A happy network medium has nothing whatsoever to do with a TV psychic. Rather, finding the right network medium means implementing network cabling that won't cause bottlenecks. Depending on whether you're building a network from the ground up or starting from scratch, you may need to take a different approach to evaluating cabling options for your network:
If you step into a job where a local area network (LAN) is already in place, cabling is probably in place, too. Evaluating the type, capabilities, and usability of an inherited network is almost always a good idea. That way, you can decide whether you can live with what you have, or whether some change will do the network good. You may learn, for example, that old cabling causes so many difficulties that you're better off replacing or upgrading it. (We've popped out ceiling tiles and found badly spliced cables hidden from view.)
If you're planning a brand-new network, one of your concerns is to determine your cabling needs.
Decide which network cabling you're going to use before ordering equipment for your network because you can often order computers and peripherals with the appropriate network interface cards (NICs) preinstalled and preconfigured. (Of course, NICs are preinstalled and preconfigured on an existing network, which means your choices have already been made for you.) The more work you save yourself, the better!
If a contractor handles your cabling maintenance, don't assume that every old cable gets replaced if it's not completely up to snuff. A contractor may choose to reuse substandard cables to save on material costs. Without proper wiring, your network may be in constant trouble (or it may not work at all).
Tip If you work with a cable contractor, require that contractor to test each network cable and insist that the contractor provide you with those test results. In fact, many companies hire one contractor to install cables and another to test them. By doing so, they ensure that the common tendency to overlook errors or potential sources of problems on a network can be avoided — plus, it never hurts to get a second opinion.
The most common cabling technology for LANs is baseband cable, which is cable set up for baseband transmission.
For this reason, we concentrate on baseband cable in this book. Check out the sidebar titled "Use the right pipes in your network's plumbing" for a description of baseband transmission and how it differs from broadband transmission.
Tip If you know what to look for, the name of a particular type of cable can tell you all about its transmission properties.
Ethernet cable notation (set down by the Institute of Electrical and Electronic Engineers, or IEEE) breaks down as follows:
The speed of the Ethernet in Mbps
The cable's technology — broadband or baseband
The cable's rated distance in hundreads of meters or the type of cable — twisted-pair or fiber-optic cable
Use the right pipes in your network's plumbing
Wiring in a network is like plumbing in a house. Just as pipes from the pathways through which water flows to and from your plumbing fixtures, a network's wiring provides the pathways through which computers transmit data using electric signals. The amount of data that computers can move through a wiring system at any one time depends on the characteristics of the wires, or pipes, installed. The larger the pipes, the more data that computers can send simultaneously.
You can think of a network's bandwidth as the size of a network's pipes. Bandwidth represents a range of usable
frequencies and is measured in hertz (Hz). A higher hertz rating for a network medium means higher available bandwidth. Higher bandwidth translates into bigger pipes to carry data. Just because you have big pipes, however, doesn't mean you always get to fill them completely. Therefore, it makes sense to try to measure the actual amount of data (called throughput) flowing through the pipes.
Different types of cabling are rated for different amounts of data flow at different distances. Remember, however, that even if a pipe is big enough to handle all the water you send through it, that pipe can still get clogged. As a result, although a given amount of data can theoretically flow through a cable, in the real world you may see less data flow than the maximum bandwidth indicates. Plumbers will tell you that mineral deposits and other
obstructions can often restrict the water flow in pipes. In keeping with our metaphor, we can say that noise, cross-talk, electromagnetic interference (EMI), and other network maladies can often degrade the actual performance of your cable. Throughput, commonly measured in bits per second (bps), describes the actual amount of data that's flowing through a cable at any one time.
If you take one pipe and divide it into little pipes, you've just reinvented the concept of broad-band transmission (in which multiple transmissions at different frequencies use the same networking medium simultaneously). If the pipe is kept whole instead of subdivided, you end up with the concept of baseband transmission (in which the entire bandwidth is used to carry only one set of frequencies and one transmission at a time).
Whew! Got all that? Maybe it's time to call Roto-Rooter!
For example, 10Base5 is an Ethernet designation that stands for [10 Mbps] [baseband] [5 x 100 meters = 500 meters].
From the name alone, you can tell that the baseband cable is rated to handle up to 10 Mbps on a segment up to 500 meters (1,640 feet) long.
Any time you see a T or an F in such a name, replace that letter with either twisted-pair or fiber-optic, respectively. For example, 10BaseT means that this particular baseband Ethernet cable is rated at up to 10 Mbps using twisted-pair cables. Likewise, 10BaseF means the same thing, except that it uses fiber-optic media instead of twisted-pair.
Cabling is easy, but comes in many varieties
Wiring and cables come in all sizes and shapes. Each type of cable has associated distance limitations. Each type also has different price tags, transmission characteristics, and so forth. The more common types of cable you find on modern networks are twisted-pair, coaxial, and fiber-optic.
Twisted-pair cable: Call it "teepee" for short!
Twisted-pair wiring comes in two flavors: unshielded twisted-pair (UTP) and shielded twisted-pair (STP). To explain shielded versus unshielded wiring in the simplest terms possible, STP incorporates a foil or wire braid around its wires, which are twisted together in pairs; UTP doesn't.
