Web Crawler (Spider)

A web crawler is a relatively simple automated program, or script, that methodically scans or "crawls" through Internet pages to create an index of the data it's looking for. Alternative names for a web crawler include web spider, web robot, bot, crawler, and automatic indexer.

There are many different uses for a web crawler. Probably the most common use associated with the term is related to search engines. Search engines use web crawlers to collect information about what is available on public web pages. Their primary purpose is to collect data so that when Internet surfers enter a search term on their site, they can quickly provide the surfer with relevant web sites.

When a search engine's web crawler visits a web page, it "reads" the visible text, the hyperlinks, and the content of the various tags used in the site, such as keyword rich meta tags. Using the information gathered from the crawler, a search engine will then determine what the site is about and index the information. The website is then included in the search engine's database and its page ranking process.

Search engines, however, are not the only users of web crawlers. Linguists may use a web crawler to perform a textual analysis; that is, they may comb the Internet to determine what words are commonly used today. Market researchers may use a web crawler to determine and assess trends in a given market. There are numerous nefarious uses of web crawlers as well. In the end, a web crawler may be used by anyone seeking to collect information out on the Internet.

Web crawlers may operate one time only, say for a particular one-time project. If its purpose is for something long term, as is the case with search engines, they may be programed to comb through the Internet periodically to determine whether there has been any significant changes. If a site is experiencing heavy traffic or technical difficulties, the spider may be programmed to note that and revisit the site again, hopefully after the technical issues have subsided.

Web crawling is an important method for collecting data on, and keeping up with, the rapidly expanding Internet. A vast number of web pages are continually being added every day, and information is constantly changing. A web crawler is a way for the search engines and other users to regularly ensure that their databases are up to date.

Resource: http://www.wisegeek.com/what-is-a-web-crawler.htm

Search Engine Optimisation (SEO)

An introduction to Search Engine Optimisation


Unfortunately simply submitting your web site to search engines will not drive traffic to your site. Although submission is an integral part of any effective search engine optimising strategy, you must achieve good search positions for anyone to find your listing. Hopefully our useful hints and tips will help you optimise your site and achieve that top ten position.


As any search engine optimisation company will tell you, getting you site listed in the first ten results for a specific keyword is as much art as a science. Anyone can get to number 1 on a unique word or trade name, but on a generic key phrase, it's much more tricky. Search engine optimising can be difficult and confusing, but once you are aware of the key optimisation techniques, time and persistence can yield a hugely gratifying reward if you get it right.


As Search Engine Optimiser's (SEO's), we ensure that the relevant words and phrases appear in the best positions on the pages. There are many other considerations, complicated by the engines modifying their preferences on a monthly basis. We pay for access to a the Wordtracker keyword database, which holds 301 million entries over the last 60 days. Using this information, we make sure that we are optimising the page in such a way that people will find it.

Site design considerations

1 Do not use frames
One of the biggest potential pitfalls for Webmasters is search engines that do not index the text within frames. A frame is an HTML page that "frames" other HTML pages. If your site uses frames you homepage is actually a frameset with no real content. Several major engines (including Excite, WebCrawler and HotBot) do not support frames, others do not index framed sites very well. If you site uses frames we recommend redesigning your site without them if you want to get good listings in the search engines.


If you must use frames, include text in the <NOFRAMES> tag. Another solution is to create pages (without frames) to act as doorways or alternate entrances to your site for the purpose of giving these engines something they can see and index.


2 Do not use dynamic URL's
Most search engine cannot list dynamic URL's which are commonly listed on database driven sites using scripting languages such as VBScript within Active Server Pages (ASP). An example of a dynamic URL is shown below.
http://www.searchengineoptimising.com/products.asp?ID=dynamic+example


3 Do not have an entirely FLASH homepage
Search engines cannot index pages made entirely with FLASH. When you submit a page to a search engine a spider will follow the links on the page and listing the rest of the site. The best way to remedy this is to create a site map that uses normal html links to every page on your site. Also add a standard HTML link on each page of you site that links to the site map.


4 Do not use image maps as the only method of navigation
Search engines cannot index the code that makes up image maps. You can use image maps in your site but you should also include standard html links. As with a Flash site, create a site map that uses normal html links to every page on your site. Also add a standard HTML link on each page of you site that links to the site map.


