Answers for YPK SHS Computer Final Exam Trial 2012

Answers for YPK SHS Computer Final Exam Trial 2012

"Sukses ya Try Out-UAS-UAN nya Sis/Gan, jjang!"
"FIGHTING!"

1. Ethernet / LAN Card
2. P2P (Peer-to-Peer)
3. Bus
4. Modem
5. Router
6. Interconnects computers in a limited area
7. MAN (Metropolitan Area Network)
8. User
9. -> Freeware, Open source programs other than made by Microsoft, Adobe, Corel, etc.
10. Unix, Dos, Windows, Mac OSX, Linux
11. Compiler, Programing Language
12. Central Processing Unit
13. -> Other than Hard disk, Flash disk, Memory Card, CD, DVD, Floppy Disk, Tape Drive
14. -> Mouse, Keyboard, Webcam, Joystick, Scanner, Touchpad, Drawing Pad
15. VGA Card
16. Hardware
17. UPS (Uninterrupted Power Supply)
18. “Menghitung”
19. Gateway/Modem (?)
20. Universal Serial Bus
21. 1, 2, & 3.
22. Rename
23. Upload
24. -> Other than Google Chrome, Safari, Firefox, IE
25. Internet Service Provider
26. ARPAnet
27. Download
28. Modulator Demodulator
29. WiFi / Ethernet Card
30. Ring Topology
31. LAN (Local Area Network)
32. Modem 33. Antenna/Wireless Access Point (?)
34. XAMPP, LAMPP, Apache
35. Manage Website
36. Hyperlink
37. Localhost or 127.0.0.1
38. <?php
39. Homepage
40. Server Side Scripting ; HTML -> Client Side Scripting
41. Duplicate File
42. Primary Key
43. Query
44. Summary of tupels in a relation
45. Manage Database
46. Currency
47. Structured Query Language
48. .accdb
49. DBMS
50. Auto Number
51. OLE Object
52. Data Manipulation Language
53. Drop
54. DML
55. Relationship
56. Break
57. ?
58. Strtoupper();
59. 19
60. Auto Increment (?)
61. Tree Topology
62. 110010
63. 181
64. $var
65. Echo
66. Header
67. Manage MySQL via Web browser
68. CSS
69. Background
70. Padding
71. Navbar / Nav-menu
72. No-repeat
73. <title></title>
74. Margin
75. <font color="">
76. 65536
77. 192.168.2.X
78. Blue
79. Topology
80. Conference Read More..

Twisted Pair Cable

Twisted pair cabling is a type of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. It was invented by Alexander Graham Bell.

Explanation

In balanced pair operation, the two wires carry equal and opposite signals and the destination detects the difference between the two. This is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields and tend to couple to both wires equally. The noise thus produces a common-mode signal which is cancelled at the receiver when the difference signal is taken. This method starts to fail when the noise source is close to the signal wires; the closer wire will couple with the noise more strongly and the common-mode rejection of the receiver will fail to eliminate it. This problem is especially apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles. One pair can induce crosstalk in another and it is additive along the length of the cable. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged. Providing the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. Differential signaling also reduces electromagnetic radiation from the cable, along with the associated attenuation allowing for greater distance between exchanges.


The twist rate (also called pitch of the twist, usually defined in twists per meter) makes up part of the specification for a given type of cable. Where nearby pairs have equal twist rates, the same conductors of the different pairs may repeatedly lie next to each other, partially undoing the benefits of differential mode. For this reason it is commonly specified that, at least for cables containing small numbers of pairs, the twist rates must differ.


In contrast to FTP (foiled twisted pair) and STP (shielded twisted pair) cabling, UTP (unshielded twisted pair) cable is not surrounded by any shielding. It is the primary wire type for telephone usage and is very common for computer networking, especially as patch cables or temporary network connections due to the high flexibility of the cables.

History

The earliest telephones used telegraph lines, or open-wire single-wire earth return circuits. In the 1880s electric trams were installed in many cities, which induced noise into these circuits. Lawsuits being unavailing, the telephone companies converted to balanced circuits, which had the incidental benefit of reducing attenuation, hence increasing range.

As electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, shared the route with electrical power lines. Within a few years the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference. In wire transposition, the wires exchange position once every several poles. In this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with a twist rate of about four twists per kilometre, or six per mile. Such open-wire balanced lines with periodic transpositions still survives today in some rural areas.

Twisted pair cables were invented by Alexander Graham Bell in 1881. By 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. Today, most of the millions of kilometres of twisted pairs in the world are outdoor landlines, owned by telephone companies, used for voice service, and only handled or even seen by telephone workers.

Unshielded twisted pair (UTP)

UTP cables are found in many Ethernet networks and telephone systems. For indoor telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T. A typical subset of these colors (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables.

For urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into smaller but identical bundles. Each bundle consists of twisted pairs that have different twist rates. The bundles are in turn twisted together to make up the cable. Pairs having the same twist rate within the cable can still experience some degree of crosstalk. Wire pairs are selected carefully to minimize crosstalk within a large cable.

UTP cable is also the most common cable used in computer networking. Modern Ethernet, the most common data networking standard, utilizes UTP cables. Twisted pair cabling is often used in data networks for short and medium length connections because of its relatively lower costs compared to optical fiber and coaxial cable.

UTP is also finding increasing use in video applications, primarily in security cameras. Many middle to high-end cameras include a UTP output with setscrew terminals. This is made possible by the fact that UTP cable bandwidth has improved to match the baseband of television signals. While the video recorder most likely still has unbalanced BNC connectors for standard coaxial cable, a balun is used to convert from 100-ohm balanced UTP to 75-ohm unbalanced. A balun can also be used at the camera end for ones without a UTP output. Only one pair is necessary for each video signal.

Cable shielding

Twisted pair cables are often shielded in attempt to prevent electromagnetic interference. Because the shielding is made of metal, it may also serve as a ground. However, usually a shielded or a screened twisted pair cable has a special grounding wire added called a drain wire. This shielding can be applied to individual pairs, or to the collection of pairs. When shielding is applied to the collection of pairs, this is referred to as screening. The shielding must be grounded for the shielding to work.

Shielded twisted pair (STP or STP-A)

STP cabling includes metal shielding over each individual pair of copper wires. This type of shielding protects cable from external EMI (electromagnetic interferences). e.g. the 150 ohm shielded twisted pair cables defined by the IBM Cabling System specifications and used with token ring networks.

Screened unshielded twisted pair (S/UTP)

Also known as Foiled Twisted Pair (FTP), is a screened UTP cable (ScTP).

Screened shielded twisted pair (S/STP or S/FTP)

S/STP cabling, also known as Screened Fully shielded Twisted Pair (S/FTP), is both individually shielded (like STP cabling) and also has an outer metal shielding covering the entire group of shielded copper pairs (like S/UTP). This type of cabling offers the best protection from interference from external sources, and also eliminates alien crosstalk.

Note that different vendors and authors use different terminology (i.e. STP has been used to denote both STP-A, S/STP, and S/UTP).

Solid core cable vs stranded cable

Solid core cable is supposed to be used for permanently installed runs. It is less flexible than stranded cable and is more prone to failure if repeatedly flexed. Stranded cable is used for fly leads at patch panel and for connections from wall-ports to end devices, as it resists cracking of the conductors. Stranded core is generally more expensive than solid core.

Connectors need to be designed differently for solid core than for stranded. Use of a connector with the wrong cable type is likely to lead to unreliable cabling. Plugs designed for solid and stranded core are readily available, and some vendors even offer plugs designed for use with both types. The punch-down blocks on patch-panel and wall port jacks are designed for use with solid core cable.

