Chapter 3 Networking


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  • Note: Topologies are diagrams. Compare to electrical circuit diagram. Real network cabling does not go in perfect circles or perfect straight lines.
  • Note: Termination prevents reflection. Consider briefly discussing this concept.
  • Note: A break in a ring breaks the circuit and stops the data flow. A break in a bus results in broken ends without termination, resulting in reflection of data to computers that are still connected.
  • Fault tolerance refers to a system’s capability to continue functioning even when some part of the system has failed. When bad things happen, a robust or fault-tolerant system continues to operate, at least to some degree.
  • A good way to separate signaling topology from physical topology is to think about an electronic schematic. The schematic shows how everything connects, but does not represent the way the piece of electronics will actually physically appear.
  • Note:
  • Note: The formula to calculate the number of connections in a fully meshed network: if y=the number of computers, then the number of connections = y(y-1)/2 First, define a “connection” as the means of communicating directly between two computers. For a wired mesh network, you can use the term “cable.” Then, have the students calculate the total number of connections needed to make a fully meshed network, given a certain number of computers. Then ask them why the number of connections is significant. They should come to the conclusion that in a wired network, this would require several network cards in each computer. This leads to the point that mesh networks are normally used for wireless networks.
  • First Note on Page 43: Point-to-multipoint topology is sometimes also called star topology, even though technically they differ.
  • Second Note on Page 43: Make sure you know all your topologies: bus, ring, star, hybrid, mesh, point-to-multipoint, and point-to-point!
  • These technologies are explained in the next two chapters.
  • The braided metal shield lessens electromagnetic interference (EMI). EMI will corrupt the signal flowing through the cable causing interference. EMI is caused by things like lights, fans, copy machines, and refrigerators.
  • A bit of techie trivia is contained in the Tech Tip on Page 44, which discusses the disputed origins of the term BNC .
  • The Tip on Page 45 mentions that coaxial cabling is very popular for satellite installations, over-the-air antennas, and some home video devices. Learn more about cable and other Internet connectivity options in Chapter 14, “Remote Connectivity.”
  • The most important aspect of Ohms ratings for network technicians to know is to use the same-rated cables within a network, otherwise you’ll run into data corruption and data loss. Note on Page 45: The Ohm rating of a particular piece of cable describes the characteristic impedance of that cable. Impedance describes a set of characteristics that define how much a cable resists the flow of electricity. This isn’t simple resistance, though. Impedance also factors into things like how long it takes the wire to get a full charge —the wire’s capacitance —and other things.
  • Note on Page 46: Have you ever picked up a telephone and heard a distinct crackling noise? That’s an example of crosstalk.
  • STP is used today for cable that is run in walls and into ceilings, because both areas have other items that can cause extreme EMI, such as lights, heating and air ducts, motors, and so on.
  • Spend time on the term “bandwidth,” giving examples of megabits per second (Mbps) and gigabits per second (Gbps). Bandwidth-efficient encoding only works as long as the cable can handle it. CAT 5e, the lowest level to support this, is an enhanced version of CAT 5 that supports higher speeds.
  • The note on Page 47 points out that the CompTIA Network+ exam is only interested in CAT3, CAT5, CAT5e, and CAT6 The Tech Tip on Page 48 points out that there is also CAT 6a cable, that doubles the bandwidth of CAT 6 to 550 MHz to accommodate 10-Gbps speeds up to 100 meters.
  • Spend time on the term “bandwidth,” giving examples of megabits per second (Mbps) and gigabits per second (Gbps). Bandwidth-efficient encoding only works as long as the cable can handle it. CAT 5e, the lowest level to support this, is an enhanced version of CAT 5 that supports higher speeds.
  • The Try This! On Page 47 is a great practical activity urging the student to go “shopping” for CAT cable to see what ratings are readily available, and to check and compare the pricing between the different grades.
  • Note: The above figure is rotated 90° to the right from the same figure in the book. Therefore, in the book, RJ-11 is on the left, while RJ-45 is on the right.
  • Note: The symbol µ stands for micro, or 1/1,000,000 th .
  • From Tech Tip on page 49: If you want to remember the connectors for the exam, try these: stick and twist for the bayonet-style ST connectors; stick and click for the straight push-in SC connectors; and little connector for the . . . little . . . LC connector.
  • From Tech Tip on page 49: If you want to remember the connectors for the exam, try these: stick and twist for the bayonet-style ST connectors; stick and click for the straight push-in SC connectors; and little connector for the . . . little . . . LC connector.
  • See the section “Networking Industry Standards — IEEE” later in this chapter.
  • See the section “Networking Industry Standards — IEEE” later in this chapter. Per Note on Page 50: Microsoft has removed the ability to network with FireWire in Windows Vista. The Tip on Page 50 points out that students should concentrate on UTP because that is where the hardest CompTIA Network+ exam questions lie. Still, understand coax, STP, and fiber-optic, and be sure to understand the reasons for picking one type of cabling over another. Even though the CompTIA Network+ exam doesn’t test too hard on cabling, this is important information that techs will use in the real networking world.
