Studies Note: computer

<div dir="ltr" style="text-align: left;" trbidi="on"><w:sdt contentlocked="t" id="89512093" sdtgroup="t"><span style="font-family: "Calibri","sans-serif"; font-size: 1.0pt; mso-ansi-language: EN-US; mso-ascii-theme-font: minor-latin; mso-bidi-font-family: "Times New Roman"; mso-bidi-language: AR-SA; mso-bidi-theme-font: minor-bidi; mso-fareast-font-family: "Times New Roman"; mso-fareast-language: EN-US; mso-fareast-theme-font: minor-fareast; mso-hansi-theme-font: minor-latin;"><w:sdtpr></w:sdtpr><w:sdt docpart="F179AB7F014043EB9301700EF66187B0" id="89512082" showingplchdr="t" storeitemid="X_4AE7E1E6-C439-46E2-93EF-4081061D593E" text="t" title="Post Title" xpath="/ns0:BlogPostInfo/ns0:PostTitle"></w:sdt></span>  </w:sdt><br /><h2></h2><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in; vertical-align: baseline;"><span style="font-family: Arial, sans-serif;">Computer labs are useful for any type of organisation.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: 8.35pt; vertical-align: baseline;"><span style="font-family: Arial, sans-serif; font-size: 11.5pt;">Computer labs are used in businesses, government agencies, colleges and other organisations and perform critical functions in each. For businesses and government agencies, computer labs are areas for group meetings and planning sessions, where the computer is the medium from which to build a strategic plan. In schools, computer labs are classrooms where students learn how to use what is perhaps the most critical tool for education since the invention of the book. In other organisations, like science labs, computer labs are areas for computation. Building a computer lab, above all else, requires taking into consideration the purpose of the lab.<o:p></o:p></span></div><div style="background: white; border-bottom: solid windowtext 1.0pt; border: none; margin-left: 16.75pt; margin-right: 0in; mso-border-bottom-alt: solid windowtext .5pt; mso-element: para-border-div; padding: 0in 0in 1.0pt 0in;"><h2 style="text-align: left;"><span style="font-family: inherit, serif;">Instructions </span></h2></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in; margin-left: 16.75pt; margin-right: 0in; margin-top: 0in; mso-list: l0 level2 lfo1; tab-stops: list 1.0in; text-indent: -.25in; vertical-align: baseline;"><span style="font-family: Wingdings; font-size: 10pt;">v<span style="font-family: 'Times New Roman'; font-size: 7pt;">  </span></span><span style="font-family: 'Times New Roman', serif; font-size: 25pt;">1</span><span style="font-family: inherit, serif;"><o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: 8.35pt; vertical-align: baseline;"><span style="font-family: Arial, sans-serif; font-size: 11.5pt;">Decide on the purpose of the computer lab. Its purpose will impact its overall design and the quality of the computers that are needed within the lab. For example, if the computer lab is meant to teach students English in India, it is unlikely to require the same advanced and expensive programs and security protocols of a U.S. intelligence agency.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in; margin-left: 16.75pt; margin-right: 0in; margin-top: 0in; mso-list: l0 level2 lfo1; tab-stops: list 1.0in; text-indent: -.25in; vertical-align: baseline;"><span style="font-family: Wingdings; font-size: 10pt;">v<span style="font-family: 'Times New Roman'; font-size: 7pt;">  </span></span><span style="font-family: 'Times New Roman', serif; font-size: 25pt;">2</span><span style="font-family: inherit, serif;"><o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: 8.35pt; vertical-align: baseline;"><span style="font-family: Arial, sans-serif; font-size: 11.5pt;">Select a well-ventilated and cool room in which to build the lab. Computers in a warm, humid environment are susceptible to overheating, whereas computers in a cool, air-conditioned environment are likely to last for a ON time.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in; margin-left: 16.75pt; margin-right: 0in; margin-top: 0in; mso-list: l0 level2 lfo1; tab-stops: list 1.0in; text-indent: -.25in; vertical-align: baseline;"><span style="font-family: Wingdings; font-size: 10pt;">v<span style="font-family: 'Times New Roman'; font-size: 7pt;">  </span></span><span style="font-family: 'Times New Roman', serif; font-size: 25pt;">3</span><span style="font-family: inherit, serif;"><o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: 8.35pt; vertical-align: baseline;"><span style="font-family: Arial, sans-serif; font-size: 11.5pt;">Create a security protocol for entering the lab. For schools, it is likely sufficient to require that a code is punched into a lock on the door in order to gain access to the room. The code can be distributed to all administrators and teachers to protect the computers from being damaged by students. For organisations that require greater security, a key card security system with a surveillance camera or two should be adequate to protect the computer lab. The key card should only be owned by those deemed trustworthy by the supervisor of the lab.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in; margin-left: 16.75pt; margin-right: 0in; margin-top: 0in; mso-list: l0 level2 lfo1; tab-stops: list 1.0in; text-indent: -.25in; vertical-align: baseline;"><span style="font-family: Wingdings; font-size: 10pt;">v<span style="font-family: 'Times New Roman'; font-size: 7pt;">  </span></span><span style="font-family: 'Times New Roman', serif; font-size: 25pt;">4</span><span style="font-family: inherit, serif;"><o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: 8.35pt; vertical-align: baseline;"><span style="font-family: Arial, sans-serif; font-size: 11.5pt;">Acquire a number of computers sufficient for handling the workload that is anticipated to take place within the computer lab. For example, if the computer lab is meant as a graphic design workstation, each graphic designer should have a computer to work with in the lab at all times; however, if the computer lab is in a standard U.S. middle school, then it only requires the same amount as the average number of student per classroom or slightly more to be sufficient for class lessons held in the computer lab.