Networks – Part 1 What is a Network?
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Whether you currently use a network, are
thinking about implementing or upgrading a network, or just
dont have a clue where to start, then this feature is for
you. We will be explaining what a network can do, how to
set one up, trouble shooting, reviewing different network
software and more.
In this first issue we explain what a
network is and what it can do. The most common type of
network in organisations is known as a LAN; this is the type of
network that we are concentrating on in this article.
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What is a LAN
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A LAN is a local area network. Within a
single building or small geographical area, a LAN enables you to
connect a group of personal computers. Staff using these
networked computers can then share information. Without a
LAN, sharing files means copying them to a disk and then walking
over to another computer. This method does not allow
several people to access the same file at the same time. In
addition to easily sharing files, people on a LAN can share a
printer, a CD-ROM drive, a modem, or even a fax machine. |
Understanding What A LAN Can Do
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A LAN can do virtually everything a
mainframe computer or minicomputer can do, at a much lower
cost. Throughout an organisation, people can share computer
resources and information, and they can work together on projects
and tasks that require coordination and communication, even
though they may not be physically close. In the event of network
crash, each person may be able to continue working on their
personal computer, whereas a crash on a mainframe or
minicomputer, on the other hand, could bring work to a halt for
an entire organisation. |
Here are a few things that you can do with a
LAN that you cannot easily do with a non-networked, stand-alone
personal computer:
a) Share files. A LAN enables many users to share a single
copy of a file stored on a central file server, which helps the
organisation keep its records, documents, and other files
consistent.
b) Transfer files. A LAN enables you to copy files from
machine to machine without having to exchange floppy disks. This
is especially useful for large files that dont fit on a
single floppy.
c) Access information and files. A LAN enables anyone
to run accounting software or other application software from any
of its workstations. Employees can access software tools from any
LAN-connected desktop computer.
d) Printer sharing. Using a LAN, you can share one or more
printers among several workstations.
e) Electronic mail. You can use a LAN as a post office to
send memos, reports, and typed messages to other people in other
parts of the building, providing a paperless interoffice
memo environment.
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Understanding The Components Of A LAN
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A LAN is a combination of computers, cables,
network adapter cards, network operating system software, and
application software. On A LAN, each personal computer is
called a workstation, except for one or more computers
designated as file servers. Each workstation and
file server contains a network adapter card. LAN cables (or
other media) connect all workstations and file servers. In
addition to an operating system, each workstation runs network
software that enables it to communicate with the files servers.
In turn, the file servers run network software that communicates
with the workstations and serves up files to those
workstations. Workstations are usually operated by
employees and file servers are usually located in a separate room
or closet.
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Workstations
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The workstations
are the various PCs or terminals connected to the file
server. Employees use these PCs on their own or, with
network software, link to the file server to access programs,
data, printers, etc. Workstations are often referred to as clients.
When you use a workstation, it behaves in
almost all respects like a stand-alone PC. If you inspect it
closely, though, youll observe four typical characteristics
that set it apart from a stand-alone computer:
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a)
Extra messages appear on-screen as the computer starts up. These
messages inform you that network software is loading at the
workstation.
b)
You have to provide your user identification (or account ID) and
a password before you can use the LAN. This is the logon
procedure.
c)
After you logon to the LAN, you see additional drive letters that
you can access.
d)
Your memos or reports may be printed in a remote location on the
LAN.
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File Servers
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In contrast to
workstations, a file server is a computer that serves all
the workstations-primarily by storing and retrieving data from
files shared on its disks. File servers are usually faster and
larger than workstations with larger amounts of RAM.
Servers must be high-quality, heavy-duty machines because, in
serving the whole network, they do many times the work of an
ordinary workstation computer. The server is usually a repository
of data for an entire organisation. In particular, the
servers hard disk(s) must be durable and reliable.
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On smaller LANs the file server may double
as a workstation. This option does, however, have
risks. Serving an entire network can be a big job that does
not leave much spare horsepower for workstation duties and if the
end-user locks up the workstation that doubles as the file
server, the network also locks up.
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Ensuring LAN Security
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With a LAN,
everyones files are stored in one big container.
