This book is concerned with post-computer communication networks and two of increasingly relying on digital computer technology, and data communication. Computer and communication networks / Nader F. Mir.—Second edition. pages cm. Includes bibliographical references and index. ISBN Series Editors: J. Rak, A.J. Sammes. The Computer Communications and Networks series is a range of textbooks, monographs and handbooks. It sets out to.
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COMPUTER COMMUNICATION NETWORKS. Department of ECE, ACE. Page 2. Every layer clubs together all procedures, protocols, and methods which it. “No man but a blockhead ever wrote, except for money.” - Samuel Johnson. The textbook world is changing. On the one hand, open source. PDF | On Jan 1, , D B Hoang and others published Computer Communication Networks—Lecture Notes.
Personal information is secured with SSL technology. Free Shipping No minimum order. Description Computer- Communication Networks presents a collection of articles the focus of which is on the field of modeling, analysis, design, and performance optimization. It discusses the problem of modeling the performance of local area networks under file transfer. It addresses the design of multi-hop, mobile-user radio networks.
Firewalls[ edit ] A firewall is a network device for controlling network security and access rules. Firewalls are typically configured to reject access requests from unrecognized sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in cyber attacks. Message flows A-B in the presence of a router R , red flows are effective communication paths, black paths are across the actual network links.
A communication protocol is a set of rules for exchanging information over a network. In a protocol stack also see the OSI model , each protocol leverages the services of the protocol layer below it, until the lowest layer controls the hardware which sends information across the media.
The use of protocol layering is today ubiquitous across the field of computer networking. This stack is used between the wireless router and the home user's personal computer when the user is surfing the web. Communication protocols have various characteristics. They may be connection-oriented or connectionless , they may use circuit mode or packet switching , and they may use hierarchical addressing or flat addressing. There are many communication protocols, a few of which are described below.
The complete IEEE protocol suite provides a diverse set of networking capabilities. The protocols have a flat addressing scheme. They operate mostly at levels 1 and 2 of the OSI model.
It is standardized by IEEE It offers connection-less as well as connection-oriented services over an inherently unreliable network traversed by data-gram transmission at the Internet protocol IP level.
At its core, the protocol suite defines the addressing, identification, and routing specifications for Internet Protocol Version 4 IPv4 and for IPv6, the next generation of the protocol with a much enlarged addressing capability.
They were originally designed to transport circuit mode communications from a variety of different sources, primarily to support real-time, uncompressed, circuit-switched voice encoded in PCM Pulse-Code Modulation format.
It uses asynchronous time-division multiplexing and encodes data into small, fixed-sized cells. This differs from other protocols such as the Internet Protocol Suite or Ethernet that use variable sized packets or frames.
ATM has similarity with both circuit and packet switched networking. This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video.
ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins.
Why do COs not guarantee that every call attempt will be successfully connected? Computer communications are characterized by rather than by continuous transmission.
What is the business case for voice and data network convergence? Explain the concept of encapsulation. Describe the wiring dilemma of fully connecting telephones. Besides span. Why is noise a problem with analog signaling? Fill-in 1. To fully interconnect telephones without a CO requires wire pairs.
How do de jure and de facto standards differ? TOM a. Token ring a. UNlX a. Public packet data networks a. Office productivity software a. De jure standards a. I00 Hz to 4. The voice band defi ned by the telephone company is the range of frequencies from a.
Analog signaling a. Telephone voice networks grew inadequate for data communications because a. The Internet a. The first computer network was a LAN. Expansion and exploration 1. NetWare is a network operating system.
PDNs can faci litate line sharing by making idle moments available to other computers. Compare early reports of convergence with later reports of progress. Search the Web for information on the convergence of voice and data networks. Frequency division multiplexing is a technique for simultaneous sharing of communications links. Create a timeline for the major developments in computer communications and networking. Go to the ISO Web site and make a list of the network standards committees and their areas of interest.
The decision to limit the bandwidth of individual telephone calls was a compromise between voice quality and line-sharing efficiency. Optical fiber transmission systems have been in use only in the last five years. Signals progress along a medium by a process called propagation. Electricity and electromagnetic waves such as radio frequency and light waves carry data as signals that travel over a physical path consisting of one or more types of transmission media connected by switching and other equipment.
