra long haul applications, line amplifiers are not used and a maximum permissible lose in a section in 44dB and it can cover upto 160km of distance.


It is basically an EDFA amplifier which boost the entire wide band optical signal coming from the out put of MUX.Here the total output power booster amplifier is constant irrespective of the number of channels being loaded to the system. Line is connected to the amplifier for transmission of signal to the distant end supporting the optical safety operation.


This is the optical fiber media over which the DWDM signal travel. Attenuation and dispersion are the main limitation factors determining transmission distance and bit rate capacity etc.Normally 22dB and 33dB are taken as the line loses for hop length of long haul and very long haul system respectively. The very long haul line length can be 120kms with out repeater but with a number of repeaters cascaded, the length may be up to 600 kms which can further be increased up to 1200kms by using dispersion compensating module. However after such a distance it needs regeneration in electrical stage instead of repeater in optical stage only.


It is two stage (EDFA) amplifier consisting of pre-amplifier and booster amplifier. With out two stages it is not possible to amplify the signal up to 33dB on EDFA principle avoiding large ASE (amplifier spontaneous emission) noise.


This amplifier along is used at the terminal to interface the DEMUX and line for receiving coming from the distant station. Hence the attenuated line signal is amplified to a level of 3dBm to 10dBm before entering into DEMUX unit.


The function of transmission of additional data at a separate wavelength of lower optical power with out any optical safety provision, accompanied with and independent of the main optical traffic signal, is performed by this OSC.The OSC helps management to control and monitor the optical line devices. The management for fault location, configuration, performance and security.


Adding or dropping of channels at optical level is possible by using optical add/drop multiplexer module. It is a unidirectional module with facility for dropping or adding optical channel of specific wavelength. The dropping and adding of the optical wavelength this performed with fixed optical filters. With the help of OADM module it is possible to insert or drop maximum for optical wave lengths at any intermediate stations.

Fig(9 ):optical add\drop MUX

Depending upon the design, pre and post optical amplifiers may or may not be present in OADM.There are two types of OADM.The first type is fixed device that is physically configured to add/drop pre defined wavelengths. The second type is reconfigurable and capable of dynamically selecting the wave length to be added or dropped.


¢ The capacity of transmission media can be upgraded easily by using DWDM technology. The capacity of existing DWDM system can be upgraded by deploying higher channel capacity system.Thus, The need of laying new fibers for increasing capacity of transmission media is avoided.
¢ Bit rate transparency: in DWDM system, optical channels can carry any transmission format. thus the different wavelengths from different systems can be transmitted simultaneously and independently over the same fiber without need for a common ATM,Gigabit Ethernet etc over a common layer. Thus DWDM system can transport any type of optical signal.
¢ Quick deployment: The DWDM technology is, generally, deployed using existing fibers. The time required for laying new fiber is much more as compared to equipment deployment time.hence, the deployment of dwdm systems can be done quickly.
¢ Economical: The DWDM system is cheaper as compared to overall cost of laying new fiber for increasing transmission capacity. In DWDM system, one optical amplifier is used for amplification of all the channels, hence per channel cost is drastically reduced as compared to providing regenerator for individual channels in SDH network.
¢ Wavelength routing: In DWDM system, by using wavelength sensitive optical routing devices, it is possible to route any wavelength to any station. Thus it is possible to use wavelength as other dimension, in addition to time and space in designing transmission network.
¢ Wavelength switching: In DWDM system, wavelength switching can be accomplished by using OADM, optical cross connect and wavelength converters.thus, it is possible to reconfigure the optical layer using wavelength switched architecture.


PROTECTION INDWDM SYSTEM: DWDM link can be designed to provide either path switched protection (two fibre working) or bi-directional line switched protection (four fibre working). The equipment protection can also be provided by using additional set of equipment .the protection facility is not available in the equipment being deployed in telecom network. In case of falure, the protection system of SDH ring will take care of the fault.


