This chapter is designed to provide you with an introduction to computer networks. It begins with the evolution of Advanced Research Projects Agency Network (ARPANET) to the internet, and then continues with the explanation of the computer network concept. This chapter discusses the types of networks, topologies, components, architectures, network operating systems (NOSs), and network media where definitions such as personal area network (PAN), local area network (LAN), metropolitan area network (MAN), wide area network (WAN), bus, ring, star, extended star, hierarchical, mesh, hosts, nodes, peer-to-peer, and clients/servers are explained. The chapter concludes with a discussion about converged networks, and the current and future computer network trends. To facilitate the understanding of the many definitions covered in this chapter, a large part of the definitions are illustrated with relevant figures.

In this chapter, we will cover:

• Understanding ARPANET and the internet
• Understanding computer networks
• Understanding types of computer networks
• Understanding computer network topologies
• Understanding computer network components
• Understanding computer network architectures
• Understanding network operating systems
• Understanding network medium
• Understanding converged networks
• Understanding computer network trends

No one can explain the history of the internet better than the internet itself! Everything started with the US government's project to build a stable and tolerant-in-defects communication network known as the Defense Advanced Research Projects Agency (DARPA). The involvement of research centers and academic institutions in the DARPA project made this project gradually evolve into the ARPANET and the Military Network (MILNET). While the MILNET project was tasked to support operational requirements, the ARPANET project was undertaken to support the need for research (https://www.internetsociety.org/). That said, from 1962 to 1985, the internet already had built its profile. Thus, based on the saying "every new beginning is some beginning’s end", the appearance of the internet on the global computer network stage formally marked the end of the ARPANET's golden era.

According to the internetsociety.org, on October 24, 1995, the Federal Networking Council (FNC) through a resolution, priory consulted with members of the internet community and intellectual property rights, defined the term internet. According to that resolution, the internet refers to the global information system, which:

• Is logically connected by a global unique address space based on the Internet Protocol (IP) or its subsequent updates;
• Is able to support the communication through a TCP/IP protocol suite or its subsequent updates and other compatible protocols, and;
• Provides, uses and makes accessible, either publicly or privately, high-level layered services on the communications and related infrastructure described in that document.

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, a computer network 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 a computer network is to humanity.

Before defining computer network, let’s first look at the general term of a network in order to then recognize the computer network definition in particular. If you do a search for the word network in the Merriam-Webster dictionary, you’ll find the definition that a "network is a group of people or organizations that are closely linked and that work with each other." On the same Merriam-Webster dictionary, the phrase networking is defined as "exchange of information or services among individuals, groups or institutions." Both of these definitions will serve us in a simple, clear, and concrete way to define computer network in the following paragraph.

From what was said in the preceding paragraph, a computer network is a group of computers connected to each other in order to share resources. When talking about resources, usually the resources can be data, network services, and peripheral devices. So, anyone who has experience with computer networks has seen that it is very easy to share files, applications, printers, and other peripheral devices in computer networks. Figure 1.1 presents an example of a computer network:

Of course, the most beautiful part of a computer network is how to design and build one. Computer network design and deployment is Designing and deploying is linked to its definition. Thus, the fundamental requirement for designing a computer network is that there must be two or more computers. Depending on the number of computers on the network and how they access the resources from the same network determines the categorization of computer network types, which will be explained in the following section.

Over time, the desire to implement the first computer network, as a result of curiosity, had already been converted to a need that would fulfill the requirements. Precisely, it also led to the development and advancement of computer networking technologies. Thus, the need to connect and interconnect more computers into computer networks, and with it, more locations, in itself resulted as the need to define topologies, architectures, technologies, and computer networking categories. In this way, the types of computer networks like PAN, LAN, MAN, and WAN were born.

A PAN is defined as a computer network that is used to connect and transmit data among devices located in a personal area, usually over Bluetooth or Wi-Fi to interconnect devices (see Figure 1.2). Occasionally, this computer network is called a home area network (HAN) too:

To understand the LAN, let's compare it with the PAN. A PAN is dominated by portable devices (for example, smartphone), while a LAN mainly consists of fixed devices. Both computer networks are covering the local area; however, the LAN has a greater coverage than the PAN, because the LAN usually can cover the floor of the building, several floors of the building, an entire building, or even a few buildings that are close to one another. From that, the main difference is that a PAN is mainly organized around an individual, while a LAN is organized around an organization, business, or legal entity. This then precisely defines the LAN as a computer network that connects two or more computers in a local area for the purpose of sharing resources, as in Figure 1.1.

