It all started as a need to share resources! Starting with the initial design of computers in the 1950s, the impetus to use computers to communicate was first realized in the 1960s as a number of university computers on different campuses were interconnected. Over time, the development and advancement of computer network technologies took place. Thus, the need to connect and interconnect more computers to computer networks and with it more geographical locations created a need for well-defined terms and concepts to describe computer networking. Because of this, types of computer networks, computer network topologies, computer network architectures, and computer network components were born. Certainly, computer networking represents one of the biggest inventions of mankind in the field of communications. Simply mention the internet and one will immediately understand how huge the benefit of computer networks is to humanity.

Before offering the definition of a computer network, let us first look at the general definition of a network in order to then recognize the computer network definition. If you search for the word network in the Merriam-Webster dictionary, you will find the following definition: "network is a group of people or organizations that are closely linked and that work with each other." In the same Merriam-Webster dictionary, the phrase networking means "exchange of information or services among individuals, groups or institutions." Based on that, the computer network is a group of computers connected to each other in order to share resources. When talking about resources in a computer network, usually the resources can be data, network services, and peripheral devices.

Obviously, when talking about computer networks it is essential to mention components of a computer network because computer networks are ultimately composed of their constituent components. Usually, computers and peripheral devices are just some of the computer network components known to most people. However, there are also intermediary devices and network media.

When talking about hosts and nodes, although their first impression might drive us towards thinking that they are the same thing, in fact they are not! The difference between hosts and nodes is that, while all hosts can be nodes, not every node can act as a host. Because every host is assigned an Internet Protocol (IP) address (see the IP addressing and subnets section for more on IP addresses). There are some nodes such as hubs, bridges, switches, modems, and access points that have no IP address assigned, but are still used for communications. So, a host is any device that offers networking resources to any other node and user on the network. In contrast, a node is any device that can generate, receive, and transmit the networking resources on the computer network. Based on that, Figure 1.1 represents a computer network with hosts (servers, printer, PC, laptop) and nodes (switch).

Since computer networks have been designed to share resources then it is very important to look at the way these resources are shared. Let us try to understand precisely, the computer network components that share resources and computer network components that request resources. For example, when accessing social networking portals on the internet, we know that our device is the network component that requests resources, while the devices where social networking applications are located are network components that provide resources. However, there are situations when these computer network components exchange roles, from requesting a resource to providing a resource and vice-versa, and that is going to be explained in the next section, Understanding network architectures.

Now, going back to the concepts of requesting a resource and providing a resource, actually, that is what is shaping the definition of clients and servers in the computer network. Clients, in most cases, are computers that request the resources in a computer network. Because they are components, the clients have an active role in the computer network. Furthermore, servers are a network component that provides resources to clients. Servers too have an active role. The following figure, Figure 1.2, presents the server with a shared printer in the role of resource provider, and the PC, laptop in the role of resource requesters.

When talking about computer networks, actually we are talking about the essential and broader concept of the elements that make up a computer network. In this form of discussion, while the computer network types deal with the area coverage, the physical and logical topologies deal with the physical arrangement and logical structure of the computer network. Having said that, the computer network architecture represents the computer network design that allows the computer network components to communicate with one another. Usually, there are two types of architectures in a computer network:

• Peer-to-peer networking (P2P): This is a computer network in which the participating computers do not play the predefined roles in the network, instead they change roles from client to server and vice-versa based on the actual activity on the network. For example, if computer A is accessing resources from computer B, then computer A acts as the client while computer B acts as the server. After some time, if computer B accesses resources from computer A, then computer B becomes a client and computer A becomes a server. As you may notice, they switch roles based on who is requesting and who is providing a resource on the network. Figure 1.1 presents an example of peer-to-peer networking:

• Client/server networking: This is a computer network in which participating computers have a predefined role. That means that in this computer network architecture, computers that access resources act as clients, while computers that provide resources act as servers. In general, this is a computer network architecture with dedicated servers that provide resources on the network. Mid-sized and enterprise computer networks are the best example of the client/server computer network. Figure 1.2 presents an example of client/server networking:

Nowadays, a lot of effort is being made to advance the development of IP addressing technologies. Specifically, IPv6 addressing is the best example of such an effort. Nevertheless, even though the IPv6 addressing technology is becoming more and more plausible, it still prefers the role of spectator in the great arena of the internet, where IPv4 addressing technology continues to be the norm.

• IPv4 addressing technology is the fourth version of IP addressing. In brief, an IPv4 address, or simply IP address, is a logical element that consists of 32 bits. It is organized into four (4) groups of eight (8) bits (octet) each divided by a decimal point. For the purpose of easier interpretation, it is represented in decimal format (for example, 192.168.1.1). Knowing that one (1) byte equals eight (8) bits, then an IP address is four (4) bytes. From that, the total number of IPv4 addresses is 2³² , or 4,294,967,296. When compared with the total world population, it is obvious that nearly 3 billion IP addresses are missing if we assign an IPv4 address to every individual.
• IPv6 addressing technology has been introduced to overcome IPv4 limitations. Similar to IPv4, IPv6 is a logical component of computer networks too. However, it consist of 128 bits organized into eight (8) groups of sixteen (16) bits (hextet) each divided by a colon. For the purpose of easier interpretation, it is represented in hexadecimal format (for example, 2001:0DB8:85A3:0000:0000:8A2E:0370:7334). From that, the total number of IPv6 addresses is 2¹²⁸ , or 340,282,366,920,938,463,463,374,607,431,768,211,456. And that is more than enough IPv6 addresses!
• IPv4 subnetting helps implement multiple logical networks within existing IPv4 classes such as A, B, and C. In subnetting, a subnet mask plays an important role in determining the size of the network. So, by definition, a subnet mask is a 32-bit address used in combination with an IPv4 address to indicate the network and its computers. Each class has a default subnet mask. Table 1.1. shows the default subnet masks for each class of IPv4 addresses.

Table 1.1. Default subnet masks for each class of IPv4 addresses: