Dense Wavelength Division Multiplexing (DWDM)

PRESENTED BY:

JYOTI CHAWLA

Agenda Introduction DWDM Technology DWDM System & Components Topology Transmission Challenges Market Dynamics Future Applications

Evolution of Fiber Optic Transmission In mid 1960’s researchers proposed optical fiber

as suitable transmission medium. In 1970 , Corning produced the first communic-

ation –grade fibers. AT& T first standardized transmission at DS3

speed(45Mbps) for multimode fibers. Thereafter, single mode fibers were shown to be

capable of transmission rates 10 times

that of older type.

In early 1980’s,MCI, followed by Sprint, adopted single mode fiber for its long distance network in

U.S.

Further developments in fiber optics was tied to use of the specific regions on the optical spectrum where attenuation is low.

These regions called windows, lie between area of high absorption.

Wavelength Regions

What is DWDM? It transmits multiple data signals using different

wavelengths of light through a single fiber. Incoming optical signals are assigned to specific

frequencies within a designated frequency band. The capacity of fiber is increased when these

signals are multiplexed onto one fiber Transmission capabilities is 4-8 times of TDM

Systems with the help of Erbium doped optical amplifier.

EDFA’s : increase the optical signal and don’t have to regenerate signal to boost it strength.

It lengthens the distances of transmission to more than 300 km before regeneration .

Why DWDM? Unlimited Transmission Capacity Transparency Scalability Dynamic Provisioning

Is DWDM Flexible? DWDM is a protocol and bit rate independent

hence, data signals such as ATM, SONET and IP can be transmitted through same stream regardless their speed difference.

The signals are never terminated within the optical layer allows the independence of bit rate and protocols,allowing DWDM technology to be integrated with existing equipment in network.

Hence, there’s a flexibility to expand capacity within any portion of their networks.

Is DWDM Expandable? “ DWDM technology gives us the ability to

expand out fiber network rapidly to meet growing demands of our customer”, said Mike Flynn, group President for ALLTEL’s communications operations.

DWDM coupled with ATM simplifies the network, reduce network costs and provide new services.

They can add current and new TDM systems to their existing technology to create a system with virtually endless capacity expansion

Structure of DWDM Link

DWDM System

Block Diagram of DWDM System

Optical Transmission Principles:

1. Channel Spacing

2. Signal Direction: Uni and Bi-directional

3. Signal Trace Network Classification

1. Ring topology vs. Mesh topology

2. Single hop vs. Multi-hop Networks Optical Amplifiers Security

DWDM Components Transmitter : Laser with precise stable waveleng-

th. Link: Optical fiber that exhibits low loss and

transmission performance in relevant wavelength spectra.

Receiver:Photo detectors and Optical demultiple-xers using thin film filters or diffractive elements.

Optical add/drop multiplexers and optical cross connect components.

DWDM Point to Point

DWDM Mesh Designs

Advantages of DWDM Point to Point Systems The DWDM point-to-point architecture is simple

to build and troubleshoot . It enables protocol transparency, increme-ntal

growth, and capacity expansion over time, while dramatically reducing start-up costs.

Point-to-point solutions are also extremely efficient.

No amplifiers or additional equipment required.

DWDM System Characteristics Well-engineered DWDM systems offer

component reliability, system availability, and system margin. Although filters were often susceptible to humidity, this is no longer the case.

An optical amplifier has two key elements: the optical fiber that is doped with the element erbium and the amplifier.

Automatic adjustment of the optical amplifiers when channels are added or removed achieves optimal system performance.

In the 1530- to 1565-nm range, silica-based optical amplifiers with filters and fluoride-based optical amplifiers perform equally well.

The system wavelength and bit rate can be upgraded but planning for this is critical.

Transmission Challenges Attenuation Attenuation is caused by :

- intrinsic factors primarily scattering and absorption- extrinsic factors, including stress from the manufacturing process, the environment, and physical bending

Rayleigh scattering - is an issue at shorter wavelengths

Rayleigh Scattering

Attenuation due to absorption - is an issue at longer wavelengths - the intrinsic properties of the material - impurities in the glass, and any atomic defects in the glass.

These impurities absorb the optical energy, causing the light to become dimmer.