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in; margin-left: 16.75pt; margin-right: 0in; margin-top: 0in; mso-list: l0 level2 lfo1; tab-stops: list 1.0in; text-indent: -.25in; vertical-align: baseline;"><span style="font-family: Wingdings; font-size: 10pt;">v<span style="font-family: 'Times New Roman'; font-size: 7pt;">  </span></span><span style="font-family: 'Times New Roman', serif; font-size: 25pt;">5</span><span style="font-family: inherit, serif;"><o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: 8.35pt; vertical-align: baseline;"><span style="font-family: Arial, sans-serif; font-size: 11.5pt;">Place each computer roughly a full shoulder's length apart from one another (i.e., two to three feet). This will ensure that people using the lab do not end up crowding each others' space.<o:p></o:p></span></div><div class="MsoNormal"><b><u><span style="font-family: Georgia, serif; font-size: 16pt;">The question is that which topology should we use?<o:p></o:p></span></u></b></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><br /></div><div class="MsoNormal" style="background: white; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt; mso-line-height-alt: 15.9pt;"><span style="font-family: "Georgia","serif"; font-size: 16.0pt; mso-bidi-font-size: 10.0pt;">                                         </span><b><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">Star networks</span></b><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> are one of the most common </span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">computer network</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> </span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">topologies</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">. In its simplest form, a star network consists of one central </span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">switch</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">, </span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">hub</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> or computer, which acts as a conduit to transmit messages. This consists of a central node, to which all other nodes are connected; this central node provides a common connection point for all nodes through a hub. </span><sup><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">[1]</span></sup><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> Thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a </span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">star</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">. If the central node is <i>passive</i>, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time (i.e. to and from the central node) plus any delay generated in the central node. An <i>active</i> star network has an active central node that usually has the means to prevent echo-related problems.<o:p></o:p></span></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi75wn-8yzEkrnRyyNk2qFIuezwNv1h1KqZ0LJOHWkX64ATGPI6t3LEjzRGi-TFb6Dllar4OwLNyZ9n1BkXvoA8dg7HfbLma5-hw6XJbw8DFGoLRgXRhyphenhyphensozTtf-iaW0ZewskDJCRn0CQo/s1600/domain1.gif" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><span style="color: black;"><img border="0" height="227" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi75wn-8yzEkrnRyyNk2qFIuezwNv1h1KqZ0LJOHWkX64ATGPI6t3LEjzRGi-TFb6Dllar4OwLNyZ9n1BkXvoA8dg7HfbLma5-hw6XJbw8DFGoLRgXRhyphenhyphensozTtf-iaW0ZewskDJCRn0CQo/s400/domain1.gif" width="400" /></span></a></div><div class="MsoNormal" style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">The star topology reduces the chance of network failure by connecting all of the systems to a central node. When applied to a bus-based network, this central hub rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, sometimes including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. The failure of a transmission line linking any peripheral node to the central node will result in the isolation of that peripheral node from all others, but the rest of the systems will be unaffected. </span><sup><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">[2]</span></sup><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"><o:p></o:p></span></div><div class="MsoNormal" style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">It is also designed with each node (file servers, workstations, and peripherals) connected directly to a central network hub, switch, or </span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">concentrator</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. The hub, switch, or concentrator manages and controls all functions of the network. It is also acts as a repeater for the data flow. This configuration is common with </span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">twisted pair cable</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">. However, it can also be used with</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">coaxial cable</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> or </span><span style="font-family: Arial, sans-serif; font-size: 10.5pt; text-decoration: none;">optical fibre</span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> cable.