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Atthe other end of the spectrum, fiber-optic patch cables for use on LANs may contain only twostrands of fiber and be pliable enough to wrap around your hand.vari-However, all fiber cabl

100BASE-T (Fast Ethernet)

As networks become larger and handle heavier traffic, Ethernet’s long-standing 10-Mbps itation becomes a bottleneck that detrimentally affects response time The need for faster LANsthat can use the same infrastructure as the popular 10BASE-T technology has been met by

lim-100BASE-T, also known as Fast Ethernet lim-100BASE-T, specified in the IEEE 802.3u

stan-dard, enables LANs to run at a 100-Mbps data transfer rate, a tenfold increase from that vided by 10BASE-T, without requiring a significant investment in new infrastructure.100BASE-T uses baseband transmission and the same star topology as 10BASE-T It also usesthe same RJ-45 modular connectors Depending on the type of 100BASE-T technology used,

pro-it may require CAT 3, CAT 5, or higher UTP

As with 10BASE-T, nodes on a 100BASE-T network are configured in a star topology tiple hubs can be connected to form link segments However, unlike 10-Mbps Ethernet networks,100BASE-T networks do not follow the 5-4-3 rule Because of their faster response require-ments, to avoid data errors they require communicating nodes to be even closer 100BASE-Tbuses can support a maximum of three network segments connected with two repeating devices.Each segment length is limited to 100 meters Thus, the overall maximum length betweennodes is limited to 300 meters, as shown in Figure 3-23

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FIGURE 3-23 A 100BASE-T network

Two 100BASE-T specifications—100BASE-T4 and 100BASE-TX—have competed for

popularity as organizations move to 100-Mbps technology 100BASE-TX is the version you

are most likely to encounter It achieves its speed by sending the signal 10 times faster and densing the time between digital pulses as well as the time a station must wait and listen for

con-a signcon-al 100BASE-TX requires CAT 5 or higher unshielded twisted-pcon-air ccon-abling Within thecable, it uses the same two pairs of wire for transmitting and receiving data that 10BASE-Tuses Therefore, like 10BASE-T, 100BASE-TX is also capable of full-duplex transmission.Full duplexing can potentially double the effective bandwidth of a 100BASE-T network to

200 Mbps

1000BASE-T (Gigabit Ethernet over Twisted-pair)

Because of increasing volumes of data and numbers of users who need to access this dataquickly, even 100 Mbps has not met the throughput demands of some networks Ethernet tech-nologies designed to transmit data at 1 Gbps are collectively known as Gigabit Ethernet.1000BASE-T is a standard for achieving throughputs 10 times faster than Fast Ethernet over

copper cable, described in IEEE’s 802.3ab standard In “1000BASE-TX,” “1000” represents

1000 Megabits per second (Mbps), or 1 Gigabit per second (Gbps) “Base” indicates that it usesbaseband transmission, and “T” indicates that it relies on twisted-pair wiring 1000BASE-Tachieves its higher throughput by using all four pairs of wires in a CAT 5 or higher cable toboth transmit and receive signals, whereas 100BASE-T uses only two of the four pairs.1000BASE-T also uses a different data encoding scheme than 100BASE-T networks use.However, the standards can be combined on the same network and you can purchase NICs thatsupport 10 Mbps, 100 Mbps, and 1 Gbps via the same connector jack Because of this com-patibility, and the fact that 1000BASE-T can use existing CAT 5 cabling, the 1-Gigabit tech-nology can be added gradually to an existing 100 Mbps network with minimal interruption ofservice The maximum segment length on a 1000BASE-T network is 100 meters It allows foronly one repeater Therefore, the maximum distance between communicating nodes on a1000BASE-T network is 200 meters

1000BASE-CX (Gigabit Ethernet over Twinax)

Another standard that supplies 1-Gigabit throughput is 1000BASE-CX This standard uses either STP or twinaxial cable, which is a cable similar to the coaxial cable discussed earlier in

the chapter, but which contains two copper conductors at its center With this type of cabling,

a specialized connector, called an HSSDC, is required 1000BASE-CX allows only short ment lengths—up to 25 meters It was designed for connecting servers or connectivity devicesover short distances However, it is rarely used

seg-Fiber-Optic Cable

Fiber-optic cable, or simply fiber, contains one or several glass or plastic fibers at its center, or

core Data is transmitted via pulsing light sent from a laser (in the case of 1- and 10-Gigabit

technologies) or a light-emitting diode (LED) through the central fibers Surrounding the

fibers is a layer of glass or plastic called cladding The cladding is a different density from the

glass or plastic in the strands It reflects light back to the core in patterns that vary depending

on the transmission mode This reflection allows the fiber to bend around corners withoutdiminishing the integrity of the light-based signal Outside the cladding, a plastic buffer pro-tects the cladding and core Because it is opaque, it also absorbs any light that might escape

