ARPANET Overview: How Important was It for the Development of the Internet?

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By Vijay Singh Khatri

Nowadays, every gadget is becoming hyper-tech. Even a fridge is filled with chips that capture data and transmit it over the Internet to us over the phone. Because of this, we can adjust the temperature of our fridge from our bed without moving a muscle. The foundation of all of this is one worldwide infrastructure, our Internet, at the center of this process. The Internet has grown significantly in the past two decades, and remote areas without access to a telephone line are now connected to the Internet and to others around the globe.

You can now book an Airbnb in Texas, U.S. while sitting at home in India. Thanks to the Internet, you can book a party online and even view a virtual tour from your computer screen. In its early days, however, the Internet was not as advanced as it is today. It was not until the early 1970s that the first four nodes of the ARPANET became operational, allowing users to access the network’s complicated features. It allowed users to exchange data between a number of connected computers. But it is not easy to create a handshake between all the networks as we are able to do these days.

ARPANET provides you with a packet-switching network to connect to, but there is no language between the different networks. Each host in the network has its own protocol, and in order to connect to the network, you need to know what each host’s language is. We will learn about ARPANET today and why it has been so essential for the development of the Internet that we use today. Let’s get started.


ARPANET stands for Advanced Research Projects Agency Network, an experimental computer network that is also known as the forerunner of the Internet. ARPA stands for Advanced Research Projects Agency (ARPA), which is a subcategory of the U.S. Defense Department.

The initial use case of ARPANET was to provide a network that could link computers at Pentagon-funded research institutions over the telephone lines. The development of ARPANET came at the height of the Cold War when military commanders were trying to find a way to create a communication bridge without the use of a central core. This was done so that enemies were not able to target a single headquarters of the operations.

The purpose of ARPANET is always more academic than that of the military. But due to the increase in the number of educational facilities connected to it, the network started to become more like a cobweb, which military officials found to be quite helpful according to their envision. The Internet, even to this day, is able to retain that form, although the scale has magnificently increased over the years.

History of ARPANET

For most of us, the Internet came into existence in the early 1990s, but in truth, the Internet is much older than that, and it was formed by the merging of several forms of personal computer networks. The most crucial individual computer network that helped in the creation of the Internet was ARPANET.

In the year 1966, ARPA conducted a program with a number of research institutions that together formed Resource Sharing Computer Networks. The goal of ARPA was to provide a link between the different computers altogether. As a result, it can boost the network’s overall computational power while also decentralising underground storage.

The U.S. government wanted to create something that was decentralized and stable so that in the case of a nuclear attack or a massive war, the information would be kept hidden and couldn’t be destroyed by bombing a specific location. Suppose there is a network of computers instead of a single computer. In that case, the other computers present on the network will work and keep on sending helpful information throughout the network even if more than one computer is destroyed.

Request For Quotation (RFQ)

After tons of meetings and discussions with ARPA, the concept finally started to look more like a practical thing than just a theoretical concept. So in the year 1968, ARPA began sending out the Request For Quotation (RFQ) to a number of institutions that would come together in order to create the first-ever Wide Area Network (WAN). The teams that came forward in the development of ARPANET were quite diverse in nature, as they consisted of electrical engineers, computer scientists, and applied mathematicians, along with graduate students. All of them worked on their discoveries and processed them in a series of documents that were called Request For Comments (RFC).

How are ARPANET Computers Created?

Before ARPANET was first developed, computers used to be massive in size and slower in processing. Sometimes these computers can’t even fit into a small room due to their enormous size. The user terminals were hardwired, and there used to be some user interface that consisted of a keyboard or punch card reader.

There are ways that allow multiple users to access those old computers simultaneously; the most common method is time sharing. Apart from this, the earlier networks used to have a direct connection between the host computers. Meaning, there is only one path by which the information can flow. In addition to this, the direct link between the host computers also leads to a limitation in the size of these computer networks. Computer networks with a size restriction on the network based on the physical presence of the computer were distinguished as Local Area Networks (LANs).

With ARPA, the developers wanted to create a network that could stretch across the length and breadth of the United States—allowing the linkage between governmental and scientific organizations with no physical barrier whatsoever.

The very first ARPANET was pretty modest as it was made using four computer systems that were present in different locations, and all four of them were linked together with each other using phone lines. In addition to this, the interfaces that all four computers followed were Interface Message Processors (IMPs). The four computers were chosen based on their pre-existing research relationship with the United States government. Each site of a computer on the first ARPANET has its own set of computer engineers who monitor every step of the processes performed by their individual computers and the network. The four host computers that were responsible for the initial structure of the ARPANET include:

  • UCLA’s university computer, which was running on the Sigma Experimental operating system SDS Sigma 7,
  • It was a Stanford Research Institute SDS-90 computer, and it was using Geni as its operating system.
  • It was powered by the OS/MVT operating system.This computer was present in the University of California’s Culler-Fried Interactive Mathematics Center.
  • The last computer that was part of the first ARPANET system was located at the University of Utah, and it was a DEC PDP-10 that was running the Tenex operating system.

