DWDM Presentation

By Ayodeji Morakinyo 1Bimonthly Presentation

Dense Wavelength Division Multiplexing

(DWDM)

AT THE SPEED OF IDEAS…

By Ayodeji Morakinyo Bimonthly Presentation 2

1. Introduction

2. Optical Transmission

3. Comparison between DWDM and TDM

4. DWDM Components

5. DWDM Networks

6. Transmission Quality Parameters

7. ALU DWDM solutions

Agenda


Introduction

Multiplexing is the process of combining two or more signals together based

on space, time or wavelength division in order to increase the amount of information

transmissible over a single communication channel per time.

EncoderCommunication

ChannelDecoder

Data Data

Noise/Interference

S

o

u

r

c

e

S

i

n

k

Attenuation

This presentation will briefly discuss Dense Wavelength Division

Multiplexing (DWDM) as a means of achieving effective fibre-optic transmission.


Optical Transmission

Optical transmission involves the sending of binary signals in form of light

pulses over an optical channel (fibre) so that they can be decoded and

demodulated at the receiving end.


DWDM Offers:

•Transparency... … ….ATM, SDH, ESCON, GE, etc.

•Scalability… … ……. … …MAN, P-to-P, Rings, Meshes, etc.

•Dynamic Provisioning… … …High BW services in days rather than months

DWDM is coupled at 193.1THz (ITU-T) and it is on the 1st layer of the

architecture so, it can accommodate ATM, SONET/SDH, ESCON, IP, etc.

DWDM

is a multiplexing technique of the fibre-optic transmission system that is

used to increase the BW of an optical fibre such that several different signals can

be transported simultaneously on the fibre.

SDH data stream + Ethernet data stream (without interference)

40Gbit/s,

100Gbit/s


Combining

SignalsSeparating

SignalsTransmission on

fibre

LASER to MUX to TRASNMISSION COMPONENTS to DEMUX to RECEIVERS

The Tx components include optical switches, amplifiers, fibre-optic

cable, couplers, etc.

DWDM Representation

λn+λn+λn+λn


Optical transmission incorporates digital processing technique with optical

transmission consequently, error can be detected and corrected.

For example, FEC allows errors and optical impairments which may be

introduced by NEs such as DXC and OADMS to be corrected.

ITU specifies 6 Tx bands for fibre-optic transmission:

There is an

undefined 7th

band: 850nm

region

O 1260 – 1310 nm

E 1360 – 1460 nm

S 1460 – 1530 nm

C 1530 – 1565 nm

L 1560 – 1625 nm

U 1625 – 1675 nm


Apart from the bandwidth multiplicity advantage, optical transmission also

provides link and ring protection to its deployers thereby, ensuring reliable business

continuity.

Again, there’s no risk of getting shocked and installers do not have to wear

special protective attires.

However, there’s a need to be careful of the laser radiation. The beam of

the laser radiation unit must not be directly observed.

Also, dispersions which often occur can be easily rectified using DCUs while

the inherent losses associated with this system of transmission are counterbalanced

by applying optical amplifiers at specific points along the transmission line. And, it is

not susceptible to EMI.


THE FIBRE-OPTIC CABLE

is a thin strand of glass or plastic that serves as the DWDM transmission

medium. It consists of the section that carries the signal and the part that protects it

from environmental and mechanical damage.

Fibre types based on manufacturing material can be:

•Glass Fibre

•Plastic-clad Silica (PCS)

•Plastic

n2

n1

Cladding

Core


Light is transmitted through fibre in guided modes i.e. TEmn and TMmn.

TE refers to transverse electric field while TM refers to the transverse magnetic field.

Hence, we have TE01 TE10 TM01 TM10 modes.

In DWDM, the fibre modes used are the single and multi-modes. However,

the single mode is preferred by transmission deployers due to the multiplied effects

of scattering and absorption on the multi-mode fibre.