From the standpoint of coverage, the MAN is bigger than the LAN and smaller than the WAN, whilst from the viewpoint of data transmission speeds, the MAN is faster than both the LAN and WAN. As it was with the PAN and LAN, the reason for the MAN's existence is the need for sharing and accessing the resources in the city or metro. From that, a MAN represents a group of LANs interconnected within the geographical boundary of a town or city, as in Figure 1.3:

Areas that are not covered by a LAN or MAN are covered by a WAN. Thus, a WAN is a computer network that covers a wide geographic area using dedicated telecommunication lines such as telephone lines, leased lines, or satellites. That being said, unlike other computer networks which have geographic restrictions of their physical reach, WAN does not. From that, it is obvious that WANs are made up of PANs, LANs, and MANs (see Figure 1.4). With that in mind, the best example of a WAN is the internet:

The intranet is a networking platform primarily designed for employees. That said, it is considered to be the private network of an organization where employees can access network services. The intranet is not just a portal; instead, it is a network that consists of hardware and software too. To better understand it, consider the intranet as an organization's extended LAN, or MAN, or even WAN network. It consists of multiple cables, network devices such as switches, routers, microwave and satellite antennas, access points, servers, computers, and various applications. All that enables employees to communicate, develop content, collaborate in joint projects, and get the job done.

In contrast, the extranet can be thought of as an intranet with a controlled access. Like the intranet, the extranet is a networking platform too; however, besides employees, the extranet enables controlled access to an organization's intranet for authorized partners, suppliers, customers, or others business-related individuals and organizations outside the company. Specifically, the extranet represents a controlled access method of the organization's intranet using internet infrastructure.

Another way to categorize computer networks is by their topology, or the way in which hosts and nodes are arranged and connected to one another, and how they communicate. The computer network mainly recognizes two types of topologies: physical, and logical.

Physical topology presents ordering, arrangement, and placement of the physical parts of a computer network, such as computers, peripheral devices, cables for data transmission, and network equipment. Thus, the physical topology of the computer network actually represents its physical structure, which is usually presented in the following shapes: bus, ring, star, extended star, hierarchical, and mesh.

Bus is the physical topology in which computers, peripheral and network devices are connected through the bus that mainly consists of a coaxial cable (see Figure 1.5):

Ring is the physical topology in which computers, peripheral and network devices form a closed cycle that takes the shape of a ring network where each device is connected to each other (see Figure 1.6). In the past, the coaxial cable was used, but nowadays in dual ring networks, optical fiber is used:

Star is the physical topology in which computers, peripheral and network devices are connected independently with a central device (see Figure 1.7). For this type of topology, mainly a twisted pair cable is used:

Extended star is the physical topology in which computers and peripheral and network devices are connected into two or more star topology networks and then the central components (that is, switches) are interconnected over a bus. In appearance, this type of topology combines star and bus topologies (see Figure 1.8). Mainly, a twisted cable pair is used for the star topology, while an optical fiber is used for the bus topology:

Hierarchical is the physical topology that represents a combination of star and bus topologies. This topology must have at least three levels of hierarchy in which star topologies connect one or more nodes to a single main node, so that all these together are related to the main trunk of the tree (see Figure 1.9). As in the case of an extended star topology, this topology uses twisted pair cables and optical fiber:

Mesh is the physical topology in which each computer is connected with every computer to form the network (see Figure 1.10). Usually, this type of topology is utilized by a WAN to interconnect LANs:

Unlike physical topology, logical topology represents the logical aspect of the computer network. In logical topology, it is the logical paths that are used to carry electric or light signals from one computer to another, or from one network node to another node. Thus, this topology represents the way in which the data accesses the transmission medium and transmits packets through it. Figure 1.11 presents the logical topology with its logical components such as computer names, network equipment, network communication technology, and IP addresses:

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.

