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Anatomy of a Local-Area Network

Local-area networks (LANs) aren't as hard to understand as you might expect. It's true that they can be quite large and complex. In fact, entire books have been written on both wire-based and wireless LANs. For the purposes of this book, however, this chapter focuses on the basics.network interface card (NIC) to connect your machine to the network

A transmission medium

A hub (or switch) that interconnects multiple end-user machines

Figure 12-1 shows you how these pieces fit together to form a simple LAN.

As you can see in transmission mediuma copper wire, in this caseto the hub. The hub brings together multiple computers and enables them to communicate with each other. That's it! By using these basic mechanisms, you can build virtually any type of LAN. It is possible to use other things to build a larger, more complex network, but these are the building blocks. You can't build a network without them!

Two words that too often get used interchangeably are hub and switch. Both serve the same function: to interconnect multiple end-user devices in a LAN. There is a technical distinction between a hub and a switch. Both serve the same function, but a switch offers much higher performance. A hub forces all the devices that it interconnects to share the same bandwidth. For example, an eight-port 10-megabit (Mb) Ethernet hub forces all eight devices to share those 10 Mb. An eight-port Ethernet switch provides each of those eight devices with its own 10-Mb connection. Looking at a hub and a switch, you would be hard pressed to tell them apart. Operationally, however, a huge distinction exists. Because all devices connected to a hub share the same bandwidth, only one device can talk at a time. A switch offers each connecting device a dedicated connection so that each device can talk simultaneously without degrading performance.

There are, however, some ways to vary the network's actual shape or technology base. For example, the type of transmission medium you use can have a profound effect on the network's shape and performance. That's true for both wire types as well as for wireless.

Wire-Based Networks

When you look at Figure 12-1, you really can't see the NIC. Usually, it is an internal component of a computer, printer, or other device attached to a network. All you see when you look is a port or cable interface. The most commonly used cable interface looks like a double-wide telephone jack. You find the same type of interface on the hub.

The transmission medium can be almost anything. The most common is twisted- pair wiring (which uses the telephone jack-like interface), but there are many other types of media. In addition to twisted-pair copper wire, you can use fiber-optic cables, coaxial cables (the same type used to deliver cable TV service to your home), and radio waves.

For the purposes of a home network, you can skip fiber-optic cables. That allows you to focus on just twisted-pair copper and wireless transmission technologies. The remainder of this section introduces your two main options for a LAN's physical transmission media (coaxial cables and twisted pair) and shows you how they are used.

Coaxial Cables

Coaxial cables were the original copper wire used in LANs. Although successful in this role, over time they fell into disuse. Coaxial cables are thicker and less flexible than twisted-pair wiring, as well as more expensive.

The first generation of Ethernet LANs used two different types of coaxial cable: thick and thin. The thick cable formed your hub or backbone and the thin cables were spliced into that backbone to enable individual computers to connect to that network. Both thick and thin coaxial cables have almost completely disappeared from the landscape due to the emergence of less expensive and less bulky alternatives. Although coaxial cable continues to enjoy one functional niche, it is hardly ever used in LANs today.

Twisted-Pair Wire

Twisted-pair wiring started out as just the wire used for telephones. It has been repeatedly enhanced over the last decade or so for even greater performance.

Twisted-pair wiring slowly but steadily overtook coaxial cables as the preferred transmission medium in LANs around the world. The market was quick to perceive two main advantages of twisted pair versus coaxial cable: The former is less expensive to purchase, installation is much easier, and it takes up less room in cable trays and ducts.

Twisted-pair wiring has many different grades. These grades are known as Categories of Performance, although that is usually shortened to just Cat-x (where x is a number). For example, Cat-3 can support a 10 megabit per second (Mbps) connection for up to 100 meters. Cat-5 is the next step up and it can support 100 Mbps up to 100 meters. There are higher categories, too, but Cat-5 is the most commonly used in LANs.

When you go shopping for cable, you might notice some newer alternatives to Cat-5 cable. An enhanced version known as Cat-5e is now available as is a whole new category: Cat-6.

The Best of Both Worlds

Today, coaxial cables are enjoying a minor renaissance thanks to the emergence of high-speed Internet service delivered over cable TV networks. If you buy Internet access from a cable company, the company installs a coaxial cable (better known as coax) in your home. Of course, they also connect it to a network device that allows you to connect your home computer to it using twisted pair. The point is that coaxial cable is still alive and well. It is just living in a much smaller niche.