5 Do not use javascript as the only method of navigation
Search engines can't follow links that are within Javascript, so your site will not get spidered unless you also have some form standard HTML hyperlinks that they can follow. You should add some form standard HTML hyperlinks to all of your pages on each of your pages so that your site will be spidered properly. An easy way to do this is to create a site map page uses standard HTML links to link to every page on your site. Then add a standard HTML link on each page of your site that links to the site map.


Carefully choose your keywords
Target the wrong keywords and all your efforts will be in vain. Choose the right keywords and you’ll see your traffic dramatically increase. Therefore, think long and hard about what keywords people are most likely to use when search for your site. Make lists of single keywords and then combine them into phrases.


Optimisation of your Title Tag
The title tag of your page is an extremely important factor to consider during the optimisation of a web page for search engines. This is because many engines and directories place a high level of importance on keywords that are found in your title tag. The title tag is also what the search engines usually use for the title of your listing in the search results.


What it looks like:
Here's the title tag of this page:
<TITLE>Hints and Tips - optimisation of your title tag for search engines</TITLE>


Where it belongs:
The correct placement for the title tag is between the <HEAD> and </HEAD> tags within the HTML the makes up your page.


Tag limits:
Generally, we recommend that your title tag, including spaces, be between 50-80 characters long. The optimum level differs from search engine to search engine, therefore we recommend using a tool such as Web CEO tool to analyse your page.


Tips for optimising your Meta Tags:
    * Make your title enticing! Don't forget that even if you get that #1 listing in the search engines your listing still needs to say something that makes the surfer want to clickthrough and visit your site.
    * Since the length of your title tag could be a little long for some engines we suggest placing the keywords at the beginning of the tag when possible so that you do not risk having them cut off.
    * Each page of your site should have a unique title tag with it's own keywords that related to the page that it appears on.


Optimisation of your page content
your page content is another very important factor in achieving better search engine listings. Your page content is the information that a visitor would read from the page. Search engines look through Did you know that just like a visitor to your site would read the copy on your page to figure out what you have to offer, the search engines do too? And what do you think the search engines are looking for when they 'read' your page copy? Keyword phrases, of course!


Page content tips:
    * We recommend that each page you submit has at contains least 200 words.
    * This text should include your most important keyword phrases, but should remain logical & readable.
    * Include the phrases that you have used in your other tags (i.e. metas, alt, headings, title, etc.) during the optimisation process.
    * Add additional content rich pages to your site. For example, how-to articles, hint and tips, or tutorials. These types of content pages not only help you in the search engines, but many other sites will link to them too.


Optimisation of your META tags
The head element contains general information (meta-information) about a document. HTML also includes a meta element that goes inside the head element. The purpose of the meta element is to provide meta-information about the document.


Most often the meta element is used to provide information that is relevant to browsers or search engines like describing the content of your document. Some search engines will use the name and content attributes of the meta tag to index your pages.


This meta element defines a description of your page:
<meta name="description" content="Free Web tutorials on HTML, CSS, XML, and XHTML">


This meta element defines keywords for your page:
<meta name="keywords" content="HTML, DHTML, CSS, XML, XHTML, JavaScript, VBScript">


The intention of the name and content attributes is to describe the content of a page. However, since too many webmasters have used meta tags for spamming, like repeating keywords to give pages a higher ranking, many major search engines have stopped using them entirely.


Where they belong:  The correct placement for both meta tags is between the <HEAD> and </HEAD> tags within the HTML the makes up your page. Their order does not really matter, but most people usually place the description first then the keywords meta. Tag limits:


    * We recommend that your Keywords Meta not exceed 1024 characters including spaces.
    * We recommend that  your Description Meta tag not exceed 250 characters including spaces.


Meta description tips:
    * Make sure you accurately describe the content of your page while trying to entice visitors to click on your listing.
    * Include 3-4 of your most important keyword phrases. Especially those used in your title tag and page copy.
    * Try to have your most important keywords appear at the beginning of your description. This often brings better results, and will help avoid having any search engine cut off your keywords if they limit the length of your description.


Meta keywords tips:
    * Aside from what we mention in the other tips below you should only use those keyword phrases that you also used in the copy of your page, title tag, meta description, and other tags. Any keywords phrases that you use that do not appear in your other tags or page copy are likely to not have enough prominence to help your listings for that phrase.
    * Don't forget plurals.
    * Don't forget common misspelling of a popular keyword that could be used to find your site.
    * Watch out for repeats! You want to include your most important phrases, but when doing so it can be difficult not to repeat one word many times. There in no limit, but we recommend that no one word be repeated in the keyword meta more than 5 times.
    * If your site has content of interest to a specific geographic location be sure to include the actual location in your keyword meta.


