1. Cabling and Topology
Chapter 3

2. Objectives Explain the different types of network topologies
Describe the different types of network cabling
Describe the IEEE networking standards

3. Introduction
Every network provides a method of getting data from one system to another
Cabling
Wireless methods
Standards ensure networking equipment works well together

4. Test Specific
Network Topologies

5. Overview of Network Topologies
Network topology
Methods of connecting computers together
Historical topologies
Bus, ring, and star
Modern topologies
Hybrid, mesh, point-to-multipoint, and point-to-point

6. Bus and Ring Topologies
Bus topology
Single bus cable
Connects all computers in a line
Ring topology
Central ring of cable
Connects all computers on the network in a ring

7. Figure 3.1 Bus and ring topologies
Note (p. 43): Note that topologies are diagrams, much like an electrical circuit diagram. Real network cabling doesn’t go in perfect circles or perfect straight lines
Figure Bus and ring topologies

8. Figure 3.2 Real-world bus topology

9. Bus and Ring Topologies (cont’d.)
Bus topology
Data flows from each computer onto the bus
Termination required at ends to prevent signal from reflecting at the ends of the cable
Ring topology
Data flows from one computer to next one in circle
No end of cable and no need for termination

10. Figure 3.3 Terminated bus topology
Note: Termination prevents reflection. Consider briefly discussing this concept. May also discuss attenuation, since bus networks can be used as a good example of this.
Figure 3.3 Terminated bus topology

11. Figure 3.4 Ring topology moving in a certain direction

12. Bus and Ring Topologies (cont’d.)
One problem with bus and ring topologies
Entire network stops working if the cable is broken at any point

13. 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!

14. Star Topology Star topology Star topology has fault tolerance
One central connection for all computers
Star topology has fault tolerance
If one cable breaks, other computers can still communicate
Not successful early on
More expensive than bus and ring
Difficult to redesign early bus and ring hardware
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.

15. Figure Star topology

16. Figure 3.7 Shrinking the ring
Note (p. 45): The most successful of the star ring topology networks was called Token Ring, manufactured by IBM
Figure Shrinking the ring

17. Figure 3.8 Shrinking the segment

18. Hybrid Topology Hybrid topology combines topologies Physical topology
Star-ring topology
Star-bus topology
Eventually won out over star-ring
Physical topology
How cables physically look
Logical (signaling) topology
How signals travel electronically
Exam Tip (p. 45): Most techs refer to the signaling topology as the logical topology today. That’s how you’ll see it on the CompTIA Network+ exam as well.

19. Mesh and Point-to-Multipoint
Wireless network topologies
Mesh topology
Every computer connects to every other computer via two or more routes
Partially meshed topology
At least two machines have redundant connections
Fully meshed topology
Every computer connects directly to every other computer

20. Figure 3.9 Mesh and point-to-multipoint topology
Exam Tip (p. 46): You won’t find partial (or full) mesh networks in an office setting. You’re more likely to see (the former at least) the term used to describe connections among networks over distance, like on a university campus.
Figure Mesh and point-to-multipoint topology

21. Figure 3.10 Partially and fully meshed topologies

22. Mesh and Point-to-Multipoint (cont’d.)
Point-to-multipoint topology
Single system acts as a common source
Requires an intelligent device in the center

23. Figure 3.11 Comparing star and point-to-multipoint technologies

24. Point-to-Point Topology
Two computers connect directly
No need for a central device
Wired or wireless
Figure Point-to-point topology

25. 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?
Exam Tip (p.47): Make sure you know all your topologies: bus, ring, star, hybrid, mesh, point-to-multipoint, and point-to-point!
Note (p. 47): The CompTIA Network+ exam objectives include client/server and peer-to-peer networks in the list of “common network topologies.” I discuss these in Chapter 12, “Advanced Networking Devices.”

26. Network Technologies
A practical application of a topology and other critical technologies
Provides a method to get data from one computer to another
Examples:
10BaseT
1000BaseF
10GBaseLX
These technologies are explained in the next two chapters.

27. Cabling and Connectors

28. Copper Cabling and Connectors
Coaxial cable
Contains a central conductor wire (usually copper)
Insulating material surrounds conductor
Braided metal shield surrounds insulating material
Referred to as coax
Center wire and braided shield share common axis or centerline
Shields transmissions from electro-magnetic interference (EMI)

29. Figure 3.13 Cutaway view of coaxial cable

30. Figure 3.14 Coaxial cable showing braided metal shielding
The braided metal shield lessens electro-magnetic 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 Coaxial cable showing braided metal shielding

