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<td bgcolor="#336666"><b><font face="Arial" size="2" color="#FFFFFF">6.1</b></font></td>
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<td bgcolor="#336666" width="100%"><b><font face="Arial" size="2" color="#FFFFFF">
<strong>Workstations and Servers</strong> </font></b></td>
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<td bgcolor="#669999" height="25"><b>
<font face="Arial" size="2" color="#FFFFFF">6.1.3</font></b></td>
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<td bgcolor="#669999" height="25" width="100%"><strong>
<font face="Arial" size="2" color="#FFFFFF">Client-server relationship</font></strong></td>
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<font face="Arial" size="2">The client-server computing model
distributes processing over multiple computers. Distributed processing
enables access to remote systems for the purpose of sharing
information and network resources. In a client-server environment, the
client and server share or distribute processing responsibilities.
Most network operating systems are designed around the client-server
model to provide network services to users. A computer on a network
can be referred to as a host, workstation, client, or server. A
computer running TCP/IP, whether it is a workstation or a server, is
considered a host computer.
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"></font><p>
<font face="Arial" size="2">Definitions of other commonly used terms
are:</font></p>
<ul>
<li>
<font face="Arial" size="2"><b>Local host</b> � The machine on which
the user currently is working.</font></li>
<li>
<font face="Arial" size="2"><b>Remote host</b> � A system that is
being accessed by a user from another system.</font></li>
<li>
<font face="Arial" size="2"><b>Server</b> � Provides resources to one
or more clients by means of a network.</font></li>
<li>
<font face="Arial" size="2"><b>Client</b> � A machine that uses the
services from one or more servers on a network.</font></li>
</ul>
<p>
<font face="Arial" size="2">An example of a client-server relationship
is a File Transfer Protocol (FTP) session. FTP is a universal method of
transferring a file from one computer to another. For the client
to transfer a file to or from the server, the server must be running
the FTP daemon or service. In this case, the client
requests the file to be transferred. The server provides the services
necessary to receive or send the file. </font></p>
<p>
<font face="Arial" size="2">The Internet is also a good example of a
distributed processing client-server computing relationship. The
client or front end typically handles user presentation functions,
such as screen formatting, input forms, and data editing. This is done
with a browser, such as Netscape or Internet Explorer. Web browsers send
requests to web servers. When the browser requests data from the
server, the server responds, and the browser program receives a reply
from the web server. The browser then displays the HTTP data that was
received. The server or back end handles the client's requests for Web
pages and provides HTTP or WWW services.</font></p>
<p>
<font face="Arial" size="2">Another example of a client-server
relationship is a database server and a data entry or query client in
a LAN. The client or front end might be running an application written
in the C or Java language, and the server or back end could be running
Oracle or other database management software. In this case, the client
would handle formatting and presentation tasks for the user. The
server would provide database storage and data retrieval services for
the user.</font></p>
<p>
<font face="Arial" size="2">In a typical file server environment, the
client might have to retrieve large portions of the database files to
process the files locally. This retrieval of the database files can
cause excess network traffic. With the client-server model, the client
presents a request to the server, and the server database engine might
process 100,000 records and pass only a few back to the client to
satisfy the request. Servers are typically much more powerful than
client computers and are better suited to processing large amounts of
data. With client-server computing, the large database is stored, and
the processing takes place on the server. The client has to deal only
with creating the query. A relatively small amount of data or results
might be passed across the network. This satisfies the client query
and results in less usage of network bandwidth. The graphic shows an
example of client-server computing. Note that the workstation and
server normally would be connected to the LAN by a hub or switch.
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"></font></p>
<p>
<font face="Arial" size="2">The distribution of functions in
client-server networks brings substantial advantages, but also incurs
some costs. Although the aggregation of resources on server systems
brings greater security, simpler access, and coordinated control, the
server introduces a single point of failure into the network. Without
an operational server, the network cannot function at all.
Additionally, servers require trained, expert staff to administer and
maintain them, which increases the expense of running the network.
Server systems require additional hardware and specialized software
that adds substantially to the cost. </font>
</p>
<p><font face="Arial" size="2"> </font>
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