Optimisation of your images using "alt"
The alt attribute is used to define an "alternate text" for an image. The value of the alt attribute is an author-defined text:


<img src="optimised.gif" alt="Search Engine Optimisation">


The "alt" attribute tells the reader what he or she is missing on a page if the browser can't load images. The browser will then display the alternate text instead of the image. It is a good practice to include the "alt" attribute for each image on a page, to improve the display and usefulness of your document for people who have text-only browsers.


Although not all search engines use the Alt tab it can help your listings on some of them. We recommend on using 2-3 words for each image and using it where ever possible.


Optimisation of Text Hyperlinks
Search engines use complex algorithms to see if what you are linking to is something closely related to the content of your page. Some of the engines look for keywords in hyperlinks and in the surrounding text of the hyperlinks. We recommend including your most important keyword phrases in the link itself and possibly the surrounding text.


Optimisation of Heading Tags
Headings are defined with the <h1> to <h6> tags. <h1> defines the largest heading. <h6> defines the smallest heading.


<h1>This is a heading</h1>
<h2>This is a heading</h2>
<h3>This is a heading</h3>
<h4>This is a heading</h4>
<h5>This is a heading</h5>
<h6>This is a heading</h6>


HTML automatically adds an extra blank line before and after a heading.


Although they are used less frequently due to new technologies, HTML heading tags can help improve your listings in the search engines also. You should include you most important keyword phrases in the heading tags on your page. Some search engines use them in the analysis of your page content.


How long should I wait before re-submitting to a particular search engine?
MSN                  30 days
Google                4-6 weeks
AltaVista            15-30 days
Fast                    15-30 days
Excite                  4-6 weeks
Northern Light     30 days
AOL                   30 days
HotBot                30 days
iWon                   30 days


Things to Avoid attempting Optimisation techniques for Search Engines

You should not try to trick a search engine in any way because you risk being blacklisted by them.
    * Excluding the meta keyword tag, do not list you keyword one after another anywhere on the page
    * An old trick is to try and keyword stuff the page by using the same colour text as the page's background. Search engines can detect this and view it as spam.
    * Do not submit the same page to any search engine more than once in any twenty-four hours.
    * Do not submit identical pages. You should instead give them different filename and change the title and, if possible, the keywords for the page.
    * Do not use any keywords in your keywords meta tag that do not directly relate to the content of your page.
    * Don't use any keywords in your keywords meta tag that do not directly relate to the content of your page.


Resource: SearchEngineOptimising.com

20 things didn't know about Windows XP

You've read the reviews and digested the key feature enhancements and operational changes. Now it's time to delve a bit deeper and uncover some of Windows XP's secrets.

1. It boasts how long it can stay up. Whereas previous versions of Windows were coy about how long they went between boots, XP is positively proud of its stamina. Go to the Command Prompt in the Accessories menu from the All Programs start button option, and then type 'systeminfo'. The computer will produce a lot of useful info, including the uptime. If you want to keep these, type 'systeminfo > info.txt'. This creates a file called info.txt you can look at later with Notepad. (Professional Edition only).

2. You can delete files immediately, without having them move to the Recycle Bin first. Go to the Start menu, select Run... and type 'gpedit.msc'; then select User Configuration, Administrative Templates, Windows Components, Windows Explorer and find the Do not move deleted files to the Recycle Bin setting. Set it. Poking around in gpedit will reveal a great many interface and system options, but take care -- some may stop your computer behaving as you wish. (Professional Edition only).

3. You can lock your XP workstation with two clicks of the mouse. Create a new shortcut on your desktop using a right mouse click, and enter 'rundll32.exe user32.dll,LockWorkStation' in the location field. Give the shortcut a name you like. That's it -- just double click on it and your computer will be locked. And if that's not easy enough, Windows key + L will do the same.

4. XP hides some system software you might want to remove, such as Windows Messenger, but you can tickle it and make it disgorge everything. Using Notepad or Edit, edit the text file /windows/inf/sysoc.inf, search for the word 'hide' and remove it. You can then go to the Add or Remove Programs in the Control Panel, select Add/Remove Windows Components and there will be your prey, exposed and vulnerable.

5. For those skilled in the art of DOS batch files, XP has a number of interesting new commands. These include 'eventcreate' and 'eventtriggers' for creating and watching system events, 'typeperf' for monitoring performance of various subsystems, and 'schtasks' for handling scheduled tasks. As usual, typing the command name followed by /? will give a list of options -- they're all far too baroque to go into here.