Absorption

Dispersion Dispersion is the spreading of light pulses as they

travel down optical fiber. Dispersion results in distortion of the signal, which limits the bandwidth of the fiber.

Two general types of dispersionChromatic Dispersion - is linear

Chromatic dispersion occurs because different wavelengths propagate at different speeds.

Increases as the square of the bit rate. Polarization Mode Dispersion - is nonlinear. Polarization mode dispersion (PMD) is caused by

ovality of the fiber shape as a result of the manufacturing process or from external stressors.

Changes over time PMD is generally not a problem at speeds below OC-192.

Smearing of the signal

Fiber Non Linear ties Because nonlinear effects tend to manifest

themselves when optical power is very high, they become important in DWDM.

These nonlinearities fall into two broad groups:

- scattering phenomena

- refractive index phenomena

Scattering Phenomena - Stimulated Brillouin Scattering (SBS) - Stimulated Raman Scattering (SRS) Solution

use moderate channel powers and densely packed channel plan that minimizes the overall width of the spectrum.

Refractive Index Phenomena This group of nonlinearities includes

- self-phase modulation (SPM) - cross-phase modulation (CPM) - four-wave mixing (FWM)

SPM - This phenomena causes the signal's spectrum to widen and can lead to crosstalk or

an unexpected dispersion penalty. Four-wave mixing

- results in cross-talk and signal-to-noise degradation.

- troublesome in the dispersion shifted fiber that is used to propagate STM-64/OC-

192. - limit the channel capacity of a DWDM

system.

Market Scope and Company Profile

KMI Corporation The DWDM systems market jumped from $4.2 billion

in 1999 to $8.9 billion in 2000. From $1.7 billion in 1997, the market has grown at a

73% CAGR over the last four years. This growth reflects several trends:

- a maturation of the long distance segment of the DWDM equipment market - stiffening competition that will lead to price pressures

From 1999 to 2000 - the number of vendors offering DWDM system-level products grew from 15 to 30 - the number of carriers that have deployed DWDM climbed from 75 to 175.

- the number of contracts for DWDM will double from 75 to 150.

- Such growth reflects the tremendous demand long-distance carriers face for transport in bandwidth.

Lucent Technologies - five-year agreement with Bell Atlantic valued at approximately $500 million for optical networking, including DWDM, network management software and SONET transmission equipment.

According to Dell'Oro Group, Lucent captured the largest market share - 34 percent (or approximately $1.3 billion) - of the $3.8 billion global DWDM equipment market in 1999.Lucent will install the DWDM optical networking system in the new, 900- mile (1,300 km) route between Xian and Wuhan which is worth more than $10 million."Getting an early lead in this market will prove to be very important," said Scott Clavenna, principal analyst at Pioneer Consulting, which has forecast the metro DWDM market to grow to nearly $1 billion by 2003.

Future of DWDMWhat the future holds Two-way video communication Digital video for our everyday use at home and at work. Change from voice telephony to digital data heavy with

video to require multiplying backbone transmission capacity.

The Ultimate Squeeze - reducing the “space” between wavelengths - expanding the range of transmission wavelengths

- better EDFAs

Develop better equipment for switching and manipulating the various wavelengths after the signal emerges from the optical “pipe.”

WDM is creating huge new information pipelines that will bring better service at lower cost. But the real information revolution won’t come until cheap WDM pipelines reach individual residences.

Applications of DWDM DWDM is ready made for long-distance

telecommunications operators that use either point-to-point or ring topologies.

Building or expanding networks Network wholesalers can lease capacity, rather

than entire fibers. The transparency of DWDM systems to various

bit rates and protocols. Utilize the existing thin fiber DWDM improves signal transmission

References http://www.cisco.com/univercd/cc/td/doc/product

/mels/cm1500/dwdm/dwdm_ovr.htm http://www.cis.ohio-state.edu/~jain/cis788-99/ftp/

dwdm/index.html http://www.iec.org http://www.igigroup.com/st.html http://www.cisco.com/univercd/cc/td/do

c/product/mels/dwdm/dwdm_fns.pdf

http://www.ee.ucl.ac.uk/lcs/papers99/dbojic.pdf