Chapter_One of Networking.pdf

Chapter One Introduction to Data Communications and Computer Networks 1 Fundamental of Networking By TW. AMU AMiT FCSE  Outlines  Basics of data communications  Basic compone...

Chapter One Introduction to Data Communications and Computer Networks 1 Fundamental of Networking By TW. AMU AMiT FCSE  Outlines  Basics of data communications  Basic components of communication network  Current and future networks  Fundamentals of Information Transmission Media and Coding  Types of networks [PP &CS]  Basic Data Communication Hardware [NIC, cables, Switch, Router, Hub, Bridge…] Fundamental of Networking By TW.  Basic types of network Topologies:2 AMU AMiT FCSE ring, bus, star, and mesh 2  Introduction  Information: defined as a collection of facts from which conclusions may be drawn is an important resource  The need of information has increased from time to time  leads to the need of sharing of information among different agents  Data communication is the exchange of information between two agents  Old paradigm:  A single powerful computer serving all the needs of an organization  Sneaker-net is Method of sharing data by copying it to a disk and carrying it from computer to computer Fundamental of Networking By TW. 3 AMU AMiT FCSE  Cntd…  New paradigm  Computer networks: a large number of separate (autonomous) but internetworked (being able to exchange information) computers doing the job  Merging of computer and communications technologies – no geographical barrier  Connection(transmission media): copper wire, fiber optics, microwaves, infrared, communication satellites, …  Definition:  A computer network is an interconnected collection of autonomous Fundamental of Networking By TW. computers. AMU AMiT FCSE 4  Cntd…  Interconnected meaning two computers have the ability to exchange information using some transmission media.  Autonomous meaning where no one computer controls any other computer (i.e. no computer can forcibly start or stop another computer)  Computers can be PC’s, workstations and other “specialized” computers such as hubs, switches and routers  The computers can be geographically located anywhere Fundamental of Networking By TW. AMU AMiT FCSE 5  Overview of Data Communications  A data communication system has 5 components 1. Message: the information to be communicated (text, numbers, pictures, sound, video - or combinations) 2. Sender: the device source of information- computer, video camera, … 3. Receiver: the device destination of the inforamtaion 4. Medium: the physical path by which a message travels from sender to receiver 5. Protocol: the set of rules that govern data communications; an agreement between the communicating devices. Fundamental of Networking By TW. 6 AMU AMiT FCSE  Communication Model  The key elements of the model are:  Source: This device generates the data to be transmitted; examples are telephones and personal computers.  Transmitter: transforms and encodes the information in such a way as to produce electromagnetic signals.  Transmission System: This can be a single transmission line or a complex network connecting source and destination.  Receiver: The receiver accepts the signal from the transmission system and converts it into a form that can be handled by the destination device. Fundamental of Networking By TW.  Destination: Takes the incoming data AMU AMiTfromFCSEthe receiver 7  Cntd… Communication Model Fundamental of Networking By TW. AMU AMiT FCSE 7  Some Key Of Communications Tasks  Transmission System Utilization: the need to make efficient use of transmission facilities that are typically shared among a number of communicating devices  Multiplexing  Congestion control techniques  Signal Generation: The properties of the signal  capable of being propagated through the transmission system  Interpretable as data at the receiver  Error detection and correction: In all communications systems, there is a potential for error that should be detected and corrected. Fundamental of Networking By TW. 9 AMU AMiT FCSE  Cntd…  Addressing and routing: a source system must somehow indicate the identity of the intended destination  A specific route must be chosen from many alternative routes  Flow control: required to assure that the source does not overwhelm the destination by sending data faster than they can be processed and absorbed  Protocols: Rules that govern data communication, including error detection, message length, and transmission speed  Attenuation: Loss of power in a signal as it travels from the sending device to the receiving device Fundamental of Networking By TW. 10 AMU AMiT FCSE  Network Categories  Based on size, ownership, the distance it covers  Local Area Network (LAN): usually privately owned and links devices in a single office, building or campus.  