Upgrading and Repairing PCs (17th Edition)

The choice of a data-link protocol affects the network hardware you choose. Because Fast Ethernet, Gigabit Ethernet, Wireless Ethernet, and other data-link protocols use different hardware, you must select the architecture before you can select appropriate hardware, including network interface cards, cables, and hubs or switches.

Network Interface Cards

On most computers, the network interface adapter takes the form of a network interface card (NIC) that fits into a PCI slot on a desktop computer or a PC Card (PCMCIA) slot on a notebook computer. Although network cards for older systems might use the ISA or EISA slot standards, these don't support high-speed network standards and are obsolete. Many recent systemsboth workstations and serversincorporate the network interface adapter onto the motherboard.

Note

You can also adapt the USB port for Ethernet use with a USB-to-Ethernet adapter, but because USB 1.1 ports run at only 12Mbps (compared to Fast Ethernet running at 100Mbps), a performance bottleneck results. USB 2.0toFast Ethernet adapters are available from several vendors and are a suitable choice if your system has USB 2.0 ports but lacks a free PCI or PC Card slot.

Network adapters have unique hardware addresses coded into their firmware. The data link layer protocol uses these addresses to identify the other systems on the network. A packet gets to the correct destination because its data link layer protocol header contains the hardware addresses of both the sending and receiving systems.

Ethernet network adapters range in price from less than $20 for client adapters to as much as $100 or more for server-optimized adapters. Token-Ring adapters, if required, are much more expensive, ranging in price from around $100 for client adapters to more than $500 for server-optimized adapters. Network adapters are built in all the popular interface-card types and are also optimized for either workstation or server use. For first-time network users, so-called network-in-a-box kits are available that contain two 10/100 Fast Ethernet or Wireless NICs (or PC Cards), a small switch, and prebuilt UTP cables for less than $100. When combined with the built-in networking software in Windows, these kits make networking very inexpensive. A number of 100/1000-BASE-TX Gigabit Ethernet adapters for use with UTP cable can be purchased for less than $60, and many switches now also feature Gigabit Ethernet ports.

For client workstations (including peer servers on peer-to-peer networks), the following sections contain my recommendations on the features you need.

Speed

Your NIC should run at the maximum speed you want your network to support. For a Gigabit Ethernet network, for example, you should purchase Ethernet cards that support 1000BASE-T's 1000Mbps speed. Most Gigabit Ethernet and Fast Ethernet cards also support slower speeds, such as Fast Ethernet's 100Mbps speed or standard Ethernet's 10Mbps speed, allowing the same card to be used on both older and newer portions of the network. To verify multispeed operation, look for network cards identified as 10/100 or 100/1000 Ethernet. In the case of wireless networking in the home, your best option remains 802.11g.

Your NIC should support both half-duplex and full-duplex operation:

• Half-duplex means that the network card can only send or only receive data in a single operation.

• Full-duplex means that the network card can both receive and send simultaneously. Full-duplex options boost network speed if switches are used in place of hubs. For example, 100Mbps Fast Ethernet cards running in full-duplex mode have a maximum true throughput of 200Mbps, with half going in each direction.

Unlike hubs, which broadcast data packets to all computers connected to it, switches create a direct connection between the sending and receiving computers. Thus, switches provide faster performance than hubs; most switches also support full-duplex operation, doubling the rated speed of the network when full-duplex network cards are used.

Bus Type

If you are networking desktop computers built from 1995 to the present, you should consider only PCI-based NICs (these computers typically have three or more PCI slots). Although many older computers still have at least one ISA or combo ISA/PCI expansion slot, the superior data bus width and data transfer rate of PCI make it the only logical choice for networks of all types. The integrated NIC found on most recent PC motherboards is also a PCI device. Alternative interfaces include USB or PC Card/Cardbus adapters that are often used for portable systems. At this time, there are also a handful of NICs based on PCI Express.

Table 18.3 summarizes the differences between all the types of interfaces network cards use.

Although a few ISA-based NICs are still on the market, their slow speeds and narrow bus widths severely restrict their performance. Most ISA-based Ethernet cards can't support speeds above 10Mbps and thus don't support Fast Ethernet or Gigabit Ethernet. A few vendors make 10/100 Ethernet cards for the ISA slot, but their performance is substantially lower than PCI cards. If you are shopping for a network card for a laptop or notebook system, look for Cardbus types, which are significantly faster than PC Cards and those using USB.

Wired Network Adapter Connectors

Wired Ethernet adapters typically have an RJ-45 connector, which looks like a large telephone jack. Fast Ethernet and Gigabit Ethernet twisted-pair cables use these connectors, but you might still find a few older adapters that support a single BNC connector (for Thinnet coaxial cables), or a D-shaped 15-pin connector called a DB15 (for Thicknet coaxial cables). A few older 10Mbps adapters have a combination of two or all three of these connector types; adapters with two or more connectors are referred to as combo adapters. Token-Ring adapters can have a 9-pin connector called a DB9 (for Type 1 STP cable) or sometimes an RJ-45 jack (for Type 3 UTP cable). Figure 18.5 shows all three of the Ethernet connectors.

