The word network has several definitions. The most commonly used meaning
describes the methods people use to maintain relationships with friends and
business contacts. Applied to computers, the term has a similar definition. A
network is a way to connect computers together so that the' communicate,
exchange information, and pool resources. In business, networks have
revolutionized the use of computer technology. Many businesses that used to rely
on a centralized system with a mainframe and a collection of terminals
(input/output devices that are connect mainframes and do not have the same
features as PCs) now use eom networks in which every employee who needs a
computer has a per computer connected to the network. Computer technology and
expertise no longer centralized in a company's mainframe and information systems
departments. The technology and expertise are distributed throughout
organization among a network of computers and computer literate. In education,
schools have also shifted to strategies built around networks personal
computers. These include LANs (local area networks), and network that connects
the computers and printers in a computer to a WANs (wide area
networks)--especially the Internet.
Whatever the setting, networks provide tremendous benefits. Four most
compelling benefits are:
Allowing simultaneous access to critical programs and data
Allowing people to share peripheral devices, such as printers and scanners
Streamlining personal communication with e-mail
Making the backup process easier
The following sections examine each of these advantages in
more detail.
Simultaneous Access
It is a fact of business computing that
multiple employees, using a computer network, often need
access to the same data at the same time. Without a net-work
that enables file sharing, employees keep separate copies of
data on different hard disks, and universally updating the
data becomes very difficult. As soon as a change is made to
the data on one machine, a discrepancy arises, and it
quickly becomes difficult to know which set of data is
correct. Storing data that is used by more than one person
on a shared storage device makes it possible to solve the
problem.
It is also true that most office workers use the same
programs. One solution to purchasing separate copies of applications for every
worker is to use network versions of programs. These programs are designed so
that only one copy of the application needs to be stored on the network server
(called an application server), with a minimum number of supporting files copied
to each employee's computer. A network server is a large central computer. (If
the server stores data files for users to access, it is commonly called a file
server.) When employees need to use a program, they simply load it from a shared
storage device into the RAM of their own desktop computers, as shown in Figure
7.1.
A network version of a software application is also a more
efficient use of hard disk space because many users can access a single shared
copy instead of storing separate copies on each user's hard disk.
Some software designed for networks is classified as
groupware. This type of software includes scheduling software, e-mail, and
document management software. Groupware allows multiple users on a network to
cooperate on projects. Users can work on the same documents, share their
insights, and keep each other abreast of their schedules so that meetings can be
set up easily. Lotus Notes and Microsoft Exchange are perhaps the best known
examples of groupware, although there are many competitors.
Shared Peripheral Devices
Perhaps the best incentive for small businesses to link
computers in a network is to share peripheral devices, especially expensive ones
such as laser printers, large hard disks, and scanners, as shown in Figure 7.2.
Many high quality laser printers cost more than $2,000, so it
is not very cost-effective for each user to have one. Sharing a laser printer on
a network makes the cost much less prohibitive. By using a process called
spooling, multiple users can send multiple print jobs to a printer. (Spooling
can also occur when a computer is not connected to a network, and multiple print
jobs are sent to a non-networked printer.) When users print a document or other
file to a net-worked printer (known as a print job), each job is stored in a
temporary spool file on the file server. As the printer finishes printing a
current job, the file server sends the next spooled job to the printer so that
it can be printed. Typically, a banner page is printed at the beginning of a new
job to separate print jobs.
Personal Communication
One of the most far reaching applications
of data communications is electronic mail (e-mail), a system
for exchanging written messages (and increasingly, voice and
video messages) through a network. E-mail is some-thing of a
cross between the postal system and a telephone answering
system. In an e-mail system, each user has a unique address.
To send someone an e-mail message, you enter the person's
e-mail address and then type the message. When you are
finished, the message is sent to the e-mail address. The
next time that user accesses the e-mail system, it reports
that mail has arrived. Some systems notify the recipient as
each message arrives by flashing a message on the computer
screen or beeping. After reading the message, the recipient
can save it, delete it, forward it to someone else, or
respond by sending back a reply message. Figure 7.3 shows
the process for sending and receiving e-mail.
In addition to sending a page or pages of mail text, many
systems allow you to attach data files--such as spreadsheet files or word
processed documents--to your message. This means that an e-mail system allows
people to share files even when they do not have access to the same storage
devices. For example, a local area network also may have a connection to a large
information network, such as America Online, Microsoft Network, or the Internet.
In this case, the person on the local network can share files with anyone on the
large information network.
E-mail is both efficient and inexpensive. Users can send
written messages without worrying about whether the other user's computer is
currently running. On centralized networks, the message is delivered almost
instantaneously, and the cost of sending the message is negligible. E-mail has
provided the modem world with an entirely new and immensely valuable form of
communication
In addition to e-mail, the spread of networking technology is
adding to the popularity of teleconferencing and videoconferencing. A
teleconference is a virtual meeting in which a group of people in different
locations conducts discussions by typing messages to each other. Each message
can be seen by all the other people in the teleconference. Teleconference
software has become more sophisticated, gradually adding such features as a
shared scratch pad where diagrams or pictures can be drawn or electronically
pasted.
The spread of networking is adding to the popularity of
collaborative software, which allows users to connect with one another over LAN
or modem links so that they can see what's happening on other users' computers.
It lets people send messages, exchange files, and sometimes even work on the
same document at the same time. If users have the necessary hardware and
software, they can actually see and speak to each other as they meet online
(instead of merely typing messages). This is a process known as
videoconferencing, as shown in Figure 7.5.
Easier Backup
In business, data is extremely valuable, so making sure
that employees back up their data is critical. One way to address this problem
is to keep all valuable data on a shared storage device that employees access
through a network. Often the person managing the network has the responsibility
of making regular backups of the data on the shared storage device from a
single, central location. Network backup software is also available that enables
backups to be made of files stored on employees' hard drives. This way, the
files do not have to be copied to the central server to be backed up.
HOW NETWORKS ARE STRUCTURED
To understand the different types of networks and how
they operate, it important to know something about how networks can be
structured. Fir there are two main types of networks, distinguished mainly by
geography local area networks (LANs) and wide area networks (WANs). Second, any
o these types can be classified according to the logical relationships among the
computers. There are networks that use servers (such as file servers an,
application servers) and those that do not (called peer-to-peer networks).
Local Area Networks
A network of computers located relatively near each other
and connected b3 a cable (or a small radio transmitter) is a local area network
(LAN). A LAN can consist of just two or three PCs connected together to share
resources, or it can include several hundred computers of different kinds. Any
network that exists within a single building, or even a group of adjacent
buildings, is considered a LAN.
A LAN permits all the computers connected to it to share
hardware, software, and data. The most commonly shared resources are disk
storage devices and printers. To LAN users, the network is (or should be)
completely transparent, which means that the shared devices on it seem to be
directly connected to the user's computer as if they were merely peripherals.
For example, a file server should appear to the LAN user simply as another disk
drive.
In addition to shared hardware, LANs can provide all the
other benefits of networks, including simultaneous access, enhanced personal
communication, and easier backup.