Materials such as copper and aluminum that easily accommodate electrical flow are called conductors. They are the vehicles that make it possible and practical to move a wide variety of information and data quickly between just about any points in the universe. Signals propagating through cables are confined to the cables and therefore follow the route the cables do. Signals traveling through air or space are not confined.
We also will look at factors to consider when there is a choice of medium and. By understanding it. Electricity flows over metallic wire cables.
Materials such as rubber. The process of electron flow is called conduction. This material is the foundation upon which computer communications are built. Within those two categories are a range of good to poor conductors and good to poor insulators. Soon after the discovery of fire. Early seafa rers depended on shipboard and lighthouse oil-fired signal lamps. For more information. For examples of would be hard-pressed to keep pace with demand. Smoke signals. For over years. Soon after electricity's discovery.
Although electricity still is a major force. Primitive man waving his hand to signal his hunting partner was using light indirectly-without daylight. Cabled and cableless may be more accurate terms. One volt is the electrical pressure required to move one amp of cur- Business NOTE rent through one ohm of resistance.
Even today. By the end of this period. If we think about it. An early cave dweller reflecting sunlight off a shiny surface to signal a companion some distance away was using light directly.
The ohm. Alternating refers to the fact that the current continually changes direction and magnitude at a regular rate. One complete journey from zero through positive and negative strength and back to zero is called a cycle and traces out a sine wave pattern. The other type is direct current DC. This important pattern comes up repeatedly in computer communications for building signals using both electricity and light waves.
The type of electricity most relevant to telecommunications is alternating current AC. His treatise covered many aspects of elec- pressure. T he ampere. Among his numerous accomplishments were his investigations into electricity and magnetism. For simplicity. Giuseppe Volta Among his many contributions to electrical current.
The volt. Typical see from the back-and-forth nature of AC does hap- household AC runs at 60 cycles per second. The answer is. If we run a varying current through a wire. B ecause the radiation effect happens without physical contact. Now the question is. We have induced a similar current in the second wire without any physical connection between the two! Now if the pattern of variations in our first wire is carrying a message signals.
What purpose do we want our wire to serve? Together these create electromagnetic waves that radiate from the wire and that mimic the pattern of change of the current in the wire. T he sine wave pattern of AC is also the pattern with which we build signals. With enough energy. A sine wave with constant maximum voltage:!: Electricity as it moves and changes: We can see wave patterns by dropping a stone into a pond-the ripples that radiate out from where the stone was dropped are water waves.
To understand wavelength. Because power drops off attenuates as it travels. He extended the work of Faraday to show the relationship between the behaviors of electric and magnetic fields. I nduced current always is weaker than the current that induced it. Because the period pattern keeps repeating over time.
One of the most significant in its later applications to communications technology was the phenomenon of electromagnetic induction based on the earlier work of Hans Christian Oersted In particular. So no matter what. He proved that electricity could be propagated as electromagnetic waves. See Figure 2. Cell phones would not be practical if the wavelengths they used required long antennas.
A wave is a regularly recurring pattern that moves away from the force that creates it. The power of radiated energy depends i n part on the power of the current that creates it. The time it takes for a sine wave to trace one complete pattern is called its period or cycle.
The more they spread. Heinrich Rudolf Hertz was a German physicist who expanded upon the work of Maxwell. We know that all electromagnetic radiation consi sts of particular wave forms-sine waves al so called sinusoids. I n addition. He also M ichael Faraday Waves and wavelength basics Many network choices and design factors involve wavelength.
James Clerk Maxwell Media can distort our signals. In communications work. Attenuation is a form of distortion in which signal energy is lost as it travels. Distortion is unwanted changes in signal shapes due to interactions between the signals and the media.
Overly attenuated signals will not be recognized by the receiver. If you stand in front of a funhouse mirror. Picture yourself in a room full of loudly talking people. In different media. The distance a wave travels in one cycle is its wavelength.
