9 Figure 3.2 Real-world bus topology Note: Topologies are diagrams. Compare to electrical circuit diagram. Real network cabling does not go in perfect circles or perfect straight lines.Figure Real-world bus topology
10 Data flow Bus topology Ring Topology Data flows from each computer onto the busTermination required at ends to prevent data reflectionRing TopologyData flows from one computer to next one in circleNo end of cable and no need for termination
11 Figure 3.3 Terminated bus topology Note: Termination prevents reflection. Consider briefly discussing this concept.Figure 3.3 Terminated bus topology
12 Figure 3.4 Ring topology moving in a certain direction
13 Problem with Bus and Ring Entire network stops working if the cable is broken at any point.
14 Figure 3.5 Nobody is talking! 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.Figure 3.5 Nobody is talking!
15 Star Star topology has a central connection for all computers Fault tolerance – benefit over bus and ringWas not successful early onMore expensive than bus and ringDifficult to redesign early bus and ring hardwareFault 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.
17 Hybrids Hybrid topology combines topologies Physical topology How cables physically lookSignaling topologyHow the signals travel electronicallyA 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.
18 Star-ring topology Star-bus topology Physical star + signaling ring Ring shrunk down into a hub-like boxCables connect to the hubStar-bus topologyPhysical star + signaling busSegment (bus) shrunk down into a hub-like box
21 Mesh and Point-to-Multipoint Mesh topologyEvery computer connects to every other computer via two or more routesTwo types of mesh topologyPartially-meshed topologyAt least two machines have redundant connectionsFully-meshed topologyEvery computer connects directly to every other computerMost fault tolerant
22 Figure 3.9 Mesh and point-to-multipoint Note:Figure Mesh and point-to-multipoint
23 Figure 3.10 Partially- and fully-meshed topologies 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)/2First, 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.Figure Partially- and fully-meshed topologies
24 Figure 3.11 Comparing star and point-to-multipoint Point-to-multipoint topologyA single system is a common sourceFirst Note on Page 43: Point-to-multipoint topology is sometimes also called star topology, even though technically they differ.Figure Comparing star and point-to-multipoint
25 Figure 3.12 Point-to-Point Two computers connect directlyNo need for a central hubWired or wirelessFigure Point-to-Point
26 Parameters of a Topology Topology is only one feature of a networkOther network featuresWhat is the cable made of?How long can it be?How do machines decide which machine should send data and when?Second Note on Page 43: Make sure you know all your topologies: bus, ring, star, hybrid, mesh, point-to-multipoint, and point-to-point!
27 Network technologyA practical application of a topology, and other technologies that comprise a networkExamples10BaseT1000BaseF10GBaseLXThese technologies are explained in the next two chapters.
29 Figure 3.13 Cutaway view of coaxial cable A central conductor wireSurrounded by an insulating materialSurrounded by a braided metal shieldThe 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.Figure Cutaway view of coaxial cable
30 Outer mesh layer of coaxial cable Shields transmissions from electromagnetic interference (EMI)Figure Coaxial cable showing braided metal shielding
31 Figure 3.15 BNC connector on coaxial cable Coaxial connectors in older networksBayonet-style BNC ConnectorsVampire taps pierced the cableA bit of techie trivia is contained in the Tech Tip on Page 44, which discusses the disputed origins of the term BNC.Figure BNC connector on coaxial cable
32 Figure 3.16 F-type connector on coaxial cable Connecting cable modemsF-type screw-on connectorThe 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.”Figure F-type connector on coaxial cable
33 RG rating for coaxial cable Developed by militaryRG-6 is predominate cable todayRG-59 cable is rarely usedFigure RG-6 cable
34 Coaxial cable Ohm rating Relative measure of resistanceRG-6 and RG-59 are rated at 75 OhmsThe 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.Figure Ohm rating (on an older RG-58 cable used for networking)
37 Twisted Pair Most common network cabling Twisted pairs of cables, bundled togetherTwists reduce crosstalk interferenceNote on Page 46: Have you ever picked up a telephone and heard a distinct crackling noise? That’s an example of crosstalk.
38 Shielded Twisted Pair (STP) Figure 3.21 Shielded twisted pair Shielding protects from electromagnetic interference (EMI)Needed in locations with excessive EMIMost common is IBM Type 1 cableSTP 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.Figure Shielded twisted pair
39 Unshielded Twisted Pair (UTP) Figure 3.22 Unshielded twisted pair Most commonTwisted pairs of wires with plastic jacketCheaper than STPAlso used in telephone systemsFigure Unshielded twisted pair
40 CAT Ratings Category (CAT) ratings are grades of cable ratings Rated in MHzMost common categories are in Table 3.1Spend 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.
