⻬ Some 10100BaseT hubs have a BNC connector on the back. This BNC connector is a Thinnet repeater that enables you to attach a full 185-
meter Thinnet segment. The segment can attach other computers, 10BaseT hubs, or a combination of both.
⻬ A basic rule of Ethernet life is that a signal cannot pass through more than three repeaters on its way from one node to another. That doesn’t
mean you can’t have more than three repeaters or hubs, but if you do, you have to carefully plan the network cabling so that the three-repeater
rule isn’t violated.
⻬ A two-port 10Base2 repeater costs about 200. Sheesh I guess that’s one of the reasons fewer people use coax cable these days.
⻬ Repeaters are legitimate components of a by-the-book Ethernet network. They don’t extend the maximum length of a single segment; they just
enable you to tie two segments together. Beware of the little black boxes that claim to extend the segment limit beyond the standard 185-meter
limit for Thinnet. These products usually work, but playing by the rules is better.
Managed Switches
A managed switch is a 10BaseT or 100BaseT switch that allows you to moni- tor and control various aspects of the switch’s operation from a remote com-
puter. Here are some of the benefits of managed switches:
⻬ Managed switches can keep network usage and performance statistics, so you can find out which parts of your network are heavily used and
which are not. ⻬ A managed switch can alert you when something goes wrong with your
network. In fact, the management software that controls the switch can even be configured to send you e-mail or dial your pager when a network
error occurs. ⻬ You can reconfigure a managed switch from any computer on the net-
work, without having to actually go to the switch. Inexpensive switches do not include management features. An unmanaged
switch is fine for a small network, but for larger networks, you should invest in managed switches. A typical managed switch can cost two or three times
as much as an equivalent unmanaged switch, but for larger networks, the bene- fits of switch management are well worth the additional cost. However, if your
network has only one or two switches, you probably don’t need management.
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Bridges
A bridge is a device that connects two networks so they act as if they were one network. Bridges are used to partition one large network into two smaller
networks for performance reasons. You can think of a bridge as a kind of smart repeater. Repeaters listen to signals coming down one network cable, amplify
them, and send them down the other cable. They do this blindly, paying no attention to the content of the messages they repeat.
In contrast, a bridge is a little smarter about the messages that come down the pike. For starters, most bridges have the capability to listen to the net-
work and automatically figure out the address of each computer on both sides of the bridge. Then the bridge can inspect each message that comes
from one side of the bridge and broadcast it on the other side of the bridge only if the message is intended for a computer that’s on the other side.
This key feature enables bridges to partition a large network into two smaller, more efficient networks. Bridges work best in networks that are highly segre-
gated. For example humor me here — I’m a Dr. Seuss fan, suppose that the Sneetches networked all their computers and discovered that, although the
Star-Bellied Sneetches’ computers talked to each other frequently and the Plain-Bellied Sneetches’ computers also talked to each other frequently, rarely
did a Star-Bellied Sneetch computer talk to a Plain-Bellied Sneetch computer.
A bridge can partition the Sneetchnet into two networks: the Star-Bellied net- work and the Plain-Bellied network. The bridge automatically learns which
computers are on the Star-Bellied network and which are on the Plain-Bellied network. The bridge forwards messages from the Star-Bellied side to the
Plain-Bellied side and vice versa only when necessary. The overall perfor- mance of both networks improves, although the performance of any network
operation that has to travel over the bridge slows down a bit.
Here are a few additional things to consider about bridges: ⻬ As I mentioned, some bridges also have the capability to translate the
messages from one format to another. For example, if the Star-Bellied Sneetches build their network with Ethernet and the Plain-Bellied
Sneetches use Token Ring, a bridge can tie the two together. ⻬ You can get a basic bridge to partition two Ethernet networks for about
500 from mail-order suppliers. More sophisticated bridges can cost as much as 5,000 or more.
⻬ If you’ve never read Dr. Seuss’s classic story of the Sneetches, you should. ⻬ If you’re not confused yet, don’t worry. Read on.
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Gateways
No, not the Bill Gates way. This kind of gateway is a superintelligent router, which is a superintelligent bridge, which is a superintelligent repeater. Notice
a pattern here?
Gateways are designed to connect radically different types of networks together. They do this by translating messages from one network’s format to
another’s format, much like the Universal Translator that got Kirk and Spock out of so many jams. Ever notice how all those planets with gorgeous females
never seemed to have a word for kiss, so Kirk had to demonstrate?
Gateways usually connect a network to a mainframe or minicomputer. If you don’t have a mainframe or minicomputer, you probably don’t need a gateway.
