Understanding Home and SOHO
Networks
If you are used to working on a single computer, the idea of
setting up a network may seem daunting. Perhaps at work you do plug into the corporate network, but maintaining and
configuring this network isn't your problem. Instead, it is handled by a staff
of highly professional overachievers. At least, that's what the folks from
corporate information technology (IT) would have you believe.
Relax! There's nothing particularly dark, deep, or mysterious
about the concepts involved in setting up a small home or office network.
I'd like to step back for a moment or two and forget about
Wi-Fi and wireless connectivity. This will give me the chance to explain
networks to you generally. As you'll see, networks are really simple. There are
no really tough concepts involved. By explaining the concepts, and showing you
the relevant vocabulary, I can help make sure that you'll make the right
purchasing decisions (and never be snowed by a salesperson's jargon!).
There is no real difference between wired and wireless networks
except that in the former information is sent and received using the wire
connections and in the latter radio transmissions are used.
In the Beginning There Was the Connection
At its most basic level, a network is simply two or more
computers or devices that are connected, as shown in Figure 4.1.
Most modern networks, including the Internet itself, use a
protocol called TCP/IP (Transmission Control Protocol/Internet Protocol) to
standardize communications.
 |
There are many devices that can be added to a network. A good
example is a network-enabled printer. However, in this chapter I'm pretty much
just going to talk about computers and devices generically, and I'll be using
the terms "computer" and "device" essentially synonymously. |
TCP/IP consists of a number of different so-called layers that specify how network transmission are broken
down into units, called packets, and reassembled,
and much more.
TCP/IP is distinct from the mechanism used to convey the
communication, meaning that if your network is operating over a wired
connection, such as 10BASE-T Ethernet, the TCP/IP transmissions pass "over" the
10BASE-T wires. Similarly, if your network operates using Wi-Fi, TCP/IP
transmissions are occurring "on top of" the Wi-Fi signals.
To Serve or Not to Serve
From a practical viewpoint, there are really two different ways
that a network can be arranged. The arrangement of a network is called a network
topology.
The simplest setup is one in which computers share resources
such as files, printers, and Internet access on an ad-hoc basis. This is often
called a peer-to-peer network. At a concept
level, which means forgetting about things like whether the connections are made
with wires or radio waves, a peer-to-peer network might look like the one shown
in Figure 4.2.
The other type of network topology, client/server, is somewhat
more complex. In this kind of setup, a centralized server computer controls and
polices many of the basic functions of the network. For example, the server is
used to authenticate users, and to make sure that they have permission to take
specific actions in respect to resources. In this kind of setup, only specific
users (or kinds of users) may be allowed to modify or delete files. (Although
individual computers can share resources directly, the sharing can only take
place if the policies established on the server allow it.)
It's hard to enforce this kind of policy on a network without a
centralized server. At a conceptual level, forgetting for the moment how the
computers are actually connected, a client/server network might look like the
one shown in Figure 4.3.
Generally, client/server networks are found in larger-scale
enterprise environments. I've described them here in case you work in an
environment that has this kind of network. But you probably don't need anything
as complex (and expensive) to administer in your home or small office. For the
sake of keeping things simple, in this chapter I'll assume you are interested in
assembling a peer-to-peer network (or already have such a network that you'd
like to add Wi-Fi capabilities to).
Hubs
A hub is a wired device that is the simplest way to connect
three or more devices. A hub is basically a box that
networked computers connect to via several ports. The hub simply replicates the
signals coming into each of its ports and sends the signals to each of its other
ports. This is another way of saying that the hub receives information from any
device plugged into it and transmits the information to all other connected
devices. It neither knows nor cares which devices the information is going to.
It is up to each individual device to pick up the data meant for it. Plugging
four devices into a hub has more or less the same result as connecting the
devices to each other.
Typical wired hubs are very inexpensive and come with four or
five sockets for connections to computers, but some hubs can have a great many
more connections.
Switches
You may have heard the term switch in connection with
networks. A switch is just an intelligent hub. Like a hub, a switch is a device
used to connect computers. But a hub has no smarts, and simply replicates the
signals coming in from each computer and passes the signal along to all the
connected computers. In contrast, a switch has built-in "intelligence" that
understands where to send transmissions.
Small networks usually don't need switches. The busier the
network becomes, the more important it is to use intelligent switches rather
than hubs.
These days, even lower-end hubs tend to have some intelligence
built-in, and are called switches.
Figure 4.4 shows an
inexpensive switch in use as a simple hub.
Routers
A router sits between one network and another. If you are
interested in setting up a small home or office network, you are likely to use a
router to connect the Internet (the largest network of all) with your small
network.
Let's suppose you have a cable modem, or a DSL modem, connected
to the Internet at your home. The router connects to the modem, and also to your
home network as you can see in Figure
4.5.
You should know that most routers also function as
hubs/switches, and provide four or five wired connection sockets. (As I'll
discuss shortly, routers also come with Wi-Fi.)
If you only plan to connect a few devices to your network, in
addition to your modem you may only need a router. You can always add hubs as
you need them.
Figure 4.6 shows a wired
router in use.
Besides their function as a kind of gateway between networks,
most routers provide some additional functionality. Routers can make Internet
access possible by translating local network addresses to ones that work on the
Internet, a feature called Network Address Translation (NAT), and by assigning
network addresses to local machines on the fly. This allows the computer (or
computers) that make up your home network to interact with servers on the
Internet.
Most routers also include features that protect your data by
blocking some kinds of information from accessing your network using what is
known as a firewall. A firewall is a
blocking mechanism—either hardware, software, or both—that blocks intruders from
scanning for or accessing a network or individual computer. For more about using
personal and network firewalls, see Part V, "Securing Your Wi-Fi Computer and
Network."
What Is the Network?
How many stars are there in the sky at night, and how vast is
the network? Before I wax too poetic, let me get to the point!
Small networks are created by connecting devices, usually via a
hub. Larger networks are simply aggregations of small networks, with the small
networks connecting to each other, and to the Internet, via routers.
Although these building blocks are very simple, it is obviously
possible to create complex network topologies using them. There are also
infinite varieties of the possible ways to arrange networks.
You'll have to fit the network topology you create to your
physical needs. How many computers do you need, and where?
As an example, Figure
4.7 shows a fairly simple network topology that has seven connected devices
and uses a router and two hubs.
It's worth stepping back for a second and thinking about what
you are creating when you string together computers to make a network. By
combining computers in a network, you've created a new entity (the network) that
has more computing power than any individual device on the network. Hallelujah!
It gets even better when you use a router to connect your network to even more
powerful external networks such as the Internet. Effectively, you've harnessed
the power of many discrete networks running all over the world in every node of
your home or small office.
When this kind of network has become commonplace (or
"ubiquitous" as they say in marketing departments), what really is the computer?
It doesn't really seem right to think of the computer as limited to a single CPU
(or box and monitor) when the computer is functioning as part of a network.
Maybe the network really is the computer. How much more powerful, and easy, it
all becomes when you don't need wires to make the network connections, and you
can take your computer (for example, the network) everywhere you go!
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