41 Rating Frequency Max Bandwidth Status with TIA/EIA Table 3.1 CAT Ratings for UTPCAT MaxRating Frequency Max Bandwidth Status with TIA/EIACAT1 <1 MHz Analog phone lines only No longer recognizedCAT2 4 MHz 4 Mbps No longer recognizedCAT3 16 MHz 16 Mbps RecognizedCAT4 20 MHz 20 Mbps No longer recognizedCAT5 100 MHz 100 Mbps No Longer recognizedCAT5e 100 MHz 1000 Mbps RecognizedCAT MHz Mbps RecognizedTable 3.1The note on Page 47 points out that the CompTIA Network+ exam is only interested in CAT3, CAT5, CAT5e, and CAT6The 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.
42 UTP BandwidthBandwidth is the maximum amount of data that will go through a cable per second100 MHz originally translated to 100 MbpsWith bandwidth-efficient encodingCAT 5e at 100 MHz = 1,000 Mbps max bandwidthCAT 6 at 250 MHz = 10,000 MbpsSpend 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.
43 Using the Correct Cable Figure 3.23 CAT level marked on box of UTP Look on the boxCAT levelFigure CAT level marked on box of UTP
44 Using the Correct Cable Look on the cableCAT levelThe 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.Figure CAT level on UTP
45 Register jack (RJ) connectors RJ-11 (two pairs of wires) for telephonesRJ-45 (four pairs of wires) for networksNote: 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.Figure RJ-11 (top) and RJ-45 (bottom) connectors
46 Fiber-Optic Fiber-optic cable transmits light Not affected by EMI Excellent for long-distance transmissionsSingle copper cable works up to a few hundred metersSingle fiber-optic cable works up to tens of kilometers
47 Composition of Fiber-Optic Core: the glass fiberCladding: reflects signal down the fiberBuffer: gives strengthInsulating jacket: protects inner componentsFigure Cross section of fiber-optic cabling
48 Standardization of Fiber-Optic Two-number designatorCore and cladding measurements62.5/125 μmNote: The symbol µ stands for micro, or 1/1,000,000th.
49 Often used in cable pairs Figure 3.27 Duplex fiber-optic cabling One for sendingOne for receivingCable may be connected together like a lamp cordFigure Duplex fiber-optic cabling
50 Fiber-Optic Light Sources Two possible light sourcesLight Emitting Diodes (LEDs) – called multimodeUsually 850 nm wavelengthLasers – called single-modePrevents modal distortion (a problem with multimode)High transfer rates over long distances1310 or 1550 nm wavelength
51 Fiber-Optic connectors ST: bayonet-styleSC: push-inLC: duplexFrom 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.
52 Figure 3.28 From left to right: ST, SC, and LC fiber-optic connectors 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.Figure From left to right: ST, SC, and LC fiber-optic connectors
53 Other Cables Classic Serial RS-232 recommended standard (RS) Dates from 1969Has not changed significantly in 40 yearsUsually 850 nm wavelengthMost common serial port is 9-pin, male D-subminiature connectorSlow data rates: about 56,000 bpsOnly point-to-point connections
55 Figure 3.30 Parallel connector Up to 2 MbpsLimited to point-to-pointIEEE 1284 committee sets standardsSee the section “Networking Industry Standards—IEEE” later in this chapter.Figure Parallel connector
56 FireWire IEEE 1394 standard Limited to point-to-point Very fast – up to 800 MbpsUnique connectorSee 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.
58 Cable Fire RatingsUnderwriters Laboratories and the National Electrical Code (NEC)Polyvinyl chloride (PVC) rating has no significant fire protectionLots of smoke and fumesPlenum-rated cableLess smoke and fumesCosts three to five times as much as PVC-rated cableRiser-rated cable for vertical runs
60 Institute of Electrical and Electronics Engineers (IEEE) defines standards 802 Working Group began in February of 1980Defines frames, speed, distances, and types of cabling for networksIEEE 1284 committee sets standards for parallel communications
61 Figure 3.32 Parallel cable marked IEEE 1284–compliant See the section “Networking Industry Standards—IEEE” on Page 51.Figure Parallel cable marked IEEE 1284–compliant
62 Table 3.2 IEEE 802 Subcommittees IEEE 802 LAN/MAN Overview & ArchitectureIEEE Higher Layer LAN Protocols802.1s Multiple Spanning Trees802.1w Rapid Reconfiguration of Spanning Tree802.1x Port Based Network Access ControlIEEE Logical Link Control (LLC); now inactiveIEEE Ethernet802.3ae 10 Gigabit EthernetIEEE Token Ring;; now inactiveIEEE Wireless LAN (WLAN); specifications, such as Wi-FiIEEE Wireless Personal Area Network (WPAN)IEEE Broadband Wireless Access (BWA); specification for implementing Wireless Metropolitan Area Network (Wireless MAN); referred to also as WiMaxIEEE Resilient Packet Ring (RPR)IEEE Radio Regulatory Technical Advisory GroupIEEE Coexistence Technical Advisory GroupIEEE Mobile Broadband Wireless Access (MBWA)IEEE Media Independent HandoverIEEE Wireless Regional Area NetworksTable 3.2Tip on Page 52: Memorize the and standards. Ignore the rest.
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