# Cabling and Topology Chapter 3.

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Cabling and Topology Chapter 3

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

Overview

Three Parts to Chapter 3 Network Topology
Most common standardized cable types IEEE Committees for network technology standards

Topology

Network topology The way that cables and other pieces of hardware connect to one another

Bus and Ring Bus topology Ring topology Single bus cable
Connects all computer in a line Ring topology Central ring of cable Connects all computers in a ring

Figure 3.1 Bus and ring topologies

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

Data flow Bus topology Ring 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

Figure 3.3 Terminated bus topology
Note: Termination prevents reflection. Consider briefly discussing this concept. Figure 3.3 Terminated bus topology

Figure 3.4 Ring topology moving in a certain direction

Problem with Bus and Ring
Entire network stops working if the cable is broken at any point.

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!

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 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.

Figure Star topology

Hybrids Hybrid topology combines topologies Physical topology
How cables physically look Signaling topology How the signals travel electronically 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.

Star-ring topology Star-bus 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

Figure 3.7 Shrinking the ring

Figure 3.8 Shrinking the segment

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

Figure 3.9 Mesh and point-to-multipoint
Note: Figure Mesh and point-to-multipoint

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)/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. Figure Partially- and fully-meshed topologies

Figure 3.11 Comparing star and point-to-multipoint
Point-to-multipoint topology A single system is a common source First 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

Figure 3.12 Point-to-Point
Two computers connect directly No need for a central hub Wired or wireless Figure Point-to-Point

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? Second Note on Page 43: Make sure you know all your topologies: bus, ring, star, hybrid, mesh, point-to-multipoint, and point-to-point!

Network technology A practical application of a topology, and other technologies that comprise a network Examples 10BaseT 1000BaseF 10GBaseLX These technologies are explained in the next two chapters.

Cabling

Figure 3.13 Cutaway view of coaxial cable
A central conductor wire Surrounded by an insulating material Surrounded by a braided metal shield 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. Figure Cutaway view of coaxial cable

Outer mesh layer of coaxial cable
Shields transmissions from electromagnetic interference (EMI) Figure Coaxial cable showing braided metal shielding

Figure 3.15 BNC connector on coaxial cable
Coaxial connectors in older networks Bayonet-style BNC Connectors Vampire taps pierced the cable A 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

Figure 3.16 F-type connector on coaxial cable
Connecting cable modems F-type screw-on connector 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.” Figure F-type connector on coaxial cable

RG rating for coaxial cable
Developed by military RG-6 is predominate cable today RG-59 cable is rarely used Figure RG-6 cable

Coaxial cable Ohm rating
Relative measure of resistance RG-6 and RG-59 are rated at 75 Ohms 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. Figure Ohm rating (on an older RG-58 cable used for networking)

Figure 3.19 Coaxial splitter
Splitting coaxial cable Figure 3.20 Barrel connector Figure Coaxial splitter

Extending coaxial cable
Figure Barrel connector

Twisted Pair Most common network cabling
Twisted pairs of cables, bundled together Twists reduce crosstalk interference Note on Page 46: Have you ever picked up a telephone and heard a distinct crackling noise? That’s an example of crosstalk.

Shielded Twisted Pair (STP) Figure 3.21 Shielded twisted pair
Shielding protects from electromagnetic interference (EMI) Needed in locations with excessive EMI Most common is IBM Type 1 cable 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. Figure Shielded twisted pair

Unshielded Twisted Pair (UTP) Figure 3.22 Unshielded twisted pair
Most common Twisted pairs of wires with plastic jacket Cheaper than STP Also used in telephone systems Figure Unshielded twisted pair

CAT Ratings Category (CAT) ratings are grades of cable ratings
Rated in MHz Most common categories are in Table 3.1 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.

Rating Frequency Max Bandwidth Status with TIA/EIA 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 MHz Mbps Recognized Table 3.1 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.

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 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.

Using the Correct Cable Figure 3.23 CAT level marked on box of UTP
Look on the box CAT level Figure CAT level marked on box of UTP

Using the Correct Cable
Look on the cable CAT level 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. Figure CAT level on UTP

Register jack (RJ) connectors
RJ-11 (two pairs of wires) for telephones RJ-45 (four pairs of wires) for networks 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. Figure RJ-11 (top) and RJ-45 (bottom) connectors

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

Composition of Fiber-Optic
Core: the glass fiber Cladding: reflects signal down the fiber Buffer: gives strength Insulating jacket: protects inner components Figure Cross section of fiber-optic cabling

Standardization of Fiber-Optic
Two-number designator Core and cladding measurements 62.5/125 μm Note: The symbol µ stands for micro, or 1/1,000,000th.

Often used in cable pairs Figure 3.27 Duplex fiber-optic cabling
One for sending One for receiving Cable may be connected together like a lamp cord Figure Duplex fiber-optic cabling

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

Fiber-Optic connectors
ST: bayonet-style SC: push-in LC: duplex 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 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

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

Serial port Figure Serial port

Figure 3.30 Parallel connector
Up to 2 Mbps Limited to point-to-point IEEE 1284 committee sets standards See the section “Networking Industry Standards—IEEE” later in this chapter. Figure Parallel connector

FireWire IEEE 1394 standard Limited to point-to-point
Very fast – up to 800 Mbps Unique connector 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.

Figure 3.31 FireWire connector

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

Networking Industry Standards – IEEE

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

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

Table 3.2 IEEE 802 Subcommittees
IEEE 802 LAN/MAN Overview & Architecture IEEE Higher Layer LAN Protocols 802.1s Multiple Spanning Trees 802.1w Rapid Reconfiguration of Spanning Tree 802.1x Port Based Network Access Control IEEE Logical Link Control (LLC); now inactive IEEE Ethernet 802.3ae 10 Gigabit Ethernet IEEE Token Ring;; now inactive IEEE Wireless LAN (WLAN); specifications, such as Wi-Fi IEEE Wireless Personal Area Network (WPAN) IEEE Broadband Wireless Access (BWA); specification for implementing Wireless Metropolitan Area Network (Wireless MAN); referred to also as WiMax IEEE Resilient Packet Ring (RPR) IEEE Radio Regulatory Technical Advisory Group IEEE Coexistence Technical Advisory Group IEEE Mobile Broadband Wireless Access (MBWA) IEEE Media Independent Handover IEEE Wireless Regional Area Networks Table 3.2 Tip on Page 52: Memorize the and standards. Ignore the rest.