ML-01-02 Introduction to Networks

Data networks have been around for a long time.

In this section we start by considering what a network is and why we use and need them. We then discuss some key technology developments that have resulted in the emergence of the different types of networks, the internet, wireless networks and mobile networks and what we can expect going forward.

What is a network

In simple terms, a network is a group or system of interconnected people or things. Some example of networks includes:

  • Network of roads (Suburb, Town, Country)
  • Network of people interested in the same things (Societies)
  • Radio network for broadcasting radio channels (Emergency Service)
  • Telephone network for supporting voice calls using phones
  • Data communication network used by computers to exchange data

As an example, a road network has multiple roads that connect with each other at numerous junctions or intersections. Going from point A to point B can be done using many routes. Route selection is decided by the road user, based on their knowledge of traffic and road conditions, approximate journey times etc.


What is a computer network

A computer network has computing nodes (clients and servers) that exchange data between themselves, over a network of interconnected network nodes (routers).

There are special network nodes that are interconnected with each other and handle the routing of data as required by the computers. Every network may have multiple routes that data can be sent over. Routers are aware of network structure, issues and link performance. Based on network status, routers make decision on the best routes to use. Each router passes the data to the next router and so on, until the destination is reached.

In the figure above, “You” are using a Smartphone, and it is a computer node on the network. On the Smartphone, you are using an application that may need to exchange data with an application on another computer node (A, B, or C). These nodes may be a Google Email Server application, the WhatsApp server application, your online banking application server etc.

Networks are owned and constructed by government or private enterprise network service providers. Examples include MTN, Vodacom, Telkom, and many other network service providers locally and internationally. Each network has its core network or backbone, as well as access nodes for connecting customer networks and computers.

What is the Internet

Network service providers across the world have interconnected their networks to allow computers to connect to each other regardless of where they may be located. This is referred to as the Internet, simply a name made up of part of the words INTERconnected NETworks.

To be part of the Internet, all parties who own networks use the way of transferring data (Internet Protocol or IP), allocating address (IP addresses) to computers, and setting up computer name servers (DNS, or Domain Name System, Servers) for helping computers determine where each other are.

Each computer that sends and receives data is a node on the network, with a specific and unique address. The unique address is a combination of the network address and the computer (host) address. For computers that want to provide services and be located on the network, domain names can be registered and these names can then be searched for by other computers using the DNS servers as a directory of names. So, when you try and find a website, for example “google.com”, your computer asks the DNS server for the actual network address by looking up the domain “google.com”. Once your computer has the correct address, it can start sending and receiving data to and from the Google server.

Joining a network

Today, most computers connect with each other over networks that comply with Internet standards. This means that each computer, when joining a network:

  • The computer is given an address that is unique. This is an IP (Internet Protocol) address that includes the address of the network it is joining (network address) and its own address on that network (host address). An example may be 192.168.1.10 where 192.168.1 is the network address, and 10 is the host address.
  • Is given the address of a Domain Name Server that can help find other computer addresses
  • Is given the address of the default network node (Router) that will send data on its behalf if it needs to connect to computers that are not on the same local network. This router joins the local network to other networks and the internet.

The IP address given to a computer when joining a network may be temporary and change each time the network is joined. In order to connect to another computer, whose address may also change from time to time, there is the concept of a domain name. Domain names are names that are given to computers that provide services to other computers (Server Nodes). This makes it easier to identify the computer and not have to focus on using IP addresses.

Finding another node on a network

On our smartphones and other computers, we use many applications. Some of these applications need to connect to applications that are on other computers. Examples may include WhatsApp, Email, Online Banking etc.

Certain computers on the network acts as Directory Services, or Domain Name Servers (DNS Servers). They help us get the IP address of a Server Node so applications on our computer can talk to applications on the server node. All we need to know is the Server Node Domain Name (e.g. google.com).

How have networks, specifically computer networks, evolved over time

Getting data from one computer to another has been going on for more than fifty years.

One of the challenges faced is that most early networks were designed for voice communication (analogue) and computer data was represented digitally. Special devices (modems) had to be developed that could take digital computer data and convert it into the analogue signals needed to transmit over networks designed for voice communication.

Over time, digital networks were developed and standardised for general use. Computer nodes needed to comply with network standards for addressing and interfacing to use network nodes.

Some early approaches that allowed two nodes to exchange data include:

  • Using modems to allow digital computer data to be converted to an analogue signal that can be sent and received over telephone network links.
  • Using point to point wireless microwave radio links
  • Using point to point wireless optical links
  • Using cabled or wired links between two points for digital data transfer.

Going beyond two computers to allow networks of computers to share links:

  • To enable multiple computers to exchange data, over shared links, methods for addressing each computer individually were defined. Special purpose equipment was then designed to allow multiple locations, each with multiple computers to have data exchanges between any computers as needed. This led to a series of standards being developed for digital network interfaces, how to exchange data between computers, and how network addresses are managed.

Why do we pay for data we send and receive

Nobody owns the Internet. Collectively, decisions are made on network rules, standards and service levels.

Each network that is part of the Internet is owned, and whoever owns it, charges for data in order to recover their costs of setting up and managing the network. When data goes from one network to another, network owners pay each other for handling their data traffic on behalf of customers. To recover their costs, and make a profit to fund their business growth, network owners charge clients for data services based on their data usage and network performance agreements.