To prevent the cable from stretching, and to protect the inner core further, strands of Kevlar(an advanced polymeric fiber) surround the plastic buffer Finally, a plastic sheath covers thestrands of Kevlar Figure 3-24 shows a fiber-optic cable with multiple, insulated fibers

Like twisted-pair and coaxial cabling, fiber-optic cabling comes in a number of different eties, depending on its intended use and the manufacturer For example, fiber-optic cablesused to connect the facilities of large telephone and data carriers may contain as many as 1000fibers and be heavily sheathed to prevent damage from extreme environmental conditions Atthe other end of the spectrum, fiber-optic patch cables for use on LANs may contain only twostrands of fiber and be pliable enough to wrap around your hand.

vari-However, all fiber cable variations fall into two categories: single-mode and multimode

SMF (Single-Mode Fiber)

SMF (single-mode fiber) uses a narrow core (less than 10 microns in diameter) through

which light generated by a laser travels over one path, reflecting very little Because it reflectslittle, the light does not disperse as the signal travels along the fiber This continuity allowssingle-mode fiber to accommodate high bandwidths and long distances (without requiringrepeaters) Single-mode fiber may be used to connect a carrier’s two facilities However, it coststoo much to be considered for use on typical data networks Figure 3-25 depicts a simplifiedversion of how signals travel over single-mode fiber

FIGURE 3-24 A fiber-optic cable

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FIGURE 3-25 Transmission over single-mode fiber-optic cable

MMF (Multimode Fiber)

MMF (multimode fiber) contains a core with a larger diameter than single-mode fiber

(between 50 and 115 microns in diameter; the most common size is 62.5 microns) over whichmany pulses of light generated by a laser or LED travel at different angles It is commonlyfound on cables that connect a router to a switch or a server on the backbone of a network.Figure 3-26 depicts a simplified view of how signals travel over multimode fiber

FIBER-OPTIC CABLE

FIGURE 3-26 Transmission over multimode fiber-optic cable

Because of its reliability, fiber is currently used primarily as a cable that connects the many ments of a network Fiber-optic cable provides the following benefits over copper cabling:

seg-◆ Nearly unlimited throughput

◆ Very high resistance to noise

◆ Excellent security

◆ Ability to carry signals for much longer distances before requiring repeaters than

copper cable

◆ Industry standard for high-speed networking

The most significant drawback to the use of fiber is its relatively high cost Also, fiber-opticcable requires special equipment to splice, which means that quickly repairing a fiber-optic cable

in the field (given little time or resources) can be difficult Fiber’s characteristics are rized in the following list:

summa-◆ Throughput—Fiber has proved reliable in transmitting data at rates that exceed

10 Gigabits (or 10,000 Megabits) per second Fiber’s amazing throughput is partlydue to the physics of light traveling through glass Unlike electrical pulses travelingover copper, the light experiences virtually no resistance and, therefore, can be reli-ably transmitted at faster rates than electrical pulses In fact, a pure glass strand canaccept up to 1 billion laser light pulses per second Its high throughput capabilitymakes it suitable for network backbones and for serving applications that generate agreat deal of traffic, such as video or audio conferencing

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◆ Cost—Fiber-optic cable is the most expensive transmission medium Because of its

cost, most organizations find it impractical to run fiber to every desktop Not only isthe cable itself more expensive than copper cabling, but fiber-optic NICs and hubscan cost as much as five times more than NICs and hubs designed for UTP net-works In addition, hiring skilled fiber cable installers costs more than hiringtwisted-pair cable installers

◆ Connector—With fiber cabling, you can use any of 10 different types of connectors.

