Data Communication and Computer Networks Lecture Notes

Data Communication and Computer Networks (CoSc-211) Introduction  Overview Concept of Data Communication Communication Model Data Representation and Data Flow Computer Networks 05/11/2025 Set By Hailemariam W. 2  Concept of Data Co...

Data Communication and Computer Networks (CoSc-211) Introduction  Overview Concept of Data Communication Communication Model Data Representation and Data Flow Computer Networks 05/11/2025 Set By Hailemariam W. 2  Concept of Data Communication Data communications: – Deals with the transmission of signals in a reliable and efficient manner – The exchange of data between two devices via some form of transmission medium such as wire cable, wireless. An effective data communication system depends on the following fundamental characteristics: – Delivery:- the system must deliver data to the correct destination – Accuracy:- the system must deliver the data accurately (no alteration) – Timeliness:- the system must deliver the data in a timely manner – Jitter:-jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. 05/11/2025 Set By Hailemariam W. 3  Data Communication Model The fundamental purpose of a communications system is the exchange of data between two parties General block diagram of a simple communication model 05/11/2025 Set By Hailemariam W. 4  Cont’d… The key elements of the communication model are: – Source:- generates the data to be transmitted Telephones, PCs – Transmitter:- transforms and encodes the information in such a way as to produce electromagnetic signals that can be transmitted across some sort of transmission system. Modem:- transforms digital bit stream into analog signal that is suitable for the transmission media being used – Transmission system:- this is either a single transmission line or a complex network connecting source and destination 05/11/2025 Set By Hailemariam W. 5  Cont’d… – Receiver: The receiver accepts the signal from the transmission system and converts it into a form that can be handled by the destination device. For example, a modem will accept an analog signal coming from a network or transmission line and convert it into a digital bit stream – Destination: Takes the incoming data from the receiver. 05/11/2025 Set By Hailemariam W. 6  Components of Data Communication A data communication system in general has five components 05/11/2025 Set By Hailemariam W. 7  Cont.. Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on. Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. Protocol. A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese. 05/11/2025 Set By Hailemariam W. 8  Data Representation and Data Flow Data Representation – Information in data communication may be in the form of:- text, numbers, image, audio and video Data Flow – Communication between two devices can be: Simplex Half duplex Full duplex (Duplex) 05/11/2025 Set By Hailemariam W. 9  Simplex Simplex is the data transmission mode in which the data can flow only in one direction, i.e., the communication is unidirectional. In this mode, a sender can only send data but can not receive it. Similarly, a receiver can only receive data but cannot send it. For Example, Radio and TV transmission, keyboard, mouse, etc. 05/11/2025 Set By Hailemariam W. 10  Half-Duplex Half-Duplex is the data transmission mode in which the data can flow in both directions but in one direction at a time. It is also referred to as Semi-Duplex. In other words, each station can both transmit and receive the data but not at the same time. When one device is sending the other can only receive and vice-versa. In this type of transmission mode, the entire capacity of the channel can be utilized for each direction. Transmission lines can carry data in both directions, but the data can be sent only in one direction at a time.. 05/11/2025 Set By Hailemariam W. 11  Full-Duplex Full-Duplex is the data transmission mode in which the data can flow in both directions at the same time. It is bi-directional in nature. It is two-way communication in which both the stations can transmit and receive the data simultaneously. Full-Duplex mode has double bandwidth as compared to the half- duplex. The capacity of the channel is divided between the two directions of communication. This mode is used when communication in both directions is required simultaneously. For Example, a Telephone Network, in which both the persons can talk and listen to each other simultaneously. 05/11/2025 Set By Hailemariam W. 12  Data Transfer Mode Synchronous Mode  Synchronous transmission mode is a mode of communication in which bits are sent one after another without any start/stop bits or gaps between them.  In this mode of data transmission, bytes are transmitted as blocks in a continuous stream of bits. Advantages of synchronous data transfer include: Higher data transfer rates: Synchronous transmission can achieve higher data transfer rates compared to asynchronous transmission because it doesn't require start and stop bits between each data byte.  Efficient use of bandwidth: By eliminating the need for start and stop bits, synchronous transmission utilizes bandwidth more efficiently. Better synchronization: ensures precise timing synchronization between the sender and receiver, reducing the likelihood of data errors. 