6. XP has IP version 6 support -- the next generation of IP. Unfortunately this is more than your ISP has, so you can only experiment with this on your LAN. Type 'ipv6 install' into Run... (it's OK, it won't ruin your existing network setup) and then 'ipv6 /?' at the command line to find out more. If you don't know what IPv6 is, don't worry and don't bother.

7. You can at last get rid of tasks on the computer from the command line by using 'taskkill /pid' and the task number, or just 'tskill' and the process number. Find that out by typing 'tasklist', which will also tell you a lot about what's going on in your system.

8. XP will treat Zip files like folders, which is nice if you've got a fast machine. On slower machines, you can make XP leave zip files well alone by typing 'regsvr32 /u zipfldr.dll' at the command line. If you change your mind later, you can put things back as they were by typing 'regsvr32 zipfldr.dll'.

9. XP has ClearType -- Microsoft's anti-aliasing font display technology -- but doesn't have it enabled by default. It's well worth trying, especially if you were there for DOS and all those years of staring at a screen have given you the eyes of an astigmatic bat. To enable ClearType, right click on the desktop, select Properties, Appearance, Effects, select ClearType from the second drop-down menu and enable the selection. Expect best results on laptop displays. If you want to use ClearType on the Welcome login screen as well, set the registry entry HKEY_USERS/.DEFAULT/Control Panel/Desktop/FontSmoothingType to 2.

10. You can use Remote Assistance to help a friend who's using network address translation (NAT) on a home network, but not automatically. Get your pal to email you a Remote Assistance invitation and edit the file. Under the RCTICKET attribute will be a NAT IP address, like 192.168.1.10. Replace this with your chum's real IP address -- they can find this out by going to www.whatismyip.com -- and get them to make sure that they've got port 3389 open on their firewall and forwarded to the errant computer.

 
11. You can run a program as a different user without logging out and back in again. Right click the icon, select Run As... and enter the user name and password you want to use. This only applies for that run. The trick is particularly useful if you need to have administrative permissions to install a program, which many require. Note that you can have some fun by running programs multiple times on the same system as different users, but this can have unforeseen effects.

12. Windows XP can be very insistent about you checking for auto updates, registering a Passport, using Windows Messenger and so on. After a while, the nagging goes away, but if you feel you might slip the bonds of sanity before that point, run Regedit, go to HKEY_CURRENT_USER/Software/Microsoft/Windows/Current Version/Explorer/Advanced and create a DWORD value called EnableBalloonTips with a value of 0.

13. You can start up without needing to enter a user name or password. Select Run... from the start menu and type 'control userpasswords2', which will open the user accounts application. On the Users tab, clear the box for Users Must Enter A User Name And Password To Use This Computer, and click on OK. An Automatically Log On dialog box will appear; enter the user name and password for the account you want to use.

14. Internet Explorer 6 will automatically delete temporary files, but only if you tell it to. Start the browser, select Tools / Internet Options... and Advanced, go down to the Security area and check the box to Empty Temporary Internet Files folder when browser is closed.

15. XP comes with a free Network Activity Light, just in case you can't see the LEDs twinkle on your network card. Right click on My Network Places on the desktop, then select Properties. Right click on the description for your LAN or dial-up connection, select Properties, then check the Show icon in notification area when connected box. You'll now see a tiny network icon on the right of your task bar that glimmers nicely during network traffic.

16. The Start Menu can be leisurely when it decides to appear, but you can speed things along by changing the registry entry HKEY_CURRENT_USER/Control Panel/Desktop/MenuShowDelay from the default 400 to something a little snappier. Like 0.

17. You can rename loads of files at once in Windows Explorer. Highlight a set of files in a window, then right click on one and rename it. All the other files will be renamed to that name, with individual numbers in brackets to distinguish them. Also, in a folder you can arrange icons in alphabetised groups by View, Arrange Icon By... Show In Groups.

18. Windows Media Player will display the cover art for albums as it plays the tracks -- if it found the picture on the Internet when you copied the tracks from the CD. If it didn't, or if you have lots of pre-WMP music files, you can put your own copy of the cover art in the same directory as the tracks. Just call it folder.jpg and Windows Media Player will pick it up and display it.

19. Windows key + Break brings up the System Properties dialogue box; Windows key + D brings up the desktop; Windows key + Tab moves through the taskbar buttons.

