39 - Optical Networking Fundamentals

www.ciscopress.comCopyright 2003

CCNA 4 Chapter 17

Optical Networking Fundamentals

By

PRAVEENKUMAR P.J


Objectives

• Basics of optical networks

• Optical fibers

• Optical transmission and multiplexing


Optical Business Drivers


Fiber-Optic Transmission System

• All communication systems have three things in common:

– A signal source– A medium for the signal to travel through– A receiver


Optical Transmitter

• An optical transmitter is simply a source of light, like a light bulb.

• The optical receiver is a semiconductor that changes light into a corresponding electrical signal.– It is generically called an optical-to-electrical

converter.


Optical Transmission

• In fiber optics, information is carried by modulating the light power, not the wavelength or frequency of the light.

• Wavelength-division multiplexing (WDM), allows more than one wavelength to be sent over a single fiber, thereby increasing the capacity of the fiber.


Reflection and Refraction

• Reflection is a light ray that bounces off the interface of two materials at the same angle it hits.

• Refraction is the bending of the light ray as it changes speed going from one material to another.


IOR

• IOR is the ratio of the speed of light in a vacuum to the speed of light in a fiber.

• IOR is a measure of the density of a fiber because denser materials (higher IOR) cause light to travel more slowly.


Optical Fibers


Fiber Types• A fiber-optic cable has three

components:– Protective outer coating — Also known as

buffer coating.– Inner cladding — The cladding is of a

different density than the core, so the light bounces against it.

– Fiber core — The core is doped with chemicals that enhance its transmission properties.


Multimode

• Multimode fiber is used to transmit many signals per fiber.

• Multimode allows many paths or modes for the light.


Single Mode

• Single-mode fiber is used to transmit one signal per fiber.

• Single-mode fiber allows only one path for the signal to travel down the middle of the fiber.

• The entire signal travels the length of the fiber at the same rate, allowing for much higher data rates.


Loss Factors

• Connector loss• Macrobending• Microbending• Absorption


Attenuation

• Attenuation refers to the decrease in the strength of a signal during transmission.

• Attenuation is a natural consequence of signal transmission over long distance.

• Two primary factors affect attenuation in optical fibers:– Length of the fiber– Wavelength of the light


Optical Filters

• Optical filters are used to identify different wavelengths or lambdas.

• Fiber bragg grating and the dielectric filter are examples of optical filters.


Optical Amplifier

• The optical amplifier (OA) is a device that amplifies an input optical signal terahertz (THz) of optical bandwidth near 1550 nm.


Optical Transmission and Multiplexing


SONET

• SONET is the standard for synchronous data transmission on optical media used in North America. SDH is the international equivalent of SONET.

• Service providers who are using a ring topology primarily deploy SONET.

• The two prevalent types of rings in networks today are unidirectional path-switched rings (UPSRs) and bidirectional line-switch rings (BLSRs).


DWDM

• DWDM is a technology that transmits multiple signals simultaneously at different wavelengths, allowing a single fiber to operate as if it were multiple fibers.

• DWDM works in conjunction with optical networks to make data transmission fast and cost effective.


SONET Overhead Hierarchy

• Section overhead (SOH)• Line overhead (LOH)• Path overhead (POH)


SONET Rings


SONET/SDH–Based TDM Transport


SONET Multiplexing Hierarchy


E/O/E Conversion


DWDM Data Transmission


DWDM Advantages

• Flexibility• Transparency• Scalability• Dynamic provisioning


Metro Versus Long-Haul DWDM

39 - Optical Networking Fundamentals

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