This chapter provides an introduction to Computer networks and covers fundamental topics The main objective of data communication and networking is to. This tutorial gives very good understanding on Data Communication and Computer. Networks. After completing this Communication and Computer Networks. Prerequisites. Before proceeding with .. PHYSICAL LAYER INTRODUCTION. Chapter 1 Introduction 3. DATA COMMUNICATIONS 3. Components 4. Data Representation 5. DataFlow 6. NETWORKS 7. Distributed Processing 7.
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DATA. COMMUNICATIONS. AND. NETWORKING. Fourth Edition. Behrouz A. Forouzan. DeAnza College with. Sophia Chung Fegan. #. Higher Education. PDF | On Nov 15, , Yekini Nureni and others published DATA introduction of mobile phones, with embedded data services. such as. Introduction to Computer Networks and. Data Communications. Learning Objectives. •. Define the basic terminology of computer networks. •. Recognize the.
As shown below a computer always sends the data and the monitor only receives the data. Similarly a key board always receives the data from the computer and computers send the data to the keyboard.
Half Duplex: In half duplex both the devices can transmit and receive the data in the data communication. But not at the same time. When one device is sending the data the other will be receiving and vice versa. The use of a walkie-talkie by police and army personal is an example for this half-duplex transmission.
The Half duplex method is like a one lane road with two directional traffic. While cars are travelling one direction , cars going the other direction must wait. In a half Duplex transmission the entire capacity of a channel is taken over by which ever of the two devices is transmitting at the time.
Full Duplex: In full duplex mode also called Duplex both stations can transmit and receive data simultaneously. One common example is mobile phone or telephone line. In full duplex ,the signals going in either direction share the capacity of the link. This sharing can occur in two ways. Either the link must contain two physically separate transmission paths.
One for sending and the other for receiving. The term modem is a composite word that refers to the two functional entities that make up the device: A demodulator converts an analog signal into a digital signal. While a demodulator resembles an analog-to-digital converter, it is not in fact a converter of any kind.
It does not sample a signal to create a digital facsimile; it merely reverses the process of modulation-that is, it performs demodulation. The Modems are DCEs. It then relays the resulting digital signal to the receiving computer via the internet. As the first and, for a long time, lone manufacturer in the marketplace, Be defined the development of the technology and provided a de facto standard upon which subsequent manufacturers have built.
Today there are dozens of companies producing hundreds of different types of modems worldwide. As complex and powerful as many models have become, they all evolved from the original and. The Bell series modems have two speeds. The option of a second speed allows for compatibility with a wider number of systems.
Both speeds operate in full-duplex mode over switched telephone lines. The slower speed, bps, uses FSK The series modems operate in either half-duplex mode over two-we switched lines or fullduplex mode over four-wire leased lines. The entire bandwidth over two-wire line is dedicated to a single direction of transmission. Four-wire lines allow for two completely separate channels, one in each direction, to be processed through single modem on each end.
These modems can be divided into two groups: Intelligent modems were first introduced by Hayes Microcomputer Products, Inc. More recently, other manufacturers have come out with Hayes compatible modems.
Traditional modems have a limitation on the data rate maximum of These modems may be used only if one party is using digital signaling such as through an Internet provider. They area symmetrical in that the downloading flow of data from the Internet provider to the PC is a maximum of 56 Kbps, while the uploading flow of data from the PC to the Internet provider can be a maximum of If one side is an Internet provider and the signal does not have to pass through a PCM converter, quantization is eliminated in one direction and the data rate can be increased to 56 Kbps.
Encoding and Modulating: In the process of data communication the data must be transformed into signals to send them from one place to another. Data stored in a computer is in the form of 0s and 1s. To transform this data from one place to another place , it must be converted into digital signals.
This is called Encoding digital data into digital signal or digital to digital conversion. The process of converting analog signal into digital signal is called analog to digital conversion or digitizing an analog signal.
The process of sending an analog signal over long distances using a high frequency carrier signal is called analog to analog conversion or modulating an analog signal. Digital to Digital Encoding: It is the representation of a digital information by a digital signal.