20. The next release of Windows XP, codenamed Longhorn, is due and won't be much to write home about. The next big release is codenamed Blackcomb.

Resource: Different websites for Collective Info

Hidden comands in XP

1- Private Character Editor
This program is for designing icons and Characters (Alphabet)
Click :start
Then :run
type :EUDCEDIT

2- iExpress
This Program is for concerting your files to EXECUTABLE files
Click : start
Then : run
type : iexpress

3-Disk Cleanup
This program used for cleaning hard disk to offer space
Click : start
Then : run
type : cleanmgr

4-Dr Watson
This program Is for repairing problems in Windows
Click : start
Then : run
type : drwtsn32

5-Windows Media Player 5.1
Opens the old media player
Click: start
Then: run
type: mplay32

Character Map = charmap
DirectX diagnosis = dxdiag
Object Packager = packager
System Monitor = perfmon
Program Manager = progman
Remote Access phone book = rasphone
Registry Editor = regedt32
File signature verification tool = sigverif
Volume Contro = sndvol32
System Configuration Editor = sysedit
Syskey = syskey
Microsoft Telnet Client = telnet

What Makes a VPN Private

What is a Virtual Private network (VPN)?

Using a public network — usually the Internet — to connect securely to a private network, such as a company's network is the basis of a VPN or virtual private network.

Companies and organizations will use a VPN to communicate confidentially over a public network and to send voice, video or data. It is also an excellent option for remote workers and organizations with global offices and partners to share data in a private manner.

One of the most common types of VPNs is a virtual private dial-up network (VPDN). A VPDN is a user-to-LAN connection, where remote users need to connect to the company LAN. Here the company will have a service provider set-up a NAS (network access server) and provide the remote users with the software needed to reach the NAS from their desktop computer or laptop. For a VPDN, the secure and encrypted connection between the company's network and remote users is provided by the third-party service provider.

Another type of VPN is commonly called a site-to-site VPN. Here the company would invest in dedicated hardware to connect multiple sites to their LAN though a public network, usually the Internet. Site-to-site VPNs are either intranet or extranet-based.

Intranet
A network based on TCP/IP protocols (an intranet) belonging to an organization, usually a corporation, accessible only by the organization's members, employees or others with authorization. Secure intranets are now the fastest-growing segment of the Internet because they are much less expensive to build and manage than private networks based on proprietary protocols.

Extranet
An extranet refers to an intranet that is partially accessible to authorized outsiders. Whereas an intranet resides behind a firewall and is accessible only to people who are members of the same company or organization, an extranet provides various levels of accessibility to outsiders. You can access an extranet only if you have a valid username and password, and your identity determines which parts of the extranet you can view. Extranets are becoming a popular means for business partners to exchange information. 

Other options for using a VPN include such things as using dedicated private leased lines. Due to the high cost of dedicated lines, however, VPNs have become an attractive cost-effective solution.

Securing a VPN

If you're using a public line to connect to a private network, then you might wonder what makes a virtual private network private? The answer is the manner in which the VPN is designed. A VPN is designed to provides a secure, encrypted tunnel in which to transmit the data between the remote user and the company network. The information transmitted between the two locations via the encrypted tunnel cannot be read by anyone else.

VPN security contains several elements to secure both the company's private network and the outside network, usually the Internet, through which the remote user connects through. The first step to security is usually a firewall. You will have a firewall site between the client (which is the remote users workstation) and the host server, which is the connection point to the private network. The remote user will establish an authenticated connection with the firewall.

VPN Encryption

Encryption is also an important component of a secure VPN. Encryption works by having all data sent from one computer encrypted in such a way that only the computer it is sending to can decrypt the data. Types of encryption commonly used include public-key encryption which is a system that uses two keys — a public key known to everyone and a private or secret key known only to the recipient of the message. The other commonly used encryption system is a Symmetric-key encryption system in which the sender and receiver of a message share a single, common key that is used to encrypt and decrypt the message.

VPN Tunneling

With a VPN you'll need to establish a network connection that is based on the idea of tunneling. There are two main types of tunneling used in virtual private networks. Voluntary tunneling is where the client makes a connection to the service provider then the VPN client creates the tunnel to the VPN server once the connection has been made. In compulsory tunneling the service provider manages the VPN connection and brokers the connection between that client and a VPN server.