Virtually all 10/100 Ethernet NICs made for client-PC use on the market today are designed to support unshielded twisted-pair (UTP) cable exclusively; Gigabit Ethernet cards made for wired (not fiber-optic) networks also use only UTP cable. If you are adding a client PC to an existing network that uses some form of coaxial cable, you have four options:

• Purchase a combo NIC that supports coaxial cable as well as RJ-45 twisted-pair cabling.

• Purchase a media converter that can be attached to the coaxial cable to allow the newer UTP-based NICs to connect to the existing network.

• Use a switch or hub that has both coaxial cable and RJ-45 ports. A dual-speed (10/100) device is needed if you are adding one or more Fast Ethernet clients.

• Replace the coaxial installation with an updated Ethernet installation.

For maximum economy, NICs and network cables must match, although media converters can be used to interconnect networks based on the same standard, but using different cable.

Network Cables for Wired Ethernet

Originally, all networks used some type of cable to connect the computers on the network to each other. Although various types of wireless networks are now on the market, many office and home networks still use twisted-pair Ethernet cabling. Occasionally you might still find some based on Thick or Thin Ethernet coaxial cable.

Thick and Thin Ethernet Coaxial Cable

The first versions of Ethernet were based on coaxial cable. The original form of Ethernet, 10BASE-5, used a thick coaxial cable (called Thicknet) that was not directly attached to the NIC. A device called an attachment unit interface (AUI) ran from a DB15 connector on the rear of the NIC to the cable. The cable had a hole drilled into it to allow the "vampire tap" to be connected to the cable. NICs designed for use with thick Ethernet cable are almost impossible to find as new hardware today.

10BASE-2 Ethernet cards use a BNC (Bayonet-Neill-Concilman) connector on the rear of the NIC. Although the thin coaxial cable (called Thinnet or RG-58) used with 10BASE-2 Ethernet has a bayonet connector that can physically attach to the BNC connector on the card, this configuration is incorrect and won't work. Instead, a BNC T-connector attaches to the rear of the card, allowing a thin Ethernet cable to be connected to either both ends of the T (for a computer in the middle of the network) or to one end only (for a computer at the end of the network). A 50-ohm terminator is connected to the other arm of the T to indicate the end of the network and prevent erroneous signals from being sent to other clients on the network. Some early Ethernet cards were designed to handle thick (AUI/DB15), thin (RG-58), and UTP (RJ-45) cables. Combo cards with both BNC and RJ-45 connectors may still be available but can run at only standard Ethernet speeds.

Figure 18.6 compares Ethernet DB-15 to AUI, BNC coaxial T-connector, and RJ-45 UTP connectors to each other, and Figure 18.7 illustrates the design of coaxial cable.

Twisted-Pair Cable

Twisted-pair cable is just what its name implies: insulated wires within a protective casing with a specified number of twists per foot. Twisting the wires reduces the effect of electromagnetic interference (that can be generated by nearby cables, electric motors, and fluorescent lighting) on the signals being transmitted. Shielded twisted pair (STP) refers to the amount of insulation around the cluster of wires and therefore its immunity to noise. You are probably familiar with unshielded twisted-pair (UTP) cable; it is often used for telephone wiring. Figure 18.8 shows unshielded twisted-pair cable; Figure 18.9 illustrates shielded twisted-pair cable.

Most Ethernet and Fast Ethernet installations that use twisted-pair cabling use UTP because the physical flexibility and small size of the cable and connectors makes routing it very easy. However, its lack of electrical insulation can make interference from fluorescent lighting, elevators, and alarm systems (among other devices) a major problem. If you use UTP in installations where interference can be a problem, you need to route the cable away from the interference, use an external shield, or substitute STP for UTP near interference sources.

Four standard types of unshielded twisted-pair cabling exist and are still used to varying degrees:

• Category 3 cable. The original type of UTP cable used for Ethernet networks was also the same as that used for business telephone wiring. This is known as Category 3, or voice-grade UTP cable, and is measured according to a scale that quantifies the cable's data-transmission capabilities. The cable itself is 24 AWG (American Wire Gauge, a standard for measuring the diameter of a wire), copper-tinned with solid conductors, 100105 ohm characteristic impedance, and a minimum of two twists per foot. Category 3 cable is largely obsolete because it is only adequate for networks running at up to 16Mbps so it cannot be used with Fast or Gigabit Ethernet.

• Category 5 cable. The newer, faster network types require greater performance levels. Fast Ethernet (100BASE-TX) uses the same two-wire pairs as 10BASE-T, but Fast Ethernet needs a greater resistance to signal crosstalk and attenuation. Therefore, the use of Category 5 UTP cabling is essential with 100BASE-TX Fast Ethernet. Although the 100BASE-T4 version of Fast Ethernet can use all four-wire pairs of Category 3 cable, this flavor of Fast Ethernet is not widely supported and has practically vanished from the marketplace. If you try to run Fast Ethernet 100BASE-TX over Category 3 cable, you will have a slow and unreliable network. Category 5 cable is commonly called CAT5 and is also referred to as Class D cable.