<o:p></o:p></span></div><div style="background: white; border-bottom: solid #AAAAAA 1.0pt; border: none; mso-border-bottom-alt: solid #AAAAAA .75pt; mso-element: para-border-div; padding: 0in 0in 2.0pt 0in;"><div class="MsoNormal" style="background-position: initial initial; background-repeat: initial initial; border: none; line-height: 15.9pt; margin-bottom: 0.1in; padding: 0in;"><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">Advantages<o:p></o:p></span></div></div><div class="MsoNormal" style="background: white; line-height: 15.9pt; margin-bottom: 1.2pt; margin-left: .25in; mso-list: l1 level1 lfo2; mso-margin-top-alt: auto; tab-stops: list .5in; text-indent: -.25in;"><span style="font-family: Wingdings; font-size: 10pt;">§<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><b><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">Better performance:</span></b><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> star topology prevents the passing of data packets through an excessive number of nodes. At most, 3 devices and 2 links are involved in any communication between any two devices. Although this topology places a huge overhead on the central hub, with adequate capacity, the hub can handle very high utilization by one device without affecting others.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; line-height: 15.9pt; margin-bottom: 1.2pt; margin-left: .25in; mso-list: l1 level1 lfo2; mso-margin-top-alt: auto; tab-stops: list .5in; text-indent: -.25in;"><span style="font-family: Wingdings; font-size: 10pt;">§<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><b><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">Isolation of devices:</span></b><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> Each device is inherently isolated by the link that connects it to the hub. This makes the isolation of individual devices straightforward and amounts to disconnecting each device from the others. This isolation also prevents any non-centralized failure from affecting the network.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; line-height: 15.9pt; margin-bottom: 1.2pt; margin-left: .25in; mso-list: l1 level1 lfo2; mso-margin-top-alt: auto; tab-stops: list .5in; text-indent: -.25in;"><span style="font-family: Wingdings; font-size: 10pt;">§<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><b><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">Benefits from centralization:</span></b><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> As the central hub is the bottleneck, increasing its capacity, or connecting additional devices to it, increases the size of the network very easily. Centralization also allows the inspection of traffic through the network. This facilitates analysis of the traffic and detection of suspicious behavior.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; line-height: 15.9pt; margin-bottom: 1.2pt; margin-left: .25in; mso-list: l2 level1 lfo3; mso-margin-top-alt: auto; tab-stops: list .5in; text-indent: -.25in;"><span style="font-family: Wingdings; font-size: 10pt;">§<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">Easy to detect faults and to remove parts.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; line-height: 15.9pt; margin-bottom: 1.2pt; margin-left: .25in; mso-list: l3 level1 lfo4; mso-margin-top-alt: auto; tab-stops: list .5in; text-indent: -.25in;"><span style="font-family: Wingdings; font-size: 10pt;">§<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: Arial, sans-serif; font-size: 10.5pt;">No disruptions to the network when connecting or removing devices.<o:p></o:p></span></div><h2 style="text-align: left;"><span style="font-family: Arial, sans-serif;"><u><span style="font-size: x-large;"> Network Switch </span></u></span></h2><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"></span><span style="font-family: "Arial","sans-serif";"> </span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">A<span class="apple-converted-space"> </span><b>network switch</b><span class="apple-converted-space"> </span>or<span class="apple-converted-space"> </span><b>switching hub</b><span class="apple-converted-space"> </span>is a<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">computer networking device</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">that connects<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">network segments</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">.<o:p></o:p></span></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">The term commonly refers to a multi-port<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">network bridge</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">that processes and routes data at the<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">data link layer</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">(layer 2) of the<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">OSI model</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">. Switches that additionally process data at the<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">network layer</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">(Layer 3) and above are often referred to as Layer 3 switches or<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">multilayer switches</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">.<o:p></o:p></span></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">The first<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Ethernet</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">switch was introduced by<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Kalpana</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">in 1990.</span><sup><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">[1]</span></sup><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"><o:p></o:p></span></div><div style="border-bottom: solid #4F81BD 1.0pt; border: none; mso-border-bottom-themecolor: accent1; mso-element: para-border-div; padding: 0in 0in 4.0pt 0in;"><div class="MsoTitle"><span class="mw-headline"><b><span style="font-family: Arial, sans-serif;">Function</span></b></span><b><span style="font-size: 80pt;"><o:p></o:p></span></b></div></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8dfiBT2y6-BDIrFhtPHgG5ugMaLQZXRZzwRYjZVXF4GbIbsKTewFCZolGMYF6-cpsukVXPfUGjJp9SGIjmn1LO6XBr84wsaZl2BLLEmu5A5v4jSIpLxkVU1C5LM5Jl85Omcsk2ZCJsDs/s1600/cutcaster-photo-800981643-Network-Switch.