There are two categories of optical fibres namely mono mode and multi mode. The mono mode fibre is used for long haul transmission and it is of following three types.
1. Non-dispersion shifted fibre(NDSF)
2. Dispersion shifted fibre(DSF)
3. Non-zero dispersion shifted fibre(NZDSF)
To optimize the performance of fibre in L (1625nm) and C (1550nm) bands, it was designed in such a way that dispersion was very low at 1310nm(S band) and this type of fibre is called NDSF.Later anew type of fibre was developed in which the zero dispersion was shifted to 1550nm region called DSF.But due to the non linear effect the DSF is not suitable for DWDM. NZDSFis designed in such away that the dispersion is low at 1550nm but not zero.


The demand of bandwidth is increasing day by day, especially for data traffic. Service providers are required to provide the bandwidth dynamically and in shortest possible time. This can only be done by DWDM. In future advanced DWDM components will be available. Thus, it will be possible to manage the optical signal dynamically, which will allow more flexibility to the service providers.


1. Shri H. Saha, Shri Nural Anowar, DWDM System & Testing TELECOMMUNICATION March “April 2002
2. P.K. Pandy, Dense Wave Length Division Multiplexing TELECOMMUNICATION November “December 2002
Post: #3

.pdf  DWDM.pdf (Size: 156 KB / Downloads: 283)
Dense wavelength division multiplexing (DWDM)

Dense wavelength division multiplexing (DWDM) is a fiber-optic
transmission technique that employs light wavelengths to transmit data
parallel-by-bit or serial-by-character.
The role of scalable DWDM systems in enabling service providers to
accommodate consumer demand for ever-increasing amounts of
bandwidth is important. DWDM is discussed as a crucial component of
optical networks that allows the transmission of e-mail, video,
multimedia, data, and voice—carried in Internet protocol (IP),
asynchronous transfer mode (ATM), and synchronous optical
network/synchronous digital hierarchy (SONET/SDH), respectively,
over the optical layer.
Post: #4
presented by:
Alpina Kulkarni

.ppt  DWDM_2.ppt (Size: 245.5 KB / Downloads: 368)
Fiber Systems Dense Wavelength Division Multiplexing (DWDM)
Brief Overview
► Problems with increasing network demands
► Solutions proposed & their limitations
► Evolution of DWDM
► Technical details
► Drawbacks
► Ongoing Research
► Conclusion
► Growing Network Usage Patterns
► Issues
 Exponential increase in user demand for bandwidth
► Doubling of bandwidth requirement every 6-9 months
 Consistency in quality of services provided
 Keeping the cost of solutions at bay
► Solutions
 Increase channel capacity: TDM, WDM
 Statistical multiplexing of users: Multiple optical fibers
► Another glimpse at the solutions
► Limitations of current solutions
► Evolution of DWDM
What is DWDM?

 Dense wavelength division multiplexing (DWDM) is a fiber-optic transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial-by-character
How does DWDM fair better?
► No O-E-O required
► Protocol & Bit Rate independence
► Increased overall capacity at much lower cost
 Current fiber plant investment can be optimized by a factor of at least 32
► Transparency
 Physical layer architecture à supports both TDM and data formats such as ATM, Gigabit Ethernet, etc.
► Scalability
 Utilize abundance of dark fibers in metropolitan areas and enterprise networks
► Capacity Expansion
Basic Components & Operation
► Transmitting Side
 Lasers with precise stable wavelengths
 Optical Multiplexers
► On the Link
 Optical fiber
 Optical amplifiers
► Receiving Side
 Photo detectors
 Optical Demultiplexers
Optical add/drop multiplexers
► Optical Amplifier
► Eliminates O-E-O conversions
► More effective than electronic repeaters
► Isolator prevents reflection
► Light at 980nm or 1480nm is injected via the pump laser
► Gains ~ 30dB; Output Power ~ 17dB
► Dispersion
 Chromatic dispersion
 Polarization mode dispersion
 Attenuation
 Intrinsic: Scattering, Absorption, etc.
 Extrinsic: Manufacturing Stress, Environment, etc.
► Four wave mixing
 Non-linear nature of refractive index of optical fiber
 Limits channel capacity of the DWDM System
Ongoing Developments
► Nortel Networks
 Metro DWDM
 OPTera Long Haul 5000 Optical Line System
► Cisco Systems
 ONS 15200 Metro DWDM Solution
► Lucent Technologies
 LambdaXtreme Transport
 WaveStar OLS 1.6T
► Agility Communications & UC Santa Barbara
 Tunable Lasers used for multiple wavelengths
► Robust and simple design
► Works entirely in the Optical domain
► Multiplies the capacity of the network many fold
► Cheap Components
► Handles the present BW demand cost effectively
► Maximum utilization of untapped resources
► Best suited for long-haul networks
Post: #5
Hello..thank you

