This post tries to explain what is the internet, intranet and extranet so that you can understand the terms and distinguish among these three terms.
What is the Internet?
Internet is most common these days, isn't it? But when somebody asks you what is the Internet how will you respond? Will you tell them Internet is world wide web. Oh Wait! World wide web (abbreviated WWW) is just one of the many services the Internet offers.
Then, what's the Internet?
We can define the Internet as a global public computer network providing a variety of information and communication facilities, consisting of interconnected networks using standardized communication protocols.
Analyzing that definition, the internet consists of three factors - (1) computer network that covers the globe, (2) offers various information and communication facilities and (3) uses standardized communication protocols.
The internet is largest network interconnecting many networks together. Often the Internet is referred as a network of networks. A LAN uses hubs and switches to connect computers and network devices to form a network. Bridges connects and extends LANS to form larger networks. Finally, there are routers to connect various kind of networks together across the globe to form the Internet.
Internet offers various services such as Communication Services (eMails, Instant Messaging, Internet Telephony etc.), Information retrieval services ( File Transfer Protocol, Archie, Gopher, VERONICA etc.), Web Services ( world wide web, video conferencing etc.)
Because the Internet is device independent and platform independent the communication over internet must follow standardized rules. These rules are called protocols. Some of the standardized Internet protocols are TCP/IP and UDP (for connection), HTTP (to transfer web pages), SMTP (for sending emails), POP (to download emails), BGP (to route packets to destination) and so on.
Organizations employ networking to connect different departments and branches so that they can communicate and share resources. Because these networks are expensive and harder to maintain, companies began to use internet technologies to connect their LANs. When the Internet become popular its networking software became widely available and usually free making sense to adopt same software internal networking.
However, the nature of the Internet and a company network is completely different. No company would like their resources publicly accessible. Though they user internet technology (network and protocols) they restrict the access to outside world other than the company authorized users.
An intranet is a private network, operated by a large company or other organisation, which uses internet technologies, but is insulated from the global internet.
Intranet is accessible only withing organization or to any employee outside organization through VPN (virtual private networking).
From above discussion, it is evident that the Internet is public global network while intranet is private (may be global) network using similar suite of software to operate the network.
Once the internet is in operation, it is possible to extend certain services to outside entities such as suppliers, customers etc. A company network that allows others to connect and user their network for certain functions become extranet.
An extranet is an intranet that is accessible to some people from outside the company, or possibly shared by more than one organisation.
For example, Public Procurement Monitoring Office (सार्वजनिक खरिद अनुगमन कार्यालय) provide access to it's intranet to public entities (government offices) so that they can set up and publish bids. It also allows access to bidders (private companies) so that they can find published bids and apply through the network. However, public entities and bidders should register to the PPMO and get login credentials to connect and use the network. Thus this PPMO intranet is an extranet.
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