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><span style="color: black;"><img border="0" height="265" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8dfiBT2y6-BDIrFhtPHgG5ugMaLQZXRZzwRYjZVXF4GbIbsKTewFCZolGMYF6-cpsukVXPfUGjJp9SGIjmn1LO6XBr84wsaZl2BLLEmu5A5v4jSIpLxkVU1C5LM5Jl85Omcsk2ZCJsDs/s400/cutcaster-photo-800981643-Network-Switch.jpg" width="400" /></span></a></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">The network switch plays an integral part in most modern<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Ethernet</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">local area networks</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">(LANs). Mid-to-large sized LANs contain a number of linked<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">managed</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">switches.<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Small office/home office</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">(SOHO) applications typically use a single switch, or an all-purpose<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">converged device</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">such as a<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">residential gateway</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">to access small office/home<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">broadband</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">services such as<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">DSL</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">or<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">cable internet</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">. In most of these cases, the end-user device contains a<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">router</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">and components that interface to the particular physical broadband technology. User devices may also include a telephone interface for<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">VoIP</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">.<o:p></o:p></span></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">An Ethernet switch operates at the data link layer of the<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">OSI model</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">to create a separate<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">collision domain</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">for each switch port. With 4 computers (e.g., A, B, C, and D) on 4 switch ports, A and B can transfer data back and forth, while C and D also do so simultaneously, and the two conversations will not interfere with one another. In the case of a hub, they would all share the bandwidth and run in<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">half duplex</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">, resulting in collisions, which would then necessitate retransmissions. Using a switch is called<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">microsegmentation</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">. This allows computers to have dedicated bandwidth on a point-to-point connections to the network and to therefore run in<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">full duplex</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">without collisions.<o:p></o:p></span></div><div style="background: white; border-bottom: solid #AAAAAA 1.0pt; border: none; mso-border-bottom-alt: solid #AAAAAA .75pt; mso-element: para-border-div; padding: 0in 0in 2.0pt 0in;"><h2 style="background-position: initial initial; background-repeat: initial initial; border: none; margin: 0in 0in 0.1in; padding: 0in;"><span class="mw-headline"><span style="font-family: Arial, sans-serif; font-size: 20pt;">Role of switches in networks</span></span><span style="font-family: Arial, sans-serif; font-size: 20pt;"><o:p></o:p></span></h2></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Switches may operate at one or more layers of the OSI model, including<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">data link</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">and<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">network</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">. A device that operates simultaneously at more than one of these layers is known as a<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">multilayer switch</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">.<o:p></o:p></span></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Ethernet</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">,<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Fibre Channel</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">,</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">ATM</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">,<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">ITU-T</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">G.hn</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">and<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">802.11</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">. This connectivity can be at any of the layers mentioned. While Layer 2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Ethernet</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">and<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">token ring</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">is easier at Layer 3.