Attached File(s)
.docx  Article.docx (Size: 14.54 KB / Downloads: 54)
Post: #6
hello..thanks everyone
Post: #7
Big Grin thanx..SmileSmileSmileSmileSmile
Post: #8
pls send me a full seminar report and ppt abt DWDM
Post: #9
To meet increasing consumer demand for service providers that provide scalable dwdm systems, the role of the amount of bandwidth is important. dwdm optical layer Internet Protocol (IP), respectively, over asynchronous transfer mode (atm) and the optical network/synchronous digital hierarchy when compatible (sonet/sdh), e-mail, video, multimedia, data, and a crucial component of the optical networks that allows the transmission of voice € carried as discussed.
Post: #10
Dense wavelength division multiplexing (Download Full Seminar Report)

.pdf  dwdm-prerequisite[1].pdf (Size: 785.07 KB / Downloads: 233)

This tutorial provides prerequisite information about dense wavelength division
multiplexing (DWDM) systems. Since DWDM systems are derived from wavelength
division multiplexing (WDM) systems, and recently the introduction of coarse
wavelength division multiplexing (CWDM) systems each of these similar technologies
will be discussed and inter related to DWDM. This material is applicable to all DWDM
courses offered by Fujitsu Network Communications, Inc. (FNC). A list of acronyms
used in this tutorial is in Table 2, and Table 3 provides DWDM terminology.

Dense wavelength division multiplexing permits rapid network deployment and
significant network cost reduction. Use of DWDM allows deployment of less fiber and
hardware with more bandwidth being available relative to standard SONET networks.

Discrete Transport Channels vs DWDM Transport

Traditional SONET, TCP/IP, ATM, and voice over Internet Protocol (VoIP)1 are
transmitted over discrete channels, each requiring a fiber pair between the end points.
Figure 1 shows nine channels, each at 10 Gb/s, using nine discrete fiber pairs. This
traditional SONET method requires 3 regenerators to condition the signals across each
fiber path between each of the nine nodes, a total of 27 regenerators.

Service Provider Advantages

The service provider uses an existing installed fiber plant more effectively by
incorporating DWDM systems. Comparing Figure 1 to Figure 2, the service provider
recovers eight fiber pairs to expand its network for its investment in two 9-channel
(wavelength) DWDM terminals and three in-line amplifiers (ILAs), as described below.
Multiplexing reduces the cost per bit sent and received over the network. In Figure 1,
the distances require three regenerator sites for traditional SONET traffic. In Figure 2,
these 27 regenerators are removed and replaced by three ILAs. The cost of an ILA is
typically 50 percent of the cost of a SONET regenerator and the single ILA carries all
nine wavelengths.

Types of Multiplexing

Multiplexing is sending multiple signals or streams of information through a circuit at
the same time in the form of a single, complex signal and then recovering the separate
signals at the receiving end. Basic types of multiplexing include frequency division
(FDM), time division (TDM), and wavelength division (WDM), with TDM and WDM
being widely utilized by telephone and data service providers over optical circuits.

Time Division Multiplexing

Time-division multiplexing (TDM), as represented in Figure 3, is a method of combining
multiple independent data streams into a single data stream by merging the signals
according to a defined sequence. Each independent data stream is reassembled at the
receiving end based on the sequence and timing.