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Step by step Internet Connection Sharing (ICS) setup in Vista

Vista lets you share your Internet connection with other computers on your network.
Logically enough, the feature that lets you do this is called Internet Connection Sharing, which gets abbreviated to ICS.
ICS can be a great way of saving time and money: instead of needing a modem and a phone line (or a DSL or cable modem) for each computer that needs Internet connectivity, you can get by with one modem and one phone line (or the equivalent). ICS is particularly good if you have a fast Internet connection such as a DSL or a cable modem that provides enough bandwidth for several computers under normal circumstances.


Set Up the Computer That Will Share the Connection
Start with the computer that will share the Internet connection. First set up your Internet connection,and then use the Network Setup Wizard to configure the computer by taking the following steps
Create and test an Internet connection using the information in the “Connecting to the Internet”.
Click on start Right-click Network and choose Properties from the context menu. You’ll see the Network and Sharing Center window.Click the Manage Network Connection link.



You’ll see the Network Connection window.You must have a minimum of two active network connections to make ICS work. The first connection is from your computer to the Internet. The second connection is from your computer to the rest of the network.



Right-click the connection to the Internet and choose Properties from the context menu.Select the Sharing tab. You’ll see sharing options like the ones shown.Check the first option to let other people use this connection to access the Internet. If you want to also allow others to manage the connection ,check the second option.Click Settings.



You’ll see the Advanced Settings dialog box shown where you can control the services that others can use on your system.




Check the standard services that you want other people to access.lick Add to add custom services to the list. You’ll see the Service Settings dialog box . Custom services require that you provide an IP address and port umber. You can make your custom service less vulnerable by choosing a different setting for the fourth field, Internal Port number for This Service, to a different value than the external port number.Click OK to add the custom service. ICS enables the option automatically.



Click OK twice to make the ICS connection functional. Vista will ensure that the connection doesn’t have any problems such as address conflicts.

Setting Up a Client Computer
Next, set up the first of your client computers. Make sure the Internet connection is still open on thecomputer you set up to share it, and then take the following steps
Open the Internet Options applet in the Control Panel. You’ll see the Internet Properties dialog box.Select the Connections tab.
Choose the Never Dial a Connection option.Click LAN Settings to display the Local Area Network (LAN) Settings dialog box.
Check the Automatically Detect Settings and the Use Automatic Configuration Script
options. Clear the Use a Proxy Server for Your LAN option. Click OK twice to change
the settings.
NOTE You may have to reboot or at least log out and then back into the system to make the connection work. Windows may not acknowledge the availability of the shared connection otherwise.

Source : http://www.windowsreference.com/windows-vista/step-by-step-internet-connection-sharing-ics-setup-in-vista/
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Configure Wireless in Windows Vista with WLAN Autoconfig

WLAN Autoconfig is the utility introduced in Windows Vista to configure your Wireless Network Adapter in your PC Laptop. This is the equivalent of Wireless Zero Configuration (WZC) service in Windows XP. A name is not necessary.. is it? This can be used instead of using the Wireless Network Configuration provided by the manufacturer like Intel. Advantage of using WLAN Autoconfig is it being a native operating system utility and the fact that there isn’t another bloated software that you don’t have to install and run on your computer. A minor downside is that advanced configurations (which we never use anyway) may not be possible.
To configure your Wireless using “WLAN Autoconfig”
1. Click Start – Control Panel
2. Click “View network status and tasks” (in classic view double-click Network and Sharing Center )
3. From Network and Sharing Center, click “Connect Network“. This will scan for a list of available networks.
4. Select your network and click Connect.
5. If the network requires (most likely) a security key or a passphrase, enter and click connect. You may choose “Display Character” if you want to see the characters you are typing.
6. Once connected, you an choose to Save the network and automatically connect to this network.

Source : http://www.windowsreference.com/windows-vista/configure-wireless-in-windows-vista-with-wlan-autoconfig/ Read More..