UTP
You've probably been exposed to UTP cable if you have any type of phone system in your organization. You may have even seen such cabling inside the walls of your home (if you watched the contractors build it).
A UTP cable consists of pairs of copper wires where a color-coded plastic jacket encases each wire. Individual pairs are twisted together, and the entire cable is wrapped in an outer jacket. Figure 7-1 depicts a cross section of a typical UTP cable. The number of twists in a cable is important because the twists improve transmission characteristics for the wires involved and improve resistance to interference. This puts a whole new twist on twisted-pair!
Figure 7-1: Let's twist again, like we did last summer.
Notice that the U in UTP means unshielded. That notation is included because another type of twisted-pair cable is shielded — STP (shielded twisted-pair). The difference is that STP includes an extra layer of shielding around the twisted wires. Both types of cable are used in modern networks, but UTP is more common because STP is more expensive. You find out more about STP later in this section.
Voice-grade UTP (CAT 1 and 2 — the next paragraph has the skinny on CAT ratings) is the kind of cable installed in most homes and in older phone systems. Voice-grade UTP cable is made to carry voice signals and is quite cheap.
Some organizations discover that they have extra phone wires already pulled and terminated in offices, so they try this cable for networking. The problem is that voice-grade UTP is not made to carry data. If you have a small LAN with little traffic, this cable may work. If you're building a big network with huge database applications, however, voice-grade UTP is unacceptable. You need to install UTP cable with a higher CAT rating.
Technical Stuff What's a CAT rating? CAT stands for category. The Electronic Industries Association (EIA) places ratings on UTP cable based on how fast such a cable can transmit data.
Here's the current roster of CAT ratings that you can find in use in the workplace:
CAT 1 and 2: Use only for voice and low-speed data CAT 3: Use for data speeds up to 16 Mbps
CAT 4: Use for data speeds up to 20 Mbps CAT 5: Use for data speeds up to 100 Mbps
CAT 5 Enhanced: Use for data speeds up to 200 Mbps CAT 6: Use for data speeds up to 600 Mbps
CAT 6 cable is different from its CAT 1 -- 5 counterparts. Each pair is individually wrapped in foil shielding, and then all pairs are enclosed in another layer of foil shielding. This extra shielding helps protect the cable from noise and other disturbances. The only question we have left is, "Why is CAT 6 called UTP when the cable is shielded?" Alas, some burning questions must go unanswered!
If you're already using UTP cable on your network and you're not sure how it's rated, call in a cable contractor to test your cables to see what you have.
Warning If you plan to install CAT 5 cable for your network, make sure that the connectors used from one end of the network to the other are also rated CAT 5. If you follow whatever connection your computer makes on the network through the wall and so on, you find numerous components along the way, including wall plates, punchdown blocks, and patch panels. All these need to be rated CAT 5 for the network to function properly at the rated data speeds.
UTP cable is cheaper and more widespread than STP, but it has a few minor foibles that you may not like. Because it's unshielded, UTP is prone to interference from external sources, such as fluorescent lighting. It's not unusual to pop ceiling tiles and find UTP cables strung over light fixtures or near elevators. This placement can lead to network interference; therefore, you should be careful how and where you place your cables.
10BaseT
10BaseT is a pretty popular version of Ethernet in broad use on today's networks. It's a star topology that uses
hubs connected with twisted-pair cable. And as its IEEE name indicates, it's an Ethernet standard rated for a transmission speeds of 10 Mbps. 10BaseT requires at least CAT 3 UTP. You can install CAT 5 for 10BaseT networks to anticipate moving to higher bandwidths such as 100BaseT. The following list tells you what you would need to construct a 10BaseT network starting from the device to the computer room:
NICs: Ethernet NICs with RJ-45 connections
Cable: CAT 3-5 UTP from NIC to transceiver (if it's an external transceiver) Transceiver: Can be external or on board the NIC
Cable: CAT 3-5 UTP from transceiver (or NIC) to wall Wall plate: RJ-45 sockets
Cabling in wall: CAT 3-5 UTP
Punchdown block: Incoming UTP wires are broght here and are pressed down into a block of wires using a special tool
Cable: CAT 3-5 UTP from punchdown block to patch panel Cable: CAT 3-5 UTP patch cable from patch panel to hub The following are some limitations to note when implementing 10BaseT:
Distance: From network device to hub, cable runs can't exceed 100 meters (328 feet).
Nodes: Can't use more than 1024 nodes on a network without subdividing that network and adding a routing device between the subdivisions.
Hubs: You may not plug more than 12 additional hubs into a main hub into a main hub to increase the total number of network devices accessible.
Another cost factor for twisted-pair cable is that it requires you to connect workstations through a hub. Although you can buy simple eight-port hubs for under $50, the added cost may still become a consideration if you're planning a large network. On the plus side, so-called smart hubs can be advantageous on a network because they can help you manage your cabling — but those smarts show up on the price tags for such equipment. At the very least, less expensive hubs always have blinking lights that can tell you which ports are active and whether data is transmitting.
In most cases, you'll be using UTP for your network cabling — that is, unless you need the extra shielding of STP or fiber-optic cabling. Most off-the-shelf NICs support UTP/STP only (it's getting harder and harder to find the combo cards that support both UTP/STP and coax). Plus, most network connection devices, such as hubs, repeaters, bridges, and routers have only UTP/STP ports.