Data Communication and Networking PDF

I. INTRODUCTION TO DATA COMMUNICATION AND NETWORKING 1. Data and Information Data refers to the raw facts that are collected while information refers to processed data that enables us to take decisions. The word data refers to any information which is presented in a form that is agreed and a...

I. INTRODUCTION TO DATA COMMUNICATION AND NETWORKING 1. Data and Information Data refers to the raw facts that are collected while information refers to processed data that enables us to take decisions. The word data refers to any information which is presented in a form that is agreed and accepted upon by is creators and users. 2. Data Communication Data Communication is a process of exchanging data or information. This process involves a communication system which is made up of hardware and software. The hardware part involves the sender and receiver devices and the intermediate devices through which the data passes. The software part involves certain rules which specify what is to be communicated, how it is to be communicated and when. It is also called as a Protocol. 3. Components of Data Communication A Data Communication system has five components as shown in the diagram below: Components of Data Communication a. Message - the information to be communicated by the sender to the receiver. b. Sender - any device that is capable of sending the data or message. c. Receiver - a device that the sender wants to communicate the data or message. d. Transmission Medium – it is the path by which the message travels from sender to receiver. e. Protocol - it is an agreed upon set or rules used by the sender and receiver to communicate data. (Language of information) 4. Characteristics of Data Communication The effectiveness of any data communications system depends upon the following four fundamental characteristics: a. Delivery - the data should be delivered to the correct destination and correct user. b. Accuracy - the communication system should deliver the data accurately, without introducing any errors. The data may get corrupted during transmission affecting the accuracy of the delivered data. c. Timeliness - data has to be delivered in a timely manner without any delay; such a data delivery is called real time transmission of data. d. Jitter - it is the variation in the packet arrival time. Uneven Jitter may affect the timeliness of data being transmitted. 5. Data Flow Devices communicate with each other by sending and receiving data. The data can flow between the two devices in the following ways. a. Simplex In Simplex, communication is unidirectional. Only one of the devices sends the data and the other one only receives the data. b. Half Duplex In half duplex both the stations can transmit as well as receive but not at the same time. c. Full Duplex In Full duplex mode, both stations can transmit and receive at the same time. Source: Introduction to Data Communication and Networking [archive.mu.ac.in] II. OPEN SYSTEMS INTERCONNECTIONS – OSI MODEL 1. Introduction The Open Systems Interconnection (OSI) model is a reference tool for understanding data communications between any two networked systems. It divides the communications processes into seven layers. Each layer both performs specific functions to support the layers above it and offers services to the layers below it. The three lowest layers focus on passing traffic through the network to an end system. The top four layers come into play in the end system to complete the process. A networking model offers a generic means to separate computer networking functions into multiple layers. Each of these layers relies on the layers below it to provide supporting capabilities and performs support to the layers above it. Such a model of layered functionality is also called a “protocol stack” or “protocol suite”. Protocols, or rules, can do their work in either hardware or software or, as with most protocol stacks, in a combination of the two. The nature of these stacks is that the lower layers do their work in hardware or firmware (software that runs on specific hardware chips) while the higher layers work in software. The Open System Interconnection model is a seven-layer structure that specifies the requirements for communications between two computers. The ISO (International Organization for Standardization) standard 7498-1 defined this model. This model allows all network elements to operate together, no matter who created the protocols and what computer vendor supports them. The main benefits of the OSI model include the following: a. Helps users understand the big picture of networking b. Helps users understand how hardware and software elements function together c. Makes troubleshooting easier by separating networks into manageable pieces d. Defines terms that networking professionals can use to compare basic functional relationships on different networks e. Helps users understand new technologies as they are developed f. Aids in interpreting vendor explanations of product functionality 2. OSI Layers a. Layer 1 – Physical Layer The physical layer of the OSI model defines connector and interface specifications, as well as the medium (cable) requirements. Electrical, mechanical, functional, and procedural specifications are provided for sending a bit stream on a computer network. Typical components of the physical layer include: Cabling system components Adapters that connect media to physical interfaces Connector design and pin assignments Hub, repeater, and patch panel specifications Wireless system components Parallel SCSI (Small Computer System Interface) Network Interface Card (NIC) b. Layer 2 – Data Link The OSI model for Data Link Layer provides a device to access the network to send and receive messages. It also offers a physical address so a device’s