There are three main network protocols for use with VPN tunnels, which are generally incompatible with each other. They include the following:

IPSec
A set of protocols developed by the IETF to support secure exchange of packets at the IP layer. IPsec has been deployed widely to implement VPNs. IPsec supports two encryption modes: Transport and Tunnel. Transport mode encrypts only the data portion (payload) of each packet, but leaves the header untouched. The more secure Tunnel mode encrypts both the header and the payload. On the receiving side, an IPSec-compliant device decrypts each packet. For IPsec to work, the sending and receiving devices must share a public key. This is accomplished through a protocol known as Internet Security Association and Key Management Protocol/Oakley (ISAKMP/Oakley), which allows the receiver to obtain a public key and authenticate the sender using digital certificates.

PPTP
Short for Point-to-Point Tunneling Protocol, a new technology for creating VPNs, developed jointly by Microsoft, U.S. Robotics and several remote access vendor companies, known collectively as the PPTP Forum. A VPN is a private network of computers that uses the public Internet to connect some nodes. Because the Internet is essentially an open network, PPTP is used to ensure that messages transmitted from one VPN node to another are secure. With PPTP, users can dial in to their corporate network via the Internet.

L2TP
Short for Layer Two (2) Tunneling Protocol, an extension to the PPP protocol that enables ISPs to operate Virtual Private Networks (VPNs). L2TP merges the best features of two other tunneling protocols: PPTP from Microsoft and L2F from Cisco Systems. Like PPTP, L2TP requires that the ISP's routers support the protocol.

VPN Equipment

Depending on the type of VPN you decide to implement, either remote-access or site-to-site, you will need specific components to build your VPN. These standard components include a software client for each remote workstation, dedicated hardware, such as a firewall  or a product like the Cisco VPN Concentrator, a VPN server, and a  Network Access Server (NAS).

Key Terms To Understanding  virtual private networks:

VPN
A network that is constructed by using public wires to connect nodes. For example, there are a number of systems that enable you to create networks using the Internet as the medium for transporting data.

VPDN
A network that extends remote access to a private network using a shared infrastructure.

Tunneling
A technology that enables one network to send its data via another network's connections. Tunneling works by encapsulating a network protocol within packets carried by the second network.

Split Tunneling

The process of allowing a remote VPN user to access a public network, most commonly the Internet, at the same time that the user is allowed to access resources on the VPN.

Encryption
The translation of data into a secret code. Encryption is the most effective way to achieve data security. To read an encrypted file, you must have access to a secret key or password that enables you to decrypt it. There are two main types of encryption: asymmetric encryption (also called public-key encryption) and symmetric encryption.

Difference Between Hubs, Routers and Switches

DEFINITIONS

Hub
A common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

Switch
In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.

Router
A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP.s network. Routers are located at gateways, the places where two or more networks connect. Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

THE DIFFERENCES

The functions of a router, hub and a switch are all quite different from one another, even if at times they are all integrated into a single device. Let's start with the hub and the switch since these two devices have similar roles on the network. Each serves as a central connection for all of your network equipment and handles a data type known as frames. Frames carry your data. When a frame is received, it is amplified and then transmitted on to the port of the destination PC. The big difference between these two devices is in the method in which frames are being delivered.


In a hub, a frame is passed along or "broadcast" to every one of its ports. It doesn't matter that the frame is only destined for one port. The hub has no way of distinguishing which port a frame should be sent to. Passing it along to every port ensures that it will reach its intended destination. This places a lot of traffic on the network and can lead to poor network response times.


Additionally, a 10/100Mbps hub must share its bandwidth with each and every one of its ports. So when only one PC is broadcasting, it will have access to the maximum available bandwidth. If, however, multiple PCs are broadcasting, then that bandwidth will need to be divided among all of those systems, which will degrade performance.


A switch, however, keeps a record of the MAC addresses of all the devices connected to it. With this information, a switch can identify which system is sitting on which port. So when a frame is received, it knows exactly which port to send it to, without significantly increasing network response times. And, unlike a hub, a 10/100Mbps switch will allocate a full 10/100Mbps to each of its ports. So regardless of the number of PCs transmitting, users will always have access to the maximum amount of bandwidth. It's for these reasons why a switch is considered to be a much better choice then a hub.


Routers are completely different devices. Where a hub or switch is concerned with transmitting frames, a router's job, as its name implies, is to route packets to other networks until that packet ultimately reaches its destination. One of the key features of a packet is that it not only contains data, but the destination address of where it's going.


A router is typically connected to at least two networks, commonly two Local Area Networks (LANs) or Wide Area Networks (WAN) or a LAN and its ISP's network . for example, your PC or workgroup and EarthLink. Routers are located at gateways, the places where two or more networks connect. Using headers and forwarding tables, routers determine the best path for forwarding the packets. Router use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.