  Many cable vendors also sell an enhanced form of Category 5 cable called Category 5e (specified by Addendum 5 of the ANSI/TIA/EIA-568-A cabling standard). Category 5e cable can be used in place of Category 5 cable and is especially well suited for use in Fast Ethernet networks that might be upgraded to Gigabit Ethernet in the future. Category 5e cabling must pass several tests not required for Category 5 cabling. Even though you can use both Category 5 and Category 5e cabling on a Gigabit Ethernet (1000BASE-TX) network, Category 5e cabling provides better transmission rates and a greater margin of safety for reliable data transmission.

• Category 6 cable. Category 6 cabling (also called CAT 6 or Class E) can be used in place of CAT 5 or 5e cabling and uses the same RJ-45 connectors as CAT 5 and 5e. CAT 6 cable handles a frequency range of 1MHz250MHz, compared to CAT5 and CAT5e's 1MHz100MHz frequency range.

• Category 7 cable. Category 7 (also called CAT 7 or Class F) is the newest cabling standard and handles a frequency range of 1MHz600MHz, which reduces propagation delay and delay skew. This enables longer network cables and larger numbers of workstations on a network. CAT 7 uses the GG45 connector developed by Nexans. This connector resembles the RJ-45 connector but has four additional contacts (see Figure 18.10). The GG45 connector contains a switch that activates a maximum of 8 out of 12 contacts. The upper 8 RJ-45 contacts are used for up to 250MHz (CAT 6) operation, whereas the 8 contacts in the outer edges are used for 600MHz (CAT 7) operation. Only 8 contacts are used at a given time. In other words, this connector is designed to be backward compatible with cables using RJ-45 connectors while supporting the newer standard.

  Figure 18.10. The GG45 connector from Nexans can accept CAT 5 and other standard network cabling using the RJ-45 connector or the new CAT 7 cabling.

Caution

If you choose to install Category 5/5e UTP cable, be sure that all the connectors, wall plates, and other hardware components involved are also Category 5rated.

If you are trying to connect prebuilt Category 5 cabling together on a Fast Ethernet network, use Category 5grade or better connectors; otherwise, you'll create a substandard section that might fail in your network.

Choosing the correct type of Category 5/5e/6/7 cable is also important. Use solid PVC cable for network cables that represent a permanent installation. However, the slightly more expensive stranded cables are a better choice for a notebook computer or temporary wiring of no more than 10-feet lengths (from a computer to a wall socket, for example) because it is more flexible and is therefore capable of withstanding frequent movement.

If you plan to use air ducts or suspended ceilings for cable runs, you should use Plenum cable, which doesn't emit harmful fumes in a fire. It is much more expensive, but the safety issue is a worthwhile reason to use it (some localities require you to use Plenum cabling).

Building Your Own Twisted-Pair Cables

When it's time to wire your network, you have two choices. You can opt to purchase prebuilt cables, or you can build your own cables from bulk wire and connectors.

You should build your own twisted-pair cables if you

• Plan to perform a lot of networking

• Need cable lengths longer than the lengths you can buy preassembled at typical computer departments

• Want to create both standard and crossover cables

• Want to choose your own cable color

• Want maximum control over cable length

• Want to save money

• Have the time necessary to build cables

Twisted Pair Wiring Standards

If you want to create twisted-pair (TP) cables yourself, be sure your cable pairs match the color-coding of any existing cable or the color-coding of any prebuilt cabling you want to add to your new network. Because there are eight wires in TP cables, many incorrect combinations are possible. Several standards exist for UTP cabling.

Tip

The keys are to be consistent, use the same scheme for all your cables, and ensure that anyone else working on your network understands the scheme used in it.

One common standard is the AT&T 258A configuration (also called EIA/TIA 568B). Table 18.4 lists the wire pairing and placement within the standard RJ-45 connector.

^[*] This pair is not used with 10BASE-T or Fast Ethernet 100BASE-TX, but all four pairs are used with Fast Ethernet 100BASE-T4 and Gigabit Ethernet 1000BASE-TX standards.

In Figure 18.11 an RJ-45 cable connector is wired to the AT&T 258A/EIA 568B standard.

Note

You also might encounter the similar EIA 568A standard. It reverses the position of the orange and green pairs listed previously.

Crossover UTP Cables

Crossover cables, which change the wiring at one end of the cable, are used to connect two (and only two) computers when no hub or switch is available or to connect a hub or switch without an uplink port to another hub or switch. The pinout for a crossover cable is shown in Table 18.5. This pinout is for one end of the cable only; the other end of the cable should correspond to the standard EIA 568B pinout, as shown previously in Figure 18.11.

Note

It should be noted that other wiring schemes exist, such as IEEE and USOC. All told, at least eight agreed-on standards exist for connecting UTP cables and RJ-45 connectors. The ones listed in this chapter are the most common.