Figure 3-27 shows four connector types: the ST (Straight Tip), SC (Subscriber Connector or Standard Connector), LC (Local Connector), and MT-RJ (Mechanical Transfer Registered Jack) connectors Each of these connectors can be

obtained for single-mode or multimode fiber-optic cable Existing fiber networkstypically use ST or SC connectors However, MT-RJ connectors are used on thevery latest fiber-optic technology LC and MT-RJ connectors are preferable to STand SC connectors because of their smaller size, which allows for a higher density ofconnections at each termination point The MT-RJ connector is unique because it

contains two strands of multimode fiber in a single ferrule, which is a short tube

within a connector that encircles the fiber and keeps it properly aligned With twostrands in each ferrule, a single MT-RJ connector provides for duplex signaling

FIGURE 3-27 Fiber-optic cable connectors

◆ Noise immunity—Because fiber does not conduct electrical current to transmit

sig-nals, it is unaffected by EMI Its impressive noise resistance is one reason why fibercan span such long distances before it requires repeaters to regenerate its signal

◆ Size and scalability—Depending on the type of fiber-optic cable used, segment

lengths vary from 150 to 40,000 meters This limit is due primarily to optical loss,

or the degradation of the light signal after it travels a certain distance away from itssource (just as the light of a flashlight dims after a certain number of feet) Opticalloss accrues over long distances and grows with every connection point in the fibernetwork Dust or oil in a connection (for example, from people handling the fiberwhile splicing it) can further exacerbate optical loss

Just as with twisted-pair and coaxial cabling, IEEE has established Physical layer standards fornetworks that use fiber-optic cable Commonly used standards are described in the followingsections

10BASE-FL

In the 10BASE-F standard, the “10” represents its maximum throughput of 10Mbps, “Base”

indicates its use of baseband transmission, and “F” indicates that it relies on a medium offiber-optic cable In fact, there are at least three different kinds of 10BASE-F All require twostrands of multimode fiber One strand is used for data transmission and one strand is used forreception, making 10BASE-F a full-duplex technology

One version of 10BASE-F is 10BASE-FL 10BASE-FL is an IEEE 802.3 standard

distin-guished from other 10 Mbps standards that use fiber-optic cable first by its purpose

10BASE-FL is designed to connect workstations to a LAN or to connect two repeaters, whereas theother two 10BASE-F standards are designed for backbone connections 10BASE-FL is alsodistinguished by its ability to take advantage of fiber-optic repeating technology Withoutrepeaters, the maximum segment length for 10BASE-FL is 1000 meters Using repeaters, it is

2000 meters FL networks may contain no more than two repeaters Like

10BASE-T, 10BASE-FL makes use of the star topology, with its repeaters connected through a bus.Because 10BASE-F technologies involve (expensive) fiber and achieve merely 10-Mbpsthroughput (whereas the fiber medium is capable of much higher throughput), it is not com-monly found on modern networks

100BASE-FX

The 100BASE-FX standard specifies a network capable of 100-Mbps throughput that uses

baseband transmission and fiber-optic cabling 100BASE-FX requires multimode fiber taining at least two strands of fiber In half-duplex mode, one strand is used for data trans-mission, while the other strand is used for reception In full-duplex implementations, bothstrands are used for both sending and receiving data 100BASE-FX has a maximum segmentlength of 412 meters if half-duplex transmission is used and 2000 meters if full-duplex is used.The standard allows for a maximum of one repeater to connect segments The 100BASE-FXstandard uses a star topology, with its repeaters connected in a bus fashion

100BASE-FX, like 100BASE-T, is also considered “Fast Ethernet” and is described in IEEE’s802.3u standard Organizations switching, or migrating, from UTP to fiber media can com-bine 100BASE-TX and 100BASE-FX within one network To do this, transceivers in com-puters and connectivity devices must have both RJ-45 and SC, ST, LC, or MT-RJ ports.Alternatively, a 100BASE-TX to 100BASE-FX media converter may be used at any point inthe network to interconnect the different media and convert the signals of one standard to signalsthat work with the other standard.

1000BASE-LX

IEEE has specified three different types of 1000Base, or 1 Gigabit, Ethernet technologies for

use over fiber-optic cable in its 802.3z standard Included in this standard is the

1000BASE-CX standard you learned about previously

Probably the most common 1-Gigabit Ethernet standard in use today is 1000BASE-LX The

“1000” in 1000BASE-LX stands for 1000-Mbps—or 1 Gbps—throughput “Base” stands forbaseband transmission, and “LX” represents its reliance on “long wavelengths” of 1300 nanome-ters (A nanometer equals 0.000000001 meters.) 1000BASE-LX has a longer reach than anyother 1-Gigabit technology available today It relies on either single-mode or multimode fiber.With multimode fiber (62.5 microns in diameter), the maximum segment length is 550 meters.When used with single-mode fiber (8 microns in diameter), 1000BASE-LX can reach 5000meters 1000BASE-LX networks can use one repeater between segments Because of its poten-tial length, 1000BASE-LX is an excellent choice for long backbones—connecting buildings in

a MAN, for example, or connecting an ISP with its telecommunications carrier

1000BASE-SX

1000BASE-SX is similar to 1000BASE-LX in that it has a maximum throughput of 1 Gbps.