Howto Speed-Up Your Wireless Access

YOUR WIRELESS NETWORK

Add a Wireless Repeater/Access Point to extend the range of your wireless network. Of course, extending the wireless network without wires is “desirable” but this effectively cuts your bandwidth in half – whenever possible use a cable, which is dramatically faster and more secure!
NOTE: The Repeater/Access Point should be the same manufacturer as your Router.
You may need to replace your 2.4GHz cordless phones with either a 900Mhz or 5.8GHz style cordless phone due to interference.
Choose your router and network adapters from the same company. Manufacturers usually have a proprietary “turbo” mode that only works when using both their router and network adapters. As a side benefit; your overall configuration is usually easier.
Upgrade your 802.11a and 802.11b devices to 802.11g, which is much faster, and is backward-compatible with 802.11b devices.NOTE: A small one room environment (i.e. apartment, dorm room) with no future expansion should use 802.11a.
If you are using 802.11g – do not allow 802.11b devices onto your wireless network. Your network slows down to talk with the slower devices!
If you are using 802.11g – consider getting an MIMO antenna (which allows faster speeds at greater distances.)
Whenever possible, connect computers using a wired connection! Yes, this is an “Anti-tip” because you’re not even using the wireless network – but a direct connection is dramatically faster and more secure!

YOUR WIRELESS ROUTER / ACCESS POINT

If possible, place your wireless router (or access point) in a central location. Obviously, the closer you are to the access point; the better. But do not necessarily place the device on your roof (or up too high) – 4 to 6 feet off the ground is perfect.
Move the router off the floor and away from walls, TVs, electronic appliances (microwave ovens), and metal objects (file cabinets). These will interfere with your network’s radio signals.
Change your wireless channel. In the US and Canada wireless networks use channels 1, 6 (usual default), and 11. Avoid possible interference with neighboring wireless networks, by changing your wireless router’s channel and see if it improves signal strength or overall speed. NOTE: This doesn’t require any changes to your computer.
Update your Router’s firmware. Most routers easily update their firmware directly from their software. Updates usually only add a new feature, or increase stability and security; but sometimes can improve performance.
Try moving “around” the router’s antenna. Yes, I know this antenna is “supposed” to be omni-directional (meaning it broadcasts in all directions) – and moving it shouldn’t matter. . .but antennas can have strong and weak spots; wiggling the antenna can make a difference.
Upgrade your router’s antenna. The antenna that comes with your device is low powered and omni-directional. Upgrade to a more powerful (powered) antenna. If your router is near an outside wall, get a high-gain antenna that focuses the wireless signals only one direction.

COMPTUER

Optimize Windows – But needless to say if Windows is running slowly, so will your wireless network.
Apply all current Windows updates, and install and update AntiVirus & AntiSpyware software. OK, this doesn’t make your computer “faster.” In fact it can actually slow your computer down – but if you never get “infected” your computer will remain “fast!”

If you’re not using Windows File Sharing – turn it off!
Upgrade your wireless network adapter’s antenna. If your antenna is not “upgradeable,” you’ll be stuck purchasing a new wireless network adapter. NOTE: Portables with built-in WiFi usually have better antennas than the cheaper adapters that most portable own.
Even though it’s more convenient to have a portable computer’s antenna horizontal – it should be oriented vertically (up & down).
Update your Windows Wireless Network Driver. While Microsoft Update, is “supposed” to notify you of updates to your drivers – it’s best to visit the manufacturers website to double-check. Updates usually only add a new feature, or increase stability and security; but sometimes can improve performance.
If upgrading a wireless network adapter, use an adapter card before using a (slower) USB adapter. USB should not be used simply because it’s “convenient” – but if there are no other viable method to upgrade from 802.11a – than use USB.

Source : http://www.windowsreference.com/wireless/howto-speed-up-your-wireless-access/ (show after click read more...) Read More..

Power Line Networking

Power-line networking is one of several ways to connect the computers in your home. It uses the electrical wiring in your house to create a network.


Like HomePNA, power-line networking is based on the concept of "no new wires." The convenience is even more obvious in this case because while not every room has a phone jack, you will always have an electrical outlet near a computer. In power-line networking, you connect your computers to one another through the same outlet.

Because it requires no new wiring, and the network adds no cost to your electric bill, power-line networking is the cheapest method of connecting computers in different rooms.

