Learning Center

Basic VPN Technologies

April 29, 2015
Basic VPN Technologies

+-*This chapter focuses on the background technologies used to build a virtual private network. As we discussed in Chapter 1, there are two competing camps at work when we talk about connecting networks. The first camp places the highest worth on the accessibility of data anywhere the user might be, and anywhere the data might be. The second emphasizes that the protection of the data itself, the content, is most important and must be protected to prevent unauthorized persons from using it. As you can see, these two concepts are not at all mutually exclusive, but more of a yin-yang. As you focus on sharing more

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Why Build a Virtual Private Network?

April 22, 2015

+-*Until now there has always been a clear division between public and private networks. A public network, like the public telephone system and the Internet, is a large collection of unrelated peers that exchange information more or less freely with each other. The people with access to the public network may or may not have anything in common, and any given person on that network may only communicate with a small fraction of his potential users. A private network is composed of computers owned by a single organization that share information specifically with each other. They’re assured that they are going to be the only ones

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Generations of Multiple 16QAM signals at 40Gbit/s using a multi- format transmitter

April 21, 2015
Generations of Multiple 16QAM  signals at 40Gbit/s using a multi- format transmitter

+-*I. INTRODUCTION With the drive of ever-increasing Internet traffic, efficient use of signal bandwidth has become a key technology to increase the transmission capacity over already installed optical fibres and amplifiers. However, a binary signal beyond 40Gbit/s is severely limited by the operating speed of electrical and optical components, and also by the rapidly reducing chromatic dispersion (CD) and the polarization mode dispersion (PMD) tolerance [1]. On the other hand, multi-level modulation formats combined with coherent detection have become a promising technology to increase the capacity of optical fibre transmission and also to extend transmission distance [1-4]. Among multi-level modulation formats, 16 quadrature amplitude modulation (QAM), which carries four bits per symbol, is

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Optical Fiber Types

April 20, 2015
Optical Fiber Types

+-*Optical fibers are characterized by their structure and by their properties of transmission. Basically, optical fibers are classified into two types. The first type is single mode fibers. The second type is multimode fibers. As each name implies, optical fibers are classified by the number of modes that propagate along the fiber. As previously explained, the structure of the fiber can permit or restrict modes from propagating in a fiber. The basic structural difference is the core size. Single mode fibers are manufactured with the same materials as multimode fibers. Single mode fibers are also manufactured by following the same fabrication process as multimode fibers. Single Mode

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Transmission of Light through Optical Fibers (2)

April 2, 2015
Transmission of Light through Optical Fibers (2)

+-*Mode Theory The mode theory, along with the ray theory, is used to describe the propagation of light along an optical fiber. The mode theory is used to describe the properties of light that ray theory is unable to explain. The mode theory uses electromagnetic wave behavior to describe the propagation of light along a fiber. A set of guided electromagnetic waves is called the modes of the fiber. Plane Waves The mode theory suggests that a light wave can be represented as a plane wave. A plane wave is described by its direction, amplitude,and wavelength of propagation. A plane wave is a wave whose

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Transmission of Light through Optical Fibers (1)

March 25, 2015
Transmission of Light through Optical Fibers (1)

+-*The transmission of light along optical fibers depends not only on the nature of light, but also on the structure of the optical fiber. Two methods are used to describe how light is transmitted along the optical fiber. The first method, ray theory, uses the concepts of light reflection and refraction.The second method, mode theory, treats light as electromagnetic waves. We must first understand the basic optical properties of the materials used to make optical fibers. These properties affect how light is transmitted through the fiber. Optical Material Properties The basic optical property of a material, relevant to optical fibers, is the index of

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Transmission of Light

March 24, 2015
Transmission of Light

+-*Fiber optics deals with the transmission of light energy through transparent fibers. How an optical fiber guides light depends on the nature of the light and the structure of the optical fiber. A light wave is a form of energy that is moved by wave motion. Wave motion can be defined as a recurring disturbance advancing through space with or without the use of a physical medium. In fiber optics, wave motion is the movement of light energy through an optical fiber. Before we introduce the subject of light transmission through optical fibers, we must first understand the nature of light and the properties of

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FIBER-OPTIC CABLE

July 16, 2014
FIBER-OPTIC CABLE

+-*CABLE CHARACTERISTICS Fiber-optic cable is jacketed glass fiber. In order to be usable in fiber-optic systems, the somewhat fragile optical fibers are packaged inside cables for strength and protection against breakage, as well as against such environmental hazards as moisture, abrasion, and high temperatures. Packaging of fiber in cable also protects the fibers from bending at too sharp an angle, which could result in breakage and a consequent loss of signal. Multiconductor cable is available for all designs and can have as many as 144 fibers per cable. It is noteworthy that a cable containing 144 fibers can be as

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FIBER-OPTIC BASICS

July 15, 2014
FIBER-OPTIC BASICS

+-*BASIC FIBER CONSTRUCTION Optical fiber consists of a thin strand (or core) of optically pure glass surrounded by another layer of less pure glass (the cladding). The inner core is the light-carrying part. The surrounding cladding provides the difference in refractive index that allows total internal reflection of light through the core. The index of the cladding is less than 1 percent lower than that of the core. Most fibers have an additional coating around the cladding. This coating, usually one or more layers of polymer, protects the core and cladding from shocks that might affect their optical or physical

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INTRODUCTION TO FIBER

July 14, 2014
INTRODUCTION TO FIBER

+-*HISTORY The use of light for the transmission of information is far from a new idea. Paul Revere’s lanterns were used to signal the approach of the British. And it was Alexander Graham Bell’s experiments over a century ago that led to his development of the photophone, a device that carried speech from one point to another by means of vibrating mirrors and a beam of sunlight. Although never a commercial success, it nevertheless demonstrated the feasibility of lightwave communications. However the technique was shunted aside and virtually forgotten for almost another hundred years. It probably would have remained in

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