Constructing the Cable

Making your own UTP cables requires a few tools that aren't commonly found in a typical toolbox. Those items that you might not already have you can typically purchase for a single price from many network-products vendors. You will need the following tools and supplies to build your own Ethernet cables:

• UTP cable (Category 5 or better)

• RJ-45 connectors

• Wire stripper

• RJ-45 crimping tool

Before you make a "real" cable of any length, you should practice on a short length of cable. RJ-45 connectors and bulk cable are cheap; network failures are not. Follow these steps for creating your own twisted-pair cables:

1. Determine how long your UTP cable should be. You should allow adequate slack for moving the computer and for avoiding strong interference sources. Keep the maximum distances for UTP cables of about 100 meters in mind.

2. Roll out the appropriate length of cable.

3. Cut the cable cleanly from the box of wire.

4. Use the wire stripper to strip only the insulation jacket off the cable, exposing the TP wires (see Figure 18.12); you'll need to rotate the wire about 1 1/4 turns to strip away all the jacket. If you turn it too far, you'll damage the wires inside the cable.

   Figure 18.12. Carefully strip the cable jacket away to expose the four wire pairs.

5. Check the outer jacket and inner TP wires for nicks; adjust the stripper tool and repeat steps 3 and 4 if you see damage.

6. As shown in Figure 18.13, arrange the wires according to the EIA 568B standard. This arrangement is listed previously, in the section "Twisted Pair Wiring Standards."

   Figure 18.13. Arrange the wire pairs for insertion into the RJ-45 connector according to your chosen scheme (EIA 568B, for instance).

7. Trim the wire edges so the eight wires are even with one another and are slightly less than 1/2" past the end of the jacket. If the wires are too long, crosstalk (wire-to-wire interference) can result; if the wires are too short, they can't make a good connection with the RJ-45 plug.

8. With the clip side of the RJ-45 plug facing away from you, push the cable into place (see Figure 18.14). Verify that the wires are arranged according to the EIA/TIA 568B standard before you crimp the plug onto the wires (refer to Table 18.4 and Figure 18.11 earlier in this chapter). Adjust the connection as necessary.

   Figure 18.14. Push the RJ-45 connector into place, ensuring the cable pairs are ordered properly.

9. Use the crimping tool to squeeze the RJ-45 plug onto the cable (see Figure 18.15). The end of the cable should be tight enough to resist being removed by hand.

   Figure 18.15. Firmly squeeze the crimping tool to attach the connector to the cable.

10. Repeat steps 49 for the other end of the cable. Recut the end of the cable if necessary before stripping it.

11. Label each cable with the following information:

    • Wiring standard

    • Length

    • End with crossover (if any)

    • ________ (a blank) for computer ID

The cables should be labeled at both ends to make matching the cable with the correct computer easy and to facilitate troubleshooting at the hub. Check with your cable supplier for suitable labeling stock or tags you can attach to each cable.

Cable Distance Limitations

The people who design computer systems love to find ways to circumvent limitations. Manufacturers of Ethernet products have made possible the building of networks in star, branch, and tree designs that overcome the basic limitations already mentioned (for more information, see the "Network Topologies" section later in this chapter). Strictly speaking, you can have thousands of computers on a complex Ethernet network.

LANs are local because the network adapters and other hardware components typically can't send LAN messages more than a few hundred feet. Table 18.6 lists the distance limitations of various types of LAN cable. In addition to the limitations shown in the table, keep the following points in mind:

• You can't connect more than 30 computers on a single Thinnet Ethernet segment.

• You can't connect more than 100 computers on a Thicknet Ethernet segment.

• You can't connect more than 72 computers on a UTP Token-Ring cable.

• You can't connect more than 260 computers on an STP Token-Ring cable.

If you have a station wired with Category 5 cable that is more than 328 feet (100 meters) from a hub, you must use a repeater. If you have two or more stations beyond the 328 feet limit of UTP Ethernet, connect them to a hub or switch that is less than 328 feet away from the primary hub or switch and connect the new hub or switch to the primary hub or switch via its uplink port. Because hubs and switches can act as repeaters, this feature enables you to extend the effective length of your network (see Figure 18.16).

Network Topologies

Each computer on the network is connected to the other computers with cable (or some other medium, such as wireless using radio frequency signals). The physical arrangement of the cables connecting computers on a network is called the network topology.

Over the last 15 years the three types of basic topologies used in computer networks have been as follows:

• Bus. Connects each computer on a network directly to the next computer in a linear fashion. The network connection starts at the server and ends at the last computer in the network. (Obsolete.)

• Star. Connects each computer on the network to a central access point.

• Ring. Connects each computer to the others in a loop or ring. (Obsolete.)

For a long while, these different topologies were often mixed, forming what is called a hybrid network. For example, you can link the hubs of several star networks together with a bus, forming a star-bus network. Rings can be connected in the same way.

Table 18.7 summarizes the relationships between network types and topologies.

The bus, star, and ring topologies are discussed in the following sections. Wireless networking, which technically doesn't have a physical topology as described here, does still employ two logical (virtual) topologies, which I discuss here as well.

