Introduction to Computer Networking - In
"Rusty" Entrekin, MCP, A+
Owner, Office Networks USA
Is A Network?
A network is a group of computers connected to
allow the sharing of information, services, and equipment.
Many Kinds Of Networks Are There?
There are three basic kinds of networks. The
first is a Local Area Network,
or LAN, which connects computers in a small area such as a
building or a department. Sometimes, a local area network
consists of more than one segment. Each segment of a LAN is
separated by a bridge, which filters out signals not
intended for particular segments. The computers within a
segment are joined together by hubs or switches,
which will be explained below.
The second kind of network is a Wide
Area Network, or WAN, which connects two or more LANs
together over public and private data communication channels.
The third is an Internetwork, which is
a connection of LANs that are connected by routers.
Routers "route" signals to their proper
destinations. The internet is an example of an
internetwork. So are intranets, which are private
internetworks. Each LAN in an internet is called a subnetwork.
Is a TAN?
A TAN, or Tiny Area Network, is simply
a very small local area network. Tans are becoming
popular in homes, home offices, and small businesses. There
are many benefits to having a TAN. Networking your computers
makes it possible to share high speed routers, printers, and
files. Once your computers are networked, you can send email
and reminders to others on your network, and home users may
even play network games with family members. With a TAN, you
can take full advantage of your router or proxy server
software, which enable an internet connection to be shared
among other computers on the network. That way, everyone on
the network can visit different places on the internet at the
Two Flavors of LANS
LANs which have no centralized control are
called peer to peer networks. These are most commonly
found in homes and very small businesses.
LANs with centralized control are called client-server
networks. Once your network grows beyond 10 computers,
this type of LAN often becomes the most practical. A client
server network has a primary
domain controller or PDC, which validates users who log
on to the network and controls their access to network
resources. This provides greater security and greatly
simplifies network administration. PDCs usually run on more
powerful hardware than desktops do, and can include one or
more powerful processors, multiple hard drives, and much more memory.
Windows Small Business Server 2011 and Windows Server 8 are designed
to serve as primary domain controllers. So is Apple's Snow
Leopard Server. Apple's newer Lion Server, although much less
expensive than Snow Leopard Server, cannot serve as a PDC for
Windows clients. However, it has many other attractive
features which are useful for small businesses and homes. A
Linux server combined with Samba can also serve as a PDC.
Windows Server 8 and SBS 2011 provide Active Directory
Services, however, which makes them the most fully
featured PDCs currently available.
connect your PC or LAN to the internet. The type of modem you
have depends on the type of internet service you use. In
general order of increasing speed and expense (there will be
exceptions), these are dial-up, satellite, cellular
broadband (such as Clear), DSL or ADSL (such as AT&T),
T-1, cable (such as Comcast), and the fastest, fiber optic.
In order for computers to communicate with
each other over a LAN or a WAN, each one must have a network
interface card, or NIC, installed. NICs are also called network
NICs "talk" to each other in binary
code by using a set of rules called protocols. The most
common protocols are TCP/IP and IPX/SPX. TCP/IP, which is the
standard internet protocol, is by far the most popular and
widely used. Every NIC has unique number assigned to is called
a MAC address. To communicate on a TCP/IP network, a
NIC must have an IP address associated with it. This
can be manually assigned, but most devices request a temporary
IP address at boot up from a DHCP server. A DHCP
server assigns temporary IP address to devices. Most routers
and domain controllers have DHCP servers built in to them.
In most new LANs, NICs transmit their signals
over Category 5 or Category 5 enhanced cable. This
cable looks kind of like a thicker version of the phone wire
that runs through the walls of your home. The connectors at
the ends of the wire look like larger versions of the
connectors on the end of a phone cord, too. Category 5 cable
can handle information transfer speeds of 100 megabits per
second (100 mbps). Cat 5e can handle faster transmission
rates. Cat 6 and 7 can handle even faster rates, but are more
expensive. When a length of cable, or the distance from a
wireless device is so long that the signals
generated by the NIC can't propagate far enough, they must be
restored by a signal amplifier known as a repeater.
The most common 100 mbps standard is called Fast
Ethernet. The most prevalent older standard, Ethernet,
has a transmission speed of 10 mbps. Gigabit Ethernet,
with data speeds of 1000 mbps, is becoming increasingly
popular as prices fall.
The 802.11 wireless standards are also very
popular. Wireless networks utilize radio waves or microwaves
rather than cable. The nice thing about them is that there is
no external wiring to mess with, and you can easily relocate
the computers in your network without the hassle of rewiring.