In this article, we'll talk about power-line networking and the technology used to make it happen. We'll also discuss the advantages and disadvantages of using a power-line network.
Pros and Cons of Power-line Networking

There are two competing power-line technologies. The original technology is called Passport, by a company named Intelogis. A new technology called PowerPacket, developed by Intellon, has been chosen by the HomePlug Alliance as the standard for power-line networking.

Here are the advantages of a power-line network:

It's inexpensive.
It uses existing electrical wiring.
Every room of a typical house has several electrical outlets.
It's easy to install.
A printer, or any other device that doesn't need to be directly connected to a computer, doesn't have to be physically near any of the computers in the network.
It doesn't require that a card be installed in the computer (although there are companies working on PCI-based systems).
The new PowerPacket technology provides a couple of other advantages as well. It is fast, rated at 14 megabits per second (Mbps). This speed allows for new applications, such as audio and video streaming, to be available throughout the house.
There are some disadvantages to connecting through power-lines when using the older Intelogis technology:

The connection is rather slow -- 50 Kbps to 350 Kbps (on older adapter system).
The performance can be impacted by home power usage.
It can limit the features of your printer.
It only works with Windows-based computers.
It uses large wall devices to access an electrical outlet.
It can only use 110-V standard lines.
It requires that all data be encrypted for a secure network.
Older wiring can affect performance.

New power-line networking products are based on Intellon's PowerPacket technology.
According to Intellon, PowerPacket technology eliminates many of these concerns, citing the following advantages:

It is very fast, rated at 14 Mbps.
It "avoids" disruptions in the power-line, maintaining the network's connections and speeds.
It does not limit the features of your printer.
It can be compatible with other operating systems (depending on driver availability).
It may have the necessary circuitry embedded within the device, necessitating only a standard power cord to access an outlet.
It works independent of line voltage and frequency of current.
It includes encryption.
In tests, it showed no signal degradation due to older wiring.

Methods
Intellon and Intelogis use different methods to establish power-line networks.

Intellon
Intellon's PowerPacket technology, which serves as the basis for the HomePlug Powerline Alliance standard, uses an enhanced form of orthogonal frequency-division multiplexing (OFDM) with forward error-correction, similar to the technology found in DSL modems. OFDM is a variation of the frequency-division multiplexing (FDM) used in phone-line networking. FDM puts computer data on separate frequencies from the voice signals being carried by the phone line, separating the extra signal space on a typical phone line into distinct data channels by splitting it into uniform chunks of bandwidth.

In the case of OFDM, the available range of frequencies on the electrical subsystem (4.3 MHz to 20.9 MHz) is split into 84 separate carriers. OFDM sends packets of data simultaneously along several of the carrier frequencies, allowing for increased speed and reliability. If noise or a surge in power usage disrupts one of the frequencies, the PowerPacket chip will sense it and switch that data to another carrier. This rate-adaptive design allows PowerPacket to maintain an Ethernet-class connection throughout the power-line network without losing any data.

This card plugs into a PCI slot in your computer and into a wall outlet to create a power-line network.
The latest generation of PowerPacket technology is rated at 14 Mbps, which is faster than existing phone-line and wireless solutions. However, as broadband access and Internet-based content like streaming audio and video and voice-over-IP become more commonplace, speed requirements will continue to increase. Along these lines, Intellon's OFDM approach to power-line networking is highly scalable, eventually allowing the technology to surpass 100 Mbps.

Intelogis
The older power-line technology used by Intelogis relies on frequency-shift keying (FSK) to send data back and forth over the electrical wires in your home. FSK uses two frequencies, one for 1s and the other for 0s, to send digital information between the computers on the network. (See How Bits and Bytes Work to learn more about digital data.) The frequencies used are in a narrow band just above the level where most line noise occurs. Although this method works, it is somewhat fragile. Anything that impinges on either frequency can disrupt the data flow, causing the transmitting computer to have to resend the data. This can affect the performance of the network. For example, this author noticed that when he was using more electricity in the house, such as running the washer and dryer, the network slowed down. Intelogis includes line-conditioning power strips with its network kit and encourages you to insert them between the wall outlet and your computer equipment to help reduce the amount of electrical-line noise.