Bus Topology

The earliest type of network topology was the bus topology, which uses a single cable to connect all the computers in the network to each other, as shown in Figure 18.17. This network topology was adopted initially because running a single cable past all the computers in the network is easier and less wiring is used than with other topologies. Because early bus topology networks used bulky coaxial cables, these factors were important advantages. Both 10BASE-5 (thick) and 10BASE-2 (thin) Ethernet networks are based on the bus topology.

However, the advent of cheaper and more compact unshielded twisted-pair cabling, which also supports faster networks, has made the disadvantages of a bus topology apparent. If one computer or cable connection malfunctions, it can cause all the stations beyond it on the bus to lose their network connections. Thick Ethernet (10BASE-5) networks often fail because the vampire tap connecting the AUI device to the coaxial cable comes loose. In addition, the T-adapters and terminating resistors on a 10BASE-2 Thin Ethernet network can also come loose or be removed by the user, causing all or part of the network to fail. Another drawback of Thin Ethernet (10BASE-2) networks is that adding a new computer to the network between existing computers might require replacement of the existing network cable between the computers with shorter segments to connect to the new computer's network card and T-adapter, thus creating downtime for users on that segment of the network.

Ring Topology

Another topology often listed in discussions of this type is a ring, in which each workstation is connected to the next and the last workstation is connected to the first again (essentially a bus topology with the two ends connected). Two major network types use the ring topology:

• Fiber Distributed Data Interface (FDDI). A network topology used for large, high-speed networks using fiber-optic cables in a physical ring topology

• Token-Ring. Uses a logical ring topology

A Token-Ring network resembles a 10BASE-T or 10/100 Ethernet network at first glance because both networks use a central connecting device and a physical star topology. Where is the "Ring" in Token-Ring?

The ring exists only within the device that connects the computers, which is called a multistation access unit (MSAU) on a Token-Ring network (see Figure 18.18).

Signals generated from one computer travel to the MSAU, are sent out to the next computer, and then go back to the MSAU again. The data is then passed to each system in turn until it arrives back at the computer that originated it, where it is removed from the network. Therefore, although the physical wiring topology is a star, the data path is theoretically a ring. This is called a logical ring.

A logical ring that Token-Ring networks use is preferable to a physical ring network topology because it affords a greater degree of fault tolerance. As on a bus network, a cable break anywhere in a physical ring network topology, such as FDDI, affects the entire network. FDDI networks use two physical rings to provide a backup in case one ring fails. By contrast, on a Token-Ring network, the MSAU can effectively remove a malfunctioning computer from the logical ring, enabling the rest of the network to function normally.

Star Topology

By far the most popular type of topology in use today has separate cables to connect each computer to a central wiring nexus, often called a switch or hub. Figure 18.19 shows this arrangement, which is called a star topology.

Because each computer uses a separate cable, the failure of a network connection affects only the single machine involved. The other computers can continue to function normally. Bus cabling schemes use less cable than the star but are harder to diagnose or bypass when problems occur. At this time, Fast Ethernet in a star topology is the most commonly implemented type of LAN; this is the type of network you build with most preconfigured wired networking kits. 10BASE-T Ethernet and 1000BASE-TX Gigabit Ethernet also use the star topology.

Wireless Network Logical Topologies

Wireless networks have different topologies, just as wired networks do. However, wireless networks use only two logical topologies:

• Star. The star topology, used by Wi-Fi/IEEE 802.11based products in the infrastructure mode, resembles the topology used by 10BASE-T and faster versions of Ethernet that use a switch. The access point takes the place of the switch because stations connect via the access point, rather than directly with each other. This method is much more expensive per unit but permits performance in excess of 10BASE-T Ethernet speeds and has the added bonus of being easier to manage.

• Point-to-Point. Bluetooth products (as well as Wi-Fi products in the ad hoc mode) use the point-to-point topology. These devices connect directly with each other and require no access point or other hub-like device to communicate with each other, although shared Internet access does require that all computers connect to a common wireless gateway. The point-to-point topology is much less expensive per unit than a star topology. It is, however, best suited for temporary data sharing with another device (Bluetooth) and is currently much slower than 100BASE-TX networks.

Figure 18.20 shows a comparison of wireless networks using these two topologies.

Hubs and Switches for Ethernet Networks

As you have seen, modern Ethernet workgroup networkswhether wireless or wired with UTP cableare usually arranged in a star topology. The center of the star uses a multiport connecting device that can be either a hub or a switch. Although hubs and switches can be used to connect the networkand can have several features in commonthe differences between them are also significant and are covered in the following sections.

All Ethernet hubs and switches have the following features:

• Multiple RJ-45 UTP connectors (wireless switches still include wired ports)

• Diagnostic and activity lights

• A power supply

Ethernet hubs and switches are made in two forms: managed and unmanaged. Managed hubs and switches can be directly configured, enabled or disabled, or monitored by a network operator and are commonly used on corporate networks. Workgroup and home-office networks use less expensive unmanaged hubs, which simply connect computers on the network using the systems connected to it to provide a management interface for its configurable features.

Note

The now-obsolete ARCnet network used its own types of hubs: passive hubs, which were unpowered, and active hubs, which used a power supply. Neither type of hub is compatible with Ethernet.