<o:p></o:p></span></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">Devices that interconnect at Layer 3 are traditionally called<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">routers</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">, so "Layer-3 switches" can also be regarded as (relatively primitive) routers.<o:p></o:p></span></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">In some service provider and other environments where there is a need for a great deal of analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">firewall</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">,</span><sup><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">[2]</span></sup><sup><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">[3]</span></sup><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">network<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">intrusion detection</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">,</span><sup><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">[4]</span></sup><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules.</span><sup><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">[5]</span></sup><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"><o:p></o:p></span></div><div style="background: white; line-height: 15.9pt; margin-bottom: 6.0pt; margin-left: 0in; margin-right: 0in; margin-top: 4.8pt;"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">In other cases, the switch is used to create a mirror image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream,<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">network hubs</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">can be useful for fanning out data to several read-only analyzers, such as<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">intrusion detection systems</span><span class="apple-converted-space"><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">and<span class="apple-converted-space"> </span></span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">packet sniffers</span><span style="font-family: "Arial","sans-serif"; mso-bidi-font-size: 11.0pt;">.<o:p></o:p></span></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><br /></div><div class="MsoNormal"><br /></div><h2 style="text-align: left;"><span style="font-family: Arial, sans-serif; font-size: 10.5pt;"> </span><span style="font-family: Arial, sans-serif;"><span style="font-size: x-large;"><u>LAN</u></span></span></h2><div class="MsoNormal"><br /></div><div class="MsoNormal"><b><span style="font-size: 14.0pt;">Definition:</span></b> <span style="font-family: "Arial","sans-serif"; font-size: 10.5pt;">A local area network (LAN) supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN.<o:p></o:p></span></div><div class="MsoNormal"><span style="font-family: "Arial","sans-serif"; font-size: 10.5pt;">Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist.<o:p></o:p></span></div><div class="MsoNormal"><span style="font-family: "Arial","sans-serif"; font-size: 10.5pt;">Specialized operating system software may be used to configure a local area network. For example, most flavors of Microsoft Windows provide a software package called Internet Connection Sharing (ICS) that supports controlled access to LAN resources.<o:p></o:p></span></div><div class="MsoNormal"><span style="font-family: "Arial","sans-serif"; font-size: 10.5pt;">The term LAN party refers to a multiplayer gaming event where participants bring their own computers and build a temporary LAN.<o:p></o:p></span></div><div class="MsoNormal"><span style="font-family: "Arial","sans-serif"; font-size: 10.5pt;">Also Known As: local area network<o:p></o:p></span></div><div class="MsoNormal"><span style="font-family: "Arial","sans-serif"; font-size: 10.5pt;">Examples:<o:p></o:p></span></div><div class="MsoNormal"><span style="font-family: "Arial","sans-serif"; font-size: 10.5pt;">The most common type of local area network is an Ethernet LAN. The smallest home LAN can have exactly two computers; a large LAN can accommodate many thousands of computers. Many LANs are divided into logical groups called subnets. An Internet Protocol (IP) "Class A" LAN can in theory accommodate more than 16 million devices organized into subnets.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in; mso-outline-level: 3;"><br /></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in; mso-outline-level: 3;"><h2 style="text-align: left;"><b><u><span style="font-size: 24pt;">About Wired LANs<a name='more'></a></span></u></b></h2></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in;"><span style="font-size: 10.5pt;">Wired LANs use Ethernet cables and network</span><span style="font-size: 10.5pt;">adapters</span><span style="font-size: 10.5pt;">. Although two computers can be directly wired to each other using an </span><span style="font-size: 10.5pt;">Ethernet crossover cable</span><span style="font-size: 10.5pt;">, wired LANs generally also require central devices like </span><span style="font-size: 10.5pt;">hubs</span><span style="font-size: 10.5pt;">, </span><span style="font-size: 10.5pt;">switches</span><span style="font-size: 10.5pt;">, or </span><span style="font-size: 10.5pt;">routers</span><span style="font-size: 10.5pt;"> to accommodate more computers.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in;"><span style="font-size: 10.5pt;">For dial-up connections to the Internet, the computer hosting the </span><span style="font-size: 10.5pt;">modem</span><span style="font-size: 10.5pt;"> must run </span><span style="font-size: 10.5pt;">Internet Connection Sharing</span><span style="font-size: 10.5pt;"> or similar software to share the connection with all other computers on the LAN. </span><span style="font-size: 10.5pt;">Broadband routers</span><span style="font-size: 10.5pt;"> allow easier sharing of cable modem or DSL Internet connections, plus they often include built-in </span><span style="font-size: 10.5pt;">firewall</span><span style="font-size: 10.5pt;"> support.