Today, a wide variety of services are integrated into most broadband routers. A router will typically include a 4 - 8 port Ethernet switch (or hub) and a Network Address Translator (NAT). In addition, they usually include a Dynamic Host Configuration Protocol (DHCP) server, Domain Name Service (DNS) proxy server and a hardware firewall to protect the LAN from malicious intrusion from the Internet.


All routers have a WAN Port that connects to a DSL or cable modem for broadband Internet service and the integrated switch allows users to easily create a LAN. This allows all the PCs on the LAN to have access to the Internet and Windows file and printer sharing services.


Some routers have a single WAN port and a single LAN port and are designed to connect an existing LAN hub or switch to a WAN. Ethernet switches and hubs can be connected to a router with multiple PC ports to expand a LAN. Depending on the capabilities (kinds of available ports) of the router and the switches or hubs, the connection between the router and switches/hubs may require either straight-thru or crossover (null-modem) cables. Some routers even have USB ports, and more commonly, wireless access points built into them.


Some of the more high-end or business class routers will also incorporate a serial port that can be connected to an external dial-up modem, which is useful as a backup in the event that the primary broadband connection goes down, as well as a built in LAN printer server and printer port.


Besides the inherent protection features provided by the NAT, many routers will also have a built-in, configurable, hardware-based firewall. Firewall capabilities can range from the very basic to quite sophisticated devices. Among the capabilities found on leading routers are those that permit configuring TCP/UDP ports for games, chat services, and the like, on the LAN behind the firewall.


So, in short, a hub glues together an Ethernet network segment, a switch can connect multiple Ethernet segments more efficiently and a router can do those functions plus route TCP/IP packets between multiple LANs and/or WANs; and much more of course.

What is Open Source

Open source refers to a program or software in which the source code (the form of the program when a programmer writes a program in a particular programming language) is available to the general public for use and/or modification from its original design free of charge.

Open source code is typically created as a collaborative effort in which programmers improve upon the code and share the changes within the community.

The rationale for this movement is that a larger group of programmers not concerned with proprietary ownership or financial gain will produce a more useful and bug-free product for everyone to use. The concept relies on peer review to find and eliminate bugs in the program code, a process that commercially developed and packaged programs do not employ.

The basics behind the Open Source Initiative, is that when programmers can read, redistribute and modify the source code for a piece of software, the software evolves.  Open source sprouted in the technological community as a response to proprietary software owned by corporations.

Proprietary software is privately owned and controlled. In the computer industry, proprietary is considered the opposite of open. A proprietary design or technique is one that is owned by a company. It also implies that the company has not divulged specifications that would allow other companies to duplicate the product.

The Open Source Initiative (OSI)

Open Source is a certification standard issued by the Open Source Initiative (OSI) that indicates that the source code of a computer program is made available free of charge to the general public. OSI dictates that in order to be considered "OSI Certified" a product must meet the following criteria:

• The author or holder of the license of the source code cannot collect royalties on the distribution of the program.
• The distributed program must make the source code accessible to the user.
• The author must allow modifications and derivations of the work under the program's original name.
• No person, group or field of endeavor can be denied access to the program.
• The rights attached to the program must not depend on the program's being part of a particular software distribution.

The licensed software cannot place restrictions on other software that is distributed with it.

 Open source software is normally distributed with the source code under an open source license. The Open Source Initiative sets the following distribution terms that open-source software must comply with;

The Open Source Definition 1. Free Redistribution The license shall not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license shall not require a royalty or other fee for such sale. 2. Source Code The program must include source code, and must allow distribution in source code as well as compiled form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost preferably, downloading via the Internet without charge. The source code must be the preferred form in which a programmer would modify the program. Deliberately obfuscated source code is not allowed. Intermediate forms such as the output of a preprocessor or translator are not allowed. 3. Derived Works The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software. 4. Integrity of The Author's Source Code The license may restrict source-code from being distributed in modified form only if the license allows the distribution of "patch files" with the source code for the purpose of modifying the program at build time. The license must explicitly permit distribution of software built from modified source code. The license may require derived works to carry a different name or version number from the original software. 5. No Discrimination Against Persons or Groups The license must not discriminate against any person or group of persons. 6. No Discrimination Against Fields of Endeavor The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research. 7. Distribution of License The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties. 8. License Must Not Be Specific to a Product The rights attached to the program must not depend on the program's being part of a particular software distribution. If the program is extracted from that distribution and used or distributed within the terms of the program's license, all parties to whom the program is redistributed should have the same rights as those that are granted in conjunction with the original software distribution. 9. License Must Not Restrict Other Software The license must not place restrictions on other software that is distributed along with the licensed software. For example, the license must not insist that all other programs distributed on the same medium must be open-source software. 10. License Must Be Technology-Neutral No provision of the license may be predicated on any individual technology or style of interface.