Knowing that the primary purpose of the computer networks has to do with sharing resources, it is very important to understand the process of how the resources are both shared and accessed. Here comes into play the concept of the client and the server, where the client is the one that always requests resources, and the server is the one that provides the requested resources. To better understand clients and servers, as well as the concept of requesting and providing resources, the following sections explain the network components.

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. Clients have an active role in the computer network (see Figure 1.11).

Furthermore, servers are network components that provide resources to clients. Servers too have an active role. The following figure, Figure 1.1, presents the server with a shared printer in the role of the resource provider, and the PC and laptop in the role of resource requesters.

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. That way, to every host there is an assigned IP address. So, a host is any device with an IP address that requests or provides networking resources to any other host or node on the network; however, there are devices such as hubs, bridges, switches, modems, and access points that have no IP address assigned, but are still used for communications. That said, a node is any device that can generate, receive, and transmit the networking resources on the computer network but has no interface with an IP address. Based on that, in Figure 1.1, server, smartphone, PC, and laptop are hosts, while switch and Access Point (AP) act as nodes.

A network interface is a component-like network card or LAN port on network equipment that enables clients, servers, peripheral devices, and network equipment to get connected and communicate with each other. The network interface has both a passive and an active (manageable network equipment) role in the computer network (see Figure 1.12):

Peripheral devices are printers, scanners, storage area networks (SANs), and any other peripheral device that provides resources to clients, either through a LAN or as a shared device on a network. These devices play both a passive and an active (like SAN and NAS) role in the computer network:

Applications and shared data are virtual network components that represent applications and files shared on the network that are usually provided by servers. These components themselves play a passive role in the computer network, but the server that hosts these services plays an active role in the computer network.

Hubs and switches are acting as central components (in Ethernet communication technology) of the computer network to enable interconnection and communication between clients, servers, and peripheral devices, as in Figure 1.14 . Most hubs are passive devices, while switches play an active role in the computer network:

Routers (see Figure 1.15) are computer network components that enable routing of the data (that is, packets) from a LAN to the internet, and vice versa. Routers have an active role in the computer network:

Network infrastructure is also the part of the discussion when we discuss about network components. So, of course, the question is, what is network infrastructure? In its simple format the answer would be that network infrastructure is any physical and logical network component that enables connection, communication, operation, management, and security of the network.

No matter what professional background you might have, it is just enough to get to know the name of the firewall and you will immediately think that there is no joke with such device. Leaving the humor aside, a firewall (see Figure 1.16) is a network device that provides security to the network infrastructure. It does so by controlling and monitoring both incoming and outgoing traffic based on configured security rules. In a nutshell, the firewall to a network infrastructure is like a security officer at an organization's main gate:

Nowadays, we often hear expressions like "I got connected to the internet with wireless" or "I've found an open wireless." This and many other similar expressions make us understand that the discussion is about the access point. That said, an AP (see Figure 1.17), often known as a wireless access point, is a network device that enables access to the wired network. With APs in a network infrastructure, the network becomes more accessible by enabling the access to organization services while on the go. In addition, it enables the support for the new trends like Bring Your Own Devices (BYOD):

Since network infrastructure has many network devices, including APs for the security purposes as well as for the quality of services (QoS), organizations will employ a wireless access controller. It is a networking device that enables organizations to centrally manage APs.

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.

Peer-to-peer is a computer network in which the participating computers do not play the predefined roles in the network, but 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 1.18 presents an example of peer-to-peer networking:

Client/server 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. Midsize and enterprise computer networks are the best example of the client/server computer network. Figure 1.19 presents an example of client/server networking:

An NOS is software that, alongside the execution of common computer programs, enables the provision of network services too. The most common network services are file and print sharing; however, today's NOSs are noticeably more advanced. Thus, NOS enables you to configure network services such as directory services, web server, mail server, database server, proxy server, DHCP server, remote access server, and many more. Just as the services provided by NOS are varied, the NOS itself is different too. So, the most popular NOSs today are Windows Server, Linux Server, and macOS X server.

