CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 25 doc

Figure 4-20 Differentiating Among ConnectionsConnection Media This section briefly discusses the connection types used by physical layer implementa-tion and an interface device, Gigabit I

Maximum Segment Length

Duplex media interface connector (MIC) straight tip (ST) connector or subscriber connector (SC)

62.5/50 micro multimode fiber

275 m (853 feet) for 62.5 micro fiber; 550 m (1804.5 feet) for 50 micro fiber

62.5/50 micro multimode fiber; 9-micron single- mode fiber

440 m (1443.6 feet) for 62.5 micro fiber; 550 m (1804.5 feet) for 50 micro fiber; 3 to 10 km (1.86 to 6.2 miles) on single-mode fiber

Figure 4-20 Differentiating Among Connections

Connection Media

This section briefly discusses the connection types used by physical layer implementa-tion and an interface device, Gigabit Interface Converter (GBIC), used between the Ethernet and fiber-optic systems This section covers the following topics:

■ RJ-45—A connector commonly used for finishing a twisted-pair cable

■ AUI—A connector that interfaces between a computer’s NIC or router interface

and an Ethernet cable

■ GBIC—A device used as an interface between the Ethernet and fiber-optic systems

RJ-45

The RJ-45 connector and jack are the most prevalent RJ-45 connectors are discussed

in more detail in the section, “UTP Implementation” later in the chapter

Attachment Unit Interface

In some cases, the type of connector on a NIC does not match the type of media that it needs to connect to An interface exists for the AUI connector The AUI is the 15-pin physical connector interface between a computer’s NIC and Ethernet cable On 10BASE5 (thicknet) Ethernet, a short cable is used to connect the AUI on the computer with a transceiver on the main cable In 10BASE2 (thinnet) Ethernet networks, the NIC con-nects directly to the Ethernet coaxial cable at the back of the computer

Gigabit Interface Converter

plugs into a Gigabit Ethernet port A key benefit of using a GBIC is that GBICs are interchangeable This feature gives users the flexibility to deploy other 1000BASE-X technology without needing to change the physical interface/module on the router or switch

The fiber-optic GBIC is a transceiver that converts serial electric currents to optical

sig-nals and that also coverts optical sigsig-nals to digital electric currents Some of the optical

GBICs include the following:

■ Short wavelength (1000BASE-SX)

■ Long wavelength/long haul (1000BASE-LX/LH)

■ Extended distance (1000BASE-ZX)

Typically, the GBIC is used as an interface between the Ethernet and fiber-optic systems,

such as Fiber Channel and Gigabit Ethernet Figure 4-21 shows a GBIC, and Figure 4-22

shows a Cisco WS-X2931 Gigabit Ethernet Module with the GBIC out

Figure 4-21 Gigabit Interface Converter (GBIC)

Figure 4-22 Cisco WS-X2931 Gigabit Ethernet Module with GBIC Out

UTP Implementation

If you look at the RJ-45 transparent end connector, you can see eight colored wires These wires are twisted into four pairs Four of the wires (two pairs) carry the positive,

or true, voltage and are considered “tip” (T1 through T4); the other four wires carry

the inverse, or false, voltage grounded and are called “ring” (R1 through R4) Tip and

ring are terms that originated in the early days of the telephone Today, these terms

refer to the positive and the negative wire in a pair The wires in the first pair in a cable

or a connector are designated as T1 and R1, the second pair is T2 and R2, and so on The RJ-45 plug is the male component, crimped at the end of the cable As you look

at the male connector from the front, with the clip facing down, the pin locations are numbered from 8 on the left down to 1 on the right, as shown in Figure 4-23 The jack, shown in Figure 4-24, is the female component in a network device, wall or cubi-cle partition outlet, or patch panel As you look at the device port, the corresponding female pin locations are 1 on the left up to 8 on the right

Figure 4-23 Pin Locations on the RJ-45 Connector

For electricity to run between the connector and the jack, the order of the wires must fol-low EIA/TIA-568-A and EIA/TIA-568-B standards, as shown previously in Figure 4-16

In addition to identifying the correct EIA/TIA category of cable to use for a connecting device (which depends on what standard is being used by the jack on the network device), you need to determine which of the following to use:

through the cable Thus, the wire connected to pin 1 is the same on both ends of the cable

trans-mit, and receive signals on the device with line connections

Figure 4-24 RJ-45 Jack and Wire Order

If the two RJ-45 ends of a cable are held side by side in the same orientation, the

col-ored wires (or strips or pins) are seen at each connector end If the order of the colcol-ored

wires is the same at each end, the cable is straight-through Figure 4-25 illustrates that

the RJ-45 connectors on both ends show all the wires in the same order

Figure 4-25 UTP Implementation: Straight-Through Cable

Specified for Ethernet, in a CAT 5 UTP cable, only wires 1, 2, 3, and 6 are used for transmit (TD) and receive (RD) signals The other four wires are not used As shown

on the left of Figure 4-25, in a straight-through cable, the RJ-45 pins 1, 2, 3, and 6 at one end are connected to pins 1, 2, 3, and 6 at the other end of the connection Gigabit Ethernet, however, uses all eight wires

You can use a straight-through cable to connect devices such as PCs or routers to other devices used as hubs or switches As Figure 4-26 shows, you should use straight-through

when only one port is designated with an x.

