4.Multiplexagem por divisão no comprimento de onda,

Multiplexagem por divisão no comprimento de onda, WDM

TRANSMISSÃO POR FIBRAS ÓPTICAS

Multiplexagem por divisão de comprimento de onda (WDM)

Princípios básicos• Características gerais dos sistemas de

multiplexagem de comprimento de onda– emissores produzem luz com diferentes

comprimentos de onda– sinais ópticos são combinados e transmitidos

numa fibra monomodo– na recepção os sinais são separados (filtrados) e

entregues a receptores



Princípios básicosBandas WDM

– UIT definiu 6 bandas contíguas que ajudam a especificar sistemas WDM

– estas bandas englobam as 2ª e 3ª janelas dos sistemas clássicos

Princípios básicosPrimeiros sistemas de multiplexagem de comprimento de onda

– até cerca de 4 comprimentos de onda– pré-normalização → dificultou oferta de lasers com comprimentos de

onda standard

Multiplexagem esparsa de comprimento de onda (CWDM, Coarse WDM)– espaçamento moderado de comprimentos de onda → 20 nm– possível utilizar lasers sem controlo de estabilidade de comprimento de

onda– grelha de comprimentos de onda normalizada pela UIT

Multiplexagem esparsa de comprimento de onda (CWDM, Coarse WDM)

Multiplexagem densa de comprimento de onda (DWDM, Dense WDM)

Multiplexagem densa de comprimento de onda (DWDM, Dense WDM)– várias dezenas (futuramente centenas) de comprimentos de onda– necessário utilizar mecanismos de controlo de estabilidade dos lasers– grelhas de frequências normalizadas pela UIT• centradas a 193,1 THz (C-Band)• espaçamentos de 12,5 / 25 / 50 / 100 GHz e múltiplos de 100 GHz– bandas prioritárias: S-Band, C-Band, L-Band


Elementos de rede

Global Network Hierarchy

Global Network Hierarchy

Long-Haul Networks• Long-haul networks are at the core of the global

network. Dominated by a small group of large transnational and global carriers, long-haul networks connect the MANs.

• Their application is transport, so their primary concern is capacity. In many cases these networks, which have traditionally been based on Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH) technology, are experiencing fiber exhaust as a result of high bandwidth demand.

• At the other end of the spectrum are the access networks. – These networks are the closest to the

end users, at the edge of the MAN. – They are characterized by diverse

protocols and infrastructures, and they span a broad spectrum of rates.

– Customers range from residential Internet users to large corporations and institutions.

Long-Haul Networks

Networking at High Speed• Pulses of infrared light guided through glass

fibers move huge blocks of data long or short distances– insensitive to electrical interference– cheap and light weight

• Telephone, Data and Cable TV– Long distances WAN - Wide Area Net’s– Short Distances LAN - Local Area Net’s– In between MAN - Metro Area Net’s

Optic Fiber based Networking1. Information is carried by light confined in glass fibers:

2. Light is modulated by pulsing the source:

Optic Fiber based Networking

• SONET/SDH are Timed Division Multiplex (TDM) protocols:–OC-3 51.84 Mb/s OC-12 622 Mb/s

OC-48 2.488 Gb/s OC-192 9.953 Gb/s

–OC-768 40 Gb/s

Bandwidth Demand

Data Traffic Overtakes Voice Traffic

Options for Increasing Carrier Bandwidth

• Faced with the challenge of dramatically increasing capacity while constraining costs, carriers have two options:

• Install new fiber or increase the effective bandwidth of existing fiber.

• Increasing the effective capacity of existing fiber can be accomplished in two ways:– Increase the bit rate of existing systems.– Increase the number of wavelengths on a fiber.

1. Increase the Bit Rate• Using TDM, data is now routinely transmitted at 2.5 Gbps

(OC-48) and, increasingly, at 10 Gbps (OC-192); recent advances have resulted in speeds of 40 Gbps (OC-768). – The electronic circuitry that makes this possible, however, is

complex and costly, both to purchase and to maintain. – Transmission at OC-192 over single-mode (SM) fiber, is 16

times more affected by chromatic dispersion than the next lower aggregate speed, OC-48.

– The greater transmission power required by the higher bit rates also introduces nonlinear effects that can affect waveform quality.

– Finally, polarization mode dispersion, another effect that limits the distance a light pulse can travel without degradation, is also an issue.

2. Increase the Number of Wavelengths

• In this approach, many wavelengths are combined onto a single fiber. – Using wavelength division multiplexing (WDM)

technology several wavelengths, or light colors, can simultaneously multiplex signals of 2.5 to 40 Gbps each over a strand of fiber.