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in; mso-outline-level: 3;"><b><span style="font-size: 22pt;">Installation<o:p></o:p></span></b></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in;"><span style="font-size: 10.5pt;">Ethernet cables must be run from each computer to another computer or to the central device. It can be time-consuming and difficult to run cables under the floor or through walls, especially when computers sit in different rooms. Some newer homes are pre-wired with</span><span style="font-size: 10.5pt;">CAT5</span><span style="font-size: 10.5pt;"> cable, greatly simplifying the cabling process and minimizing unsightly cable runs.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in;"><span style="font-size: 10.5pt;">The correct cabling configuration for a wired LAN varies depending on the mix of devices, the type of Internet connection, and whether internal or external </span><span style="font-size: 10.5pt;">modems</span><span style="font-size: 10.5pt;"> are used. However, none of these options pose any more difficulty than, for example, wiring a home theater system.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in;"><span style="font-size: 10.5pt;">After hardware installation, the remaining steps in configuring either wired or wireless LANs do not differ much. Both rely on standard </span><span style="font-size: 10.5pt;">Internet Protocol</span><span style="font-size: 10.5pt;"> and </span><span style="font-size: 10.5pt;">network operating  system</span><span style="font-size: 10.5pt;">configuration options. Laptops and other portable devices often enjoy greater <b>mobility</b> in wireless home network installations (at least for as long as their batteries allow).<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in; mso-outline-level: 3;"><b><span style="font-size: 22pt;">Cost<o:p></o:p></span></b></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in;"><span style="font-size: 10.5pt;">Ethernet cables, hubs and switches are very inexpensive. Some connection sharing software packages, like ICS, are free; some cost a nominal fee. Broadband routers cost more, but these are optional components of a wired LAN, and their higher cost is offset by the benefit of easier installation and built-in security features.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in; mso-outline-level: 3;"><b><span style="font-size: 22pt;">Reliability<o:p></o:p></span></b></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in;"><span style="font-size: 10.5pt;">Ethernet cables, hubs and switches are extremely reliable, mainly because manufacturers have been continually improving Ethernet technology over several decades. Loose cables likely remain the single most common and annoying source of failure in a wired network. When installing a wired LAN or moving any of the components later, be sure to carefully check the cable connections.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in;"><span style="font-size: 10.5pt;">Broadband routers have also suffered from some reliability problems in the past. Unlike other Ethernet gear, these products are relatively new, multi-function devices. Broadband routers have matured over the past several years and their reliability has improved greatly.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in; mso-outline-level: 3;"><b><span style="font-size: 22pt;">Performance<o:p></o:p></span></b></div><div class="MsoNormal" style="background: white; margin-bottom: .0001pt; margin-bottom: 0in;"><span style="font-size: 10.5pt;">Wired LANs offer superior performance. Traditional Ethernet connections offer only 10 </span><span style="font-size: 10.5pt;">Mbps</span> <span style="font-size: 10.5pt;">bandwidth, but 100 Mbps Fast Ethernet technology costs little more and is readily available. Although 100 Mbps represents a theoretical maximum performance never really achieved in practice, Fast Ethernet should be sufficient for home file sharing, gaming, and high-speed Internet access for many years into the future.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in;"><span style="font-size: 10.5pt;">Wired LANs utilizing hubs can suffer performance slowdown if computers heavily utilize the network simultaneously. Use Ethernet switches instead of hubs to avoid this problem; a switch costs little more than a hub.<o:p></o:p></span></div><div class="MsoNormal" style="background: white; margin-bottom: .25in; margin-left: 0in; margin-right: 0in; margin-top: .25in; mso-outline-level: 3;"><b><span style="font-size: 20pt;">Security<o:p></o:p></span></b></div><div class="MsoNormal" style="background: white;"><span style="font-size: 10.5pt;">For any wired LAN connected to the Internet, firewalls are the primary security consideration. Wired Ethernet hubs and switches do not support firewalls. However, firewall software products like </span><span style="font-size: 10.5pt;">ZoneAlarm</span><span style="font-size: 10.5pt;"> can be installed on the computers themselves. Broadband routers offer equivalent firewall capability built into the device, configurable through its own software.<span style="color: #333333;"><o:p></o:p></span></span></div><div class="MsoNormal"><span style="font-family: Georgia, serif; font-size: 10.5pt;"></span><span style="font-family: Georgia, serif; font-size: 10.5pt;"><o:p></o:p></span></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikqD-fElauGMPXiOyqYZtP81cBsob9VB5gnA5VvJYJOYL6c26T0Ui68lYOrBfJo1BIkcGkM-RJhAI8OZm-xoGPghuBPakJ1fPZC76Ohgvdi2xQw-388Euw2FeUw2B4T2N68G_GfyYZZrQ/s1600/computerlab.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="456" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikqD-fElauGMPXiOyqYZtP81cBsob9VB5gnA5VvJYJOYL6c26T0Ui68lYOrBfJo1BIkcGkM-RJhAI8OZm-xoGPghuBPakJ1fPZC76Ohgvdi2xQw-388Euw2FeUw2B4T2N68G_GfyYZZrQ/s640/computerlab.jpg" width="640" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div></div>