Figure 4-26 Interconnecting Devices Using Straight-Through Cable

With crossover cable, the RJ-45 connectors on both ends show that some of the wires

on one side of the cable are crossed to a different pin on the other side of the cable Specifically for Ethernet, pin 1 at one RJ-45 end should connect to pin 3 at the other end Pin 2 at one end should connect to pin 6 at the other end, as shown in Figure 4-27

Figure 4-27 UTP Implementation—Crossover

You can use a crossover cable to connect similar devices, switch to switch or switch to

hub Figure 4-28 shows that you use a crossover cable when both ports are designated

with an x or when neither port is designated with an x.

Figure 4-28 Interconnecting Devices Using Crossover Cable

The following are the guidelines for the type of cable to use when interconnecting

net-working devices

Use straight-through cables for the following cabling:

■ Switch to router

■ Switch to PC or server

■ Hub to PC or server

Use crossover cables for the following cabling:

■ Switch to switch

■ Switch to hub

■ Hub to hub

■ Router to router

■ PC to PC

■ Router to PC

In this lab, you learn to wire an RJ-45 data jack for installation in a wall plate using a punch-down tool

LAN Connection Devices

Many types of devices are connected to make up a LAN These are called the LAN hardware components This section discusses some of the common hardware compo-nents that are used in a LAN environment LAN devices can include repeaters, hubs, bridges, switches, and routers with switches being the most prevalent device in modern LANs

Repeaters

As mentioned in the section, “LAN Physical Layer” and shown in Figure 4-19, many types of media exist, and each one has advantages and disadvantages One of the dis-advantages of the CAT 5 UTP cable that is primarily used is cable length The maximum length for UTP cable in a network is 100 meters (approximately 333 feet) If you have

to expand the network beyond that limit, you need to add a repeater In most Ethernet networks this repeater normally takes the form of hub, which is a multiport repeater, or

a newer technology switch

The term repeater comes from the early days of visual communication when a person situated on a hill would repeat the signal that was just received from the person on the previous hill to communicate the signal to the person on the next hill Telegraph, tele-phone, microwave, and optical communications all use repeaters to strengthen their signals over long distances

The purpose of a repeater, shown in Figures 4-29 and 4-30, is to regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media Repeaters are commonly used if too many network nodes exist or the number of cables

is insufficient The Four Repeater Rule for 10 Mbps bus-based Ethernet, also know as the 5-4-3 Rule, is used as a standard when extending LAN segments This rule states that

no more than five network segments can be connected end-to-end using four repeaters, but only three segments can have hosts (computers) on them Although the 5-4-3 rule

is important when applied to bus-based networks, it does not have much validity with switches and extended star topologies

Figure 4-29 Repeaters

Figure 4-30 Repeaters Connect Two End Nodes

Hubs

Hubs are actually multiport repeaters In many cases, the difference between the two

devices is the number of ports that each provides While a typical repeater has just 2

ports, a hub generally has from 4 to 24 ports, as shown in Figure 4-31 Additionally,

hubs are most commonly used in Ethernet 10BASE-T or 100BASE-T networks,

although other network architectures use them as well

Application Presentation Session Transport Network Data Link Physical

End Node

Application Presentation Session Transport Network Data Link Physical End Node

Repeater

Figure 4-31 Eight-Port Hub

Using a hub changes the network topology from a linear bus, where each device plugs directly into the wire, to a star With hubs, data arriving over the cables to a hub port

is electrically repeated on all the other ports connected to the same network segment, except for the port on which the data was sent

Hubs come in two basic types:

■ Active—Anactive hub must be plugged into an electrical outlet because it needs power to amplify the incoming signal before passing it out to the other ports

■ Intelligent—Anintelligent hub are sometimes called smart hubs These devices

basically function as active hubs, but also include a microprocessor chip and diagnostic capabilities They are more expensive than active hubs, but are useful

in troubleshooting situations

All devices that are attached to a hub hear all traffic Therefore, hubs maintain a single collision domain A collision is a situation where two end stations send data over the network wire at the same time

Sometimes, hubs are called concentrators because they serve as a central connection point for an Ethernet LAN

Bridges

At times, you need to break up a large LAN into smaller, more easily managed seg-ments This strategy decreases the amount of traffic on a single LAN and can extend

In this lab, you are introduced to the variety and prices of network compo-nents out in the market This lab looks specifically at Ethernet hubs and NICs