During the manufacturing process, all impurities cannot be removed from

the material. These residual impurities are therefore responsible for the inherent

attenuation characteristic of the fibre-optic cable. The other resultant effect of

scattering and absorption is modal dispersion.

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

AbsorptionScattering


DISPERSION & ATTENUATION

Dispersion and Attenuation occur in fibre-optic transmission using DWDM

and these influence the quality of light signal transmitted along the line. Since both

problems are inherent in this transmission system, adequate solution must be

provided. This may be in form of dispersion compensating devices.

Due to dispersion, clarity is reduced with distance and speed and the light

waves tend to scatter.

Due to attenuation, power levels are reduced with distance.


PATCH CORDS & COUPLERS

Patch cords are small fibre optic cables of narrow diameters used to

connect the terminal points of one equipment to another on the distribution

frame. They are also used to connect to test devices when troubleshooting or

measuring power levels of optical signals.

Generally, fibre optic cables can

either be single mode or multimode. As such,

patch cords come in both SMF and MMF types.

But SMF is mostly used due to its smaller

diameter which in turn reduces the modal

dispersion.

In MMF, modal dispersion occurs

because the rays of light entering at one end

of the fibre do not all arrive at the other end at

the same time.


Patch cords could also be classified based on their type of end connectors. For

example, we have FC, LC, MU, SC, ST, MT-RJ, etc.

SC

MT-RJ

SMA

FC


COUPLERS

Couplers are fibre-optic materials used to join one patch cord to another or

to extend connections from one patch panel to another. They are often employed

during ADM installation to fix patch cords to the trays. This allows for neat and orderly

arrangement in the trays.

When the two end connectors of a patch cord are of the same type, it is

called a coupler.


TEST KITS & EQUIPMENT

During and after fibre-optic transmission installation, there is a critical need

to perform certain tests to ensure proper functionality of the equipment before

provisioning can be allowed.

The test kits and equipment for DWDM but are not limited to:

•Fiberscope

•Cleaners and cleaning set

•Optical Spectrum Analyzer (OTDR)

•Gigabit Ethernet Tester

•Splicing & Labelling Machines

•Crimping tools, screw drivers, tapes, etc, are used during installation.

MTS6000MTS8000

GB TESTER


Cleaning spray

OLP

Cleaning set (pads & swabs) Gigabit Analyzer

OLAOLS


DWDM Vs TDM

DWDM TDM

Increase the number of wavelengths

Can handle 40Gbps and above. The

specific limits of this technology are

still unknown.

All signals arrive at the same time

rather than being broken up and

carried in time slots.

Increase the bit rate

At 40Gbps, severe technical issues

occur. PMD and CMD are the most

common ones.

To increase capacity, time must be

sliced into smaller intervals so that

the bits from multiple sources can

carried on the link


Incoming

Streams

with bit

rate of

2.5Gbps

Outgoing

Streams

with bit rate

of

4 X 2.5Gbps

In TDM, a particular data stream is assigned a time slot with other data

streams and the allotted time slots repeat over a given interval.


MUXES & DEMUXES

Multiplexers combine several laser signals of different wavelengths together

to produce a converged beam. Examples of this cards are BMDX 1000, BMDX 1100.

. . .

Multiplexers basically comprise lens and prisms which diffract the impinging

light rays and refocus them into a single beam. The reverse is the case for DEMUXES

DWDM Components


Demultiplexers perform the reverse function of multiplexers. They separate

the received multiplexed signals (originally combined into a beam by the MUX) into

their wavelength components and couple them into their individual fibres.

DEMUX

. .

.

MUX/DEMUX alike are either passive or active. Passive designs are based

on prism, waveguide and filters while active designs are different from the passive

ones because they have tunable filters.


TRANSPONDERS

Transponders convert energy from one form to another (e.g. electrical to

optical energy or vice versa). They accept input from different physical media and

protocols in various traffic formats and map them into wavelengths on the MUX.

Transponders perform the 3R functions of

retiming, reshaping & reamplification.

Examples of transponder cards in DWDM are

the TRBD and the TRBC cards.

