TCP/IP - The Internet Protocol Stack

Contents

1. Introduction

2. History of TCP/IP

3. TCP/IP and the ISO 7-Layer Reference Model

4. TCP/IP System Protocols

5. TCP/IP Application Protocols

6. The Future of TCP/IP

7. Bibliography

1. Introduction

Scientists declare that the reason for human predominance in nature can be found in communication. Communication means the exchange of information. Communication enables the creation of a social order which is a condition for a peaceful coexistence of all individuals. Since technical progress has made computer communication possible, utilizability of computers seems to have multiplied. LANs (Local Area Network) link many PCs (Personal Computer). So employees of a company can share documents, information sources and different programs. WANs (Wide Area Network) connect branch offices on a continent with each other. But there is one very network, which is the most important one and which ties millions of computers anywhere in the world together: the Internet.

The Internet is a GAN (Global Area Network), which means that a computer anywhere in the world can go online (can be part of the Internet). This computer only needs a telephone connection and some rules how to communicate with all the other computers in the Internet. These rules form the TCP/IP protocol stack. Although there are many different protocol stacks for the different types of networks, TCP/IP has become the most important protocol stack of the Internet.

2. History of TCP/IP

At the end of the fifties, the Department of Defence sought a way to ensure communication between military bases and cities after a nuclear attack. But neither any cable nor any computer would be able to resist the power of nuclear bombs. And if there was a central authority, which should control the network, this authority would probably be one of the first targets to be bombed. In 1964 the scientists of the Department of Defence found that only a decentralised network could be the solution. In such a network, information is not directly transmitted from sender to recipient as known from a telephone connection. Since a network consists of many computers, the whole network can be subdivided into many knots. Each computer in this network forms such a knot. In a decentralised network, information is transmitted from knot to knot until it reaches its destination. If one knot is destroyed, there will still remain other knots to transfer the information. This transmission is called "Dynamic Rerouting".

In the sixties, this draft of a network was tested by several American universities (namely the Massachussetts Institute of Technology (MIT) and the University of California Los Angeles). In 1968, a subcompany of the Department of Defence, the Advanced Research Project Agency (ARPA), developed the first decentralised network and was in charge of it. High-speed-computers formed the knots of that network. By the end of 1969 a network came into existence, which was called the ARPANET and which consisted of four knots. One of these knots could be operated by another knot via remote-control. This means, that a user at any knot was able to control a computer which could be right at the other end of the continent. This was of high value since computer time was quite precious and expensive, these days. In 1971, this network was made up of 15 knots. In 1972,

37 knots already formed the ARPANET. Soon the system was extended to transmit files and news via e-mail (electronic mail). Only military personnel or military scientists had access to that network. But this restriction was soon given up. The first two years had shown, that the ARPANET was not mainly used for remote-control but for information exchange.

The ARPANET grew very fast, because of its decentralised architecture. Computer of any Operating System (OS), i.e. MacOS, MS-DOS, WINDOWS or UNIX were able to join this network. The computer only had to use the "Network Control Protocol" (NCP), which was later replaced by the actual standard "Transmission Control Protocol" (TCP/IP, where IP is the abbreviation for Internet Protocol) in 1982. In 1973, there was the first international APRANET connection to Great Britain and Norway. This connection was called "DARPA Internet" or simpler: Internet. One year later, the ARPANET consisted of 1000 knots, which were from now on called hosts because these computers are hosting the information.

Nowadays the Internet is growing faster than the telephone networks or the fax services. The diagram in figure 1 gives an idea of the growth of the Internet in the last ten years.

This survey was made by the "Internet Software Consortium" (www.isc.org).

illustration not visible in this excerpt

Figure 1 Internet Hosts

3. TCP/IP and the ISO 7-Layer Reference Model

The concept of a layering model is shown in figure 2. Sender and receiver can only communicate through different layers and each layer has its own interface to the neighbouring layer.

illustration not visible in this excerpt

Figure 2 Conceptual organization of protocol software in layers

[...]