31. Coaxial Connectors in Older Networks
Bayonet-style BNC Connectors
Vampire taps pierced the cable
Tech Tip: What’s in a Name? (p. 48)
Techs all around the globe argue over the meaning of BNC. A solid percentage says with authority that it stands for “British Naval Connector.” An opposing percentage says with equal authority that it stands for “Bayonet Neill-Concelman,” after the stick-and-twist style of connecting and the purported inventors of the connector. The jury is still out, though this week I’m leaning toward Neill and Concelman and their bayonet-style connector.
Figure BNC connector on coaxial cable

32. Connecting Cable Modems
F-connector screws on, making a secure connection
Exam Tip (p. 49): Coaxial cabling is also very popular with satellite, over-the-air antennas, and even some home video devices. This book covers cable and other Internet connectivity options in great detail in Chapter 14, “Remote Connectivity.”
Figure F-type connector on coaxial cable

33. Radio Grade (RG) Ratings
Developed by the U.S. military
Ohm rating is the only important measure
RG-6 and RG-59 cables are rated at 75 ohms
Note that RG means “Radio Grade.”
Figure RG-6 cable

34. Figure 3.18 Ohm rating (on an older, RG-58 cable used for networking)
Note (p. 49): The Ohm rating of a particular piece of cable describes the 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 in things like how long it takes the wire to get a full charge—the wire’s capacitance—and more.
Figure Ohm rating (on an older, RG-58 cable used for networking)

35. Splitting Coaxial Cable
Figure Coaxial splitter

36. Extending Coaxial Cable
Figure Barrel connector

37. Twisted Pair Most common network cabling
Twisted pairs of cables, bundled together
Twists reduce crosstalk interference
Two types
Shielded twisted pair
Unshielded twisted pair
Note (p. 50): Have you ever picked up a telephone and heard a distinct crackling noise? That’s an example of crosstalk.

38. Figure 3.21 Shielded twisted pair
Shielding protects from electro-magnetic interference (EMI)
Needed in locations with excessive electronic noise
Most common is IBM Type 1 cable
Figure Shielded twisted pair

39. Unshielded Twisted Pair
Most common
Twisted pairs of wires with plastic jacket
Cheaper than STP
Also used in telephone systems
Cross Check: OSI Seven-Layer and TCP/IP Model (p. 50)
You’ve seen UTP cabling before when Dana accessed documents on Janelle’s PC at MHTechEd. Refer to Chapter 2, “Network Models,” and cross-check your memory. At what layer of the OSI seven-layer model would you put UTP cabling? For that matter, at what layer would you put network topology? How about on the TCP/IP model?
Figure Unshielded twisted pair

40. Category (CAT) ratings
UTP has a variety of variations
Example: number of twists per foot
CAT ratings help installers choose the right cable for the right network technology
Rated in MHz, indicating highest frequency cable can handle
Most common categories shown in Table 3.1

41. Tech Tip: Industry Standards Bodies (p. 51)
Several international groups set the standards for cabling and networking in general. Ready for alphabet soup? At or near the top is the International Organization for Standardization (ISO). The American National Standards Institute (ANSI) is both the official U.S. representative to the ISO and a major international player. ANSI checks the standards and accredits other groups, such as the Telecommunications Industry Association (TIA). The Electronic Industries Alliance (EIA) (until 2011) worked with TIA to set the standards for UTP cabling, among many other things.

42. Bandwidth
Bandwidth is the maximum amount of data that will go through a cable per second
10 MHz originally translated to 10 Mbps
Current networks use bandwidth-efficient encoding schemes
CAT 5e cable can handle throughput of up to 1000Mbps
Exam Tip (p. 51): The CompTIA Network+ exam is only interested in your knowledge of CAT 3, CAT 5, CAT 5e, CAT 6, and CAT 6a cables.

43. Figure 3.23 CAT level marked on box of UTP
Try This! Shopping Spree! (p. 51)
Just how common has CAT 6 or CAT 6a become in your neighborhood? Take a run down to your local hardware store or office supply store and shop for UTP cabling. Do they carry CAT 6? CAT 5? CAT 7? What’s the difference in price? If it’s not much more expensive to go with the better cable, the expected shift in networking standards has occurred and you might want to upgrade your network.
Figure CAT level marked on box of UTP

44. Figure 3.24 CAT level on UTP CAT level Tech Tip: CAT 6a (p. 52)
The CAT 6a update doubles the bandwidth of CAT 6 to 500 MHz to accommodate 10-Gbps speeds up to 100 meters. (The 100-meter limitation, by the way, refers to the Ethernet standard, the major implementation of UTP in networks. Chapter 4 covers Ethernet in great detail.)
Other standards are in the works or already here, however, that go well beyond just Ethernet traffic. CAT 7a, for example, can handle 10GBase-T Ethernet or accommodate cable television, telephones, and Gigabit Ethernet at the same time. Sweet. Nothing beyond CAT 6 is on the exam.
Figure CAT level on UTP