Local and remote Loop backs are created on

the transponder cards to allow for troubleshooting

purposes. Consequently, faults in the transmission path

can be identified with the aid of test devices.


AMPLIFIERS

are devices used to boost signal power after multiplexing and before

demultiplexing. Due to attenuation, there are limits to how long a fibre can

propagate a signal with integrity before it has to be regenerated. With the use of

optical amplifiers, this can be achieved. Examples are the ALU LOFA cards.

Post-Amplifiers: are placed directly

after the optical transmitter to

provide maximum output power.

In-Line Amplifiers: modify a small

input signal and boost it for

retransmission down the fibre.

Pre-Amplifiers: are placed prior to

the receiver so that much larger

signals can presented to it.


EDFA: is an optical amplifier made out of erbium

material. Erbium is a rare-earth element which

when excited emits light around 1.54μm and

this makes it suitable for usage in DWDM optical

amplifier manufacture. Other dopants used to

manufacture fibre amplifiers are Tellurite and

Thulium.

What happens in the EDFA?

When a weak signal enters the EDFA, light at 980nm or 1480nm is injected

using a laser pump held in place by a coupler and this stimulates the erbium atoms to

release their stored energy as additional 1550nm light. As this process continues down

the fibre, the signal grows stronger.


OADMS

Oftentimes along the fibre span and due to access needs, the insertion or

removal of certain wavelengths becomes necessary. OADMs are DWDM equipment that

make this possible.

Though similar to the SDH ADMs, OADMs only add/drop optical signal and no

conversion from optical to electrical form occurs.

Fixed OADMs: are physically

configured to drop specific

wavelengths while adding others.

Reconfigurable ADMs: are

capable of dynamically selecting

which wavelengths are dropped

and added.


DWDM Networks

DWDM Networks basically consists of the core (long haul), distribution

(MAN) and access networks.

Long Haul/Backbone/Core Network: are located at the core of global network

consisting of transnational and global carriers. It is the central part of a telecom

network that provides services to the customers through MANs.

BB or LH networks usually have mesh and/or ring topologies that provide

flexible connections between several devices (switches and routers). Examples of

technologies used at this network level are DWDM, SDH, ATM, IP, GBE, etc.

The BB primarily functions as:

•operation & maintenance centre

•user request authentication

•call control/switching with number portability

•service charge handling unit

•service invocation such as call transfer or waiting

•the gateway


DWDM Networks


Metropolitan Area Network/ Distribution Network: lies at a critical junction that has

many characteristics as the access networks e.g. protocols & channel speeds.

Like access networks, MANs have been traditionally SDH-based using point-

to-point or ring topologies with ADMs. But because it must meet the needs of the

ever-increasing bandwidth at LH network while addressing the growing connectivity

requirements at the access level, an efficient means of achieving simpler and faster

provisioning such as DWDM is of key importance.

Access Networks: are closest to the end users at the edge of the MAN. It is the part

of the telecoms network that connects subscribers to their immediate service

provider.

Access networks are characterised by diverse protocols and infrastructures

and span a broad spectrum of access rates.

customers range from residential internet users and individual service

subscribers to large corporations & institutions.


TOPOLOGIES IN DWDM NETWORKS

Point-to-Point Topology: are characterised by ultra-high channel speeds (10 to

40Gbps), high signal integrity and reliability, and fast path restoration. It can be

implemented with or without an OADM. In LH networks, the distance between Tx and

Rx can be hundreds of Kilometres with about 10 amplifiers installed between the

endpoints.


In Point-to-Point topology, protection can either be at system level where switchover

is the responsibility of the client equipment (e.g. router or switch) or at card level

where switching (in case of failure) is performed by the DWDM systems.

Ring Topology: allows several nodes to provide access to routers, switches or

servers by adding or dropping wavelengths on the optical channel. This topology can

be configured to support most forms of traffic, accommodate hub stations and one or

more OADMs. It is mostly found in the MANs and spans up to a few or ten of

kilometres. Bit rate is in the range of 622Mbps to 10Gbps/channel.


