What is ARPANET? The creation of the internet

Developed by ARPA, a US government agency, ARPANET was the first successful attempt at allowing computers to communicate and share information.

Before the ARPANET project, computers were standalone machines that couldn’t easily connect with one another. The development of ARPANET was a groundbreaking moment because it was the first time computers could send messages, share data, and collaborate over long distances.

Knowing about ARPANET’s development is essential because today’s internet would not exist without it. As the first network to use packet switching, it formed the foundation for all packet-switching networks.

Before ARPANET, computers worked in isolation. Communication with other machines wasn’t possible. These computers were large, expensive, and typically stored in specialized environments like universities, laboratories, or government institutions. They had limited connectivity and centralized control, meaning computer resources were controlled by a single machine. Users would typically interact with the computer using punch cards.

In the early sixties, Paul Baran — an engineer working for the US think tank Rand Corporation — developed the concept of decentralized network architecture using packet switching.

Baran was focused on developing survivable communication networks. He was tasked with creating a computer network that could continue functioning during a nuclear attack. That’s how Baran developed the concept of packet switching (initially known as “hot-potato routing”).

Packet switching technology is a method of communication that involves transmitting data across a network by breaking it into smaller units called data packets. These packets contain the transmitted data and additional information about its source and destination.

In Baran’s system, communications were divided into tiny pieces and passed around using distributed network nodes. The idea was that if one of the nodes was affected by an explosion, the rest could continue functioning. Baran’s concept became the key component of ARPANET — the very first packet-switched network.

The development of ARPANET started in 1966. The project aimed to connect various research institutions and universities working on defense-related assignments.

ARPANET was created through a collaboration between researchers, data scientists, engineers, and organizations funded by the U.S. Department of Defense’s Advanced Research Projects Agency. The contract to build ARPANET was awarded to a technology company, Bolt, Beranek, and Newman (BBN).

The company worked on designing and implementing the necessary hardware and software components. The initial ARPANET architecture included four nodes: UCLA, SRI, UCSB, and the University of Utah.

In 1969, a team of graduate students at UCLA attempted to send the first packet-switched message using ARPANET. The message’s destination was a computer at the Stanford Research Institute (SRI), marking a significant milestone in computer networking as the first message between two computers.

The system crashed, resulting in incomplete transmission. However, the moment is still considered the birth of ARPANET and the first successful attempt at computer-to-computer communication.

ARPANET utilized many technologies, including the TCP/IP protocol, interface message processors, and packet switching. Here’s how each of ARPANET’s main components worked.

Packet switching

Packet switching was the key concept that enabled ARPANET’s operation. Here’s how it worked:

• The data being transmitted between two computers was broken down into smaller units called packets.
• Each packet contained a portion of the data with information about its destination.
• The packets were transmitted individually across the network and routed independently based on the addressing information.

The packet-switching approach helped organizations improve their use of computing resources with multiple packets sent and received simultaneously.

TCP/IP Protocol

TCP, which replaced the earlier NCP protocol, was vital in enabling more reliable communication over ARPANET. The main functions of TCP/IP were:

• Providing reliable data transmission between multiple computers connected to the network.
• Introducing flow control mechanisms that prevented data overflow and network congestion.
• Checking for errors to ensure the integrity of the received data and prevent the transmission of corrupt data packets.
• Providing more flexibility than the previously used NCP protocol, like working with different types of networks and devices.

These and several other TCP functions allowed computer terminals to communicate and exchange information on ARPANET.

Interface message processors

Interface message processors (IMPs) were important components of ARPANET, serving as intermediaries between host computers and the network. Here’s how they worked:

• IMPs were specialized computers designed to connect the host computers and the ARPANET network. Each host computer had a dedicated IMP responsible for transmitting and receiving data packets.
• The interface message processors acted as gateways. They translated data from the host computers into packets to be transmitted across the network. IMPs also added the necessary information to data packets and ensured they were correctly routed to their destinations.
• When a host computer wanted to send data, it would send it to its dedicated IMP. The IMP would break the data into packets, add appropriate information (e.g., headers) and transmit them.
• The receiving interface message processor would strip off the headers and deliver the data to the host computer.

Overall, the IMPs acted as important intermediaries in the ARPANET communication process.

During the early stages of ARPANET, it wasn’t popular. Due to its restricted access and complexity, only small groups of data scientists, graduates, and researchers directly involved with the network were using it.

ARPANET created opportunities for the development of other packet-based networks. However, these networks couldn’t communicate with each other due to a lack of standardization. Each organization used its own network with varying standards and protocols, making it difficult to establish a connection.

To address this issue, a group of researchers and engineers at UCLA, known as the Network Working Group (NWG), created the Network Control Protocol (NCP). The NCP was the first host-to-host protocol that allowed host computers to communicate with each other by establishing set rules and procedures for exchanging data. ARPA also developed several standards and protocols that were crucial for the early stages of computer networking, including Telnet and File Transfer Protocol (FTP).

Even with the NCP, ARPANET was not taking off. To spread the word about packet switching and make the world notice, Lawrence Roberts, one of ARPANET’s project managers, decided to give a public demonstration of the network and its potential at the International Conference on Computer Communication (ICCC).

During the early stages of ARPANET, it wasn’t popular. Due to its restricted access and complexity, only small groups of data scientists, graduates, and researchers directly involved with the network were using it.

The demonstration went successfully and marked a change in the attitude towards packet switching. Following the demonstration, ARPANET grew rapidly. Many government computers and universities joined the network, and ARPANET became operational in 1975. It was transferred to the Defense Communications Agency.

With the expansion of ARPANET, it became evident that the NCP had significant limitations. It was a simple protocol that didn’t meet the evolving needs of ARPANET.

In 1977, the TCP/IP (the Transmission Control Protocol/Internet Protocol) was developed. TCP aimed to create a reliable transport protocol that could handle data transmission across diverse networks. It improved upon the NCP in many ways, such as introducing more reliability, error detection capabilities, and flow control.

The TCP was implemented on various host computers connected to ARPANET, with its performance and reliability extensively tested. As ARPANET evolved, TCP proved to be a successful and indispensable protocol.

ARPANET was the pioneering network that laid the foundation for creating the internet (or the World Wide Web) as we know it.

ARPANET was decommissioned in 1989, 20 years after it was first used to send a message between two computers.

ARPANET’s most significant computer technology advancement, public packet switching, still enables various types of data transmission today — from sending an instant message to watching a Reel on Instagram.

Many, if not most, devices we use and rely on today are “smart,” which means they can connect to the global network. This connectivity is possible because of shared communication protocols. ARPANET was crucial in developing protocols still used in modern networks today.

As technologies evolved, ARPANET was replaced by the National Science Foundation Network (NSFNET). That’s when the era of the modern internet officially began.

However, the developments after ARPANET wouldn’t have been possible without the foundation it laid for modern networking and communication. Packet switching, distributed network architecture, TCP/IP, the adoption of file encryption technologies, and many other ARPANET contributions paved the way for the internet we rely on today.