Keep the following points in mind: ⻬ Gateways are necessary only because of the mess that computer manu-
facturers got us into by insisting on using their own proprietary designs for networks. If computer manufacturers had talked to each other 20
years ago, we wouldn’t have to use gateways to make their networks talk to each other today.
⻬ Gateways come in several varieties. My favorite is ornamental wrought iron.
It’s a RAID
In most small networks, it’s a hassle if a disk drive goes south and has to be sent to the shop for repairs. In some large networks, a failed disk drive is
more than a hassle: It’s an outright disaster. Big companies don’t know how to do anything when the computer goes down. Everyone just sits around,
looking at the floor, silently keeping vigil ‘til the computers come back up.
A RAID system is a fancy type of disk storage that hardly ever fails. It works by lumping several disk drives together and treating them as if they were one
humongous drive. RAID uses some fancy techniques devised by computer nerds at Berkeley. These computer nerds guarantee that if one of the disk
drives in the RAID system fails, no data is lost. The disk drive that failed can be removed and repaired, and the data that was on it can be reconstructed
from the other drives.
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Here are a few additional thoughts on RAID: ⻬ RAID stands for Redundant Array of Inexpensive Disks, but that doesn’t
matter. You don’t have to remember that for the test. ⻬ A RAID system is often housed in a separate cabinet that includes its
own RAID disk controller. It’s sometimes called a disk subsystem. Note that some server computers have RAID systems built in, however.
⻬ In the coolest RAID systems, the disk drives themselves are hot-swappable. That means that you can shut down and remove one of the disk drives
while the RAID system continues to operate. Network users won’t even know that one of the disks has been removed because the RAID system
reconstructs the data that was on the removed disk, using data from the other disks. After the failed disk has been replaced, the new disk is
brought online without a hitch.
Server Farms
Large networks with multiple servers often have their servers bunched together in one room; the result is known as a server farm no, there’s no
E-I-E-I-O protocol. If you have more than two or three servers, you might want to consider some or all of the following methods of dealing with them:
⻬ You can use inexpensive wire shelving to hold your servers. You can also get special wire shelves designed to hold keyboards, monitors, and
processors, providing easy access to cabling. For a more professional look, you can get customized LAN-management furniture designed to
hold multiple server computers in just about any configuration you need.
⻬ If you have limited space, you can use a device known as a KVM switch to connect several server computers to a single keyboard, monitor, and
mouse. KVM stands for keyboard, video, and mouse. That way, you can control any of the servers from the same keyboard, monitor, and mouse
by turning a dial or pressing a button on the KVM switch.
⻬ To save even more space, you can get rack-mounted servers instead of servers built in standard computer cases. Rack-mounted servers can be
attached to the same standard 19-inch racks that rack-mounted hubs and patch panels mount to.
⻬ A recent trend in server farms is the use of blade servers. These are com- plete servers that fit on a single card, which can be mounted vertically
in a special rack-mounted case designed to hold several servers.
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Gigabit Ethernet
Most small networks operate just fine with standard 100BaseT Ethernet connections. However, if your network is large enough to merit a high-speed
backbone connection, you may want to look into Gigabit Ethernet. Gigabit Ethernet is a relatively new version of Ethernet, which runs at 1000 Mbps
instead of 100 Mbps.
Gigabit Ethernet, also known as 1000BaseX, was initially designed to operate over fiber-optic cables but will eventually be able to work over Category-5
UTP cable as well. That’s one of the reasons you should take care to install only top-quality Category-5 cable and keep the cable lengths under 100 meters.
Of course, Gigabit Ethernet is more expensive than 10BaseT or 100BaseT. A Gigabit Ethernet switch can cost several thousand dollars, and you need one
at each end of the backbone.
Storage Area Networks
A storage area network, also called SAN, is designed for managing very large amounts of network storage — in some cases, downright huge amounts. A
SAN consists of three components: storage devices possibly hundreds of them, a separate high-speed network usually fiber-optic that directly con-
nects the storage devices to each other, and one or more SAN servers that connect the SAN to the local area network. The SAN server manages the stor-
age devices attached to the SAN and allows users of the LAN to access the storage.
Setting up and managing a Storage Area Network is a job for a SAN expert. If you’re interested, you can find more information about storage area net-
works at the home page of the Storage Networking Industry Association at www.snia.org
.
Protocol Analyzer
A protocol analyzer is a device that attaches to your network and examines all of the packets that are zipping along inside the cables. In the hands of a
seasoned pro, a protocol analyzer can help diagnose all kinds of networking problems — performance problems, security breaches, broken connections,
and so on.
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