Free Software Licensing
All open source software is not distributed under the same licensing agreement. Some may use a free software license, a copyleft, or GPL compatible. The GNU GPL license is a free software license and a copyleft license, while a "GNU Lesser General Public License" is a free software license, but not a strong copyleft license. There are many different types of licenses for free software . some GNU GPL compatible, some not.

The Open Source Initiative approves open source licenses after they have successfully gone through the approval process and comply with the Open Source Definition (above). There is currently well over fifty licenses that have been approved by the OSI.

For example, the GNU General Public License (GPL) is one license that accompanies some open source software that details how the software and its accompany source code can be freely copied, distributed and modified. The most widespread use of GPL is in reference to the GNU GPL, which is commonly abbreviated simply as GPL when it is understood that the term refers to the GNU GPL. One of the basic tenets of the GPL is that anyone who acquires the material must make it available to anyone else under the same licensing agreement. The GPL does not cover activities other than the copying, distributing and modifying of the source code.

Some Successful Open Source Projects

Sendmail
Sendmail is an open source mail transfer agent (MTA) used for routing and delivery e-mail. The original version of Sendmail was written by Eric Allman in the early 1980s. It is estimated that Sendmail is installed on 60 to 80 percent of the Internet's mail-server computers.

Apache Web server
Often referred to as simply Apache, a public-domain open source Web server developed by a loosely knit group of programmers. The first version of Apache, based on the NCSA httpd Web server, was developed in 1995. Core development of the Apache Web server is performed by a group of about 20 volunteer programmers, called the Apache Group. However, because the source code is freely available, anyone can adapt the server for specific needs, and there is a large public library of Apache add-ons.

Linux
(Pronounced lee-nucks or lih-nucks). A freely distributable open source operating system that runs on a number of hardware platforms. The Linux kernel was developed mainly by Linus Torvalds. Because it's free, and because it runs on many platforms, including PCs and Macintoshes, Linux has become an extremely popular alternative to proprietary operating systems.

GNOME
Acronym for GNU Network Object Model Environment. (Pronounced guh-nome.) GNOME is part of the GNU project and part of the free software, or open source, movement. GNOME is a Windows-like desktop system that works on UNIX and UNIX-like systems and is not dependent on any one window manager. The current version runs on Linux, FreeBSD, IRIX and Solaris. The main objective of GNOME is to provide a user-friendly suite of applications and an easy-to-use desktop.

What Is a MAC Address

A MAC (Media Access Control) address, sometimes referred to as a hardware address or physical address, is an ID code that's assigned to a network adapter or any device with built-in networking capability, such as a printer. While an IP address can potentially be assigned to any device, a MAC address is "burned into" a given device from the factory. A MAC address takes the form of six pairs of hexadecimal digits, usually separated by colons or dashes and will look something like this: 01:1F:33:69:BC:14. Hexadecimal digits can include only the numbers 0-9 and letters A-F.

The first three pairs of digits in the MAC address are called the OUI (Organizational Unique Identifier), which identifies the company that manufactured or sold the device. For example, a MAC address that begins with 00:1F:33 denotes a Netgear product. The last three pairs of digits are specific to the device and can be more or less considered a serial number of sorts. Together, the two parts of the MAC address form an ID that's unique to a particular device.

To understand how MAC addresses are used, first consider that when you type www.abc.com into your Web browser, it can't get there until a DNS (Domain Name Service) server looks up the corresponding IP address for the Web site allowing a connection to take place. While MAC addresses don't have any real significance on the Internet, they're used in a similar way on a LAN (local area network).

Given that IP addresses can't be permanently assigned to a device — after all, a particular address can belong to one computer today and another one tomorrow — MAC addresses allow communication between devices on a local network by making it possible to reliably distinguish one computer from another. Just as DNS matches a Web site name to an IP address on the Internet, a technology called ARP (Address Resolution Protocol) matches an IP address to the corresponding MAC address of a specific device to which that IP address is currently assigned.