However, it relies on only multimode fiber-optic cable as its medium This makes it lessexpensive to install than 1000BASE-LX Another difference is that 1000BASE-SX uses shortwavelengths of 850 nanometers—thus, the “SX,” which stands for “short.” The maximum seg-ment length for 1000BASE-SX depends on two things: the diameter of the fiber and the modal

bandwidth used to transmit signals Modal bandwidth is a measure of the highest frequency

of signal a multimode fiber can support over a specific distance and is measured in MHz-km

It is related to the distortion that occurs when multiple pulses of light, although issued at thesame time, arrive at the end of a fiber at slightly different times The higher the modal band-width, the longer a multimode fiber can carry a signal reliably

When used with fibers whose diameters are 50 microns each, and with the highest possiblemodal bandwidth, the maximum segment length on a 1000BASE-SX network is 550 meters.When used with fibers whose diameters are 62.5 microns each, and with the highest possiblemodal bandwidth, the maximum segment length is 275 meters Only one repeater may beused between segments Therefore, 1000BASE-SX is best suited for shorter network runsthan 1000BASE-LX—for example, connecting a data center with a telecommunications closet

in an office building

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10-Gigabit Fiber-Optic Standards

As you have learned, the throughput potential for fiber-optic cable is extraordinary, and tists continue to push its limits Now there are standards for transmitting data at 10-Gbps over

scien-fiber, all described in IEEE’s 802.3ae standard All of the 10-Gigabit options rely on a star

topology and allow for only one repeater They differ according to their signaling methods andmaximum allowable segment lengths

One 10-Gigabit option is 10GBASE-SR, in which the “10G” stands for its maximum put of 10 Gigabits per second, “base” stands for baseband transmission, and “SR” stands for

through-“short-reach.” 10GBASE-SR relies on multimode fiber and transmits signals with wavelengths

of 850 nanometers As with the 1-Gigabit standards, the maximum segment length on a10GBASE-SR network depends on the diameter of the fibers used It also depends on themodal bandwidth used For example, if 50-micron fiber is used, with the maximum possiblemodal bandwidth, the maximum segment length is 300 meters If 62.5-micron fiber is used withthe maximum possible modal bandwidth, a 10GBASE-SR segment can be 66 meters long

A second standard defined in IEEE 802.3ae is 10GBASE-LR, in which the “10G” stands

for 10 Gigabits per second, “base” stands for baseband transmission, and “LR” stands for reach.” 10GBASE-LR carries signals with wavelengths of 1310 nanometers through single-mode fiber Its maximum segment length is 10,000 meters

“long-A third 10-Gigabit option is 10GB“long-ASE-ER, in which “ER” stands for “extended reach.” Like

10GBASE-LR, this standard requires single-mode fiber, through which it transmits signals withwavelengths of 1550 nanometers It allows for segments up to 40,000 meters, or nearly 25 miles

Summary of Physical Layer Standards

To obtain Network+ certification, you must be familiar with the different characteristics andlimitations of each type of network discussed in this chapter To put this information in con-text, Table 3-2 summarizes the characteristics and limitations for Physical layer networkingstandards, including Ethernet networks that use coaxial cable, twisted-pair cable, and fiber-optic cable

Table 3-2 Physical layer networking standards

Maximum Maximum Transmission Distance per Physical

10BASE-T 10 100 CAT 3 or higher UTP Star

100BASE-TX 100 100 CAT 5 or higher UTP Star

1000BASE-T 1000 100 CAT 5 or higher UTP Star

Table 3-2 Continued

Maximum Maximum Transmission Distance per Physical

1000BASE-CX 1000 25 Twinaxial cable Star

1000BASE-LX 1000 Up to 550, depending MMF Star

on wavelength and fiber core diameter

1000BASE-SX 1000 Up to 500, depending MMF Star

on modal bandwidth and fiber core diameter 10GBASE-SR 10,000 Up to 300, depending MMF Star

on modal bandwidth and fiber core diameter

*Although most modern networks use a star-bus hybrid, if you are studying for the Network+certification exam, you should remember the simple topology on which the network is based

