Topics covered in this tutorial

• TCP/IP history and development
• TCP/IP as a standard
• ISOC, IANA and IAB
• Requests for Comment
• The TCP/IP protocol suite

Development of TCP/IP

TCP/IP stands for Transmission Control Protocol/Internet Protocol, which is named after the primary protocols in the suite. It has become an industry standard protocol and, although it was originally designed for WANs, it is now widely used on LANs as well.

The original research was performed in the late 1960s and early 1970s by the Advanced Research Projects Agency (ARPA), which is the research arm of the US Department of Defense (DOD). The DOD wanted to build a network to connect a number of military sites. The key requirements for the network were as follows:

• It must continue to function during nuclear war (development took place during the 'cold war'). The 7/8th rule required that the network should continue to function even when 7/8th of the network was not operational
• It must be completely decentralized with no key central installation that could be destroyed and bring down the whole network
• It must be fully redundant and able to continue communication between A and B even though intermediate sites and links might stop functioning during the conversation
• The architecture must be flexible as the envisaged range of applications for the network was wide (anything from file transfer to time-sensitive data such as voice)

ARPA hired a firm called BBN to design the network. The prototype was a research network called ARPANET (first operational in 1972). This connected four university sites using a system described as a packet switching network.

Prior to this development, any two computers wanting to communicate had to open a direct channel (known as a circuit) and information was then sent. If this circuit were broken, the computers would stop communicating immediately, which the DOD specifically wanted to avoid.

Packet switching introduced the ability for one computer to forward information to another, thereby superseding circuit-switched networks. To ensure information reached the correct destination, each packet was addressed with a source and destination and the packet was then transferred using any available pathway to the destination computer.

It was divided into small chunks or packets (originally 1008 bits). Sending large chunks of information has always presented problems, often because the full message fails to reach its destination at the first attempt, and the whole message then has to be resent. The facilities within the new protocol to divide large messages into numerous small packets meant that a single packet could be resent if it was lost or damaged during transmission, rather than the whole message.

The new network was decentralized with no one computer controlling its operation where the packet switching protocol controlled most of the network operations.

TCP/IP is a very robust protocol and can automatically recover from any communication link failures. It re-routes data packets if transmission lines are damaged or if a computer fails to respond, utilizing any available network path. The figure below shows an example of an Internet system. A packet being sent from Network A to Network F may be sent via Network D (the quickest route). If this route becomes unavailable, the packet is routed using an alternate route (for example, A B C E F).



Once ARPANET was proven, the DOD built MILNET (Military Installation in US) and MINET (Military Installation in Europe). To encourage the wide adoption of TCP/IP, BBN and the University of California at Berkeley were funded by the US Government to implement the protocol in the Berkeley version of UNIX. UNIX was given freely to US universities and colleges allowing them to network their computers. Researchers at Berkeley developed a program interface to the network protocol called Sockets and wrote many applications using this interface.

During the early 1980s, the National Science Foundation (NSF) used Berkeley TCP/IP to create the Computer Science Network (CSNET) to link US universities. They saw the benefit of sharing information between universities and ARPANET provided the infrastructure. Meanwhile, in 1974 a successor to ARPANET was developed named NSFNET. This was based on a backbone of six supercomputers into which many regional networks were allowed to connect.

The first stage in the commercial development of the Internet occurred in 1990 when a group of telecommunications and computer companies formed a non-profit making organization called Advanced Networks and Services (ANS). This organization took over NSFNET and allowed commercial organizations to connect to the system. The commercial Internet grew from these networks.

The Internet consists of thousands of networks world-wide, connecting research facilities, universities, libraries and private companies. Many of these networks have dedicated computers or disks for maintaining archives of information that are accessible to the public.

Why is TCP/IP so Popular?

There are numerous reasons for the increased popularity of TCP/IP; some of these include:

• TCP/IP is an industry standard protocol
• It is a routable protocol suite
• It is provided on almost all network operating systems, and therefore allows connectivity between dissimilar systems (for instance, from a UNIX computer to a Windows NT computer)
• It provides connectivity with the Internet
• The protocols are in the public domain and are freely available, which makes it a popular choice for software companies. There are no restrictions on its use and no royalties to pay
• It is a well designed protocol
• It is an open standard where no single vendor has any control over the protocol and anyone is allowed to use it and develop applications based on it