Fiber Attenuation

All transmission fiber suffers from the losses brought about by attenuation, as shown in
Figure 40. The characteristics of the common fibers have the following in common:
• The 1550-nm window has the lowest attenuation.
• The large spike is due to absorption by water molecules. This has been
greatly reduced on today’s fibers, allowing almost optimum minimum

Attenuation of Optical Signal
Amplification is needed in an optical network because photons leak out or are
absorbed by the fiber.
Fiber nonlinearities limit the allowable launch power into a fiber. These include a
variety of effects, such as self-phase modulation (SPM), cross-phase modulation
(XPM), stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and
four-wave mixing (FWM).
Light is limited to power increments of photons, so there is a lower limit to the amount
of power/number of photons a receiver needs to correctly detect 1s and 0s.

Signal Amplification

An optical power budget is maintained throughout the network. Distributed
amplification overcomes the power limits of transmission over fiber

• Amplifiers add noise to the desired signal as well as amplification.
• The number of amplifications that are possible before a signal must be
terminated is limited by the effects of noise.
• Some amplifier cross-talk and intersymbol interference1 restricts the
transmission distance.

Chromatic Dispersion Tolerance
• Standard SMF fiber has an average of 17 ps/nm/km of dispersion
• A 10-Gb/s receiver can tolerate about 800 ps/nm of dispersion
• A 500-km system generates 17 ps/nm/km x 500 km = 8500 ps/nm of
Post: #11
Dense Wavelength Division Multiplexing (DWDM)

.docx  Dense Wavelength.docx (Size: 109.37 KB / Downloads: 20)

Introduction of DWDM

The following discussion provides some background on why dense wavelength division multiplexing (DWDM) is an important innovation in optical networks and what benefits it can provide. We begin with a high-level view of the segments of the global network and the economic forces driving the revolution in fiber optic networks. We then examine the differences between traditional time-division multiplexing (TDM) and wavelength division multiplexing (WDM). Finally, we explore the advantages of this new technology.
Over the last decade, fiber optic cables have been installed by carriers as the backbone of their interoffice networks, becoming the mainstay of the telecommunications infrastructure. Using time division multiplexing (TDM) technology, carriers now routinely transmit information at 2.4 Gbit/s on a single fiber, with some deploying equipment that quadruples that rate to 10 Gbit/sec. The revolution in high bandwidth applications and the explosive growth of the Internet, however, have created capacity demands that exceed traditional TDM limits. As a result, the once seemingly inexhaustible bandwidth promised by the deployment of optical fiber in the 1980s is being exhausted. To meet growing demands for bandwidth, a technology called Dense Wavelength Division Multiplexing (DWDM) has been developed that multiplies the capacity of a single fiber. DWDM systems being deployed today can increase a single fiber’s capacity sixteen fold, to a throughput of 40 Gbit/s. This cutting edge technology when combined with network management systems and add-drop multiplexers enables carriers to adopt optically-based transmission optical networks that will meet the next generation of transmitted bandwidth demand at a significantly lower cost than installing new fiber .


The today’s life is very fast life for which we have the fast equipment with us for example internet to stimulate the speed of internet we need the different type of technology like TDM and FDM but now we need the most speed hence we have introduced the DWDM which will give us an tremendous speed hence the our objective is to make an brief introduction about the DWDM
From both technical and economic perspectives, the ability to provide potentially unlimited transmission capacity is the most obvious advantage of DWDM technology. The current investment in fiber plant can not only be preserved, but optimized by a factor of at least 32. As demands change, more capacity can
be added, either by simple equipment upgrades or by increasing the number of lambdas on the fiber, without expensive upgrades. Capacity can be obtained for the cost of the equipment, and existing fiber plant investment is retained. Bandwidth aside, DWDM’s most compelling technical advantages can be summarized as follows:
• Transparency—Because DWDM is a physical layer architecture, it can transparently support both TDM and data formats such as ATM, Gigabit Ethernet, ESCON, and Fibre Channel with open interfaces over a common physical layer.