Cable Design and Management

Organizations that pay attention to their cable plant—the hardware that makes up the

enter-prise-wide cabling system—are apt to experience fewer Physical layer network problems,smoother network expansions, and simpler network troubleshooting Cable management is asignificant element of a sound network management strategy

In 1991, TIA/EIA released its joint 568 Commercial Building Wiring Standard, also known

as structured cabling, for uniform, enterprise-wide, multivendor cabling systems Structured

cabling suggests how networking media can best be installed to maximize performance andminimize upkeep Structured cabling specifies standards without regard for the type of media

or transmission technology used on the network (It does, however assume a network based onthe star topology.) In other words, it is designed to work just as well for 10BASE-T networks

as it does for 1000BASE-LX networks Structured cabling is based on a hierarchical designthat divides cabling into six subsystems, described in the following list and illustrated in Fig-ure 3-28

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◆ Entrance facilities—The point at which a building’s internal cabling plant begins.

The entrance facility separates LANs from WANs and designates where the

telecommunications service carrier (whether it’s a local phone company, dedicated, orlong-distance carrier) accepts responsibility for the (external) wire The point of divi-sion between the service carrier’s network and the internal network is also known as

the demarcation point (or demarc).

◆ Backbone wiring—The interconnection between telecommunications closets, equipment

rooms, and entrance facilities On a campus-wide network, the backbone includes not

only vertical connectors between floors, or risers, and cabling between equipment rooms,

but also cabling between buildings The TIA/EIA standard designates distance limitationsfor backbones of varying cable types, as specified in Table 3-3 On modern networks,

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FIGURE 3-28 TIA/EIA structured cabling subsystems

backbones are usually composed of fiber-optic or UTP cable The cross connect is thecentral connection point for the backbone wiring.

Table 3-3 TIA/EIA specifications for backbone cabling

Cross Connects to Equipment Room to Telecommunications Telecommunications Cross Connects to

UTP 800 m (voice specification) 500 m 300 m

Single-mode 3000 m 500 m 1500 m fiber

Multimode 2000 m 500 m 1500 m fiber

◆ Equipment room—The location of significant networking hardware, such as servers

and mainframe hosts Cabling to equipment rooms usually connects tions closets On a campus-wide network, each building may have its own equip-ment room

telecommunica-◆ Telecommunications closet—A “telco room” that contains connectivity for groups of

work-stations in its area, plus cross connections to equipment rooms Large organizations mayhave several telco rooms per floor Telecommunications closets typically house patchpanels, punch-down blocks, hubs or switches, and possibly other connectivity hard-

ware A punch-down block is a panel of data receptors into which horizontal cabling from the workstations is inserted If used, a patch panel is a wall-mounted

panel of data receptors into which patch cables from the punch-down block areinserted Figure 3-29 shows a patch panel and Figure 3-30 shows a punch-downblock Finally, patch cables connect the patch panel to the hub or switch Becausetelecommunications closets are usually small, enclosed spaces, good cooling and ven-tilation systems are important to maintaining a constant temperature

◆ Horizontal wiring—The wiring that connects workstations to the closest

telecom-munications closet TIA/EIA recognizes three possible cabling types for horizontalwiring: STP, UTP, or fiber-optic The maximum allowable distance for horizontalwiring is 100 m This span includes 90 m to connect a data jack on the wall to thetelecommunications closet plus a maximum of 10 m to connect a workstation to thedata jack on the wall Figure 3-31 depicts a horizontal wiring configuration

◆ Work area—An area that encompasses all patch cables and horizontal wiring

neces-sary to connect workstations, printers, and other network devices from their NICs to

the telecommunications closet A patch cable is a relatively short section (usually

between 3 and 25 feet long) of cabling with connectors on both ends The TIA/EIAstandard calls for each wall jack to contain at least one voice and one data outlet, aspictured in Figure 3-32 Realistically, you will encounter a variety of wall jacks Forexample, in a student computer lab lacking phones, a wall jack with a combination

of voice and data outlets is unnecessary

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FIGURE 3-29 Patch panel

FIGURE 3-30 Punch-down block

FIGURE 3-31 Horizontal wiring

Adhering to standard cabling hierarchies is only part of a smart cable management strategy You oryour network manager should also specify standards for the types of cable used by your orga-nization and maintain a list of approved cabling vendors Keep a supply room stocked withspare parts so that you can easily and quickly replace defective parts.