V is the velocity of light in a given medium. Cycle timeT and frequency f are inversely related: For electromagnetic radiation. Attenuation is primarily due to the resistance of the medium to electrical llow. Noise is unwelcome energy appearing in our transmission media. There are many types of noise and distortion impairments. If impairments are severe enough. We can calculate this distance by using the standard relationship between distance d.
Impu lse noise. EMI also affects wireless signals. Delay distortion stems from the way wires affect signal velocity.
Crosstalk is the result of energy induced in one wire by signals radiating from another. Examples include crosstalk and impulse noise. Thermal noise is distributed uniformly over the entire electromagnetic spectrum.
If we send various frequencies down our wire. Gaussian noise. It typically comes from nearby electrical equipment such as an elevator motor. If the delays are large enough. You may have experienced this phenomenon when talking on a telephone and suddenly hearing a conversation from a phone call between two other parties. Electromagnetic interference EMI is unwanted energy induced in our line by radiation from any external source of electromagnetic energy.
Because signals are composed of a range of frequencies. B ecause thermal noise cannot be eliminated. B ecause delay differences are magnified by distance. We will discuss the two most common types of guided e lectrical media: Without a circuit.
UTP is the most common. One wire carries the signal. If so. The output of a nonlinear system contains powers of the input. STP is often preferred in certain electrically "noisy" environments or where especially sensitive equipment that could be affected by EMJ is in use. The wires are insulated and twisted around each other in a spiral fashion.
The number of twists per inch is the twist rate. The metal is almost always copper. Although the twists in UTP are often sufficient to alleviate external noise effects. The output of a linear system is a simple multiple of the input.
Signals from a non-linear system contain multiples of the original frequencies called harmonics that were not present in the signals to start with.
In STP. The shielding works in two directions. This is STP. Within a cable bundle. Harmonics may have some of the same frequencies as other original signals traveling in the system.
Twisted pair Currently. Twisting reduces crosstalk from external radiation. Networks in offices with large copier machines. The type of filler and the amount of space greatly affect the bandwidth and noise resistance of the cable. Far less common for networks than it used to be. Even the vaunted twisted pair is being replaced by fiber in many applications. But it wasn't always so. A typical office building There are several forms of backbones. To handle inter-network traffic G enerally speaking.
Coax also is more costly and more difficult to modify when changes to the network are necessary. The wire and the shield are electrically isolated by the space between them. The original Ethernet LAN. From one perspective. As such. But even in its thin version. Where heavy-duty electrical machinery Hospitals have equipment that can interfere w ith or is in use.
Individual coax cables can be bundled together. A wire conductor running through the center of the cable axially is surrounded co-axially by a conducting braided metal or foil shield. More telling. As with STP. Coax is still common in other parts of the television distribution system and in long-distance telephone transmission.
Coaxial In contrast to UTP. It also weighs more. Because of these drawbacks. It has a larger minimum bend radius. IBM designed eight varia- most common comprising a number of wire categories tions. It evolved into a that lock with one-quarter turn.
The word antenna conjures up images o f thin metal wands extending from automobile fenders. Cat 5e 5 enhanced and cat 6 are Coax is graded by RG radio government numbers. Cat 7 is now under consideration. For computer communications. RG 11 50 ohms. UTP connectors are denoted by RJ radio jack num- opposition to electrical flow.
Among them are: The cat 6 standard was released in June All UTP cables to date use the same connector. STP originally was a bulky cable. This looks like the connector com- ohms. By the same token. In this grouping. If this is done to excess. Antennas come in a wide variety of shapes and sizes. The EMR spectrum. For that reason. More expensive than anything else is correct- not initially installed there.
The largest cost component is f or installation and Following t hese simple ideas will help ensure that testing labor. See Table 2. Broadly speaking. Some speeds become possible. You can experience this phenomenon by touching a radio anrenna connection or a TV rabbit-ears antenna-weak reception may improve.
The natural limit to line-of-sight antennas is the horizon. Although this bending is not enough to force microwaves to full y follow the curvature of the earth. This is called diffraction. Depending on the material involved. EMR can pass through. Higher-frequency EMR tends to travel in straight though spreading lines. The higher the frequency of the EMR. The line-of-sight requirement is cased somewhat by reflection. The next time you use a cell phone.
