Comp science notes


Published on

Published in: Education, Technology
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Comp science notes

  3. 3. Introduction to networking data communication Data communication is the transmission of data and information over a communications channel between two devices Communications between computers can be as simple as cabling two computers to the same printer. It can be as complex as a computer at NASA sending messages through an elaborate system of relays and satellites as shown by the animation in the next slide. A network is collection of computing devices connected in order to communicate and share resources. Connections between the devices can be physical using wires or cables or wireless using radio waves or infrared signals.
  4. 4. Communication systems
  5. 5. Data and data signals Data/ information are entities that convey meaning within a computer or computer system. In data communication, the two terms means the same. Data can be transmitted over physical or wireless media. To be transmitted it must first be converted into a signal. Signals are the electric or electromagnetic encoding of data and are used to transmit data. signals can be analog or digital. Data Signals can be analog or digital. Analog signals have an infinite number of values in a range represented using sine wave while digital signal is discrete, discontinuous voltage pulses represented using square wave
  6. 6. Analog signal
  7. 7. Digital signal
  8. 8. Forms of information Familiar forms of information carried by data communication are:  Text: Alphabetic characters  Numeric data: Information in the form of numbers,  Graphical data: In the form of pictures or diagram that can be sent by fax machines or computers.  Sound:  Video: Pictures accompanied by sound.  Multimedia: A combination of the different text, video and sound.
  9. 9. Channel A communications channel, also called a communications line or link, is the path that the data follows as it is transmitted from one computer to another Any communications channel has a direction associated with it as shown below.
  10. 10. Channels types
  11. 11. DTE and DCEData Terminal Equipment (DTE): Sources ordestinations of information. Comprises ofcommunications equipment such as terminals, hostcomputer, printer etc.Data Circuit Terminating Equipment (DCE): Made upof interface devices such as the modem, switches,routers etc. Mediu m DT DC DC DT E E E E Sourc Interfa Sour Destinati e ce ce on
  12. 12. Data communications interfacing
  13. 13. Illustration of DTE-DCE setupDTE-computer DCE-modems DTE-computer
  14. 14. Types of networks LAN (Local Area Network)Network in small geographical Area (Room, Building or a Campus) MAN (Metropolitan Area Network)Network in a City WAN (Wide Area Network) Network spread geographically (Country or across Globe)
  15. 15. Benefits of Networks Resource Sharing  Hardware (computing resources, disks, printers)  Software (application software) Information Sharing  Easy accessibility from anywhere (files, databases)  Search Capability (WWW) Communication  Email  Message broadcast Remote computing
  16. 16. Networks topologies Computer network Topology refers to the physical layout of the network devices and cabling and how all the components communicate with each other. There are four basic types of computer network topologies:  mesh,  bus,  ring,  star
  17. 17. Common Topologies Physical layout of network devices Four types: mesh, bus, ring, and star Lesson 3—Networking BASICS 17
  18. 18. Mesh Topology A mesh topology is also called a point-to- point topology. Each device is connected directly to all other devices on the network. A mesh topology is sometimes used in a wide area network (WAN) setting to ensure that all the sites continue to transmit in the event of a cable failure or another similar problem. Mesh topologies are rarely used in a LAN. Lesson 3—Networking BASICS 18
  19. 19. Mesh Topology Lesson 3—Networking BASICS 19
  20. 20. Bus Topology The most common type of multipoint topology is a bus topology. A computer network bus topology is characterized by one starting point and one ending point. A bus network topology works well for smaller networks and is inexpensive to install. However, it can become slow when more devices are added to the network Lesson 3—Networking BASICS 20
  21. 21. Bus Topology Lesson 3—Networking BASICS 21
  22. 22. Ring Topology It is a circular with no ends. Packets are sent from one device to the next. It does not slow down as more devices are added. Lesson 3—Networking BASICS 22
  23. 23. Ring Topology Lesson 3—Networking BASICS 23
  24. 24. Star Topology A star topology describes a network in which all the devices are connected to a central device known as a hub, which is responsible for receiving and forwarding packets to other devices on the network. Because everything is centralized in a star topology, it is the easiest topology to manage and troubleshoot Lesson 3—Networking BASICS 24