Because the current crop of power-line networks are designed to work on 110-volt electrical systems, the technology is not very useful to countries outside of North America that use different standards.

Cost And Installation
Intelogis provides a kit that connects two computers and one printer for $59. Additional adapters cost about $40. There are specific versions for computers or printers, so make sure you get the correct one. Since the network does not affect power usage or consumption, no additional monthly costs are incurred.

The cost of PowerPacket technology is expected to be comparable to HomePNA solutions and significantly less than 802.11 wireless solutions.

The physical connection between each computer and the Intelogis power-line network uses the computer's parallel port. A wall device is plugged directly into the electrical outlet (it will not operate properly if plugged into a surge protector).

A parallel cable is plugged into the wall device and into the parallel port of the computer. The power-line network must be the last item connected to the parallel port. For this reason, if you have anything else connected to the parallel port, such as a scanner or Zip drive, it must have a pass-through for the parallel port. Unless you have a second parallel port on your computer, your printer must be connected to the network through a wall device of its own. Something to keep in mind is that current power-line networks do not support bidirectional printing. "Bidirectional" means that data is sent in both directions, allowing your printer to send information back to your computer, such as how much ink is left and if there is a paper jam. This will not keep your printer from working, but it is worth noting that you will lose the use of such features.

Initial PowerPacket devices connect via a USB or Ethernet cord from the computer to a small wall adapter. Subsequent devices will have the circuitry built in, meaning the only connection needed would be the power cord.

Once the physical connections are made, installation of the software is a snap. The software automatically detects all nodes (computers and printers) on the network. Whether your Internet connection is by cable modem, DSL or normal modem, the included proxy server software allows you to share the Internet with your other computers. You can easily add computers by simply plugging a new adapter in and installing the software. Additional printers can be added using the printer plug-in adapter. File and printer sharing is done through Windows.

There are two common types of home networks: peer-to-peer and client/server. Client/server networks have a centralized administrative system that provides information to all of the other devices. Peer-to-peer means that each device can talk directly to each other device on the network without consulting a central system first. Intelogis Passport technology uses a client/server network. The first computer that you install the software on becomes the Application Server. In essence, it is the director of the network, controlling the flow of data and telling each device on the network where to find the other devices. Intellon's PowerPacket technology uses a peer-to-peer network. Read More..

Network Basic Hardware Components

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.12) or optical cable ("optical fiber").

Network interface cards

A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses.

Repeaters

A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. Repeaters work on the Physical Layer of the OSI model.

Hubs

A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address. It works on the Physical Layer of the OSI model..

Bridges

A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges broadcast to all ports except the port on which the broadcast was received. However, bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address to that port only.

Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

Bridges come in three basic types:

Local bridges: Directly connect local area networks (LANs)
Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
Switches

A network switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets. A switch is distinct from a hub in that it only forwards the frames to the ports involved in the communication rather than all ports connected. A switch breaks the collision domain but represents itself as a broadcast domain. Switches make forwarding decisions of frames on the basis of MAC addresses. A switch normally has numerous ports, facilitating a star topology for devices, and cascading additional switches. Some switches are capable of routing based on Layer 3 addressing or additional logical levels; these are called multi-layer switches. The term switch is used loosely in marketing to encompass devices including routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier).

Routers

A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet (Internet protocol information from Layer 3 of the OSI Model). In many situations, this information is processed in conjunction with the routing table (also known as forwarding table). Routers use routing tables to determine what interface to forward packets (this can include the "null" also known as the "black hole" interface because data can go into it, however, no further processing is done for said data).

Firewalls

Firewalls are the most important aspect of the network and its security in today's era. Due to maximization of attacks on the networks from various groups stealing data, denying services etc the firewall is playing a vital roles in computer networks.
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Types of Backbone Networks & Overlay Network

Global Area Network

A Global Area Network (GAN) is a network used for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial wireless LANs.