05/11/2025 Set By Hailemariam W. 13  Asynchronous Mode Asynchronous data transfer mode is a method of data transmission where data is sent without a synchronized clock signal. Asynchronous data transfer works: Start bit: Before transmitting each data byte, the sender inserts a start bit, which is always a 0 (low) signal. This signals the beginning of a new character. Data bits: The actual data bits, representing the character being transmitted, are sent after the start bit. The number of data bits per character can vary, typically ranging from 5 to 9 bits, with 8 bits being the most common configuration. Stop bit(s): After the data, stop bits are sent to signal the end of the character. Stop bits are always set to 1 (high) to distinguish them from data bits. The stop bit(s) provide time for the receiver to prepare for the next character. 05/11/2025 Set By Hailemariam W. 14  Cont… 05/11/2025 Set By Hailemariam W. 15  According to the number of bits sent simultaneously in the network: Serial:-is a data transmission mode in which the data bits are sent serially one after the other at a time over the transmission channel. In serial data transmission, the system takes several clock cycles to transmit the data stream. In this mode, the data integrity is maintained, as it transmits the data bits in a specific order, one after the other. This type of transmission mode is best suited for long-distance data transfer, or the amount of data being sent is relatively small. 05/11/2025 Set By Hailemariam W. 16  Cont… Parallel:- Parallel data transmission mode is a mode in which the data bits are sent parallelly at a time. This mode of transmission is used when a large amount of data has to be sent in a shorter duration of time. It is mostly used for short-distance communication. For n-bits, we need n-transmission lines. So, the complexity of the network increases but the transmission speed is high. If two or more transmission lines are too close to each other, then there may be a chance of interference in the data, degrading the signal quality. 05/11/2025 Set By Hailemariam W. 17  What is Computer Networking? Networks: is a set of devices connected by communication links – Networking deals with the technology and architecture of the communications networks used to interconnect communicating devices An interconnection of computers and computing equipment using either wires or radio waves over small or large geographic areas – Two computers are said to be interconnected if they are able to exchange information 05/11/2025 Set By Hailemariam W. 18  Why do we need Networking? Business applications – Resource sharing: the goal is to make all programs, equipment, and especially data available to anyone on the network without regard to the physical location of the resource and the user. Sharing common printer, data/information sharing – Provide a powerful communication medium among employees. email, videoconferencing and others – Help companies in doing business electronically with other companies, especially suppliers and customers. online booking, order online – It is called e-commerce (electronic commerce) 05/11/2025 Set By Hailemariam W. 19  Cont’d… The client and server machines connected by a network 05/11/2025 Set By Hailemariam W. 20  Cont’d… Home Applications – Some of the more popular uses of networking (Internet) for home users are as follows: Access to remote information. Person-to-person communication. Interactive entertainment. Electronic commerce. Mobile Users – Portable office: some one can do activities that he/she is supposed to do from office while walking or driving using portable electronic equipment Example: to send and receive telephone calls, faxes, and electronic mail, surf the Web, access remote files, and log on to remote machines. Social Issues – Exchange messages with like-minded individuals. Example: politics, religion, sport, teaching/learning… etc 05/11/2025 Set By Hailemariam W. 21 05/11/2025 Set By Hailemariam W. 22 Data Encoding & Transmission  Overview Digital and Analog Signals Encoding Techniques Transmission Impairments Transmission Media 05/11/2025 Set By Hailemariam W. 24  Digital and Analog Signals Data transmission occurs between Tx and Rx over some transmission medium (guided or unguided) In any media, communication is in the form of electromagnetic waves All forms of information (voice, video or data) that would be transmitted in any media can be represented by electromagnetic signals. – Depending on the transmission medium & the communication environment either analog or digital signals are used to convey information 05/11/2025 Set By Hailemariam W. 25  Analog Signal – Is one in which the signal intensity varies in a smooth fashion over time. i.e. the signal takes Continuous values in some interval – E.g. voice and video Digital Signal – The signal intensity maintains a constant level for some period of time and then abruptly changes to another constant level. i.e. it takes Discrete values – Sequence of voltage pulses that may be transmitted over a wire medium – e.g. constant positive voltage level represented by 1 and a constant negative voltage level by 0 05/11/2025 Set By Hailemariam W. 26  Data and Signals (Encoding Techniques) A data (analog or digital) can be represented by analog or digital signal. – Digital data can be represented by:- analog or digital signal – Analog data can be represented by:- analog or digital signal Digital data can be represented by digital signals with a different voltage level for the two binary digits. E.g. wired LAN Digital data are represented by analog signal by using a modem (modulator or demodulator) – E.g. the modem converts a series of binary values (voltage pulses) into an analog signal Similarly, analog data can be represented by digital signals – E.g. a codec (coder-decoder) used to represent voice data by digital signals (bit streams) Analog data can also be represented by electromagnetic signals (analog signal) – Analog data are modulated by a carrier frequency to produce analog signal in a different frequency band. E.g. telephone. 