This is made all the more d iffi cult by the fact that reflected and refracted signals take different Their signals pass through some objects and a lso depend on re flection and diffraction to reach relay station antennas that arc not in an unobstructed line of sight. Consider these examples: Gravitational force attracts EMR as it docs every thing e lse. Although they ostensibly require line of sig ht.
This means that two antennas whose Iinc of sight is obstructed may still communicate. The other depicts light as particles quantum optics. We may consolidate these theories by thinking of light as a particle whose motions are wavelike. We use a diffraction grating to separate a light beam into its component wavelengths. Optical fiber is not drawn from ordinary window g lass. By the late s.
If you are interested in learning more about light and light phenomena.
When a ray of light hits another medium. The notion that light could be guided by a medium at all first "came to light" in the s when John Tyndall found that a narrow stream of water could direct a beam of light along its trajectory. See Tyndall's light pipe in Appendix G.
We now accept two complementary explanations. Although light rays can be beamed through the air and space just as radio waves and microwaves can. One considers light to be waves of energy wave optics. When we wish to describe a particular phenomenon. About 2. This premise was good enough for some time. Realistic use of light to carry signals had to await the development of a more useful medium than water. So e lusive this quest has been that a great many theories have been proposed.
This greatly multiplies the transmission capacity of light-based systems in a process called wavelength division multiplexing. The premise was that light consists of rays that move outward from their source in straight lines as long as they are traveling in a consistent medium air.
Silica is a component fibe rs. To give you an idea of the purity of optical fiber. Now that light sources and fiber are more close ly compatible. For a time. Each strand or the entire cable may be jacketed as well. A common criterion for attenuation is the halfpower point.
Some cables are made of plastic mainly as silicates and oxides. Although they are cheaper and easier to of ordinary sand. Optical fiber cables In an optical fiber cable. For communications. Silicon is different from silicone. Sec Table 2. One particularly vital issue was matching the wavelengths of the light that could be produced with the wavelengths that the fibers could carry best.
Most componen ts and gives its name to Silicon Valley. We see that light can travel Silicon is used in many computer work with. Attenuation of light is the primary way we measure the relative purity of different kinds of glass. It is surrounded by cladding designed to reflect light to keep it within the core: This table shows typical values.
Because the extremely thin fibers are easily broken. Sec Figure 2. Table 2. Rather than wait for the perfect match. The silica used to make glass optical fiber is a California. This keeps the light beam in the core as i t travels along.
At these diameters. I f you want to learn more. They have relatively large core diameters Step index core density is constant from the center to the edges. Optical fiber types Two basic types of optical fiber are multimode and single mode. We see that step index core diameter is about the same as a human hair. Graded index core density is greatest at the center o f the core and decreases is graded toward the edges.
Typical core diameter. Lm is now available. LI11 micrometers. Now we can understand how T yndall's light pipe worked-the optical density of a water stream is much greater than that of the surrounding air. The two varieties o f multi mode cores are step index and graded index. Single-mode core is uniformly dense but has very much smaller diameters than multimode fiber typically ranging from 8 f.
All in all. Careful attention must be paid to avoid excess stretching. Because labor cost is the biggest expense item. Joining splicing fiber cables and attaching them to connectors also requires special care and devices. Special devices are used to avoid this problem.
Even if the bend is not too severe. Cladding J. For optical communications systems. Lm Core It is critical not to curve the cable more than its specified minimum bend radius to avoid damaging the fiber. Aside from breaking the fibers. Simply lowering a cable down a shaft. This highlights the technical difficulties of producing a light source small enough that it can be physically coupled to the fiber.
Each ray. Light beam signals are composed of many rays. Why does the second result matter? Because it can cause signal distortion or loss. The third situation is the worst. Sometimes the entire spectrum is referred to as " light. The technology available to economically manufacture lasers or LEOs that produce particular light wavelengths is a limiting factor in the communications chain.
As Figure 2. Particular wavelengths in that range determine the colors we see. Infrared light used in optical communications systems has wavelengths outside the range detectable by the human eye.