Evolution of DWDM

Time-Division Multiplexing

Time-division multiplexing (TDM) was invented as a way of maximizing the amount of voice traffic that could be carried over a medium. In the telephone network before multiplexing was invented, each telephone call required its own physical link. This proved to be an expensive and unsalable solution. Using multiplexing, more than one telephone call could be put on a single link.TDM can be explained by an analogy to highway traffic. To transport all the traffic from four tributaries to another city, you can send all the traffic on one lane, providing the feeding tributaries are fairly serviced and the traffic is synchronized. So, if each of the four feeds puts a car onto the trunk highway every four seconds, then the trunk highway would get a car at the rate of one each second. As long as the speed of all the cars is synchronized, there would be no collision. At the destination the cars can be taken off the highway and fed to the local tributaries by the same synchronous mechanism, in reverse. This is the principle used in synchronous TDM when sending bits over a link. TDM increases the capacity of the transmission link by slicing time into smaller intervals so that the bits from multiple input sources can be carried on the link, effectively increasing the number of bits transmitted per second (see Figure 3.1).

Wavelength Division Multiplexing

WDM increases the carrying capacity of the physical medium (fiber) using a completely different method from TDM. WDM assigns incoming optical signals to specific frequencies of light (wavelengths, or lambdas) within a certain frequency band. This multiplexing closely resembles the way radio stations broadcast on different wavelengths without interfering with each other (see Figure 1-7). Because each channel is transmitted at a different frequency, we can select from them using a tuner. Another way to think about WDM is that each channel is a different color of light; several channels then make up a “rainbow.”

Development of DWDM Technology

Early WDM began in the late 1980s using the two widely spaced wavelengths in the 1310 nm and 1550 nm (or 850 nm and 1310 nm) regions, sometimes called wideband WDM. Figure 2-2 shows an example of this simple form of WDM. Notice that one of the fiber pair is used to transmit and one is used to receive. This is the most efficient arrangement and the one most found in DWDM systems.
The early 1990s saw a second generation of WDM, sometimes called narrowband WDM, in which two to eight channels were used. These channels were now spaced at an interval of about 400 GHz in the 1550-nm window. By the mid-1990s, dense WDM (DWDM) systems were emerging with 16 to 40 channels and spacing from 100 to 200 GHz. By the late 1990s DWDM systems had evolved to the point where they were capable of 64 to 160 parallel channels, densely packed at 50 or even 25 GHz intervals. As Figure 2-3 shows, the progression of the technology can be seen as an increase in the number of wavelengths accompanied by a decrease in the spacing of the wavelengths. Along with increased density of wavelengths, systems also advanced in their flexibility of configuration, through add-drop functions, and management capabilities. Increases in channel density resulting from DWDM technology have had a dramatic impact on the carrying capacity of fiber. In 1995, when the first 10 Gbps systems were demonstrated, the rate of increase in capacity went from a linear multiple of four every four years to fourevery year

The challenges of today’s telecommunication network

To understand the importations of DWDM and optical networking, these capabilities must be discussed in the context of the challenges faced by the telecommunications industry, and in particular, service provider. The forecasts of the presumption that a given individual would only use network band width six month of each hour . these formulas did not factor in the amount of traffic generated by internet access ,faxes , multiple phone lines ,modems’ ,teleconferencing and data and voice transmission . in fact , today many people use the band width equivalent of 180 minutes or more each hour .
Therefore, an enormous amount of band width capacity is required to provide the services demands by consumer .at the transmission speed of one Gbps , one thousand books can be transmitted per second .however today , if one million families decide they want to see video on web site and sample the new emerging video application ,then network transmission rate of terabits are required . with a transmission rate of one Tbps , it is possible to transmit 20 million simultaneous 2-way phone calls or transmit the text form 300 years- worth of daily newspapers per second .
Post: #12
can u provide the seminar report please

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