ARPANET – The Foundation

Before we dive to understand how the Internet actually works, let’s roll back to history and see how the Internet that we know today started with different projects from different countries which later together made the foundation of the Internet.

ARPANET – The Foundation

The Advanced Research Project Agency was the US military organization that came up with an idea to bridge a network to help scientists and engineers connect across the country over telephone lines. But connection over telephone lines was based on circuit switching which meant your computer can only be connected to only one other computer at a time and that line had to be engaged until you disconnected, this is not the way modern Internet works. APRA came with an idea of Packet Switching the concept that powers today’s internet. In Packet Switching the information or data that is to be shared over the network is broken into packets which take different paths rather than one, at the receiving computer the data is integrated. This way data congestion over a line was minimised. Today a website can connect to 10 or more different computers at the same time from around the world, monitoring and connecting thousands of other queries along.

The NPL Data Network

ARPANET and NPL Data Network were the first that pioneered the concept of packet switching. NPL was a local area computer network operated by a team from the National Physical Laboratory in London. It didn’t run for long as funding was stopped by the government.

The CYCLADES

CYCLADES was French initiative to build a network based on ARPANET which held the host responsible for the reliable delivery of the data rather than the network itself. Failures from CYCLADES Network help form the language of the Internet TCP/IP. This way different networks became operational in different countries. All were based on packet switching but talked different languages. There was a need to transfer and communicate among countries across the globe. To fulfill this need there had to be a universal network. This gave birth to the language of the internet – TCP/IP.

TCP/IP Model – The Backbone

TCP – Transmission Control Protocol IP – Internet Protocol Are a set of instructions that a data has to follow for transmission over a network. This model has four architectures.

1) Application Layer

• It is a framework with which the user interacts. It includes all the applications and softwares that we use in our daily life. Information in this layer follows in different protocols depending upon the type for example – FTP for file, DNS – domain name to IP address of the server, HTTP for web access, TFTP, SMTP.

• Information in this layer is in DATA form

2) Transport Layer – Host To Host

• It’s the connection between the user & receiver, it ensure the data is intact in the process of transmission. It follows two different protocols TCP and UDP. In TCP, if a user sends a packet, receiver has to send an acknowledgement on receiving the packets. If a packet is lost on the way, the same packet has to be sent again(retransmission of data) but not the whole file, this protocol is used in email services. This is the reason why it takes some time for the email to reach the destination. UDP is fast and used when the information exchange has to be instant, like internet calling, chatting or accessing a website. If you make a call to your friend sometimes in between there is a call drop it’s because the information is lost on the way, unlike TCP it doesn’t give an acknowledgement, so if a packet is lost it need not be sent again.

• Information in this layer is in PACKETS.

3) Internet Layer

• IP protocol works on this layer who’s job is to give the ip address of sender and receiver to the packets so that they reach and come back to the right destinations. It sets routing information for the packets.

• Information is in the form of PACKET FRAMES.

4) Data Link Physical

• It is a medium of data transfer between the above layers and the physical network, like the router of your home.

• Information in this layer is in bits.

HOW THE INTERNET WORKS? If you think the internet works on satellite, then you are more wrong than ever. The Internet is nothing but interconnection of different devices and servers via optical fibre. Consider this analogy, all the human architectures of the world are the different devices, all the roads of the world are these optical fibre cables, you are a packet of information that wants to go to his friend’s house, so how do you go? simply take the route that connects your house and your friends. This is what the internet is, all the devices are connected to each other that sends information or packets to other devices or to servers via the road i.e optical fibres. You would be thinking that your smartphone is not connected to a cable, it is wirelessly connected to the optical cable via cellular network or your router. There are miles and miles of optical cables deployed under the sea connecting countries across the globe.

We buy data plans from Tier-2 companies and they pay a part of it to Tier-2 companies. When you connect your device to the Internet either via broadband or Wi-Fi or ethernet, you can transfer and request for information from a distant server. First the information goes from your phone to your ISP, then through the optical cables to the server of that website, which sends back the requested data via optical cables, to the ISP cell tower then to your phones application. Now let's dive deep. Any device connected to the internet has an IP Address which is identified uniquely by string of numbers. You can consider an IP address same as your home address which is used for delivery of post or parcels, same way an IP address is used for delivery and retransmission of packets on the internet. As said any device connected to the internet has an IP address so does a server. A server stores an website and every website has its own IP Address, you can directly visit the website by entering the IP. It is difficult for us to remember so many IP Addresses so to resolve this problem Domain Name is used which points to the address of that website. To link the domain name and ip address a huge directory like a phone book called DNS (Domain Name System) is used. IF you don't know a person's phone number you can look into the phone directory, the same service is provided by DNS to the internet. The DNS servers are operated and managed by ISP that's why they can block the ip address of a website in a country if the government asks to do so. When you type youtube.com, your browser sends a request to the DNS to get the IP address of the website. On receiving the IP address of the website it sends your request in the form of packets via different routes to the destination server. On receiving the request the server processes the information and the data travels in binary form through the optical cable via cellular tower in form of electromagnetic waves or through ethernet cable or the broadband. IP Name assignment and Domain name registration is authorized by ICANN (Internet Corporation For Assigned Names and Number) located in LA USA.