Wide Area Network (WAN): covering large geographic area; may utilize public, leased, or private communications equipment Fundamental of Networking By TW. AMU AMiT FCSE 10  Cntd…  Metropolitan Area Network (MAN): designed to extend over an entire city; it may be a single network or interconnected LANs  Personal Area Network (PAN): meant for one person. e.g. a wireless network connecting a computer with its mouse, keyboard and printer. Fundamental of Networking By TW. 12 AMU AMiT FCSE  Cntd …  Network Architecture: includes the type of computers on the network and determines how network resources are handled.  Two common types (Peer to Peer and Client to Server) A. Peer-to-peer: Each node considered as equal in terms of resource sharing and responsibilities  pros  Cons  Easy to set up  Only < 10 nodes  Less expensive  Demands moderate level of skill to  Very low level of security administer  Performance suffers when a  User is able to control their own Fundamental of Networking By TW. resources AMU AMiT FCSE computer is accessed 12  Cntd…  Peer-to-peer networks are good choices for environments where:  There are 10 users or fewer  Users share resources, such as printers, but no specialized servers exist  Security is not an issue  The organization and the network will experience only limited growth within the foreseeable future Fundamental of Networking By TW. 14 AMU AMiT FCSE  Cntd… B. Client to Server Model: the client request for a service and the server deliver the resource(resourceful).  Consists of a group clients connected to a server  Server – with more RAM, larger hard disk, more processing power… Fundamental of Networking By TW. 15 AMU AMiT FCSE  Cntd… Servers in networking 1. File and Print Servers: File and print servers manage user access and use of file and printer resources. 2. Application Servers: Application servers make the server side of client/server applications, as well as the data, available to clients.  an application server differs from a file and print server. With a file and print server, the data or file is downloaded to the computer making the request. With an application server, the database stays on the server and only the results of a request are downloaded to the computer making the request. Fundamental of Networking By TW. 16 AMU AMiT FCSE  Cntd… 3. Mail Servers: Mail servers operate like application servers in that there are separate server and client applications, with data selectively downloaded from the server to the client. 4. Fax Servers: Fax servers manage fax traffic into and out of the network by sharing one or more fax modem boards. 5. Directory Services Servers: Directory services servers enable users to locate, store, and secure information on the network. Fundamental of Networking By TW. 17 AMU AMiT FCSE  Network Topology  Topology refers to the way in which multiple devices are interconnected via communication links.  There are two types of topology: physical and logical.  Physical Topology  Refers to the way in which a network is laid out physically  Refers to the arrangement or physical layout of computers, cables, and other components on the network  Can be referred as Physical layout, Design, Diagram, Map  Two or more devices connect to a link; two or more links form a topology  Logical topology: is bound to network protocols and describe how data is Fundamental of Networking By TW. 18 moved across the network AMU AMiT FCSE  Cntd…  A network's topology affects its capabilities  The choice of one topology over another will have an impact on:  The types of equipment that the network needs  The growth of the network – scalability  The way the network managed  Four basic topologies are possible: bus, star, ring, mesh, and hybrid Fundamental of Networking By TW. AMU AMiT FCSE 19  Cntd… 1. Bus: multipoint (one long cable acts as a backbone to link all the devices in the network)  Advantages Easy to connect a computer or peripheral to a bus. Requires less cable length than a star topology.  Disadvantages  Entire network shuts down if there is a break in the main cable.  Terminators are required at both ends of the backbone cable.  Difficult to identify the problem if the entire network shuts down.  