In this process of encoding the binary 1s and 0s generated by a computer are translated into a sequence of voltage pulses that can be transmitted over a cable or wire. This process is shown in the diagram below. There are three types of digital encodings. Unipolar ,Polar and Bi-polar. Unipolar encoding uses only one level of value.
One is DC component and the other is synchronization. Due to these limitations ,this encoding is not widely used. The DC component problem arises because the average amplitude of a uni-polar encoded signal is non- zero. This causes what is called a direct current component. When a signal contains a DC component, it cannot travel through the media that cannot handle DC components.
The Synchronization problem in uni-polar encoding occur when ever the data stream includes a long uninterrupted series of 1s or 0s.
Compared to polar encoding this scheme is very costly. Polar Schemes: In polar schemes, the voltages are on the both sides of the time axis. For example, the voltage level for 0 can be positive and the voltage level for I can be negative.
The bi-phase refers to two methods. Types of polar encodings is shown below. In polar NRZ encoding, two levels of voltage amplitude are used. There are two versions of polar NRZ: The figure also shows the value of r, the average baud rate, and the bandwidth.
If there is no change, the bit is 0; if there is a change, the bit is 1. The synchronization problem sender and receiver clocks are not synchronized also exists in both the schemes. While a long sequence of datas can cause a problem in both schemes, a long sequence of 1s affects only NRZ-L.
Another problem with NRZ-L occurs when there is a sudden change of polarity in the system. For example, if twisted-pair cable is the medium, a change in the polarity of the wire results in all 0s interpreted as I s and all I s interpreted 0s.
NRZ-I does not have this problem. The receiver does not know when one bit has ended and the next bit is starting. Hence the Return-to-zero RZ scheme is used.
This scheme uses three values: In RZ, the signal changes not between bits but during the bit. In Figure below we see that the signal goes to 0 in the middle of each bit.
It remains there until the beginning of the next bit. The main disadvantage of RZ encoding is that it requires two signal changes to encode a bit and therefore occupies greater bandwidth. This scheme has no DC component problem 14 But the problem is the complexity: RZ uses three levels of voltage, which is more complex to create.
Introduction to Data Communications and Networking
As a result of all these deficiencies, the scheme is not used today. Instead, the betterperforming schemes like Manchester and differential Manchester schemes are used. The best solution for the problem of synchronization is the Bi-phase encoding. This bi-phase encoding consists of two important encodings namely Manchester and Differential Manchester encodings. In Manchester encoding, the duration of the bit is divided into two halves. The voltage remains at one level during the first half and moves to the other level in the second half.
The transition at the middle of the bit provides synchronization. There is always a transition at the middle of the bit, but the bit values are determined at the beginning of the bit.
If the next bit is 0, there is a transition; if the next bit is 1, there is none. Figure below shows both Manchester and differential Manchester encodings. First, there is no baseline wandering. There is no DC component because each bit has a positive and negative voltage contribution. The only drawback is the signal rate. The reason is that there is always one transition at the middle of the bit and maybe one transition at the end of each bit.
Manchester and differential Manchester schemes are also called bi-phase schemes.
Channel capacity The maximum rate at which data can be transmitted over a communication channel under given conditions is referred as the channel capacity.
Four important parameters are related in the evaluation of channel capacity. The rate at which data can be transmitted. The bandwidth of the transmitted signal. Measured in cycles per second Hz.
The average level of unwanted signals over communication path. Expressed as the ratio between signal and noise. The rate at which error can occur.
Here the SNR ratio assumes only white noise thermal noise where as other noise like impulse noise, attenuation noise and delay noise are not taken into account. When signals travel through imperfect transmission media, the imperfection causes signal impairment.
This means that the signal at the beginning of the medium is not the same as the 16 What is sent is not what is received. The impairment of signals is mainly caused due to attenuation, distortion, and noise in the medium. Attenuation Attenuation means a loss of energy. When a signal, simple or composite, travels through a medium, it loses some of its energy in overcoming the resistance of the medium.
That is why a wire carrying electric signals gets warm. Some of the electrical energy in the signal is converted to heat. To compensate for this loss, amplifiers are used to amplify the signal. Distortion means that the signal changes its form or shape. Distortion can occur in a composite signal made of different frequencies.