Signal lights on the front of the hub or switch indicate which connections are in use by computers; switches also indicate whether a full-duplex connection is in use. Multispeed hubs and switches also indicate which connection speed is in use on each port. Your hub or switch must have at least one RJ-45 UTP connector for each computer you want to connect to it.

How Hubs Work

A computer on an Ethernet network broadcasts (sends) a request for network information or programs from a specific computer through the cable to the hub, which broadcasts the request to all computers connected to it. When the destination computer receives the message, it sends the requested information back to the hub, which broadcasts it again to all computers, although only the requesting computer acts on the information. Thus, a hub acts similarly to a radio transmitter and receiver that sends a signal to all radios, but only the radios set for the correct station can send or receive the information. Switches, due to the features explained in the next section, have largely replaced hubs on retail store shelves.

How Switches Differ from Hubs

Switches, as shown in Figure 18.21, are similar to hubs in both form factor and function. As with hubs, they connect computers on an Ethernet network to each other. However, instead of broadcasting data to all computers on the network as hubs do, switches use a feature called address storing, which checks the destination for each data packet and sends it directly to the computer for which it's intended. Thus, a switch can be compared to a telephone exchange, making direct connections between the originator of a call and the receiver.

Because switches establish a direct connection between the originating and receiving PC, they also provide the full bandwidth of the network to each port. Hubs, by contrast, must subdivide the network's bandwidth by the number of active connections on the network, meaning that bandwidth rises and falls depending on network activity.

For example, assume you have a four-station network workgroup using 10/100 NICs and a Fast Ethernet hub. The total bandwidth of the network is 100Mbps. However, if two stations are active, the effective bandwidth available to each station drops to 50Mbps (100Mbps divided by 2). If all four stations are active, the effective bandwidth drops to just 25Mbps (100Mbps divided by 4)! Add more active users, and the effective bandwidth continues to drop.

By replacing the hub with a switch, the effective bandwidth for each station remains 100Mbps because the switch doesn't broadcast data to all stations.

Most 10/100 NICs and Fast Ethernet or 10/100 switches also support full-duplex (simultaneous transmit and receive), enabling actual bandwidth to be double the nominal 100Mbps rating: 200Mbps. Table 18.8 summarizes the differences between the two devices.

As you can see, using a switch instead of a hub greatly increases the effective speed of a network, even if all other components remain the same.

Because of the improved performance of switches, I recommend them instead of hubs for networks of any size. When it comes time to purchase a hub or switch, you'll often find that the price difference is negligible between the two, so the switch makes good economic sense as well.

Additional Hub and Switch Features You Might Need

Although older hubs and switches run at only a single speed and have only a few RJ-45 connectors, it makes sense to upgrade to newer, more flexible equipment. Most recent hubs and switches have the following useful features, which are worth asking for:

• Multispeed hubs/switches. If you are adding Gigabit Ethernet (1000BASE-TX) or Fast Ethernet (100BASE-TX) clients to an existing 10BASE-T network, you need a multispeed hub or switch to connect the various types of Ethernet together.

  Even if you are building a brand-new Gigabit Ethernet or Fast Ethernet network, a multispeed hub or switch is useful for occasionally hosting a "guest" PC that has only a slower-speed NIC onboard. Even though most Gigabit Ethernet and Fast Ethernet switches and hubs on the market today are actually 10/100/1000 or 10/100 multispeed models, you might still encounter a single-speed only unit. These single-speed units should be used only on networks that will never have a need to support a slower connection.

• Wireless access point. Many switches today also feature a built-in wireless access point that supports 802.11b/g or 802.11a (dual-mode access points support all three). If you plan to implement a wireless network in the future, getting a switch with a wireless access point built in now is worth the minimal increase in cost.

• Stackable hub or switch with an uplink port. A stackable hub or switch is one that can be connected to another hub or switch (and often stacked on top of it), enabling you to add computers to your network without replacing the hub or switch every time it runs out of connections. Most hubs and switches on the market today are stackable (but very small) hubs, and some older models might lack this feature. You can use this feature to add 10/100/1000 features to an older 10BASE-T-only network and connect a multispeed hub or switch to the uplink port on your 10BASE-T hub.

• "Extra" ports beyond your current requirements. If you are connecting four computers together into a small network, you need a four-port hub or switch (the smallest available). But, if you buy a hub or switch with only four ports and want to add another client PC to the network, you must add a second hub or switch or replace the hub or switch with a larger one with more ports.

  Instead, plan for the future by buying a hub or switch that can handle your projected network growth over the next year. If you plan to add two workstations, buy at least an eight-port hub or switch (the cost per connection drops as you buy hubs and switches with more connections). Even though most hubs and switches are stackable to support the growth of your network, the more ports a hub or switch has, the less expensive per port it will be.

To determine whether a hub or switch is stackable, look for an uplink port. This port looks like an ordinary RJ-45 UTP port, but it is wired differently, enabling you to use a standard-pinout RJ-45 UTP cable to connect it to another hub. Without the uplink port, you'd have to use a specially wired crossover cable.