Not meant to be used as a stand-alone solution in a large building. Fundamental of Networking By TW. AMU AMiT FCSE 20  Cntd… 2. Star: each device has a dedicated point-to-point link only to a central controller, usually called a Concentrator  Advantages  robust; a failure of a link has no effect on others  fault identification and isolation are easy  less expensive than mesh (but more expensive than others)  Disadvantage  Single point of failure  Requires more cable length than a linear topology  More expensive than linear bus topologies because of the cost of the concentrators. Fundamental of Networking By TW. 21 AMU AMiT FCSE  Cntd… 3. Ring: each device has a dedicated point-to-point connection only with the two devices on either side of it. a signal is passed along the ring in one direction, from device to device, until it reaches its destination each device incorporates a repeater Fundamental of Networking By TW. AMU AMiT FCSE 22  Cntd… 4. Mesh: every device has a dedicated point-to-point link to every other device every device must have n-1 I/O ports  Advantages  no traffic problem  robust; a failure of a link has no effect on others  privacy or security  fault identification and isolation are easy  Disadvantages: amount of cabling and I/O ports needed (expensive) 5. Hybrid topology: A combination of two network topologies.  E.g. star and bus Fundamental of Networking By TW. AMU AMiT FCSE 23  Internetworking  Interconnection among or between public, private, commercial, industrial, or governmental networks Called also internet  Three variants  Intranet  Extranet  Internet  internet  Intranet: a set of networks that is under the control of a single administrative entity  Internet: Global network of networks  worldwide interconnection of networks  internet –refers to bridged network in general  Extranet: is a private network similar to an intranet, but typically open to external Fundamental of Networking By TW. parties, such as business partners, suppliers, AMU AMiT FCSE key customers, etc 24  Mode of transmission  refers to the direction of signal flow between two linked devices  It can be  Simplex: unidirectional, only one of the devices can transmit E.g. TV transmission, radio  Half-duplex: both can transmit and receive, but not at the same time E.g. wireless handset (walkie -Talkie)  Full-duplex: both can transmit and receive at the same time E.g. Telephone transmission Fundamental of Networking By TW. 25 AMU AMiT FCSE  Transmission media  Is a physical media that carries a signal from the transmitter to the receiver  The information or signal transmitted from one device to another is through electromagnetic signals.  Electromagnetic signals include power, voice, radio, waves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays.  These signals can travel through vacuum, air or any other transmission medium  The measurement of the quantity of data that can be passed down(transmitted) a communication link in a given time is done in terms of bandwidth (bits per second). Fundamental of Networking By TW. 26 AMU AMiT FCSE  Cntd…  Two basic categories  Guided  Unguided  Guided: uses a cabling system that guides the signals along a specific path. E.g. Fiber Optics, Twisted Pair, Coaxial Cable etc.…  Unguided: consists of a means for the data signals to travel but nothing to guide them along a specific path - wireless. E,g., Radio wave, Satellite, etc. Fundamental of Networking By TW. 27 AMU AMiT FCSE  Types of connection  Point-to-point: provides a dedicated link between two devices  Multipoint: more than two devices share (spatially -simultaneously -or temporally by taking turns) a single link  Direct link: signals propagate directly from transmitter to receiver  No intermediate devices other than amplifiers or repeaters  This can apply to both guided and unguided medium Fundamental of Networking By TW. 28  Indirect link: Systems connected through a switched communication network AMU AMiT FCSE  Uses of Computer Networks a. Business applications  for resource sharing including programs, equipment, data (mostly databases on central servers), …  a communication medium – e-mail, writing a report together by making changes on an online document  videoconferencing – to hold meetings by hearing and seeing each other  electronic business  business to business - placing orders, …  business with consumers, usually called e-commerce – home shopping Everything: government, commercial companies, … Fundamental of Networking By TW. 29 AMU AMiT FCSE  Fundamental of information transmission media $ Encoding  Data transmission occurs between transmitter and receiver over some transmission me dium  Transmission media may be classified as guided or unguided  In both cases communication is in the form of electromagnetic waves  The successful transmission of data depends on  the quality of the signal being transmitted  the characteristics of the transmission medium Fundamental of Networking By TW. 30 AMU AMiT FCSE  Cntd… Fundamental of Networking By TW. 31 AMU AMiT FCSE  Analog and digital data representation  In transmitting data from a source to a destination:  the nature of the data  the transmission media used to propagate the data  what processing or adjustments may be required along the way