Each signal component has its own propagation speed see the next section through a medium and, therefore, its own delay in arriving at the final destination.
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Differences in delay may create a difference in phase if the delay is not exactly the same as the period duration. In other words, signal components at the receiver have phases different from what they had at the sender.
The shape of the composite signal is therefore not the same. Figure below shows the effect of distortion on a composite signal. Several types of noise, such as thermal noise, induced noise, crosstalk, and impulse noise, may corrupt the signal. Thermal noise is the random motion of electrons in a wire which creates an extra signal not originally sent by the transmitter.
Induced noise comes from sources such as motors and appliances.
data communication and networking by behrouz a. forouzan 4th edition
These devices act as a sending antenna, and the transmission medium acts as the receiving antenna. Crosstalk is the effect of one wire on the other. One wire acts as ascending antenna and the other as the receiving antenna. Impulse noise is a spike a signal with high energy in a very short time that comes from power lines, lightning, and so on.
SNR is actually the ratio of what is wanted signal to what is not wanted noise. Broadband LANs transmit multiple radio frequency signals on the same cable, usually coaxial or sometimes fiber.
This ability to send many types of communication simultaneously over the same cable, including voice, video, and data, distinguishes broadband LANs from the other common baseband LANs. For this operation, broadband LANs use the technique called frequency division multiplexing. Each channel in a broadband system is separated from the adjacent channel by a guard band, a frequency range over which no data will be transmitted. The simplest broadband LAN will be split into two channels, one for inbound data, one for outbound.
Each of these gross channels may be split into two or many more channels. Broadband LANs use a tree-and-branch topology. The root of the tree is the head end, or central re- transmission facility.
The trunk cable is attached to this root. Baseband System: Baseband methodology allows several devices to share a cable by means of a time-sharing technique. Each device is assigned a specific time slot some thousandths or millionths of a second in length in which to transmit. Only one device can transmit in a given time interval. This technique is called time division multiplexing.
Baseband transmission is associated with specific network and performance characteristics. There must be a protocol included in the network to assign time slots and provide access to the network.
Modems are not required to connect devices to the cable when communicating digital information. It explains well the analaog and digital transmission.
The transmission happen over the media, so the transmission media have been covered well in the book both the type of media and the impairments. Data link layer covers the link control and the access mechanism staring from framing to flow and the error control.
The flow control have been conceptually covered well in chapters 11 and chapter 12 with suitable examples Network layer is covered in four chapters covering the logical addressing, subnet masking.
Then the IPv4 and IPv6 packet formats are explained. The examples covered are very useful for analyzing and designing the networks.
Standards organizations also do research and development for standards of the future. In practice, the standards organizations mentioned, cooperate closely with each other. The standardization process starts off with ISO commissioning a sub-committee workgroup. The workgroup issues working drafts and discussion documents to interested parties including other standards bodies in order to provoke discussion and comments. This will generate a lot of questions, much discussion and usually some disagreement on what the standard should provide and if it can satisfy all needs usually not.
All conflicting views should be taken into account, often by way of compromise, to progress to a draft proposal of the working group. The draft proposal is discussed by the member countries' standard bodies and other organizations within each country. Comments and suggestions are collated and national views will be formulated, before the members of ISO vote on the proposal. If rejected, the draft proposal has to consider the objections and counter-proposals to create a new draft proposal for another vote.
After a lot of feedback, modification, and compromise the proposal reaches the status of a draft international standard , and ultimately an international standard.
The process normally takes several years to complete. The original paper draft created by the designer will differ substantially from the standard, and will contain some of the following 'features':. International standards are reissued periodically to handle the deficiencies and reflect changing views on the subject. A lesson learned from ARPANET , the predecessor of the Internet, was that standardization of protocols is not enough, [ citation needed ] because protocols also need a framework to operate.
It is therefore important to develop a general-purpose, future-proof framework suitable for structured protocols such as layered protocols and their standardization. This would prevent protocol standards with overlapping functionality and would allow clear definition of the responsibilities of a protocol at the different levels layers.
In the OSI model , communicating systems are assumed to be connected by an underlying physical medium providing a basic and unspecified transmission mechanism.