Note

The uplink port on your hub or switch is also used to connect the hub or switch to a router or gateway device that provides an Internet connection for your network. In cases where multiple hubs or switches are to be used, they are usually connected directly to the router or gateway instead of chained (or stacked) off each other.

Typically, hubs and switches with an uplink port allow you to use the port along with all but one of the normal ports on the hub. For example, one of my associates uses a five-port switch from Linksys that also contains a router (for Internet access) and an uplink port. If his office network expands beyond five computers, he can use the uplink port to add another switch to expand the network and provide the new stations, as well as the original network, with Internet access.

Hub and Switch Placement

Although large networks have a wiring closet near the server, the workgroup-size LANs found in a small office or home office network obviously don't require anything of the sort. However, the location of the hub or switch is important, even if your LAN is based solely on a Wi-Fi architecture.

Ethernet hubs and switches require electrical power, whether they are small units that use a power "brick" or larger units that have an internal power supply and a standard three-prong AC cord.

In addition to electrical power, consider placing the hub or switch where its signal lights will be easy to view for diagnostic purposes and where its RJ-45 connectors can be reached easily. This is important both when it's time to add another user or two and when you need to perform initial setup of the switch (requiring a wired connection) or need to troubleshoot a failed wireless connection. In many offices, the hub or switch sits on the corner of the desk, enabling the user to see network problems just by looking at the hub or switch.

If the hub or switch also integrates a router for use with a broadband Internet device, such as a DSL or cable modem, you can place it near the cable or DSL modem or at a distance if the layout of your home or office requires it. Because the cable or DSL modem usually connects to your computer by the same Category 5 cable used for UTP Ethernet networking, you can run the cable from the cable or DSL modem to the router/switch's WAN port and connect all the computers to the LAN ports on the router/switch.

Except for the 328-ft. (100-meter) limit for all forms of UTP Ethernet (10BASE-T, 100BASE-TX, and 1000BASE-TX), distances between each computer on the network and the hub or switch aren't critical, so put the hub or switch wherever you can supply power and gain easy access.

Although wireless networks do offer more freedom in terms of placing the switch/access point, you should keep in mind the distances involved (generally up to 150 feet indoor for 802.11b/g) and any walls or devices using the same 2.4GHz spectrum that might interfere with the signal.

Tip

Decide where you plan to put your hub or switch before you buy prebuilt UTP wiring or make your own; if you move the hub or switch, some of your wiring will no longer be the correct length. Although excess lengths of UTP cable can be coiled and secured with cable ties, cables that are too short should be replaced. You can buy RJ-45 connectors to create one long cable from two short cables, but you must ensure the connectors are Category 5 if you are running Fast Ethernet; some vendors still sell Category 3 connectors that support only 10Mbps. You're really better off replacing the too-short cable with one of the correct length.

More on Wireless Ethernet Hardware

All types of 802.11 wireless networks have two basic components:

• Access points

• NICs equipped with radio transceivers

An access point is a bookend-size device that uses one or more RJ-45 ports to attach to a 10BASE-T or 10/100 Ethernet network (if desired) and contains a radio transceiver, encryption, and communications software. It translates conventional Ethernet signals into wireless Ethernet signals that it broadcasts to wireless NICs on the network and then performs the same role in reverse to transfer signals from wireless NICs to the conventional Ethernet network.

For coverage of a large area, purchase two or more access points and connect them to an Ethernet switch or hub. This enables users to roam inside a building without losing contact with the network. Some access points can communicate directly with each other via radio waves, enabling you to create a wireless backbone that can cover a wide area (such as a warehouse) without the need to run any network cabling. You can also purchase a wireless Ethernet range extender that can receive and boost weak Wi-Fi signals.

Access points are not necessary for direct peer-to-peer networking (also called ad hoc mode), but they are required for a shared Internet connection or a connection with another network. When access points are used, the network is operating in the infrastructure mode.

NICs equipped for wireless Ethernet communications have a fixed or detachable radio antenna. Because a major market for wireless Ethernet use is notebook computer users, a few vendors sell only PC Cards in their wireless Ethernet product lines, but most vendors support PCI cards for desktop computers. Most vendors also offer wireless USB adapters for use in both desktop and notebook computers. Because you can mix and match Wi-Ficertified products that use the same frequency band, you can incorporate any mix of desktop and notebook computers into your wireless network. Figure 18.22 illustrates typical wireless network hardware.

In cases where a Wi-Fienabled system receives multiple Wi-Fi signals, client systems lock onto the strongest signal from access points and automatically roam (switch) to another access point when the signal strength is stronger and the error level is lower than the current connection. Of course, if you want the system to lock onto a specific signal, that can be done via the OS or manufacturer-provided software.

Additional hardware you might need to add to your network includes

• Wireless bridges. These devices enable you to connect a wired Ethernet device, including non-computer items such as video games or set-top boxes, to a wireless network.

• Wireless repeaters/range extenders. A repeater can be used to stretch the range of an existing wireless network. Some can also be used as access points or wireless bridges.