to assure that the received data are understandable  Generally whether we are dealing with analog or digital entities  The term analog and digital correspond, roughly to continuous and discrete respectively Data: Entities that convey meaning can be i. analog: data take on continuous values on some interval, i.e. continuously varying patterns of intensity. E.g. Audio, video, temperature, etc Fundamental of Networking By TW. ii. Digital: data take on discrete values. AMU AMiT E.g. FCSE text or character strings 32  Cntd… Signals: Electric or electromagnetic representations of data  Can be also digital or analog  analog signal is a continuously varying electromagnetic wave that may be propagated over a variety of media.  Three important characteristics: Amplitude, Frequency, Phase  Frequency Spectrum of a signal is the collection of all component frequency  Bandwidth of a signal is the range of component frequencies or the width of the frequency spectrum  Amplitude: The value of the signal at any point. measured in volts, amperes, or watts Fundamental of Networking By TW. 33 AMU AMiT FCSE  Cntd… Fundamental of Networking By TW. 34 AMU AMiT FCSE  Cntd… Frequency : The number of periods in one second Period : the amount of time, in seconds, a signal needs to complete one cycle. Period and frequency have inverse relationship. Fundamental of Networking By TW. 35 AMU AMiT FCSE  Cntd… Phase: The position of the waveform relative to time zero Fundamental of Networking By TW. 36 AMU AMiT FCSE  Cntd…  A digital signal is a sequence of voltage pulses that may be transmitted over a wire medium  Bit Interval: the time required to send a single bit  Bit rate: the number of bit intervals per second usually expressed in bits per second (bps)  Signaling is the physical propagation of the signal along a suitable medium Transmission  Communication of data by propagation and processing of signals  The way signals are treated is a function of the transmission system  Analog transmission is a means of transmitting analog signals without regard to their c ontent the signals may represent analog data (e.g., voice) )  Digital transmission, in contrast, is concerned with the content of the signal. Fundamental of Networking By TW. 37 AMU AMiT FCSE  Cntd…  Which is the preferred method of transmission?  Digital transmission is preferable  The reasons are  Digital technology are:  Continuing to drop in cost and size  Analog equipment has not shown a similar drop  Data integrity  With the use of repeaters the effect of noise and other signal impairments are not cumulative (increasing)  Capacity utilization  High degree of multiplexing  Security and privacy  Encryption techniques can be readily applied to digital data and to analog data that have been digitized Fundamental of Networking By TW. 38 AMU AMiT FCSE  Transmission Impairments  Signal received may differ from signal transmitted  Analog - degradation of signal quality  Digital - bit errors  A binary 1 is transformed into a binary 0 and vice versa  Caused by  Attenuation and attenuation distortion  Delay distortion  Noise  Solution  Amplifiers – analog signal  Repeaters – digital signal Fundamental of Networking By TW. 39 AMU AMiT FCSE  Cntd… Attenuation: it is a phenomenon which occurs when signal strength falls off with distance  It depends on medium, such as Fiber optic cables carries signal without attenuation up to 2Km.  In communicating entities, received signal strength:  must be enough to be detected  must be sufficiently higher than noise to be received without error Delay Distortion: this distortion can only occur in guided media  Propagation velocity varies with frequency  various frequency components of a signal will arrive at the receiver at different Fundamental of Networking By TW. times AMU AMiT FCSE 40  Cntd… Noise: additional signals inserted between transmitter and receiver is known as noise  Noises can be caused by  Thermal: Due to thermal worry of electrons in a conductor  Crosstalk: A signal from one line is picked up by another  Impulse Noise : is sharp quick spikes on the signal caused from electromagnetic interference, lightning, sudden power switching, electromechanical switching, etc  inter-modulation noise means a noise may occurred during changing from digital to analog or from analog to digital. Fundamental of Networking By TW. 41 AMU AMiT FCSE  Signal vs data  Analog signals can represent analog and digital data and digital signals can represent digital as well as analog data  Analog data are a function of time and occupy a limited frequency spectrum.  