data can be sent on the network. The layer functions with a device’s networking software when sending and receiving messages and provides error-detection capability. Common networking components that function at data link layer include: Network interface cards Ethernet and Token Ring switches Bridges c. Layer 3 – Network The network layer of the OSI model provides an end-to-end logical addressing system so that a packet of data can be routed across several layer 2 networks. Note that network layer addresses can also be referred to as logical addresses. Initially, software manufacturers, such as Novell, developed proprietary layer 3 addressing. However, the networking industry has evolved to the point that it requires a common layer 3 addressing system. The Internet Protocol (IP) addresses make networks easier to both set up and connect with one another. The Internet uses IP addressing to provide connectivity to millions of networks around the world. When passing packets between different networks, it may become necessary to adjust their outbound size to one that is compatible with the layer 2 protocol that is being used. The network layer accomplishes this via a process known as fragmentation. A router’s network layer is usually responsible for doing the fragmentation. All reassembly of fragmented packets happens at the network layer of the final destination system. Two of the additional functions of the network layer are diagnostics and the reporting of logical variations in normal network operation. While the network layer diagnostics may be  initiated by any networked system, the system discovering the variation reports it to the original sender of the packet that is found to be outside normal network operation. The variation reporting exception is content validation calculations. If the calculation done by the receiving system does not match the value sent by the originating system, the receiver discards the related packet with no report to the sender. Retransmission is left to a higher layer’s protocol. Some basic security functionality can also be set up by filtering traffic using layer 3 addressing on routers or other similar devices. d. Layer 4 – Transport The transport layer of the OSI model, offers end-to-end communication between end devices through a network. Depending on the application, the transport layer either offers reliable, connection-oriented or connectionless, best-effort communications. Some of the functions offered by the transport layer include: Application identification Client-side entity identification Confirmation that the entire message arrived intact Segmentation of data for network transport Control of data flow to prevent memory overruns Establishment and maintenance of both ends of virtual circuits Transmission-error detection Realignment of segmented data in the correct order on the receiving side Multiplexing or sharing of multiple sessions over a single physical link e. Layer 5 – Session The session layer provides various services, including tracking the number of bytes that each end of the session has acknowledged receiving from the other end of the session. This session layer allows applications functioning on devices to establish, manage, and terminate a dialog through a network. Session layer functionality includes: Virtual connection between application entities Synchronization of data flow Creation of dialog units Connection parameter negotiations Partitioning of services into functional groups Acknowledgements of data received during a session Retransmission of data if it is not received by a device f. Layer 6 – Presentation The presentation layer, is responsible for how an application formats the data to be sent out onto the network. The presentation layer basically allows an application to read (or understand) the message.  Examples of presentation layer functionality include: Encryption and decryption of a message for security Compression and expansion of a message so that it travels efficiently Graphics formatting Content translation System-specific translation g. Layer 7 – Application The application layer provides an interface for the end user operating a device connected to a network. This layer is what the user sees, in terms of loading an application (such as Web browser or e-mail). The application layer is the data the user views while using these applications. Examples of application layer functionality include: Support for file transfers Ability to print on a network Electronic mail Electronic messaging Browsing the World Wide Web Source: OSI Model by Global Knowledge III. NETWORKING CONCEPT Network is an interconnectivity of two or more devices or system for purpose of sharing data. It is a communication mechanism that ties the isolated computer systems into the organization. In a networking environment, being able to communicate and share data encourages continuity and compatibility so that administrative function can be systematized. 