  • See the section “Networking Industry Standards — IEEE” on Page 51.
  • Tip on Page 52: Memorize the 802.3 and 802.11 standards. Ignore the rest.
  • Chapter 3 Networking

    1. 1. Cabling and Topology Chapter 3
    2. 2. Objectives• Explain the different types of network topologies• Describe the different types of network cabling• Describe the IEEE networking standards
    3. 3. Overview
    4. 4. Three Parts to Chapter 3• Network Topology• Most common standardized cable types• IEEE Committees for network technology standards
    5. 5. Topology
    6. 6. • Network topology – The way that cables and other pieces of hardware connect to one another
    7. 7. Bus and Ring• Bus topology – Single bus cable – Connects all computer in a line• Ring topology – Central ring of cable – Connects all computers in a ring
    8. 8. Figure 3.1 Bus and ring topologies
    9. 9. Figure 3.2 Real-world bus topology
    10. 10. • Data flow – Bus topology • Data flows from each computer onto the bus • Termination required at ends to prevent data reflection – Ring Topology • Data flows from one computer to next one in circle • No end of cable and no need for termination
    11. 11. Figure 3.3 Terminated bus topology
    12. 12. Figure 3.4 Ring topology moving in a certain direction
    13. 13. • Problem with Bus and Ring – Entire network stops working if the cable is broken at any point.
    14. 14. Figure 3.5 Nobody is talking!
    15. 15. Star• Star topology has a central connection for all computers• Fault tolerance – benefit over bus and ring• Was not successful early on – More expensive than bus and ring – Difficult to redesign early bus and ring hardware
    16. 16. Figure 3.6 Star topology
    17. 17. Hybrids• Hybrid topology combines topologies – Physical topology • How cables physically look – Signaling topology • How the signals travel electronically
    18. 18. • Star-ring topology – Physical star + signaling ring – Ring shrunk down into a hub-like box – Cables connect to the hub• Star-bus topology – Physical star + signaling bus – Segment (bus) shrunk down into a hub-like box – Cables connect to the hub
    19. 19. Figure 3.7 Shrinking the ring
    20. 20. Figure 3.8 Shrinking the segment
    21. 21. Mesh and Point-to-Multipoint• Mesh topology – Every computer connects to every other computer via two or more routes• Two types of mesh topology – Partially-meshed topology • At least two machines have redundant connections – Fully-meshed topology • Every computer connects directly to every other computer • Most fault tolerant
    22. 22. Figure 3.9 Mesh and point-to-multipoint
    23. 23. Figure 3.10 Partially- and fully-meshed topologies
    24. 24. • Point-to-multipoint topology – A single system is a common source Figure 3.11 Comparing star and point-to-multipoint
    25. 25. Point-to-Point• Two computers connect directly• No need for a central hub• Wired or wireless Figure 3.12 Point-to-Point
    26. 26. Parameters of a Topology• Topology is only one feature of a network• Other network features – What is the cable made of? – How long can it be? – How do machines decide which machine should send data and when?
    27. 27. • Network technology – A practical application of a topology, and other technologies that comprise a network – Examples • 10BaseT • 1000BaseF • 10GBaseLX
    28. 28. Cabling
    29. 29. Coaxial Cable• A central conductor wire• Surrounded by an insulating material• Surrounded by a braided metal shield Figure 3.13 Cutaway view of coaxial cable
    30. 30. • Outer mesh layer of coaxial cable – Shields transmissions from electromagnetic interference (EMI)Figure 3.14 Coaxial cable showing braided metal shielding
    31. 31. • Coaxial connectors in older networks – Bayonet-style BNC Connectors – Vampire taps pierced the cable Figure 3.15 BNC connector on coaxial cable
    32. 32. • Connecting cable modems – F-type screw-on connector Figure 3.16 F-type connector on coaxial cable
    33. 33. • RG rating for coaxial cable – Developed by military – RG-6 is predominate cable today – RG-59 cable is rarely used Figure 3.17 RG-6 cable
    34. 34. • Coaxial cable Ohm rating – Relative measure of resistance – RG-6 and RG-59 are rated at 75 OhmsFigure 3.18 Ohm rating (on an older RG-58 cable usedfor networking)
    35. 35. • Splitting coaxial cable Figure 3.19 Coaxial splitter
    36. 36. • Extending coaxial cable Figure 3.20 Barrel connector
    37. 37. Twisted Pair• Most common network cabling• Twisted pairs of cables, bundled together• Twists reduce crosstalk interference
    38. 38. Shielded Twisted Pair (STP)• Shielding protects from electromagnetic interference (EMI)• Needed in locations with excessive EMI• Most common is IBM Type 1 cable Figure 3.21 Shielded twisted pair