The layers above it are numbered from one to seven ; the n th layer is referred to as n -layer. Each layer provides service to the layer above it or at the top to the application process using the services of the layer immediately below it. The layers communicate with each other by means of an interface, called a service access point.
Corresponding layers at each system are called peer entities. To communicate, two peer entities at a given layer use an n -protocol, which is implemented by using services of the n-1 -layer. When systems are not directly connected, intermediate peer entities called relays are used. An address uniquely identifies a service access point. The address naming domains need not be restricted to one layer, so it is possible to use just one naming domain for all layers.
Connection-oriented networks are more suitable for wide area networks and connectionless networks are more suitable for local area networks. As a result, the IETF developed its own standardization process based on "rough consensus and running code".
The standardization process is described by RFC Classification schemes for protocols usually focus on domain of use and function. As an example of domain of use, connection-oriented protocols and connectionless protocols are used on connection-oriented networks and connectionless networks respectively. For an example of function consider a tunneling protocol , which is used to encapsulate packets in a high-level protocol, so the packets can be passed across a transport system using the high-level protocol.
A layering scheme combines both function and domain of use. Despite the fact that the underlying assumptions of the layering schemes are different enough to warrant distinguishing the two, it is a common practice to compare the two by relating common protocols to the layers of the two schemes.
Lists of network protocols. The functionality of the layers has been described in the section on software layering and an overview of protocols using this scheme is given in the article on Internet protocols. The functionality of the layers has been described in the section on the future of standardization and an overview of protocols using this scheme is given in the article on OSI protocols.
In networking equipment configuration, a term-of-art distinction is often drawn: The term "protocol" strictly refers to the transport layer, and the term "service" refers to protocols utilizing a "protocol" for transport. Conformance to these port numbers is voluntary, so in content inspection systems the term "service" strictly refers to port numbers, and the term "application" is often used to refer to protocols identified through inspection signatures.
Protocols upon which transport layer relies, like IPv4, are distinguished by their "address family. From Wikipedia, the free encyclopedia. The sender has not means to distinguish these cases and therefore, to ensure all data is received, must make the conservative assumption that the original transmission was lost.
Tema 4: Error Correction, p. This layerist organization was chosen for simplicity and clarity. IEEE Network: Computer Networking: A Top-Down Approach. Lascano and S. Daigneau, Service Design Patterns: Upper Saddle River, NJ: Addison-Wesley Professional, Fowler, Patterns of Enterprise Application Architecture, 1 edition.
Buschmann, K. Henney, and D. Chichester England; New York: Wiley, Computer Networks Journal of the ACM. Coaxial cable Fiber-optic communication Optical fiber Free-space optical communication Molecular communication Radio waves Transmission line. Space-division Frequency-division Time-division Polarization-division Orbital angular-momentum Code-division.
Category Outline Portal Commons. Computer science. Computer architecture Embedded system Real-time computing Dependability. Network architecture Network protocol Network components Network scheduler Network performance evaluation Network service.
Interpreter Middleware Virtual machine Operating system Software quality. Programming paradigm Programming language Compiler Domain-specific language Modeling language Software framework Integrated development environment Software configuration management Software library Software repository. Software development process Requirements analysis Software design Software construction Software deployment Software maintenance Programming team Open-source model.
Model of computation Formal language Automata theory Computational complexity theory Logic Semantics. Algorithm design Analysis of algorithms Algorithmic efficiency Randomized algorithm Computational geometry. Discrete mathematics Probability Statistics Mathematical software Information theory Mathematical analysis Numerical analysis.
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Interaction design Social computing Ubiquitous computing Visualization Accessibility.Differences in delay may create a difference in phase if the delay is not exactly the same as the period duration. Lascano and S. Based on the requirements, there are two possible line configurations. Connection-oriented networks are more suitable for wide area networks and connectionless networks are more suitable for local area networks. Without a protocol ,two devices may be connected but can not communicate.
Software development process Requirements analysis Software design Software construction Software deployment Software maintenance Programming team Open-source model. Either the link must contain two physically separate transmission paths. In a bus, this redundancy is eliminated.
The devices are not directly linked to one another. This activity is referred to as protocol development.
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