In ring topology, protection can either be Unidirectional Protection Switched

Ring (UPSR) where just two fibre pairs are used or Bidirectional Line Switched Ring (BLSR)

where up to 4 fibres may be used.


Mesh Topology: consists of interconnected optical nodes that are three or

more point-to-point connections linked together. It begins with point-to-point links

equipped with OADM nodes at the onset and subsequently interconnects them such

that the network evolves into a mesh without complete redesign.

It is expected that, in the near future, redundancy will migrate from system,

card and fibre levels to the wavelength level. When this happens, a data channel will

be able to change wavelength as it makes its way through the network because of a

fault.


Tx Quality Parameters

OSNR

is the ratio of power in the signal to the noise that is with the signal. In

most cases, an OSNR of 10dB or better is needed for error-free operation.

OSNR= 10log(Ps/Pn)

Where: Ps is the signal power and Pn is the noise power.

Each in-line amplifier (repeater) gives some noise to the system. The

build-up of amplifier noise is therefore proportional to the number of amplifiers.

And as such, total accumulated noise equals the product of Noise per repeater

and the total number of repeaters.

Total Accumulated Noise = Noise of 1 repeater Total No of repeatersx


BER

is the ratio of error bits to the total transmitted bits. BER is a dimensionless

and the performance parameter is often expressed as percentage.

Bit synchronization problems and attenuation are factors affecting bit error rate but

it may be improved by ensuring that adequate error detection and correction

techniques are applied and signal strength is fairly strong.

1 1 0 0 1 0 1

Data streams of ones and zeroes


Q FACTOR

is a measure of how noisy a pulse is for diagnostic purposes. The higher the

Q-factor, the freer the pulse is from noise.

It is a dimensionless parameter that describes how under-damped a

resonator is or relative to the stored energy of the resonator. If the Q-factor of a

laser cavity is abruptly changed from a low value to a high one, the laser will emit a

pulse of light that is much more intense than the laser’s normal continuous output.

Eye pattern shows the eye is as open as

possible and indicates that the data can be

recovered easily with low effects from noise.


1626LM

ALU DWDM Solutions

is a scalable Alcatel DWDM platform initially developed for the core

network for LH and ULH applications. It provides a high transmission capacity on a

single optical fibre by multiplexing up to 96 x 10Gb/s (STM64/OC192) channels on a

25GHz grid.

It is used for:

•regional terrestrial application

•reconfigurable OADM: line terminal, line repeater

and access to traffic

•band OADM

•Back-to-back terminal

•upgrading existing infrastructure


1640WM

is a core Alcatel DWDM system supporting up to

160 channels in C and L ands with 50GHz spacing and

standard synchronous bit rates from 2.5Gbps to 10Gbps.

1686WM

is a regional and metropolitan Alcatel DWDM

system scalable up to 32 channels in C band and 40

channels in L band. It supports different bit rates from

100Mbps to 10Gbps.


1696MS

is a cost-effective metropolitan Alcatel DWDM

system supporting a broad range of data rates, easily

customized for intra-city networks.

1830PSS

is a scalable optical transport platform for regional

and MAN transport and services delivery. It provides 88

channel support, wavelength tracking and single fibre

bidirectional transmission. It also supports point-to-point

linear, ring and mesh-capable networks and is 2.5G/10G/40G

transport ready.


It is obvious that DWDM enables bandwidth multiplication, provides extra

resilience, improves scalability, permits multiple logical topologies over single

physical MAN and therefore makes optical transmission more effective.

That is why many telecoms service providers adopt it regardless of its

initially high cost of implementation.

But true investors know that on the long run, the capital will yield good

returns by improving their QoS and customer/subscriber base.


Thank You for Your attention

AT THE SPEED OF IDEAS…

DWDM Presentation

Documents

optical fibre

optical channel fibre

system of transmission

optical amplifiers

dwdm components

optical switches

optical impairments

fibre laser

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