Whatever the source. The second result i s the most complex. The extreme thinness of optical fiber magnifies the problem of manufacturing light sources-coupling a light source to these fibers requires that the source's output dimension be comparable to fiber core diameters. This is a major practical issue. Our eyes are sensitive to a range of light wavelengths called the visible spectrum. If the angle of incidence i s precisely goo.
If you want to explore LEOs and lasers furth er. To further complicate the issue. The first possibility is the ideal. Single mode carries the same information. The longer the cable. This is what single-mode fiber is about. Essentially only o ne ray of light enters-the one that travels straight through the core that is. Refraction of the differently angled rays also reduces the distance they have to travel. This means that more of the original rays carry through the fiber.
Graded index multimode C. As shown in Figure 2. Graded index fiber was designed as a partial solution to the zigzag and curved cable problems.
Others have to do with the light sources typically used and light absorption. Another consideration: Rarely can cables be installed in completely straight lines.
This is one factor that limits the practical length of step index multimode cable. For these situations. Because rays traveling d ifferent distances reach the receiver at different times. Capacity is much greater as well. The more sharpl y a cable is bent. Because its core density decreases from center to edge.
Single-mode tiber has such small diameters that issues of zigzag paths disappear. Although graded index relaxes cable length limits somewhat. Single-mode fiber cables should be used for long-distance transmissions and very highspeed communications. This should help the student in the analysis and design of modern communications systems, which are better understood at a system level.
A suitable selection of chapters from this book provides the necessary teaching material for a one-semester undergraduate course on the basics of telecommunications, but some advanced material can be also used in graduate classes as complementary reading.
The book is also a useful comprehensive reference for telecommunications professionals. The numerical solutions for these exercises are provided in the companion website, www. The content of each chapter is briefly summarized below. The chapter revises the basics of signal theory and introduces both continuous and discrete time signals, and their Fourier transform with its properties.
The concepts of energy, power and bandwidth are also reviewed, together with the vector representation of signals by linear space methodologies. Lastly, this chapter introduces the basics of random variables and random processes, their common statistical description, and how statistical parameters are modified by linear systems.
Chapter 3 Describes how information produced by a source, either analog or digital, can be effectively encoded into a digital message for efficient transmission. We will first introduce the reference scheme for analog-to-digital conversion, and focus on quantization, the operation of approximating an analog value with a finite digit representation. We will also present the fundamentals of information theory with the notion of information carried by a digital message.
Lastly we introduce the principles of source coding, state the fundamental performance bounds and discuss some coding techniques. Chapter 4 Models a transmission medium. Firstly, a description of the two-port network is given. A model of noise sources is then provided and its description in terms of parameters such as the noise temperature and the noise figure is presented.
A characterization, especially in terms of power attenuation, of transmission lines, power lines, optical fibers, radio propagation and underwater propagation concludes this chapter. Chapter 5 Deals with digital modulations. The general theory is first presented, relying on concepts of linear spaces and hypothesis testing. Performance is measured by the bit error probability, which again can be expressed in terms of system parameters.
Then, the most important modulations are presented as examples of the general concept. These include pulse amplitude modulation, phase shift keying, quadrature amplitude modulation, frequency shift keying and others.
A comparison between the different modulation schemes is carefully drawn. Then, more advanced modulation techniques are briefly presented, namely orthogonal frequency division multiplexing and spread spectrum.
Finally, the performance of the digital approach is compared against analog transmission, explaining why digital transmission is so widely used. Chapter 6 Investigates how an information message can be robustly encoded into the signal for reliable transmission over a noisy channel.
We describe the principles of channel coding techniques, where robustness is obtained at the price of reduced information rate and complexity of the decoding process. Then, based upon the fundamentals of information theory introduced in Chapter 3, we aim to establish upper bounds on the amount of information that can be effectively carried through a noisy channel, by introducing the concept of channel capacity. We conclude by describing briefly how recently devised coding schemes allow such upper bounds to be approached closely while maintaining moderate complexity.
Chapter 7 Introduces some basic statistical methods that are widely used in the performance analysis of telecommunication networks.
The topics covered are the elementary theory of discrete-time and continuous-time Markov chains and birth-death processes.