Such data can be represented by an electromagnetic signal occupying the same spectrum  Digital data can be represented by digital signals  Different voltage level for each of the two binary digits is used  Digital data can also be represented by analog signals  Using modem  Analog data can be represented by digital signals  Using codec Fundamental of Networking By TW. 42 AMU AMiT FCSE Analog Signals Carrying Analog and Digital Data Fundamental of Networking By TW. 43 AMU AMiT FCSE Digital Signals Carrying Analog and Digital Data Fundamental of Networking By TW. 44 AMU AMiT FCSE  Encoding and Modulation Techniques Encoding: the process of preparing data for efficient and accurate transmission Modulation: the process of encoding a baseband source signal Sm (t) onto a carrier signal Four combinations  Digital data, digital signal  Analog data, digital signal  Digital data, analog signal  Analog data, analog signal Fundamental of Networking By TW. 45 AMU AMiT FCSE  Digital Data, Digital Signal: A digital signal is a sequence of discrete, discontinuous voltage pulses  Each pulse is a signal element.  Binary data are transmitted by encoding each data bit into signal elements E.g. binary 0 is represented by -5V and binary 1 by +5V  At the receiving end the receiver:  must know the timing of each bit. That is, the receiver must know with some accuracy when a bit begins and ends  must determine whether theFundamental signal level for each bit position is high (1) or low (0) of Networking By TW. 46 AMU AMiT FCSE  Cntd…  Success factors:  the signal-to-noise ratio  the data rate  the bandwidth  The encoding scheme that can be used can also improve performance  Encoding schemes 1) Non-return to Zero /NRZ  NRZ-L  NRZ-I 2) Bi-phase  Manchester  Differential Manchester 3) Return to Zero (RZ) (reading Assignment) Fundamental of Networking By TW. 47 AMU AMiT FCSE  Cntd…. NRZ: Uses two different voltage levels (one positive and one negative) as the signal elements for the two binary digits  E.g. Absence of voltage for zero, constant positive voltage for one  More often, negative voltage for one value and positive for the other  Two Variants  NRZ-L  NRZ-I NRZ-L: Digital 1s are represented as one voltage (amplitude), while digital 0s are represented as another:  Cheap to implement  Check for voltage of each bit  A long series of 1s or 0s produces a flat,of unchanging Fundamental voltage level (produces synchronization Networking By TW. 48 problems) AMU AMiT FCSE  Cntd…. NRZ-I: Digital 1s are represented by a voltage change (high-to-low, or low-to-high), while 0s are represented as a continuation of the same voltage level:  1  existence of a signal transition at the beginning of the bit time (either a low-to-high or a high-to-low transition)  0  no signal transition at the beginning of the bit time  Even cheaper to implement (only check for changes)  A long series of 0s produces a flat, unchanging voltage level Fundamental of Networking By TW. 49 AMU AMiT FCSE  Cntd…. NRZ Pros and Cons Pros  Easy to engineer  Make good use of bandwidth Cons  dc component  Lack of synchronization capability  Used for magnetic recording  Not often used for signal transmission Fundamental of Networking By TW. 50 AMU AMiT FCSE  Biphase Manchester  Transition in middle of each bit period  Transition serves as clocking  Low to high represents one  High to low represents zero  Used by IEEE 802.3 Used in 802.3 baseband coaxial cable and carrier sense multiple acess / collision detection (CSMA/CD) twisted pair. Differential Manchester  Mid bit transition is clocking only  Transition at start of a bit period represents zero  No transition at start of a bit period represents one Note: this is a differential encoding scheme  Used by IEEE 802.5  Used in 802.5 (token ring)Fundamental with twisted pair.By TW. of Networking 51 AMU AMiT FCSE  Biphase Fundamental of Networking By TW. 52 AMU AMiT FCSE  Digital Data, Analog Signals  The most familiar use of this transformation is for transmitting digital data through the public telephone network using modem  Basis for analog signaling is a continuous, constant-frequency signal known as the carrier frequency.  Digital data is encoded by modulating one of the three characteristics of the carrier: amplitude, frequency, or phase or some combination of these.  