Networks – Part 1 What is a Network?

Whether you currently use a network, are thinking about implementing or upgrading a network, or just don’t 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.


What is a LAN

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

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 don’t 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.


Understanding The Components Of A LAN

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.



The workstations are the various PC’s or terminals connected to the file server. Employees use these PC’s 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, you’ll observe four typical characteristics that set it apart from a stand-alone computer:


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.


File Servers

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 server’s hard disk(s) must be durable and reliable.


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.


Ensuring LAN Security

With a LAN, everyone’s 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 everyone’s 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 can’t 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 system’s 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.


Using Passwords

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.


Limiting Access

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.


Protecting Data

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 can’t afford to lose.  With a network in place you need to get serious about file backup, data redundancy, and power protection.


File Backup

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 you’ll 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 you’re 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 it’s better than nothing.  If you have to restore a file, you may find that your backup copy isn’t 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 can’t.  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 safety’s 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 today’s backup is labelled C, you have yesterday’s backup copies on B and the previous day’s 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 drive’s read/write heads. Have these magnetic heads been cleaned regularly. Also rotate in fresh tapes to replace older ones, which become brittle over time.


Data Redundancy

Backup also means redundancy. You’re 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 moment’s hesitation. Note that multiple hard disks and multiple servers aren’t a substitute for a good file backup procedure.


Power Protection

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 it’s working on at the time of a power failure. For a word processor, this means that you lose what you’ve 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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