When you consider the cost of running cable through walls,
wireless networks can be competitive in price with wired
802.11b transfers data at a rate of 11 mbps.
802.11a can be faster, but is not compatible with the more
common "b" standard. The faster 54 mbps 802.11g
standard is backwards compatible with "b," however.
The latest wireless "n" standard (802.11n), builds
on previous standards by combining multiple wireless channels
and antennas in one device, and depending on how many of these
are used (as well as other factors), these routers range from
54 mbps to 600 mbps.
The wireless "n" standard is just as
'fast' or even 'faster' as Fast Ethernet. However, wireless
devices cannot (yet) compete with the data transfer speeds of
A wired network may also be made available to
wireless capable devices such as smart phones and laptops by
means of a wireless access point. This connects to the
wired network by means of a fast or gigabit ethernet port.
Cables, Hubs & Switches
If you only have two computers in your
network, you can connect them using two Fast Ethernet NICs and
a specially wired cable called a crossover cable. If
you have more than two, though, you'll also need a hub
or a switch, and will need to use regular category 5 or
higher cable instead. Both hubs and switches have multiple
ports for connecting the computers in a network. If you have
more computers than there are ports, multiple hubs or switches
can be joined to your network.
Switches provide better performance than hubs.
Each computer on a hub hears all of the signals from all of
the PCs, and must sort through it. This can slow down a busy network. On a switch,
however, computers have their own "private line"
when communicating with each another, and hear only the
praffic intended for them.. If your office network
will be busy with large files or a lot of traffic, or your
home network will be bustling with network games, a switch is
the best choice. Most of the latest Ethernet and 802.11 wireless
internet routers have a switch built-in.
Exactly Is a Server?
When one computer provides a service to
another computer, such as the sharing of files, the sharing of
a high speed
modem, or the sharing of a printer, it is operating as a server, and
the computer receiving the benefit of the service is acting as
a client. Any computer on a network can be designated
as a print server, a proxy server, an email
server, a fax
server, or a file server. If that is the sole
purpose behind that computer, it is known as a dedicated
Most small businesses want to be able to share
files. Some small business even use database driven software
that requires you to do this. Windows 7 Professional limits
file sharing to 20 concurrent connections. XP Professional
limits it to10. If you want more of your PCs to be able to
connect to a file sharing computer than that at one time,
then you need a PC with an operating system which is designed
for that. Windows Server 8, Windows Small Business Server
2011, and Apple OSX Lion Server are. Some open source (free)
versions of Linux are designed for that, too. Lastly, there
are some handy little units you can buy called NAS (Network
Attached Storage) devices. These usually run on Linux, and
permit file sharing, too.
business prefer to control their email in-house. Microsoft
provides a popular email application for this purpose called Exchange.
Exchange runs on Microsoft server products such as Windows
Server 8 and SBS 2011. OSX Lion Server and certain versions of
Linux also provide email sever applications.
It is becoming increasingly popular, however, for businesses
and individuals to use Cloud (internet based) email
servers. The most common of these for personal use are Gmail,
Windows Live, Yahoo, and AOL. These are not in common use for
businesses because they do not permit you to use your domain
name in your email address (such as email@example.com).
are cloud based email servers for businesses, too. These allow
you to use your domain name.
servers host websites. These can be in-house or cloud based.
Windows Server 8 and SBS 2011 use Internet Information
Services (IIS) for this purpose. OSX Lion Server and Linux
also provide this capability.
Servers and Routers
It's kind of obvious that print servers print
documents, fax servers send and receive faxes, and file
servers store and retrieve files. But it may not be so obvious
to you what a proxy server is. Every computer on a TCP/IP
network is assigned a unique numerical address called an IP
address. When hackers know what your IP address is, it's
easier for them to break into your system. A proxy server
prevents them from discovering your computer's IP address by
"representing" your computer with another IP
address. The proxy server talks to other computers on the
internet on behalf of your computer, and forwards replies back
to it over your local area network. A cost saving aspect of
this is that one proxy server can represent many computers.
proxy server can provide internet access to all of the other
computers on your network. That way, you don't have to buy an
expensive high speed modem and pay for separate connection
services for all of the computers on your network. Some of the
Windows Operating Systems have Internet sharing built-in.
The most popular devices that do the job of
a proxy server, however, are called Network Routers. These
usually have a switch and wireless access point built in.
These also provide firewall services to protect your network
from hackers. There are also dedicated firewall devices
to speak with a Microsoft Certified Professional today!