45. Registered Jack (RJ) Connectors
RJ-11 (two pairs of wires) for telephones
RJ-45 (four pairs of wires) for networks
Figure RJ-11 (left) and RJ-45 (right) connectors

46. Fiber-Optic Cable Transmits light rather than electricity
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. Fiber-Optic Cable (cont’d.)
Core: the glass fiber
Cladding: reflects signal down the fiber
Buffer material to give strength
Insulating jacket: protects inner components
Figure Cross section of fiber-optic cabling

48. Fiber-Optic Cable (cont’d.)
Two-number designator used
Core and cladding measurements
Most common fiber-optic cable size: 62.5/125 μm
Almost all network technologies use fiber optic cable with pairs of fibers
One fiber used for sending
One fiber for receiving
Note (p. 53): For those of you unfamiliar with it, the odd little u-shaped symbol describing fiber cable size (µ) stands for micro, or 1/1,000,000.

49. Figure 3.27 Duplex fiber-optic cable

50. Types of Cabling Multimode fiber (MMF) Single-mode fiber (SMF)
Uses light emitting diodes (LEDs)
Single-mode fiber (SMF)
Prevents modal distortion
Signals sent at the same time do not arrive at the same time because path lengths vary slightly
Enables a network to achieve high transfer rates over long distances
Note (p. 53): A nano—abbreviated as n—stands for 1/1,000,000,000, or one-billionth of whatever. Here you’ll see it as a nanometer (nm), one-billionth of a meter. That’s one tiny wavelength!

51. Types of Cabling (cont’d.)
Fiber optic wavelengths measured in nm
Almost all multimode cables transmit 850-nm wavelengths
Single-mode transmits either 1310 or 1550 nm
Depending on the laser

52. Connector Types ST and SC have unique ends LC is always duplex
Figure From left to right: ST, SC, and LC fiber-optic connectors

53. Figure 3.29 FC connector Tech Tip: What’s in a Name? (p. 54)
Most technicians call common fiber-optic connectors by their initials—such as ST, SC, or LC—perhaps because there’s no consensus about what words go with those initials. ST probably stands for straight tip, although some call it snap and twist. But SC and LC? How about subscriber connector, standard connector, or Siemon connector for the former, and local connector or Lucent connector for the latter? If you want to remember the connectors for the exam, try these: snap 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. I have no clue what the FC connector label means (though some say it means fiber channel today). In practice, it’s the connector you screw into place, thus eliminating problems with high-vibration environments.
Figure FC connector

54. Other Cables Classic serial RS-232 recommended standard (RS)
Dates from 1969
Has not changed significantly in 40 years
Most common serial port is 9-pin, male D-subminiature (DB-9) connector
Slow data rates: about 56,000 bps
Only point-to-point connections

55. Serial port
Figure Serial port

56. Figure 3.31 Parallel connector
Parallel Connectors
As ancient as serial ports
Can run up to 2 Mbps
Tend to be much slower when used for networking
Uses 25-pin female DB type connector
Exam Tip (p. 54): Concentrate on UTP—that’s where the hardest CompTIA Network+ exam questions come into play. Don’t forget to give coax, STP, and fiber-optic a quick pass, and make sure you understand the reasons for picking one type of cabling over another. Even though the CompTIA Network+ exam does not test too hard on cabling, this is important information that you will use in real networking.
Figure Parallel connector

57. Fire Ratings
Developed by Underwriters Laboratories and the National Electrical Code (NEC)
Polyvinyl chloride (PVC) rating
No significant fire protection
Lots of smoke and noxious fumes

58. Fire Ratings (cont’d.) Plenum-rated cable Less smoke and fumes
Costs three to five times as much as PVC-rated cable
Most city ordinances require plenum cable for network installations

59. Fire Ratings (cont’d.) Riser-rated cable
Proper cable to use for vertical runs between floors of a building
Provides less protection than plenum cable
Most installations today use plenum for runs between floors

60. Networking Industry Standards – IEEE

61. IEEE
Institute of Electrical and Electronics Engineers (IEEE) defines standards for use and implementation of technology
IEEE 802 Working Group
Began in February 1980
Defines frames, speed, distances, and types of cabling for networks
IEEE 1284 committee sets standards for parallel communications

62. Figure 3.32 Parallel cable marked IEEE 1284–compliant

63. When preparing for the CompTIA Network+ exam, concentrate on the IEEE and standards. You will see these again in later chapters.
Table 3.2 shows the currently recognized IEEE 802 subcommittees and their areas of jurisdiction. I’ve included the inactive subcommittees for reference. The missing numbers, such as and , were used for committees long-ago disbanded. Each subcommittee is officially called a Working Group, except the few listed as a Technical Advisory Group (TAG) in the table.