05/11/2025 Set By Hailemariam W. 27  Digital Data Analog Signal: ASK, FSK, PSK, All involve altering one or more characteristics of a carrier frequency to represent binary data. Analog data, digital signals: Pulse Code Modulation (PCM) involves sampling analog signal and quantizing Analog Data Analog Signal: Analog data are modulated by a carrier frequency to produce an analog signal in a different frequency band e.g. (AM) (FM) (PM) Digital to Digital : e.g. Unipolar , polar and bipolar (Manchester and differential) 05/11/2025 Set By Hailemariam W. 28  Analog and Digital Signaling of Analog and Digital Data Analog--Digital 05/11/2025 Set By Hailemariam W. 29  Analog and Digital Transmission 05/11/2025 Set By Hailemariam W. 30  Transmission Impairment Signals that are transmitted through any transmission system may not be received perfectly. i.e. the received signal may differ from the transmitted signal due to various transmission impairments:- Such as – Attenuation – Distortion – Noise 05/11/2025 Set By Hailemariam W. 31  Attenuation Attenuation means a loss of energy – When a signal travels through a medium, it loses some of its energy due to the resistance of the medium. – This introduces:- Loss of signal strength (received signal must have sufficient strength so that the electronic circuitry in the receiver can detect the signal) The signal must have a level higher than noise to be received without error The attenuation varies with frequency (the received signal is distorted) To compensate for this loss, amplifiers or repeaters are used to amplify the signal at a regular interval And equalize attenuation across a band of frequencies. i.e. smooth out attenuation effects 05/11/2025 Set By Hailemariam W. 32  Distortion 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 through a medium and, therefore, its own delay in arriving at the final destination. – Delay distortion:-because the received signal is distorted due to varying delays at its constituent frequencies Differences in delay may create a difference in phase. 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. 05/11/2025 Set By Hailemariam W. 33  Noise Noises are unwanted signals that are inserted somewhere between transmission and reception – These are the major limiting factors in communication system performance They may be categorized into:- – Thermal noise:-random motion of electrons (a function of temperature) – Induced noises: due to sources such as motors and appliances – Crosstalk: the effect of one wire on the other (it is an unwanted coupling between signal paths) E.g. it can occur by electrical coupling between nearby twisted pairs – Impulse noise: is a spike (a signal with high energy in a very short duration) that comes from external electromagnetic disturbances such as power lines, lightning, and so on 05/11/2025 Set By Hailemariam W. 34  Distortion Noise Attenuation 05/11/2025 Set By Hailemariam W. 35  Transmission Media A transmission medium can be broadly defined as anything that can carry information from a source to a destination. Transmission media is a pathway that carries the information from sender to receiver. Transmission media can be divided into two broad categories: – Guided Media and – Unguided Media 05/11/2025 Set By Hailemariam W. 36  Guided Media Guided media provide a physical path along which the signals are propagated. These include twisted pair, coaxial cable, and optical fiber. Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current. Optical fiber is a cable that accepts and transports signals in the form of light. 05/11/2025 Set By Hailemariam W. 37  Twisted Pair Cable The oldest, least expensive, and most commonly used media A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together. Highly susceptible to electrical noise, interference, and tapping‘ of the signal as compared to the other guided media It is divided into two – Shielded twisted-pair (STP) – Unshielded twisted-pair (UTP) The wires are twisted in order to avoid cross talk. 05/11/2025 Set By Hailemariam W. 38  Unshielded twisted-pair (UTP) Is the most common twisted-pair cable. Is subjected to external electromagnetic interference, including interference from nearby twisted pair and from noise generated in the environment. The Electronic Industries Association (EIA) has developed standards to classify unshielded twisted-pair cable into six categories (Cat): 05/11/2025 Set By Hailemariam W. 39  Cont… 05/11/2025 Set By Hailemariam W. 40  Shielded Twisted Pair Cable This provides better performance at higher data rates However, it is more expensive and more difficult to work with. It is designed to be used for outdoor connection 05/11/2025 Set By Hailemariam W. 41  Types of Ethernet cables Straight through cable: used to connect two different devices – Router to a hub – Computer to a switch – LAN port to a switch, hub, or computer 05/11/2025 Set By Hailemariam W. 43  Cross over cable: used to connect two devices of the same type without a hub or router – One end of the cable is wired in T568A and the other end of the cable is wired in T568B Computer to a router Computer to a computer Router to a router Switch to a switch Hub to a hub 05/11/2025 Set By Hailemariam W. 44  Cont… Rollover cable: used to connect a device to a router or switch’s console port. also known as a console cable or a Cisco console cable, is a type of serial cable that is used to connect a computer or terminal to the console port of a networking device, such as a router or switch. This cable is commonly used for configuration, troubleshooting, and maintenance purposes. 