there are three basic encoding or modulation techniques  Amplitude-shift keying (ASK)  Frequency-shift keying (FSK)  Phase-shift keying (PSK) Fundamental of Networking By TW. 53 AMU AMiT FCSE  Cntd…  Amplitude-shift keying (ASK): the two binary values are represented by two different amplitudes of the carrier frequency – one of the amplitudes is zero the other with value one  Frequency-shift keying (FSK): the two binary values are represented by two different frequencies near the carrier frequency Fundamental of Networking By TW. 54 AMU AMiT FCSE  Analog Data, Digital Signals  To send continuous data such as voice information over a digital transmission medium  Example: To transfer analog voice signals off a local loop to digital end office within the phone system, one uses a codec  The most common technique for using digital signals to encode analog data is Pulse Code Modulation(PCM) Pulse Code Modulation(PCM) Steps  sample the continuous data - to measure the value of the continuous data at equal interval  Each sample is called Pulse  the resulting pulse is quantized - assigned a value  each value is transformed to assign-and-magnitude Fundamental of Networking By TW. binary number 55 AMU AMiT FCSE  Analog Data, Analog Signal  There are two principal reasons  A higher frequency may be needed for effective transmission  Modulation permits frequency-division multiplexing  The principal techniques for modulation using analog data are:  amplitude modulation (AM)  frequency modulation (FM)  phase modulation (PM) Fundamental of Networking By TW. 56 AMU AMiT FCSE  Multiplexing  term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium  to share an expensive resource  multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred  A reverse process, known as demultiplexing, can extract the original channels on the receiver side  The two most basic forms of multiplexing are :  Time-division multiplexing (TDM) –for digital signal  Frequency-division multiplexing (FDM) –for analog signal Fundamental of Networking By TW. 57 AMU AMiT FCSE  Cntd… FDM  The frequency spectrum is divided into frequency bands, with each user having exclusive possession of some band  possible when the useful bandwidth of the transmission medium exceeds the required bandwidth of signals to be transmitted  the frequency-division multiplexing (FDM) used for analog signals.  A number of signals can be carried simultaneously if each signal is modulated onto a different carrier frequency  carrier frequencies are sufficiently separated that the bandwidths of the signals do not overlap Fundamental of Networking By TW. 58 AMU AMiT FCSE  Cntd… TDM  The users take turns, each one periodically getting the entire bandwidth for a little burst of time.  time-division multiplexing (TDM) is used for digital signals  With TDM, there is no inter-modulation noise, whereas we have seen that this is a concern for FDM.  possible when the achievable data rate (sometimes, called bandwidth) of the medium exceeds the data rate of digital signals to be transmitted  Multiple digital signals (or analog signals carrying digital data) can be carried on a single transmission path by interleaving portions of each signal in time. Fundamental of Networking By TW. 59 AMU AMiT FCSE  Data communication hardware Networking hardware  are physical devices that allow hardware on a computer network to communicate and interact with one another  Hub - connecting multiple devices from different stations  cannot filter data (sent to all connected devices)  they do not have intelligence to find out the best path for data packets which leads to inefficiencies and wastage.  Switch -A switch operates in the layer 2, i.e. data link layer of the OSI model.  It is an intelligent network device  It uses MAC addresses to send data packets to selected destination ports.  It uses packet switching technique to receive and forward data packets from the source Fundamental of Networking By TW. 60 AMU AMiT FCSE to the destination device  Data communication hardware … Router - a device used to connect two or more different networks ( two LANs or two WANs).  The routers evaluate the best route from a sender to a receiver.  By perform in a routing protocol to create the network topology  It is layer 3 device of the OSI model Bridge - It combines two LANs to form an extended LAN.  are intelligent devices that allow the passing of only selective packets from them.  only passes those packets addressed from a node in one network to another node in the other network. Fundamental of Networking By TW. 61 AMU AMiT FCSE  Data communication hardware … Repeater - a devices operating at physical layer of the OSI model  It amplify or regenerate an incoming signal before retransmitting it.  It also known as signal boosters. NIC - allows communications between computers connected via local area network (LAN) as well as Internet Protocol (IP).  NIC allows both wired and wireless communications.  NIC is both a physical layer and a data link layer device Cables - the physical medium used to transfer data from one device to another twister pair cable ( Unshielded and shielded twisted pair cable ) coaxial cable ( thin net and think net ) Fundamental of Networking By TW. 62 AMU AMiT FCSE fibler optica cable (Single mode and multimode) End of Chapter One Questionif Any? Fundamental of Networking By TW. 63 AMU AMiT FCSE