Internet

The Internet is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is based on the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the United States Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW).

Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

Intranets and extranets

Intranets and extranets are parts or extensions of a computer network, usually a local area network.

An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.

An extranet is a network that is limited in scope to a single organization or entity and also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities—a company's customers may be given access to some part of its intranet—while at the same time the customers may not be considered trusted from a security standpoint. Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Overlay network

An overlay network is a virtual computer network that is built on top of another network. Nodes in the overlay are connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network.


A sample overlay network: IP over SONET over Optical
For example, many peer-to-peer networks are overlay networks because they are organized as nodes of a virtual system of links run on top of the Internet. The Internet was initially built as an overlay on the telephone network .

Overlay networks have been around since the invention of networking when computer systems were connected over telephone lines using modem, before any data network existed.

Nowadays the Internet is the basis for many overlaid networks that can be constructed to permit routing of messages to destinations specified by an IP address. For example, distributed hash tables can be used to route messages to a node having a specific logical address, whose IP address is known in advance.

Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees to achieve higher-quality streaming media. Previous proposals such as IntServ, DiffServ, and IP Multicast have not seen wide acceptance largely because they require modification of all routers in the network.[citation needed] On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from Internet service providers. The overlay has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes a message traverses before reaching its destination.

For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast). Academic research includes End System Multicast and Overcast for multicast; RON (Resilient Overlay Network) for resilient routing; and OverQoS for quality of service guarantees, among others.
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Types of networks based on physical scope

Common types of computer networks may be identified by their scale.

Local area network

A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines).


The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 40 and 100 Gbit/s. All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.

Personal area network

A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters.[4] A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

Home area network

A home area network (HAN) is a residential LAN which is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a CATV or Digital Subscriber Line (DSL) provider. It can also be referred as an office area network (OAN).

Wide area network

A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.



Campus network

A campus network is a computer network made up of an interconnection of local area networks (LAN's) within a limited geographical area. The networking equipments (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling etc.) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.).

In the case of a university campus-based campus network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls.

Metropolitan area network

A Metropolitan area network is a large computer network that usually spans a city or a large campus.


A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.

Virtual private network

VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point.

Internetwork

An internetwork is the connection of two or more private computer networks via a common routing technology (OSI Layer 3) using routers. The Internet is an aggregation of many internetworks, hence its name was shortened to Internet.

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What is Computer Network (Explicit Edition)

A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources. Networks may be classified according to a wide variety of characteristics.

Introduction

A computer network allows sharing of resources and information among interconnected devices. In the 1960s, the Advanced Research Projects Agency (ARPA) started funding the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. It was the first computer network in the world. Development of the network began in 1969, based on designs developed during the 1960s.

Purpose

Computer networks can be used for several purposes:

• Facilitating communications. Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.
• Sharing hardware. In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer.
• Sharing files, data, and information. In a network environment, authorized user may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.
• Sharing software. Users connected to a network may run application programs on remote computers.
• Information preservation.
• Security.
• Speed up. Sharing software. Users connected to a network may run application programs on remote computers.

Network classification

The following list presents categories used for classifying networks.

Connection method

Computer networks can be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as optical fiber, Ethernet, wireless LAN, HomePNA, power line communication or G.hn.

Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges, or routers. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium. ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network.

Scale

Networks are often classified as local area network (LAN), wide area network (WAN), metropolitan area network (MAN), personal area network (PAN), virtual private network (VPN), campus area network (CAN),storage area network (SAN), and others, depending on their scale, scope and purpose, e.g., controller area network (CAN) usage, trust level, and access right often differ between these types of networks. LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations, such as a building, while WANs may connect physically separate parts of an organization and may include connections to third parties.

Functional relationship (network architecture)

Computer networks may be classified according to the functional relationships which exist among the elements of the network, e.g., active networking, client–server and peer-to-peer (workgroup) architecture.

Network topology

Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network. Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. Even if networked computers are physically placed in a linear arrangement and are connected to a hub, the network has a star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.

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