– Without having to lay new fiber, the effective capacity of existing fiber plant can routinely be increased by a factor of 16 or 32. Systems with 128 and 160 wavelengths are in operation today, with higher density on the horizon.

SONET and TDM• The telecommunications industry adopted the Synchronous

Optical Network (SONET) or Synchronous Digital Hierarchy (SDH) standard for optical transport of TDM data.

• SONET and SDH, are two standards that specify interface parameters, rates, framing formats, multiplexing methods, and management for synchronous TDM over fiber.

• SONET/SDH takes n bit streams, multiplexes them, and optically modulates the signal, sending it out using a light emitting device over fiber with a bit rate equal to (incoming bit rate) x n.

• Thus traffic arriving at the SONET multiplexer from four places at 2.5 Gbps will go out as a single stream at 4 x 2.5 Gbps, or 10 Gbps.

– This principle is illustrated in Figure 1-5, which shows an increase in the bit rate by a factor of four in time slot T.

SONET TDM

• The original unit used in multiplexing telephone calls is 64 kbps, which represents one phone call.

• Twenty-four (in North America) or thirty-two (outside North America) of these units are multiplexed using TDM into a higher bit-rate signal with an aggregate speed of 1.544 Mbps or 2.048 Mbps for transmission over T1 or E1 lines, respectively

TDM and SONET Aggregation

• SONET/SDH does have some drawbacks: As with any TDM, the notions of priority or congestion do not exist in SONET or SDH.

• Also, the multiplexing hierarchy is a rigid one. When more capacity is needed, a leap to the next multiple must be made, likely resulting in an outlay for more capacity than is initially needed.

TDM and SONET Aggregation

Ethernet in SONET Inefficiencies

To summarize, the demand placed on the transport infrastructure by bandwidth-hungry applications and the explosive growth of the Internet has exceeded the limits of traditional TDM. Fiber, which once promised seemingly unlimited bandwidth, is being exhausted, and the expense, complexity, and scalability limitations of the SONET infrastructure are becoming increasingly problematic.


TRANSMISSÃO POR FIBRAS ÓPTICAS

• DWDM is a core technology in an optical transport network. The essential components of DWDM can be classified by their place in the system as follows:• On the transmit side, lasers with precise, stable wavelengths• On the link, optical fiber that exhibits low loss and

transmission performance in the relevant wavelength spectra, in addition to flat-gain optical amplifiers to boost the signal on longer spans

• On the receive side, photodetectors and optical demultiplexers using thin film filters or diffractive elements

• Optical add/drop multiplexers and optical cross-connect components

Components and Operation

• 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


In a WDM system, each of the wavelengths is launched into the fiber, and the signals are demultiplexed at the receiving end.

Like TDM, the resulting capacity is an aggregate of the input signals, but WDM carries each input signal independently of the others. This means that each channel has its own dedicated bandwidth; all signals arrive at the same time, rather than being broken up and carried in time slots.



• The difference between WDM and dense wavelength division multiplexing (DWDM) is fundamentally one of only degree.

• DWDM spaces the wavelengths more closely than does WDM, and therefore has a greater overall capacity.

Atenção • WDM and DWDM use single-mode fiber to

carry multiple lightwaves of differing frequencies.

• This should not be confused with transmission over multimode fiber, in which light is launched into the fiber at different angles, resulting in different “modes” of light.

• A single wavelength is used in multimode transmission.

TDM and WDM Compared• SONET TDM takes synchronous and asynchronous

signals and multiplexes them to a single higher bit rate for transmission at a single wavelength over fiber. Source signals may have to be converted from electrical to optical, or from optical to electrical and back to optical before being multiplexed.

• WDM takes multiple optical signals, maps them to individual wavelengths, and multiplexes the wavelengths over a single fiber.

• Another fundamental difference between the two technologies is that WDM can carry multiple protocols without a common signal format, while SONET cannot.

TDM and WDM Interfaces

High-Speed Enterprise WAN Bandwidth Migration

WHY 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.

• Scalability—DWDM can leverage the abundance of dark fiber in many metropolitan area and enterprise networks to quickly meet demand for capacity on point-to-point links and on spans of existing SONET/SDH rings.

• Dynamic provisioning—Fast, simple, and dynamic provisioning of network connections give providers the ability to provide high-bandwidth services in days rather than months.

WHY DWDM?