Figure 12-2 shows you this hybrid of a wire-based home network built using both twisted pair and coaxial cable.

Perhaps the best way to think of the two choices for a LAN wire is that you have two different tools designed for two entirely different purposes. Although they are used interchangeably, time and experience have sorted them into different roles. Coaxial cable has met all the needs of a community's cable TV service and can even do a nice job of delivering high-speed Internet access to your home. Twisted pair has proven itself far superior to coax when it comes to connecting things to your LAN.

Benefits of Wire-Based Networks

Wire-based networks, such as any of the Ethernet variations (10 Mbps Ethernet, 100 Mbps Fast Ethernet, and 1 Gigabit Ethernet), offer two main benefits: speed and reliability. Although both wireless and wire-based networks seem to continuously get faster, the wire-based media have a distinct advantage when it comes to speed. You can purchase relatively inexpensive switches for your home or office that support Ethernet at either 10 Mb, 100 Mb, or even 1 Gigabit (which is 1000 Mb or 1 billion bits per second).

With wireless LANs, your options are limited to 2 Mbps, 11 Mbps, or (if you have one of the new wireless networks) 54 Mbps. Although that's not bad, it's far short of the 1 Gigabit (Gb) that you can get with a wire-based network. Plus, a wireless network operates much more like a hub in that the amount of bandwidth must be shared by all the devices. Thus, your 54 Mbps wireless network actually doesn't operate as fast as the published operating speed.

Ethernet can actually run at speeds of 10 Gbps, but that is typically reserved for network backbones. You can get NICs and switches that allow 10, 100, or 1000 (1 Gb) connections for individual computers.

The other advantage of a wire-based network is reliability. That might sound a bit odd, but it's true. Many things can disrupt a signal that's traveling over something as fragile and unprotected as radio waves. Unless you're sporting a new XM radio, chances are good you've experienced static on your car radio during an electrical storm or when you approach the edges of that radio station's transmission area. That static is really a breakdown in the reliability of the transmission. Wire-based networks are more of a closed system and not as susceptible to such interference. Interference can still happen, it just doesn't happen as easily as with a wireless network.

Drawbacks of Wire-Based Networks

You should be aware of wire-based networks' two drawbacks: tidiness and inflexibility. Having worked with and around telecommunications gear for a couple of decades, rest assured that properly installed wiring is beautiful. Unfortunately, aside from the professional technicians who install carrier-class networks (top-level interstate or international networks), precious few people even know how to install wire the right way. Even fewer people would take the time to actually do so in a home network!

That might sound counterintuitive. After all, if you are going to install something that will remain in place for years, you would want to do it right. Unfortunately, logic takes a back seat to convenience when it comes to network wiring. Consequently, home networks that interconnect more than just two or three devices tend to get really messy. For one thing, all wires (power cables as well as network cables) tend to come in standard sizes that often have nothing in common with where you install them. That means that you have to coil up the excess and hide that unsightly mess.

The other drawback to wire-based networks is that after you have installed the wiring, making changes becomes difficult and possibly even expensive. Depending on how widespread your network is, your cabling can be limited to a single room or spread throughout a campus environment. In larger environments, changes might mean ripping out the old wire and reinstalling new wire. Those are small and manageable problems, but they are inherent in every wire-based network.

Wireless Networks

I'll be the first to admit that wireless networks can be a bit of an oxymoron. It is rare to find a truly wireless network. Some useful networks were built, however, with less wire than the more traditionally constructed networks. Wireless networks employ either radio waves, microwaves, or light waves to carry their signals through the air. That's in contrast to wire-based networks, which use electricity to carry a signal over a wired (usually copper or fiber optic) median.

The notion of a wireless network is compelling: You are spared the expense of purchasing and installing cables. Moves and rearrangements are easy, because you don't have to rip up or reinstall any network wires. At least you won't have to worry about cabling between the computer and the hub. That's the only part of a network that benefits from the wireless technology in a typical home network.

Although it is possible to build a completely wireless network at home, such networks are not the norm. Wireless technologies are maturing, but they certainly aren't ubiquitous, nor can they match the features and performance of a wire-based network. That is made a bit clearer in Figures 12-3 and 12-4. Figure 12-3 shows a typical home network constructed using both wire and wireless technologies. Figure 12-4 shows a purely wireless network.