05/11/2025 Set By Hailemariam W. 45  Connectors The most common UTP connector is RJ45 (RJ stands for registered jack) 05/11/2025 Set By Hailemariam W. 46 How to prepare an Ethernet cable Strip cable end: remove the insulating sheath Untwist wire ends: and straighten them Arrange wires: based on the type of cable needed Trim wires to size: cut wire around half a inch Attach connector: e.g. RJ-45 Crimp: using crimper Test 05/11/2025 Set By Hailemariam W. 47  Strip cable end and untwist wire ends Strip 1 – 1½” of insulating sheath Sort wires by insulation Avoid cutting into conductor colors insulation 05/11/2025 Set By Hailemariam W. 48  Arrange wires Two standards: – TIA/EIA 568A: GW-G OW-Bl BlW-O BrW-Br – TIA/EIA 568B: OW-O GW-Bl BlW-G BrW-Br 05/11/2025 Set By Hailemariam W. 49 Trim wires and attach a connector Maintain wire order, left-to- Trim all wires evenly right, with RJ45 tab facing Leave about ½” of wires downward exposed 05/11/2025 Set By Hailemariam W. 50  Check Do all wires extend to end? Is sheath well inside connector? Sheath is not well inside connector Wires are not extended to end 05/11/2025 Set By Hailemariam W. 51  Crimp, then Test Carefully place the connector into the Crimper and squeeze down the handles tightly 05/11/2025 Set By Hailemariam W. 52  Coaxial Cable Coaxial cable (or coax) carries signals of higher frequency ranges than those in twisted pair cable. To connect coaxial cable to devices, we need coaxial connectors (Bayonet Neill-Concelman (BNC)) BNC connector (most common )- used for TV set, BNC T connector- To branch out Ethernet networks BNC terminator- is used at the end of the cable to prevent the reflection of the signal. 05/11/2025 Set By Hailemariam W. 53  Fiber Optic Cable A fiber-optic cable is made of glass or plastic and transmits signals in the form of light. Optical fibers use reflection to guide light through a channel. The speed of the light depends on the density of the medium through which it is traveling (the higher density, the slower the speed). 05/11/2025 Set By Hailemariam W. 54  Fiber optic connector There are three types of connectors for fiber-optic cables – The subscriber channel (SC) connector is used for cable TV. It uses a push/pull locking system. – The straight-tip (ST) connector is used for connecting cable to networking devices. It uses a bayonet locking system and is more reliable than SC. – MT-RJ is a connector that is the same size as RJ45. 05/11/2025 Set By Hailemariam W. 55  Advantages of Optical fiber Fiber-optic cable has several advantages over metallic cable. – Higher bandwidth. – Less signal attenuation. – Immunity to electromagnetic interference. – Resistance to corrosive materials. – Light weight. Disadvantage: – Installation and maintenance. – Cost 05/11/2025 Set By Hailemariam W. 56  Unguided Media Unguided media, also known as wireless media, refers to the transmission of data through the air or space without the use of physical cables or wires. Unlike guided media, which includes cables like twisted pair, coaxial cable, and fiber optics, unguided media uses electromagnetic waves to transmit data. Some common examples of unguided media include: 1. Radio Waves: Radio waves are commonly used for wireless communication, such as broadcasting radio and TV signals, cellular communication, and Wi-Fi networks. 2. Microwaves: Microwaves are often used for point-to-point communication over long distances, such as in satellite communication and microwave transmission systems. 05/11/2025 Set By Hailemariam W. 57  Cont… 3. Infrared Waves: Infrared waves are used for short-range communication, such as in remote controls, infrared data transmission, and some indoor wireless networks. 4. Light Waves: Light waves are used in optical communication systems, such as free-space optical communication and visible light communication (VLC). Unguided media offer the advantage of mobility and flexibility, allowing devices to communicate wirelessly without the constraints of physical connections. However, they are susceptible to interference from other devices or environmental factors, which can affect signal quality and reliability. Proper security measures, such as encryption and authentication, are essential to protect data transmitted over unguided media from unauthorized access or interception. 05/11/2025 Set By Hailemariam W. 58  Signal propagation Unguided signals can travel from the source to the destination in several ways: – Ground Propagation:-radio waves travel through the lowest portion of the atmosphere, hugging the earth. – Sky propagation:- radio waves radiate upward into the ionosphere where they are reflected back to earth. – Line-of-sight propagation- very high-frequency signals are transmitted in straight lines directly from antenna to antenna. 05/11/2025 Set By Hailemariam W. 59  Frequency bands The frequencies of signals that propagate on the ground or sky or line of site are different and application area varies accordingly 05/11/2025 Set By Hailemariam W. 60  Frequency bands 05/11/2025 Set By Hailemariam W. 61  Quiz One What are the three modes of data communication and briefly explain each of them. Draw the block diagram of a simple data communication model. Give a physical example for each block. What is the device used to convert analog signal in to digital; and digital signal into analog? What are the three transmission impairments? List devices used when preparing twisted pair cable and discuss their purpose? 05/11/2025 Set By Hailemariam W. 62