Create documentation for your cabling plant, including the locations, installation dates, lengths,and grades of installed cable Label every data jack, punch-down block, and connector Usecolor-coded cables for different purposes (cables can be purchased in a variety of sheath col-ors) For example, you might want to use pink for patch cables, green for horizontal wiring,and gray for vertical (backbone) wiring Be certain to document your color schemes Keep yourdocumentation in a centrally accessible location and be certain to update it as you change thenetwork The more you document, the easier it will be to move or add cable segments.Finally, plan for how your cabling plant will lend itself to growth For example, if your organi-zation is rapidly expanding, consider replacing your backbone with fiber and leave plenty ofspace in your telecommunications closets for more racks

As you will most likely work with twisted-pair cable, the next section explains how to installthis type of cabling from the server to the desktop

Installing Cable

So far, you have read about the variety of cables used in networking and the limitations ent in each You may worry that with hundreds of varieties of cable, choosing the correct oneand making it work with your network is next to impossible The good news is that if you fol-low both the manufacturers’ installation guidelines and the TIA/EIA standards, you are almostguaranteed success Many network problems can be traced to poor cable installation techniques.For example, if you don’t crimp twisted-pair wires in the correct position in an RJ-45 connec-tor, the cable will fail to transmit or receive data (or both—in which case, the cable will not

inher-FIGURE 3-32 A standard TIA/EIA outlet

function at all) Installing the wrong grade of cable can either cause your network to fail orrender it more susceptible to damage.

With networks moving to faster transmission speeds, adhering to installation guidelines is amore critical concern than ever A Category 5 UTP segment that flawlessly transmits data at

10 Mbps may suffer data loss when pushed to 100 Mbps In addition, some cable turers will not honor warranties if their cables were improperly installed This section outlinesthe most common method of installing UTP cable and points out cabling mistakes that canlead to network instability

manufac-In the previous section, you learned about the six subsystems of the TIA/EIA structured cablingstandard A typical UTP network uses a modular setup to distinguish between cables at eachsubsystem Figure 3-33 provides an overview of a modular cabling installation

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FIGURE 3-33 A typical UTP cabling installation

In this example, patch cables connect network devices (such as a workstation) to the wall jacks.Longer cables connect wire from the wall jack to a punch-down block in the telecommunica-tions closet From the punch-down block, patch cables bring the connection into a patch panel.From the patch panel, more patch cables connect to the hub, switch, or other connectivitydevice, which in turn connects to the equipment room or to the backbone, depending on thescale of the network All of these sections of cable make network moves and additions easier.Believe it or not, they also keep the telecommunications closet organized

Although you may never have to make your own patch cables, you might have to replace anRJ-45 connector on an existing cable TIA/EIA has specified two different methods of insert-ing UTP twisted pairs into RJ-45 plugs: TIA/EIA 568A and TIA/EIA 568B Functionally,there is no difference between the standards You only have to be certain that you use the samestandard on every RJ-45 plug and jack on your network, so that data is transmitted and receivedcorrectly Figure 3-34 depicts pin numbers and assignments for the TIA/EIA 568A standardwhen used on an Ethernet network Figure 3-35 depicts pin numbers and assignments for theTIA/EIA 568B standard (Although networking professionals commonly refer to wires in Fig-ures 3-34 and 3-35 as “Transmit” and “Receive,” their original “T” and “R” designations standfor “Tip” and “Ring,” based on early telephone technology.)

If you terminate the RJ-45 plugs at both ends of a patch cable identically, following one of the

TIA/EIA 568 standards, you will create a straight-through cable A straight-through cable is

so named because it allows signals to pass “straight through” between terminations However,

in some cases you may want to reverse the pin locations of some wires—for example, when youwant to connect two workstations without using a connectivity device or when you want toconnect two hubs through their data ports This can be accomplished through the use of a

crossover cable, a patch cable in which the termination locations of the transmit and receive

wires on one end of the cable are reversed, as shown in Figure 3-36 In this example, theTIA/EIA 568B standard is used on the left side, whereas the TIA/EIA 568A standard is used

on the right side Notice that only pairs 2 and 3 are switched, because those are the pairs ing and receiving data

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FIGURE 3-34 TIA/EIA 568A standard terminations