As you can see in Figure 12-3, most wireless home networks are only wireless from the computer to the network. Many other devices tend to require physical wiring, including the Internet router and the printer. These physically wired connections use Fast Ethernet (100 Mbps) technology and operate at 100 Mbps. This "wireless" network is really a hybrid constructed of a coaxial cable from the Internet service provider, a twisted-pair wire from the cable modem to a wire-based Ethernet switch, and a twisted-pair wire from the Ethernet switch to the wireless hub.

Although you can't see this in the illustration, one of the home computers in this illustration uses an external wireless access point that conforms to the Wireless G standard and operates at 54 Mbps. To physically connect the computer to that access point requires the use of a Universal Serial Bus (USB) cable. It might not be long, but it's still a cable. Arguing from a purist's perspective, that USB cable between the computer and the wireless access pointnot to mention all the other wiresmakes this a "less wire" rather than a truly wireless solution.

For the sake of comparison, Figure 12-4 shows you an example of a purely wireless home network. This network can't do much, but it is completely wireless!

In Figure 12-4, there is no printer, no Network Attached Storage, nor anything else connected to the network besides a laptop and a PC. Internet access is courtesy of a cellular modem built into the laptop computer. This network was built using Wireless G technology and operates at 54 Mbps. About the only things you can do with this small but completely wireless network are share files andwhen the laptop is on the networkshare the Internet connection.

When you compare the networks in Figures 12-3 and 12-4, it becomes easy to see that you do pay a fairly heavy price for truly wireless technology. Sure, it's easy to install a wireless network, but the performance pales in comparison to a wire-based Ethernet. You will likely find your options limited unless you are willing to look at mixing wire and wireless technologies.

Please don't misconstrue this as wireless networks bashing. This is an attempt to show you the limits of the technology. If you are willing to not be a purist, a hybrid network with wireless access points and a modest amount of wire connecting certain peripherals can give you as feature-rich a network as you can hope to have!

Benefits of Wireless Networks

Now that you know a couple ways to build a home network, you should easily identify the benefits of a wireless network. They are easy to installno cables or cable-management worries. They also help you keep a tidy house. You don't have to worry about pre-cut cable sizes not quite matching your home environment. Nor will you have to pay extra for a custom-made cable that is the perfect size for your environment.

The greatest benefit of all is mobility. There is no end to the ways wireless network technology can enhance your mobility. Companies are quickly moving toward wireless access for their conference rooms and other public spaces. You may enjoy being able to just pick up you laptop and move to quieter areas of the house without breaking the network connection (or your train of thought).

Drawbacks of Wireless Networks

If the advantages of a wire-based network are speed and reliability, it is logical to conclude that the drawbacks of a wireless network are speed and reliability! Wireless LANs are becoming faster, but so are wire-based LANs. In the time it took for wireless to go from 2 to 54 Mbps, wire-based LANs stretched from 10 to 100 Mb and then up to 1 Gbps. Wireless networks are designed for flexibility and mobility, not speed or reliability.

Wireless transmissions are also quite fragile. Depending on the technology, rain, fog, and smoke can impede your outdoor wireless technologies. Thunderstorms, other forms of electrical interference, and even other electrical devices can all impede your indoor transmissions. Remember: You bought it for flexibility and mobility, not reliability!

Security is another drawback inherent in wireless networks. Let's face it: You are transmitting over public radio waves. Just as anybody can listen to a radio station if they are within its range, anybody close enough to your wireless network can pick off your transmissions. Wire-based LANs aren't perfect, but it is a little harder to intercept data transmitted in a wire-based network than it in a wireless LAN.

You might categorize this as either a benefit or a drawback, but many of today's wireless LANs operate at the same frequency as a microwave oven. The wireless LAN transmits at low power levels while the oven operates at a much higher power level. That's fairly logical; you can't cook food with a wireless LAN even though it uses the same frequency as a microwave oven. If your microwave oven leaks waves, they will stomp on your wireless LAN. Your wireless LAN will become almost completely useless. You won't be able to send or receive anything while the oven is in use. If your wireless LAN sometimes seems to slow down or you can't use it at all, check to see if your microwave oven is in use. If you can correlate the oven's usage with slowdowns in your wireless LAN, it is time to buy a new oven! Please note that if you live in an apartment, condo, or otherwise in close proximity to your neighbors, your wireless LAN might suffer if their microwave oven has seen better days. There's not much you can do about that unless you are willing to buy a new microwave oven for all your neighbors! You decide whether the microwave oven integrity test is a benefit or drawback of wireless LANs!