1. Protocols in Networking A protocol is a set of rules that govern data communications. It defines what is communicated, how it is communicated, and when it is communicated. Elements of a Protocol a. Syntax - refers to the structure or format of the data, meaning the order in which they are presented. b. Semantics - refers to the meaning of each section. It is the particular pattern to be interpreted, and kind of action to be taken based on that interpretation. c. Timing – it denotes to two characteristics: when data should be sent and how fast they can be sent. 2. Standards in Networking Standards are essential in creating and maintaining an open and competitive market for equipment manufacturers and in guaranteeing national and international interoperability of data and telecommunications technology and processes. Standards provide guidelines to manufacturers, vendors, government agencies, and other service providers to ensure the kind of interconnectivity. Data communication standards fall into two categories: a. De facto (meaning "by fact" or "by convention") Standards that have not been approved by an organized body but have been adopted as standards through widespread use are de facto standards. De facto standards are often established originally by manufacturers who seek to define the functionality of a new product or technology. b. De jure (meaning "by law" or "by regulation") Those standards that have been legislated by an officially recognized body are de jure standards The following standard creation committees provides the general standard organization in networking. a. International Organization for Standardization (ISO). b. International Telecommunication Union-Telecommunication Standards Sector (ITU-T). c. American National Standards Institute (ANSI). d. Institute of Electrical and Electronics Engineers (IEEE). e. Electronic Industries Association (EIA) 3. Types of Network The following types are based on geographical coverage of a network. a. Personal Area Network (PAN) It is the interconnection of information technology devices within the range of an individual person. b. Local Area Network (LAN) It is interconnection that links the devices in a single office, building, or campus. c. Metropolitan Area Network (MAN) It is a network with a size between a LAN and a WAN. It normally covers the area inside a particular large area. d. Wide Area Network (WAN) Provides long-distance transmission of data and information over large geographic areas that may comprise a country, a continent, or even the whole world. 4. Network Topology Network topology refers to the way in which a network is laid out physically. Devices are connected thru a link, and set of links form a topology. The topology of a network is the geometric representation of the relationship of all links and linking devices (usually called nodes) to one another. In determining the system reliability, a network should consider its functionality and flexibility of its network topology. a. Bus Topology The bus topology is also known as linear bus, that consists of a single cable that runs to every work-station or devices. In this topology, all the nodes are connected to the single cable (called bus), by the help of interface connectors. This central cable is the back bone of the network and every devices communicates with the other device through this bus. Advantages: Cheap and easy to implement Require less cable Does not use any specialized network equipment Disadvantage: Network disruption when computers are added or removed A break in the cable will prevent all systems from accessing the network Difficult to troubleshoot b. Ring Topology The ring topology connects computers on a single circle of cable. There are no terminated ends. A ring topology connects one device to the next and the last device to the first. The signal travels around the loop in one direction and pass through each device. Unlike the passive bus topology, each computer acts like a repeater to boost the signal and send it on to the next device. Because the signal passes through each computer, the failure of one computer can impact the entire network. Advantages: Cable faults are easily located, making troubleshooting easier Ring networks are moderately easy to install Disadvantage: Expansion to the network can cause network disruption A single break in the cable can disrupt the entire network. c. Star Topology In the star topology, devices are connected by cable segments to centralized component and device has a dedicated point-to-point link only to a central controller, usually called a hub or switch. Signals are transmitted from the sending device through the hub or switch to all devices on the network and does not allow direct traffic between devices. Advantages: Cable Easily expanded without disruption to the network Cable failure affects only a single user Easy to troubleshoot and isolate problems Disadvantage: Requires more cable A central connecting device allows for a single point of failure More difficult to implement d. Mesh Topology In a mesh topology, every device has a dedicated point-to-point link to every other device. The term dedicated means that the link carries traffic only between the two devices it connects. Advantages: Provides redundant paths between devices The network can be expanded without disruption to current uses Disadvantage: Requires more cable than the other LAN topologies Complicated implementation e. Hybrid Topology Hybrid topology is the integration of two or more different topologies to form a resultant topology which has good consideration on all the constituent basic topologies rather than having characteristics of one specific topology. Advantages: Reliable, scalable, flexible and effective network design due to the comibination of simple topologies Disadvantage: Complexity of design and infrastructure Source: ResearchGate Data Communication & Networking by Yekini Yureni Network Topologies by csl.mtu.edu IV. DATA TRANSMISSION METHOD 1. Analog Data Transmission Analog transmission defines the idea of providing signal in a modulating characteristics. Analog signals are modified to represent analog data, and this conversion is also known as Analog Modulation. Modulation is the basic to the transmission of a message signal over a channel and is defined as the process by which some characteristic of a carrier is varied in accordance with a modulating wave. In analog modulation, the modulating wave consists of an analog message signal and the carrier consists of a sine wave. Techniques of Analog Transmission a. Amplitude Modulation - the amplitude of the carrier signal is modified to reflect the analog