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Computer Communication Networks HINF411 Section 89 Lecture Notes Prepared by: Akram Gasmelseed, Ph.D., CEng, mIEEE Professor of Biomedical Engineering 1st Semester 1445 Instructor Name : Akram Gasmelseed, PhD, CEng, mIEEE Affiliation : Associate Professor, Department of Health Informatics, College...

Computer Communication Networks HINF411 Section 89 Lecture Notes Prepared by: Akram Gasmelseed, Ph.D., CEng, mIEEE Professor of Biomedical Engineering 1st Semester 1445 Instructor Name : Akram Gasmelseed, PhD, CEng, mIEEE Affiliation : Associate Professor, Department of Health Informatics, College of Public Health & Health Informatics, Qassim University Website : http://www.faculty.qu.edu.sa/76555/ http://akram.fke.utm.my E-mail : [email protected] ; [email protected] Breakdown of Assessments and the Grading Weights Assessment type Percentage Time Attendance* - Starting from semester Mid term 30% Week 4 Assignments 10% Starting from Week 2 Presentations 10% Starting from Week 2 Quizzes 10% Starting from Week 2 Final Exam 40 % Total 100% *Attendance References Computer Networks: A Systems Approach: Larry L. Peterson, Bruce S. Davie, Morgan Kaufmann; 4th edition (2007). Computer Networks: Andrew S. Tanenbaum, David J. Wetherall, Prentice Hall; 5th edition (2010) Computer Networking A Top-Down Approach: James F. Kurose, Keith W. Ross, Addison Wesley; 5th edition (2009) Simple Steps to Data Encryption, A Practical Guide to Secure Computing: Peter Loshin; 2013 Elsevier Inc Syllabus OSI model; Internetworking and Routing; TCP/IP; Wireless Communications; Cybersecurity Lab PC/Laptop; Python ; (C-language); Cryptool Software Introduction What is understood by the term ‘communication’? The term communication is defined as the act of disseminating information. It presupposes that: there is information to disseminate the desire or requirement to disseminate exists there is an agency to send/transmit information there is a means of encoding information there is a medium to carry the information there is a recipient to receive the information the recipient is capable of understanding the information received Communication: In a face-to-face conversation between two individuals following takes place: In any communication between two entities the following properties are required: Conversion of brain waves into speech. Modulation Agreement of both individuals on which vocabulary to use. Signal compatibility Agreement of both individuals on volume level at which both can be heard comfortably. Signal strength Agreement of both individuals on the rate of talking at which each can understand the other’s speech. Data rate Agreement of both individuals on the rules used to decide when to speak and when to listen, i.e. how the flow of information is managed. Protocol Conversion of the audio signals into brain waves. Demodulation Communication Model Source : generates data to be transmitted Transmitter : Converts data into transmittable signals Transmission System : Carries data Receiver : Converts received signal into data Destination : Takes incoming data Diagram of Simplified Communication Model: Key Communications Tasks: Transmission System Utilization Interfacing Signal Generation Synchronization Exchange Management Error detection and correction Addressing and routing Recovery Message formatting Security Network Management Simplified Data Communications Model: Basic Elements of a Communication System: In any communication between two entities the following 10 elements can be identified: A Sender. A Receiver. Addressing, to identify where the Receiver is. Protocol – a set of co-operation rules to achieve communication. Transmission code - an agreed “language” to be used. Transmission rate - the speed at which “what is being communicated” is being sent. Transmission synchronisation - how to recognise what is being communicated. Transmission medium. Error detection and correction. Transmission efficiency - how much overhead must be added to manage the transmission. Transmission Media: Two wire -“telegraph wires” seen in old films. Simplest arrangement, with two wires, separated by air. Can pick up interference, and suffer “crosstalk”. Only reliable for low data rates. Twisted Pair - currently used for domestic phones Two insulated wires twisted together. Any interference affects both wires equally. May also have an additional protective screen of metallic foil – “shielded twisted pair”. Suitable for short distance medium speed links. Suffers from “skin effect”, leading to higher resistance at higher data rates. “Skin effect” – HF signals carried only on skin of wire, in effect reducing the area of the wire from a solid wire to a tube of the same diameter. Coaxial cable - commonly seen on TV aerial leads Single central wire, separated from woven outer conductor by plastic insulation. Not prone to interference. Can support medium to high data rates. Optical Fibre Similar to coaxial cable in appearance: Uses single strand of glass as core, with light shield around it. Immune to electrical interference , and difficult to eavesdrop Often used in industrial or other electrically “noisy” environments. Capable of high data rates Mechanically weaker than electrical wires, and difficult to join. Microwaves -ultra high frequency radio waves Line of sight from sender to receiver. No need for wires, so good across rivers, or main roads Extremely high data rates Satellite microwaves: Mainly through space so long lines of sight. Little human interference, but affected by extreme solar activity. Terrestrial microwaves: Need repeater stations if lines of sight short Curvature of earth, or mountains, or buildings Data Transmission Terminology: Transmission may be simplex, half-duplex or duplex. Simplex – in one direction only. Half-duplex – in both directions, but only in one direction at any time. Full-duplex – in both directions simultaneously, if required. Transmission media may be guided or unguided. Guided – the medium is bounded and the transmission contained within it (e.g. fibre-optic or electrical cable) Unguided – the medium is unbounded (e.g. radio waves in the air, or in space). In a direct link, (or data link), a transmission path: Propagates signals directly from transmitter (sender) to receiver With no intermediate devices. except amplifiers (or repeaters) to increase signal strength. In guided transmission media A configuration is point-to-point if it provides a direct link between two devices, and those are the only two devices sharing the medium. A configuration is multipoint, if more than two devices share the same medium. Data Encoding: Encoding means changing how data are represented. This can be for convenience: Morse code alphabet used in early radio transmissions. Encoding to hide the meaning of data is “encryption”. Computer data are represented in an encoded form for storage or transmission within and between computers. The most common codes used to store digital data are: ASCII (American Standards Committee for Information Interchange) EBCDIC (Extended Binary Coded Decimal Interchange Code) Data are transmitted using electromagnetic signals. Data exists in analogue or digital forms. Analogue or digital data can be encoded using either analogue or digital signals. For example digital data can be transmitted using analogue signals. The telephone network traditionally used analogue signals to represent voices. The telephone network was well-established when transmission of digital computer data became necessary. The latter allows normal computer communications using widely available telephone lines. This is achieved using Modems Analog vs. Digital Signal: Data Encoding: Modulation is the conversion of the digital signal into an analogue signal, and demodulation converts the analogue signal back into a digital signal. These processes are carried out by a Modem. Another device used is a Codec (coder-decoder). All transmissions occur within a range of frequencies called the Bandwidth.