ARPANET Protocol Types

Now that we know how ARPANET was formed and which computers were added to the first-ever ARPANET, Let’s now discuss the protocols that were used by ARPANET. With the creation of ARPANET, there were no procedures to be found, and there were no systems located in a central location to let different computers share information. So everything has to be done for the first time.

One of the things that we have to thank ARPANET for was the creation of protocols that host computers of the network and the IMPs are going to follow in order to connect with the network and in order to use it so they can send or receive data over the ARPANET. A group named the Network Working Group was formed to come up with the list of protocols. This group worked on the protocols and started their implementation using RFCs.

During the initial working hours on this project, the group was able to figure out two specific tasks that needed to be completed. The first one was to create something that allows users to log into the system remotely and then make it possible for them to move files from one machine to another. This form of remote login later became the Telnet that we all use these days. The moving of files back and forth became the File Transfer Protocol (FTP).

These were the first two protocols that the group submitted to Larry Roberts, who was the head of the project. According to Roberts, these two protocols were not ambitious, and they were not taking full advantage of the ARPANET. So he asked the group to create more protocols for the system. This resulted in the development of the Network Control Program (NCP), which works as a symmetric host-to-host protocol. With the use of NCP, the computers connected to the network are able to communicate with each other, and it also allows the network to add more hosts to the network in order to make it more accessible to other people.

A Packet of Data that Changed the ARPANET

ARPANET came into existence after people thought about inventing a network that could share information over a larger distance without having to create dedicated phone connections in the first place. This resulted in the creation of packet switching. The first iteration of this methodology used to be called “hot-potato routing.” The packets are present in the form of tiny clusters of digital information that are broken down into much smaller pieces of data from the larger messages. This has to be done in order to maintain expediency.

Let’s take a modern-day example to showcase how these data packets work. So let’s say you have sent an email to your friend, and in that mail, there are several documents for the project on which the two of you are working together. The email that you have sent via the Internet will be split into a number of electronic packets that contain information about the mail and the documents present in it.

These packets will be sent across the network to your friend’s email in a random fashion. All the packets are not going to follow the same route, and they do not need to travel in sequential order to reach the destination. That is because they are collected and precisely put into a sequence by a modem, which is located at the receiver’s end. Each packet has its own header, revealing what information it contains from the larger message.

The Fall of ARPANET

During the first ten years of its development and usage, ARPANET worked as a test bed that led to networking innovations. New applications and network protocols are being discovered using it; some are Telnet, FTP, and NCP. During its working years, ARPANET was not able to communicate with other computing networks that inevitably sprang up in its wake. The design for ARPANET to connect with them requires it to have too much control and too much standardization among machines and equipment present on the network.

In 1973, Vinton Cerf and Bob Kahn started working on finding new ways to make ARPANET connect with other networks, mainly SATNET and ALOHANET. The first one is a satellite network, while the latter one is a Hawaii-based packet radio system.

By the year 1975, ARPANET was given to the defense communication agency. By that time, the network was not in the experimental stage, nor was it alone in the market for a network. A number of networks have been invented since the creation of ARPANET, and some of them were CSNET, CNET, BITNET, and NSFNET. The ARPANET eventually replaced the last ones. The term “internet” was adopted in 1983, and it was at the same time that TCP/IP came into existence. In 1983, ARPANET was divided into two parts; MILNET was commissioned to be used by military and defence agencies. At the same time, the civilian version uses ARPANET. The word Internet was initially coined to provide a much easier way to refer to the combination of these two networks and their internetworking.

ARPANET’s end date arrived in mid-1982, when the communication protocol NCP used in it was turned off for the day.This caused only websites that have switched to Cerf’s TCP/IP language to communicate with one another. All the other ones stopped working. After that, on January 1, 1983, NCP was consigned to history, and the rise of the TCP/IP protocol happened, and it quickly became a universal protocol. The final nail in the coffin for ARPANET came in 1985 when TCP/IP was built into a version of the UNIX operating system.

Then, both free and commercial online services like Prodigy, FidoNet, Usenet, Gopher, and NSFNET became the Internet’s backbone. ARPANET ceased to be important, and it was decommissioned in 1990. Tim Berners-Lee created the World Wide Web two years later, forever changing networking.


We can defintely induce from the above article that the Internet we enjoy today came into existence with APRANET, and defintely it was human’s greatest achievement.

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