Unless you provide for security and privacy, anyone can look at -
and modify - any file. Any user can easily rifle through
the personal papers of any other user, including the personnel
records and confidential records. You may want to set up a
security system on a LAN for the following reasons: |
a) Limiting damage: It is possible for someone to
accidentally type something that they did not mean to. For
example DEL instead of DIR in the wrong
place could destroy a number of files rather than listing
them. Someone typing the wrong thing on a LAN can wipe out
everyones files in addition to their own.
b) Protecting confidentiality: If you know that anyone in the
company, including the office gossip, can read any of your files
at any time, you cant store important files on the
LAN. If personnel records are accessible via the network
without protection then any member of staff could read their own
records or find out confidential information about colleagues.
c) Preventing fraud: If all employees know that they have
access to the accounting systems accounts payable files, an
unscrupulous person may be tempted to tell the computer to issue
a cheque in his or her name.
d) Preventing malicious damage: If a disgruntled employee has
access to all files on the LAN, they may corrupt or modify
them. By the time someone detects the damage, the company
could have serious problems. The capability to share files
is a double-edged sword; it also provides the opportunity to
corrupt or destroy files.
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Using Passwords
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Each LAN user identifies himself or herself
with a password - a secret word known only to that
user. Properly used, passwords verify the identity of the
person logging on to the LAN. Proper password
administration guidelines include encouraging people to use
hard-to-guess passwords, change passwords regularly, and keep
passwords secret.
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Limiting Access
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Another key to security is limiting access
within the LAN on a directory-by-directory or server-by-server
basis. For example, you can give a person the right to open and
read files in a directory but restrict modification to those
files. Alternatively, you may make an entire directory
off-limits. And to protect important files from even your
own typing errors, you can mark files as read only so that
you cannot delete or modify them.
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Protecting Data
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Files servers, like other computers,
sometimes fail. Whether the failure is the result of a loss
of electrical power or a hard disk crash, you want to minimise
the effect of a server failure. Data is important; it
represents an investment of time and energy that you cant
afford to lose. With a network in place you need to get
serious about file backup, data redundancy, and power protection.
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File Backup
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The method you use to make backup copies of
your data depends mostly on how much data you have. Floppy may do
the job on a very small LAN, but in most cases youll likely
use a tape drive to copy files to a magnetic tape
cartridge. No matter what device you use to make backup
copies, you should make frequent and regular copies of your data
in case something happens to your computer or its data.
If youre the person in your office
that makes backup copies, you can choose one of a number of
approaches depending on how often your data changes and how
important it is. Examples include:
Occasional: You may get by with
occasionally copying individual files to one or more floppy
disks. This approach is the least secure, but its better
than nothing. If you have to restore a file, you may find
that your backup copy isnt as recent as you would like
resulting in the need for significant amounts of work to be
re-input
Serious: If you make backup
copies regularly using a backup utility such as a BACKUP.EXE, and
are using more than one set of disks or tapes, then you are
serious about backups. You know exactly how
much time has elapsed since the last backup copy was made, which
means that you know exactly the disks to restore a file.
Professional: Data centres with
multimillion-pound mainframe computers use this method, and there
is no reason why you cant. Essentially, you always
have three copies of data on three sets of disks (or magnetic
tapes). To make backup copies, first identify each set of disks
as A, B, or C. (For safetys sake, it is advisable to have
two A sets, two B sets, and two C sets.) Rotate the three sets of
disks so that if todays backup is labelled C, you have
yesterdays backup copies on B and the previous days
on A. Tomorrow use the A set to make backup copies. You may even
extend this approach to a fourth set of disks and make sure that
the oldest copy is taken offsite. This method is
sometimes known as the grandfather/father/son scheme.
The reliability of your backup depends on
the cleanliness of your drives read/write heads. Have these
magnetic heads been cleaned regularly. Also rotate in fresh tapes
to replace older ones, which become brittle over time.
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Data Redundancy
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Backup also means redundancy. Youre
better off with two medium-size file servers than with one giant
server. If a file server breaks down, you can get by temporarily
with the other server. Of course, you should make the second
server part of your backup procedure.
Manufacturers of file server computers
recognize the need for data redundancy and offer models that
contain disk arrays - multiple hard disks that mirror each
other. If one hard disk dies, another carries on without a
moments hesitation. Note that multiple hard disks and
multiple servers arent a substitute for a good file backup
procedure.
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Power Protection
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Power failures happen, and usually happen
when least expected or at the most inconvenient time.
Thunderstorms will often cause a failure, but they can happen at
other times too. To some extent, nearly all software will
corrupt files its working on at the time of a power
failure. For a word processor, this means that you lose what
youve keyed in since the last time you saved the file. For
an accounting program, it may mean that you lose everything you
keyed in since the last time you backed up the files to tape.
To protect yourself, place your servers on
an uninterruptible power supply (UPS).
On a UPS, if the power fails, batteries keep
the server running for a period of time that allows you to shut
down the server safely without losing files. In addition, a
UPS isolates the server from spikes and sags in the supply of
commercial electrical power.
You now have an understanding of what a
network is, the advantages of implementing a network, and some of
the considerations in keeping it secure. In the next
article we review the alternative network software available to
you whether you are a small, medium or large organisation.
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