    39. 39. Unshielded Twisted Pair (UTP)• Most common• Twisted pairs of wires with plastic jacket• Cheaper than STP• Also used in telephone systems Figure 3.22 Unshielded twisted pair
    40. 40. CAT Ratings• Category (CAT) ratings are grades of cable ratings• Rated in MHz• Most common categories are in Table 3.1
    41. 41. Table 3.1 CAT Ratings for UTP CAT Max Rating Frequency Max Bandwidth Status with TIA/EIA CAT1 <1 MHz Analog phone lines only No longer recognized CAT2 4 MHz 4 Mbps No longer recognized CAT3 16 MHz 16 Mbps Recognized CAT4 20 MHz 20 Mbps No longer recognized CAT5 100 MHz 100 Mbps No Longer recognized CAT5e 100 MHz 1000 Mbps Recognized CAT 6 250 MHz 10000 Mbps Recognized
    42. 42. UTP Bandwidth• Bandwidth is the maximum amount of data that will go through a cable per second• 100 MHz originally translated to 100 Mbps• With bandwidth-efficient encoding – CAT 5e at 100 MHz = 1,000 Mbps max bandwidth – CAT 6 at 250 MHz = 10,000 Mbps
    43. 43. Using the Correct Cable• Look on the box CAT level Figure 3.23 CAT level marked on box of UTP
    44. 44. Using the Correct Cable• Look on the cable CAT level Figure 3.24 CAT level on UTP
    45. 45. Register jack (RJ) connectors• RJ-11 (two pairs of wires) for telephones• RJ-45 (four pairs of wires) for networks Figure 3.25 RJ-11 (top) and RJ-45 (bottom) connectors
    46. 46. Fiber-Optic• Fiber-optic cable transmits light• Not affected by EMI• Excellent for long-distance transmissions – Single copper cable works up to a few hundred meters – Single fiber-optic cable works up to tens of kilometers
    47. 47. Composition of Fiber-Optic• Core: the glass fiber• Cladding: reflects signal down the fiber• Buffer: gives strength• Insulating jacket: protects inner components Figure 3.26 Cross section of fiber-optic cabling
    48. 48. Standardization of Fiber-Optic• Two-number designator – Core and cladding measurements – 62.5/125 μm
    49. 49. Often used in cable pairs• One for sending• One for receiving• Cable may be connected together like a lamp cord Figure 3.27 Duplex fiber-optic cabling
    50. 50. Fiber-Optic Light Sources• Two possible light sources – Light Emitting Diodes (LEDs) – called multimode • Usually 850 nm wavelength – Lasers – called single-mode • Prevents modal distortion (a problem with multimode) • High transfer rates over long distances • 1310 or 1550 nm wavelength
    51. 51. Fiber-Optic connectors• ST: bayonet-style• SC: push-in• LC: duplex
    52. 52. Figure 3.28 From left to right: ST, SC, and LCfiber-optic connectors
    53. 53. Other Cables• Classic Serial – RS-232 recommended standard (RS) • Dates from 1969 • Has not changed significantly in 40 years • Usually 850 nm wavelength – Most common serial port is 9-pin, male D-subminiature connector – Slow data rates: about 56,000 bps – Only point-to-point connections
    54. 54. Serial portFigure 3.29 Serial port
    55. 55. • Parallel – Up to 2 Mbps – Limited to point-to-point – IEEE 1284 committee sets standards Figure 3.30 Parallel connector
    56. 56. • FireWire – IEEE 1394 standard – Limited to point-to-point – Very fast – up to 800 Mbps – Unique connector
    57. 57. Figure 3.31 FireWire connector
    58. 58. Cable Fire Ratings• Underwriters Laboratories and the National Electrical Code (NEC) – Polyvinyl chloride (PVC) rating has no significant fire protection • Lots of smoke and fumes – Plenum-rated cable • Less smoke and fumes • Costs three to five times as much as PVC-rated cable – Riser-rated cable for vertical runs
    59. 59. Networking Industry Standards – IEEE
    60. 60. • Institute of Electrical and Electronics Engineers (IEEE) defines standards – 802 Working Group began in February of 1980 • Defines frames, speed, distances, and types of cabling for networks • IEEE 1284 committee sets standards for parallel communications
    61. 61. Figure 3.32 Parallel cable marked IEEE 1284–compliant
    62. 62. Table 3.2 IEEE 802 Subcommittees IEEE 802 LAN/MAN Overview & Architecture IEEE 802.1 Higher Layer LAN Protocols 802.1s Multiple Spanning Trees 802.1w Rapid Reconfiguration of Spanning Tree 802.1x Port Based Network Access Control IEEE 802.2 Logical Link Control (LLC); now inactive IEEE 802.3 Ethernet 802.3ae 10 Gigabit Ethernet IEEE 802.5 Token Ring;; now inactive IEEE 802.11 Wireless LAN (WLAN); specifications, such as Wi-Fi IEEE 802.15 Wireless Personal Area Network (WPAN) IEEE 802.16 Broadband Wireless Access (BWA); specification for implementing Wireless Metropolitan Area Network (Wireless MAN); referred to also asWiMax IEEE 802.17 Resilient Packet Ring (RPR) IEEE 802.18 Radio Regulatory Technical Advisory Group IEEE 802.19 Coexistence Technical Advisory Group IEEE 802.20 Mobile Broadband Wireless Access (MBWA) IEEE 802.21 Media Independent Handover IEEE 802.22 Wireless Regional Area Networks