data. b. Frequency Modulation - the frequency of the carrier signal is modified to reflect the change in the levels of the modulating signal. c. Phase Modulation - In the modulation technique, the phase of carrier signal is modulated in order to reflect the change in of analog data signal. Digital to Analog Data Conversion a. Amplitude Shift Keying - the amplitude of analog carrier signal is modified to reflect binary data. When binary data represents digit 1, the amplitude is held otherwise it is set to 0. Both frequency and phase remain same as in the original carrier signal. b. Frequency Shift Keying - the frequency of the analog carrier signal is modified to reflect binary data. This technique uses two frequencies. One of them is chosen to represent binary digit 1 and the other one is used to represent binary digit 0. Both amplitude and phase of the carrier wave are kept intact. c. Phase Shift Keying - the phase of the original carrier signal is altered to reflect the binary data. When a new binary symbol is encountered, the phase of the signal is altered. Amplitude and frequency of the original carrier signal is kept intact. 2. Digital Data Transmission Digital communication is defined as the method to transfer information from one place to another using digital signals (binary data). In digital communication system, the signal used to transfer information should be discrete in time and discrete in amplitude. Techniques in Digital Transmission a. Parallel Transmission It is a digital signal transmission in binary data that are organized into groups of n bits and sending of data n bits at a time. This requires set of communication channel for transmission between devices. b. Serial Transmission In serial transmission one bit follows another that only requires one communication channel to transmit data between two communicating devices. Synchronous Transmission This methods send bits one after another without start or stop bits or gaps providing a real-time exchange of data. Asynchronous Transmission This method send thru start bit at the beginning and one or more stop bits at the end of each byte providing gaps between each byte. Reference: Data Communication and Networking by Yekeni N. Asafe, Adebari F. Adebayo, Bello Olalekan Computer Engineering Department, Yaba College of Technology, Lagos Nigeria V. DATA TRANSMISSION MEDIA Transmission media (communication channel) is a pathway that carries the information from sender to receiver. Data is transmitted normally through electrical, electromagnetic signals and frequencies. 1. Transmission Media Classification a. Wired / Guide Media It is a bounded transmission media that are in the form the cables that are tangible or have physical existence and are limited by the physical geography. 4-20 mA HART Fieldbus (Foundation Fieldbus, Profibus, Modbus) Fiber Optics b. Wireless or Unguided Media Transmission Media data signals flows through the air without using cables and not bounded by physical geography. The propagation of signal is thru ground, sky or line of sight to provide communication between devices. Radio Waves and Microwaves Ultrasonic Infrared and Bluetooth 2. Transmission Channel Parameter a. Bandwidth The range of frequencies contained in a composite signal is its bandwidth. The bandwidth is normally a difference between two numbers. The bandwidth of a composite signal is the difference between the highest and the lowest frequencies contained in that signal. The bandwidth determines the channel capacity. b. Bit Rate Bit rate is used to describe digital signals in the form of the number of bits sent in one second, expressed in bits per second (bps). Most digital signals are non-periodic, and thus period and frequency are not appropriate characteristics. Data rate limit is one of the most important consideration in data communications in determining how fast a device can send data, in bits per second over a channel. Data rate depends on three factors: The bandwidth available The level of the signals The quality of the channel (level of noise) c. Bit Length The bit length is the distance one bit occupies on the transmission medium. It is equal to product of the speed of propagation and bit duration. 3. Transmission Media Problem and Impairment Data is transmitted through transmission medium which are not perfect. The imperfection causes signal impairment. Due to the imperfection error is introduced in the transmitted data that can possibly change the sender to receiver. a. Noise Noise is any unwanted signal that is mixed or combined with the original signal during transmission. Due to noise the original signal is altered and signal received is not same as the one sent. Noise is sharp quick spikes on the signal caused from electromagnetic interference, lightning, sudden power switching, electromechanical switching, etc. b. Attenuation Distortion Attenuation results in loss of energy. When a signal travels through a medium, it loses some of its energy in overcoming the resistance of the medium. The electrical energy in the signal may convert to heat and provides distorted signals. c. Crosstalk Crosstalk is when one line induces a signal into another line that can cause severe disruption of the data transfer. Cross talk can be caused by overlapping of bands in a multiplexed system or by poor shielding of cables running close to one another. d. Echo or Signal Return All media have a preferred termination condition for perfect transfer of signal power. The signal arriving at the end of a transmission line should be fully absorbed otherwise it will be reflected back down the line to the sender and appear as an Echo. Reference: Data Communication and Networking by Yekeni N. Asafe, Adebari F. Adebayo, Bello Olalekan Computer Engineering Department, Yaba College of Technology, Lagos Nigeria