• Wireless router. Use this in place of a standard access point to enable a wireless network to connect to the Internet through a cable modem or other broadband device (refer to Chapter 17, "Internet Connectivity," for details). For additional flexibility, many wireless routers also include a multiport switch for use with wired Ethernet networks, and some also include a print server.

• Specialized antennas. The "rabbit ears" antennas used by most access points and routers are adequate for short distances, but longer distances or problems with line-of-sight reception can be solved by attaching specialized ceiling, wall, omnidirectional, or directional antennas in place of the standard antenna.

• Signal boosters. In addition to or as an alternative to replacement antennas, some vendors also sell signal boosters that piggyback onto an existing access point or router. Note that, in most cases, these signal boosters are vendor specific.

Security and Other Features

When I was writing the original edition of Upgrading and Repairing PCs, the hackers' favorite way of trying to get into a network without authorization was discovering the telephone number of a modem on the network, dialing in with a computer, and guessing the password, as in the movie War Games. Today, war driving has largely replaced this pastime as a popular hacker sport. War driving is the popular name for driving around neighborhoods with a notebook computer equipped with a wireless network card on the lookout for unsecured networks. They're all too easy to find, and after someone gets onto your network, all the secrets in your computer can be theirs for the taking.

Because wireless networks can be accessed by anyone within signal range who has a NIC matching the same IEEE standard of that wireless network, wireless NICs and access points provide for encryption options. Most access points (even cheaper SOHO models) also provide the capability to limit connections to the access point by using a list of authorized MAC numbers (each NIC has a unique MAC), thus limiting access to authorized devices only.

Caution

In the past, it was thought that the SSID feature provided by the IEEE 802.11 standards was also a security feature. That's not the case. A Wi-Fi network's SSID is nothing more than a network name for the wireless network, much the same as workgroups and domains have network names that identify them. The broadcasting of the SSID can be turned off (when clients look for networks, they won't immediately see the SSID), which does provide a marginal security benefit. However, in general, the SSID should never be considered to be a security item in any way. In fact, many freely available (and quite powerful) tools exist that allow snooping individuals to quickly discover your SSID even if it's not being broadcast, allowing them to connect to your unsecured wireless network.

All Wi-Fi products support at least 40-bit encryption through the wired equivalent privacy (WEP) specification, but the minimum standard on recent products is 64-bit WEP encryption. Many vendors offer 128-bit or 256-bit encryption on some of their products. However, the 128-bit and stronger encryption feature is more common among enterprise products than small-office/home-officeoriented products. Unfortunately, the WEP specification has been shown to be notoriously insecure against determined hacking. Enabling WEP will keep a casual snooper at bay, but someone who wants to get into your wireless network won't have much trouble breaking WEP.

For that reason, all wireless network products introduced after 2003 incorporate a different security standard known as Wi-Fi Protected Access (WPA). WPA is derived from the developing IEEE 802.11i security standard. WPA-enabled hardware works with existing WEP-compliant devices, and software upgrades are often available for existing devices to make them WPA capable.

You should match the encryption level and encryption type used on both the access points and the NICs for best security. Remember that, if some of your network supports WPA but other parts support only WEP, your network must use the lesser of the two security standards (WEP). If you want to use the more robust WPA security, you must ensure that all the devices on your wireless network support WPA. Because WEP is easily broken and the specific WEP implementations vary between manufacturers, I recommend using only devices that support WPA.

Some products' access points can be managed via a web browser and provide diagnostic and monitoring tools to help you optimize the positioning of access points. Most products feature support for Dynamic Host Configuration Protocol (DHCP), allowing a user to move from one subnet to another without difficulties.

Figure 18.23 illustrates how a typical IEEE 802.11 wireless network uses multiple access points.

Users per Access Point

The number of users per access point varies with the product; Wi-Fi access points are available in capacities supporting anywhere from 15 to as many as 254 users. You should contact the vendor of your preferred Wi-Fi access point device for details.

Although wired Ethernet networks are still the least expensive network to build if you can do your own wiring, Wi-Fi networking is now cost-competitive with wired Ethernet networks when the cost of a professional wiring job is figured into the overall expense.

Because Wi-Fi is a true standard, you can mix and match access point and wireless NIC hardware to meet your desired price, performance, and feature requirements for your wireless network, just as you can for conventional Ethernet networks provided you match up frequency bands or use dual-band hardware.

Notebook Computers with Integrated Wi-Fi Adapters

Major notebook computer makers, including Dell, IBM, and Toshiba, are now integrating built-in 802.11b/g or 802.11a/b/g wireless adapters and antennas into most of their notebook computers. Although computers with built-in Wi-Fi hardware are a little more expensive than comparable models lacking Wireless Ethernet support, building the adapter and antenna into notebook computers provides for a more durable and less cumbersome way to equip portable systems than the normal PC Card and external antenna arrangement that must be fitted to notebook computers that don't have internal Wi-Fi support.

Most notebook computers with Wi-Fi hardware onboard use the mini-PCI interface for the wireless adapter and place the antenna inside the screen housing. This enables computers with built-in Wi-Fi hardware to have one more open PC Card slot than computers that must use an external PC Card adapter and antenna.