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Basics of networks

Introduction

Networks serve for communication. They bridge a more or less large distance between the participants. Let us first consider the simple case of communication between only two participants.

One of the participants acts as the sender (source), the other as the recipient (destination) of the message. These roles - transmitter and receiver - are not fixed forever, but generally change. The sender formulates the message and then sends it to the recipient via the network. Different networks have always been used for different applications.

Here are a few examples:

  • The Roman emperor sends an order to a governor in a distant province. Ridden messengers serve as a network.
  • You send a postcard home from your holiday.
  • A professor calls the secretary's office.
  • The bank employee sends an electronic quote request to the exchange.
  • A student sends a message as SMS to a fellow student.
  • A user sends a file to a print server for printing.


These simple examples already reveal some of the main topics around networks. The first fundamental problem is:

  • How does the message get from sender to receiver?

        This raises the question of addressing and mediation. First, a unique destination address is required to identify the recipient. Then, starting from the start address, a route to the destination can be defined.

Other basic questions concern the performance of the canal:

  • How fast can how much data be transferred?
    Both physical limits (how many packets fit into a Postbus?) and the distribution of the load among the different nodes in the network must be considered.
    Other aspects play a role in the design and operation of networks, such as, among others:
    • Physical realisation
    • network architecture
    • surcharges
    • Security to third parties
    • Reliability in case of transmission errors
    • reliability

We will focus in particular on the connection between computers. Traditionally, this differs in requirements and technology from communication networks used for telephone connections. However, the boundaries between the various networks, especially between computer networks and other communication networks, are becoming increasingly blurred due to progressive digitalization. For example, systems that make it possible to make phone calls via computer connections ( Voice over IP ) are becoming increasingly widespread. A major advantage here is the elimination of a second, separate cabling. Mobile devices already offer combinations of telephone and computer. The transition to digital content, such as audio or photography, is also well advanced in the entertainment sector. The general trend is towards intelligent end devices. This means that the networking of all these devices is playing an increasingly important role. Think of the vision of an intelligent house in which sensors and devices for climate control, lighting, security, communication and entertainment are interlinked.

In the course of this so-called convergence of different networks, it is foreseeable that the techniques of computer communication will be used in more and more areas in the future. However, the combination of different services with very different requirements in terms of reliability and response time leads to new, demanding challenges for network design.

The main function of IP (Internet Protocol) is to add address information to data packets and forward them via the network to the corresponding destination address. To understand how IP works, you need to be familiar with the concepts that determine the intermediate and final destination addresses of a data packet.

To determine the location of a target host with respect to the source computer, IP addresses are divided into classes. This is called class-based IP addressing. You must assign IP addresses to all computers connected to the network. Network segments connected via a router are called subnets. Dividing the network into subnets for the purpose of assigning IP addresses is called subnetting.


The term host is often used to describe any device on a network that sends and receives information using an IP address. All computers, printers and routers in a TCP/IP network are hosts and require at least one IP address for communication.

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