SONET with DWDM• By using DWDM as a transport for TDM, existing SONET equipment investments can be preserved.

• Often new implementations can eliminate layers of equipment. For example, SONET multiplexing equipment can be avoided altogether by interfacing directly to DWDM equipment from ATM and packet switches, where OC-48 interfaces are common (see Figure 1-10).

DWDM Eliminates Regenerators

Upgrading with DWDM

WDM Systems Overview


• O sistema WDM (Wavelength Division Multiplexing) é uma evolução do sistema óptico ponto-a-ponto tradicional. O seu princípio de funcionamento é essencialmente o mesmo da multiplexação pela divisão em freqüência (FDM), em que vários sinais são transmitidos através do mesmo meio com o uso de diferentes portadoras. A tecnologia WDM possibilita a transmissão de várias portadoras ópticas em uma mesma fibra, cada uma delas carregando determinado fluxo de dados.

Wavelength Division Multiplexing

• All of the current systems use a range of wavelengths between 1540 nm and 1560 nm.

• There are two reasons for this: –First to take advantage of the “low

loss” transmission window in optical fibre and second to enable the use of erbium doped fibre amplifiers.

• Wavelength Division Multiplexing (WDM) is the basic technology of optical networking. – It is a technique for using a fibre (or optical device)

to carry many separate and independent optical channels.

• The principle is identical to that used when we tune our television receiver to one of many TV channels. – Each channel is transmitted at a different radio

frequency and we select between them using a “tuner” which is just a resonant circuit within the TV set.


WDM with Two Channels


• A técnica WDM utiliza a banda espectral na região de 1.300 nm e 1.500 nm, que são as duas janelas de comprimento de onda onde as fibras ópticas possuem perda de sinal muito baixa. Inicialmente, cada janela era usada para transmitir apenas um único sinal digital. – O desenvolvimento dos componentes ópticos, como os

lasers de realimentação distribuída (DFB), os amplificadores de fibras dopadas com érbio (EDFAs), e os fotodetectores e os filtros ópticos, permitiu a utilização de cada janela para a transmissão de vários sinais ópticos, cada um ocupando uma pequena fração da janela total disponível.

• Os sistemas WDM evoluíram para as tecnologias DWDM e CWDM.

• O DWDM (Dense Wavelength Division Multiplexing) refere-se a sistemas que utilizam um espaçamento menor que 200 GHz entre os comprimentos de onda.

• O CWDM (Coarse Wavelength Division Multiplexing) refere-se a sistemas mais baratos que utilizam espaçamentos maiores entre os comprimentos de onda, que ficam normalmente em torno de 0,1 GHz.

Um sistema de transmissão WDM ponto-a-ponto.

Sistemas WDM ponto-a-ponto e em anel

• A Figura 6.1 ilustra um sistema WDM ponto-a-ponto constituído por três nós. Nesse enlace, o nó A transmite os dados para o nó C através de um nó intermediário B. O sistema pode operar nas bandas S, C, L e U, ou uma combinação delas, com os sinais ópticos espaçados de 100 GHz (0,8 nm) ou 50 GHz (0,4 nm), de acordo com o padrão ITU. No nó A, os sinais elétricos de equipamentos de transmissão são inseridos nos dispositivos ópticos que os convertem em diferentes comprimentos de onda.

• Esses equipamentos podem ser da plataforma SDH, switches ATM, roteadores IP ou LSRs (label switch routers). Os níveis de potência de cada sinal óptico são ajustados usando-se atenuadores ópticos controláveis para evitar efeitos não-lineares na fibra. Os sinais ópticos são multiplexados em sinal WDM por um guia de onda seqüencial (AWG) ou por um multiplexador-acoplador. O sinal WDM é amplificado antes de ser transmitido na fibra e, no nó intermediário B, o sinal é amplificado novamente antes do demultiplexador AWG. Cada sinal óptico demultiplexado é inserido em um comutador óptico (OADM ou OXC), que ode ser totalmente óptico (OOO) ou óptico-elétrico-óptico (OEO).


Conversão de comprimento de onda em um enlace ponto-a-ponto.


• No nó C, o sinal óptico é novamente amplificado e demultiplexado em diferentes comprimentos de onda, que são detectados por um conjunto de fotodetectores. Os sinais elétricos já convertidos são encaminhados para as interfaces das redes de dados clientes. Os transponders geralmente desempenham esta função de ser a interface que detecta e converte o sinal da rede WDM em sinal de dados cliente, que podem ser ainda demultiplexados no domínio do tempo para possibilitar taxas de dados menores, Figura 6.2.

• Esta conversão é realizada pelos transponders, que serão detalhados neste capítulo.

• Os transponders também convertem os comprimentos de onda que chegam das redes de dados clientes para a grade ITU de comprimentos de onda. O sinal também pode ser derivado no nó B, se o destino for esse nó, como ilustra a Figura 6.3.

Derivação de um sinal óptico em um enlace ponto-a-ponto.

• Um anel WDM é construído utilizando-se a mesma estrutura do enlace ponto-a-ponto de 3 nós. Neste caso, o anel WDM é composto de vários nós com comutadores ópticos e nós de passagem. Um enlace pode ser estabelecido no anel por meio da inserção de um sinal óptico em determinado nó do anel e da derivação em outro nó, Figura 6.4. O comutador óptico utilizado para o estabelecimento de um anel WDM é o OADM (optical add drop multiplexer) que permite a inserção e a derivação dos sinais ópticos.


Constituição de um anel WDM.

Evolution of DWDM

DWDM Functional Schematic

DWDM Functional Schematic

DWDM Systems

The system performs the following main functions:• Generating the signal —The source, a solid-state

laser, must provide stable light within a specific, narrow bandwidth that carries the digital data, modulated as an analog signal.

• Combining the signals —Modern DWDM systems employ multiplexers to combine the signals. There is some inherent loss associated with multiplexing and demultiplexing. This loss is dependent upon the number of channels but can be mitigated with optical amplifiers, which boost all the wavelengths at once without electrical conversion.

DWDM Systems

• Transmitting the signals —The effects of crosstalk and optical signal degradation or loss must be reckoned with in fiber optic transmission. These effects 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 received 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, it is actually more technically difficult.

• Receiving the signals —The demultiplexed signal is received by a photodetector. In addition to these functions, a DWDM system must also be equipped with client-side interfaces to receive the input signal. This function is performed by transponders.

DWDM Systems

systems with Bandwidth of WDM systems with EDFAs

Systems Concepts• Optical Communication system use several

Multiplexing techniques; all include TDM (Time Division Multiplexing)

• TDM standards (SONET, SDH): ex. OC-192 = STM-64 = 10 Gb/s– Modulation is ISK –Intensity Shifted Keying and NRZ format

• DWDM systems use Gb/s lasers at different lambdas– Aggregated bit rate = NxB– Channel spacing 50-100 GHz; ITU grid– Total optical bandwidth limited by bandwidth of optical

amplifiers– Total power NxP(nonlinear optical effects are important)

DWDM: Mux, Transponder, OXC

• A Figura 14 nos mostra a representação de um Sistema WDM, onde vários sinais ópticos de mesma intensidade, com espaçamento adequado e com comprimentos de onda altamente estáveis, são combinados em um dispositivo óptico passivo, denominado Multiplexador Óptico, ou Mux.Óptico, ou ainda simplesmente Mux.

TransponderNa realidade é muito difícil obter comprimentos de onda entrantes em um Multiplexador Óptico, com sinais de mesma intensidade e, com espaçamento adequado entre eles. Para resolver esta situação foi desenvolvido dentro do Sistema WDM um subsistema chamado de Transponder que se encontra de modo simplificado ilustrado na Figura 15, que tem por finalidade uniformizar a intensidade e comprimentos de onda dos sinais ópticos recebidos e, impor um espaçamento adequado

Internacionalmente, os Transponders, dependendo dos tipos das funções que internamente executam, como resumidamente encontra-se explicado na Tabela 3 abaixo, são designados como 1R, 2R e, 3R.

Aplicação prática de um OADM, inserido em um Enlace

• Alguns Fabricantes incorporam em seus produtos a possibilidade de executar a inserção e retirada de Comprimentos de Onda, de forma remota, permitindo desta forma o chamado ROADM (do Inglês: R econfigurable O ptical A dd and D rop) , ou seja, um OADM Reconfigurável.

OXCOutro elemento fundamental, a ser usado na arquitetura de uma Rede Totalmente Óptica (em inglês, All Optical Network: AON ) é o chamado Optical Cross Connect, abreviado como OXC, ou seja, em uma tradução livre; Chave Óptica.

Dense WDM Links

Dense WDM LinksTransmitters

– In practical terms the transmitter is always a laser. It must have a linewidth which (after modulation) fits easily within its allocated band. It must not go outside the allocated band so it should have chirp and drift characteristics that ensure this. Depending on the width of the allocated band, these characteristics don't need to be the most perfect obtainable. However they do have to be such that the signal stays where it is supposed to be.