  25. 25. Star Topology Lesson 3—Networking BASICS 25
  26. 26. Hybrid Topologies They are variations of two or more topologies. Star bus – used to connect multiple hubs in a star topology with a bus. Star ring – wired like star, but functions like a ring. Lesson 3—Networking BASICS 26
  27. 27. Transmission MediaCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  28. 28. Data transmission• A communication link is established by using physical or wireless medium. In most cases it is a pair of electric conductors, fiber optic cables or using electromagnetic waves on the free space.• Thus media are roughly grouped into guided or unguided media.
  29. 29. Classes of transmission media
  30. 30. GUIDED MEDIAGuided media, are those that provide a conduit (physicalconnection) from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.Three categories of guided mediaTwisted-Pair CableCoaxial CableFiber-Optic Cable
  31. 31. Twisted Pair Cables• The oldest and still most common transmission medium is twisted pair.• Consists of two insulated copper wires twisted together.• Can be used for either analog or digital transmission.• Twisting reduces the effects of the external interferences.• Common applications are the telephone system and Local Area Network of computers.
  32. 32. Unshielded Twisted Pair (UTP) Cables• The commonly used UTP cables are categorized as CAT 3, CAT 5 and CAT 5e.
  33. 33. Coaxial Cables• The construction and shielding of the coaxial cable give it a good combination of high bandwidth and noise immunity.• The energy loss due to skin effect is also minimized.
  34. 34. Coaxial Cable Center conductor Dielectric Braided material Outer outer cover conducto rCopyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 3.39
  35. 35. Optical fiber • A unidirectional optical transmission system has three components ; light source, transmission medium and detector. • The light source works such that a pulse of light indicates “1” and absence of light indicates “0”. • The detector at the receiving end generates an electric pulse when light falls on it.
  36. 36. Optical Transmission Ctd.• Optical Transmission is based on the theoretical principle called Total Internal Reflection in physics.Light Source Total Internal Reflection • A light ray incident at or above the critical angle is trapped inside the fiber.
  37. 37. Fibre cable structureCore -- a very narrow strand of high quality glass.Cladding -- again, made from high quality glass,with a slightly different index of refraction of thecore.Buffer/outer jacket -- usually constructed fromplastic
  38. 38. Figure 7.14 Fiber construction
  39. 39. Comparison of Fibre Optics & Copper Wire •Fiber has many advantages. • Higher Bandwidth • Low attenuation • Not affected by electromagnetic interferences. • Not affected by corrosive chemicals. • Lighter in weight • Secured from wiretappers. •Do not induce high voltages when lightening takes place.
  40. 40. UNGUIDED MEDIA: WIRELESSUnguided media transport electromagnetic waveswithout using a physical conductor. This type ofcommunication is often referred to as wirelesscommunication.Topics discussed in this section:Radio WavesMicrowavesInfrared
  41. 41. Figure 7.19 Wireless transmission waves
  42. 42. Broadcast Radio Description of broadcast radio antennas  Omnidirectional  Antennas not required to be dish-shaped  Antennas need not be rigidly mounted to a precise alignment Applications  VHF and part of the UHF band; 30 MHZ to 1GHz  Covers FM radio and UHF and VHF television  Cellular telephony  Wireless LANs
  43. 43. Microwaves• Above 100MHz, the waves travel in straight lines and can therefore be narrowly focused.• Parabolic antennas are used.• Microwaves do not pass through buildings well.• Used to establish links when laying physical cables are very expensive or impracticable.• Satellite communications.
  44. 44. Figure 7.21 Unidirectional antennas
  45. 45. Terrestrial Microwave Parabolic dish Narrow beam – line of sight on towers to avoid obstacles Series of towers for long distance Applications:  Long haul telephone  Voice and TV  Short point to point between buildings Main Source of loss  Attentuation – especially with rainful  Repeaters or amplifiers 10 to 100km  Interference with overlapping bands
  46. 46. Satellite Microwave It is essentially a microwave relay station Uplink  Receives transmission on one frequency Downlink  Transmits on a second frequency Operates on a number of frequency bands known as transponders Point to Point  Ground station to satellite to ground station Multipoint  Ground station to satellite to multiple receiving stations
  47. 47. Infrared Description of broadcast radio antennas  Transmitters/receivers (transceivers) modulate non- coherent infrared light  Transceivers must be within line-of-sight of each other either directly or via reflection  Unlike microwave, infrared does not penetrate walls Applications  Small LANs  Short point-to-point connections