Upgrading and Repairing PCs

Network Cable Installations

If you have to run cables (of any type) through existing walls and ceilings, the cable installation can be the most expensive part of setting up a LAN. At every branching point, special fittings connect the intersecting wires. Sometimes, you also need various additional components along the way, such as hubs, repeaters, or MSAUs.

Note As an alternative to wired networks, more and more companies and home users are exploring wireless networks using radio waves and other technologies. Although these networks are not yet as fast as wired solutions such as Fast Ethernet, they are useful for solutions in which wiring isn't feasible or when speed is not important. See the section "Wireless Network Standards," later in this chapter, for details.

With the development of easy-to-build (or prebuilt) Category 5 twisted-pair cabling, high-speed and low-cost NICs and hubs, and built-in basic networking in current versions of Windows, installing and setting up a network today is far easier than ever before. For small cubicle/office networking in which no wire must be routed through walls and in which Windows peer networking software will be used, you should be able to set up the network yourself.

If your wiring must go through walls, be run through dropped ceilings, be piggybacked on air ducts, or be run between floors, you might want to have professional network-cable specialists install the cable. A good company knows the following:

• When UTP (unshielded twisted-pair) cabling is adequate

• Where STP (shielded twisted-pair) cabling might be necessary to avoid excessive cable runs and interference

• How to route cable between rooms, floors, and nonadjacent offices

• How to use wall panels to make cable attachments look better and more professional

• When you must use fireproof Plenum cable

• How to deal with sources of electrical interference, such as elevator motors, transmitters, alarm systems, and even florescent office lighting, by using fiber-optic or shielded cable

If you decide you need professional cable installation, be sure to get a firm price quote first because the cost of a complex cable installation might make a wireless network a more appealing choice.

Selecting the Proper Cable

A network is only as fast as its slowest component; to achieve the maximum speeds of the network, all its components, including cables, must meet the standards. Two standard types of twisted-pair cabling exist:

• 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, 100–105 ohm characteristic impedance, and a minimum of two twists per foot. Category 3 cable is adequate for networks running at up to 16Mbps. This cable usually looks like "silver" telephone cable, but with the larger RJ-45 connector. Category 3 cabling is obsolete because it doesn't support Fast Ethernet or greater network speeds.

• 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. Thus, for practical purposes, if you mix Category 3 and Category 5 cables, you should use only 10BASE-T (10Mbps) Ethernet hubs; 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 network, Category 5e cabling provides better transmission rates and a greater margin of safety for reliable data transmission.

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 1MHz–250MHz, compared to CAT5 and CAT5e's 1MHz–100MHz frequency range.

You should use existing Category 3 cable for your LAN only if you are content with the 10Mbps speeds of 10BASE-T and if the cable is in good condition. The silver exterior on Category 3 cabling can become brittle and deteriorate, leading to frequent network failures. If you are installing new wiring for a new network or replacing deteriorated Category 3 cable, you should use Category 5, Category 5e, or Category 6 cabling. All three types are widely available either in prebuilt assemblies or in bulk.

The newest standard—Category 7 cabling (also called CAT 7 or Class F)—handles a frequency range of 1MHz–600MHz and reduces propagation delay and delay skew, which enables longer network cables and larger numbers of workstations on a network. CAT 7 uses the GG45 connector developed by Nexans. The GG45 connector resembles the RJ-45 connector but has four additional contacts (see Figure 20.16). The GG45 connector contains a switch that activates a maximum of 8 out of 12 contacts. The upper 8 RJ45 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.

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

Choosing the correct type of Category 5/5e 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" 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 (and it is required by some localities).

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

TP 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 key is to be consistent and use the same scheme for all your cables and to 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 20.6 lists the wire pairing and placement within the standard RJ-45 connector.

Table 20.6. RJ-45 Connector Wire Pairing and Placement for AT&T 258A/EIA 568B Standard

Wire Pairing	Wire Connected to Pin #	Pair Used For
White/blue and blue	White/blue - #5 Blue - #4	Not used[1]
White/orange and orange	White/orange - #1 Orange - #2	Transmit
White/green and green	White/green - #3 Green - #6	Receive
White/brown and brown	White/brown - #7 Brown - #8	Not used[1]

^[1] 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 20.17 you can see a RJ-45 cable connector wired to the EIA 568B/AT&T 258A 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 together when no hub or switch is available or to connect a hub or switch without an uplink (stacking) port to another hub or switch. The pinout for a crossover cable is shown in Table 20.7. This pinout is for one end of the cable only; the other end of the cable should correspond to the standard TIA 568B pinout, as shown previously in Figure 20.17.

Table 20.7. RJ-45 Connector Wire Pairing and Placement for Crossover Variation on EIA 568B Standard

Wire	Pin #	Wire	Pin #
White/blue	5	White/orange	3
Blue	4	Orange	6
White/green	1	White/brown	7
Green	2	Brown	8

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.

Making Your Own UTP Cables

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 (see Figure 20.18):

• 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:

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.

An excellent online source for this process is http://www.duxcw.com/digest/Howto/network/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. 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 20.8 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.

Table 20.8. Network Distance Limitations

Network Adapter	Cable Type	Maximum	Minimum
Ethernet	10BASE-2 10BASE-5 (drop) 10BASE-5 (backbone) 10BASE-T 100BASE-TX 1000BASE-TX	185m (607 ft.) 50m (164 ft.) 500m (1,640 ft.) 100m (328 ft.) 100m (328 ft.) 100m (328 ft.)	0.5m (1.6 ft.) 2.5m (8.2 ft.) 2.5m (8.2 ft.) 2.5m (8.2 ft.) 2.5m (8.2 ft.) 2.5m (8.2 ft.)
Token-Ring	STP UTP	100m (328 ft.) 45m (147 ft.)	2.5m (8.2 ft.) 2.5m (8.2 ft.)
ARCnet	Passive hub drop Active hub	30m (98 ft.) 600m (1,968 ft.)	Varies by cable type Varies by cable type

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" 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 20.23).