Combining the Signals (Channels)– There are several ways of combining the signals. The most obvious is

to use a number of 3-dB splitters or Y-junctions connected in cascade. The problem with this is that you lose 3 dB at each stage. With a large number (say 32) signals each one will be reduced to 1/32 nd of its initial strength.

– This is fine with a small number of channels but when you have a relatively large number then you will probably have to amplify the combined signal immediately after it is mixed.

– Gratings and planar waveguide gratings have much lower loss and their loss is not dependent on the number of channels so these are most often used in systems with more than four channels.

Transmission and Amplification– In transmission on a fibre the main issue is controlling

crosstalk effects.– Channel spacings, widths and power levels are system

variables that can be used to minimise crosstalk.– Amplification is a major issue. The ability to amplify the

mixed signal is one of the things that makes WDM possible.

• Separating the Channels at the Receiver– This is more difficult than combining them. There are

several possible techniques we can use:. Reflective (Littrow) gratings. Waveguide grating routers. Circulators with in-fibre bragg gratings. Splitters with individual Fabry-Perot filters

– These are discussed later in this chapter.

Dense WDM Links

• Receiving the Signals– The receiver is relatively straightforward and is generally

the same as a non-WDM receiver. This is because the signal has been de-multiplexed before it arrives at the detector.

Dense WDM Links

Operation of a Transponder Based DWDM System

• Within the DWDM system a transponder converts the client optical signal from back to an electrical signal and performs the 3R functions (see Figure 2-25).

• This electrical signal is then used to drive the WDM laser. Each transponder within the system converts its client's signal to a slightly different wavelength. The wavelengths from all of the transponders in the system are then optically multiplexed.

• In the receive direction of the DWDM system, the reverse process takes place. Individual wavelengths are filtered from the multiplexed fiber and fed to individual transponders, which convert the signal to electrical and drive a standard interface to the client.

Transponder Functions

Operation of a Transponder Based DWDM System

Os Parâmetros que normalmente definem um Amplificador Óptico, são os seguintes: Faixa de Operação [ nm ] Faixa de Variação de Potencia de Entrada [ dBm ] Faixa de Variação de Ganho [ dB ] Figura de Ruído [ dB ] Potência de Saída [ dBm ] Eficiência da Conversão de Potência [ % ] PDG ( Polarization Dependent Gain ) [ dB ] PMD ( Polarization Mode Dispersion ) [ ps ]

DWDM Transport Layer

Resumo

Princípio básico de funcionamento da WDM

Princípio básico de funcionamento do desmultiplexador de WDM


Bandas da 3ª janela

Potência devida à diafonia

Estimativa da penalidade de potênciadevida à filtragem óptica

Máximo débito binário de transmissão do sinal WDM

Exemplo de cálculo do máximo débito binário de transmissão do sinal WDM

Fourth Generation (4G) Wireless

• Use Wave Ready transponders to convert each service to a different wavelength and then multiplex all services together for transport across a single fiber link.

• Each wavelength behaves as a new fiber and the network gains a service-independent optical channel with each wavelength added, up to 80 wavelengths on a single fiber.

Fourth Generation (4G) Wireless

WaveReady ApplicationsChannel In-Fill

• The innovative Wave Ready channel in-fill system enhances the capacity of legacy networks by adding new wavelengths to existing fiber and avoiding the need for new fiber.

• Channel in-fill offers significant savings over replacement or upgrades:– Extends the life of existing hardware investments– Saves cost for those systems that can still be

upgraded

WaveReady ApplicationsChannel In-Fill

Optical Solutions for the Entire Network Lifecycle

Topologies and Protection Schemes for DWDM

Optical Networking - The DWDM Forest

Point-to-Point Topologies

DWDM Hub and Satellite Ring Architecture

Mesh, Point-to-Point, and Ring Architectures

Next Generation Metropolitan Optical Network

Conclusion• A wealth of technologies have been developed

for high speed networking based on a few simple physical phenomena:– Reflection and refraction (geometric optics) Optic

fibers– Interference Optical Spectrum Analysis high

resolution distance measurements Filters, mux/demux, isolators, et cetera external modulators

– Atomic transitions and Raman scattering LEDs, LASERs Light detectors - PIN diodes, APDs Optical Amplifiers

– Index of Refraction Chromatic and Polarization Mode Dispersion

Obrigado pela atenção dispensada

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4.Multiplexagem por divisão no comprimento de onda,