The Windows Server (see Figure 1.20) is Microsoft's OS designed for servers. It is a Graphical User Interface (GUI)-based OS; however, since Windows Server 2008, there is a Server Core option that is based on the Command Line Interface (CLI). As of the Windows Server 2012 R2 version, they are offered only in 64-bit platform. The New Technology File System (NTFS) continues to be Microsoft's Windows Server filesystem; however, Windows Server 2012 has introduced the Resilient File System (ReFS) as an attempt to succeed the NTFS:

If there is something worth mentioning in the world of information technology in general, operating systems in particular, it is unequivocally the Linux OS (see Figure 1.21). That is because the world of technology knows no innovative initiative to have gathered more volunteers than Linux itself. Unlike Windows Server, known to be proprietary OS, Linux server is licensed under the GNU GPL (free software license) and distributed by several distros such as Red Hat, SUSE, Oracle, Novell, Ubuntu, Debian, Mandrake, Mandriva, and so on. The Linux community is one of the largest communities in the world of volunteer developers from across the globe that would contribute to further Linux development. In essence, Linux is CLI-based, but there are also versions of graphical user interfaces like KDE and GNOME among the most popular. Linux, like Windows Server, is offered in 64-bit platform too:

Perhaps by age, macOS X Server (see Figure 1.22) is younger than Windows Server and Linux Server NOSs, but in terms of reliability it is gaining more and more industrial support. In its heart, macOS X Server is basically a version of Unix OS, but has been customized to conform to the familiar GUI of Apple OS for Mac computers. Like Windows Server and Linux Server, macOS X Server is offered in 64-bit too. It is worth mentioning the unique fact that the macOS X Server runs only on Apple's hardware. It is a GUI-based NOS; however, considering the UNIX origin, obviously it can be administered entirely through the CLI as well:

Depending on whether it is a physical medium (cable) or a wave-based communication (wireless), mainly the following networking mediums for data transferring and communication are used:

• Metallic mediums, copper wires in twisted pairs and coaxial cables transmit electrical impulses
• Glass mediums, fibre optic cable transmit pulses of light
• Air mediums, waves and rays from the electromagnetic spectrum transmit signals in different frequencies

Twisted pairs, as in Figure 1.23, is a cable that contains four twisted pairs of copper; a total of eight wires, each with a specified color. The single wires are twisted around each other forming twisted pairs, and then the pairs are twisted around each other forming the cable; and that is done to reduce electromagnetic interference (EMI) and cross-talk. Usually, it is available in two types: unshielded twisted pair (UTP), and shielded twisted pair (STP). Mainly, it is used for designing LANs. The maximum distance that the twisted pairs medium can successfully carry a signal in an Ethernet network is 100 m.

Coaxial, as in Figure 1.24, is a copper cable presented in two forms: thin coaxial, with a length up to 185 m; and thick coaxial, with a length up to 500 m. In the past, it was used to implement computer networks with the bus and ring physical topologies. Nowadays, it is mainly used by cable Internet Service Providers (ISP) for transferring data and video signal:

Fibre optic, as in Figure 1.25, is a cable made up of glass through which the light is transmitted. Based on the light transmission, it is offered in two modes:

• Single mode utilizes only one light, and can reach a length from 40 km to 60 km
• Multimode utilizes multiple lights, and can reach a length from 2 km to 3 km.

Apart from its traditional usage in WANs, today fibre optic is used a lot for the implementation of fiber to the home (FTTH), and MAN networks:

Infrared and Bluetooth are wireless technologies for transmission of data over short distances. Infrared, as the name explains, uses infrared rays, and requires the line of sight to transmit the infrared signal. On the contrary, Bluetooth operates under 2.4 GHz frequency standard, and it does not suffer from the line of sight communication.

Radio waves, otherwise known as electromagnetic radiation, uses electromagnetic waves with a longer spectrum of wavelengths than infrared rays. Since they operate on different frequencies, hence, it makes it possible to cover large areas. Radio waves have found application in WAN's.

Whereever the infrared, Bluetooth and radio waves cannot reach the destination, it will be reached by satellite signals. Unlike aforementioned wireless technologies, satellite technology uses a wide spectrum of wavelengths and frequencies. Today, it is estimated that there are more than 2,000 satellites in Earth's orbit that enable telecommunications around the globe.

Converged networks, known also as triple-play services networks, are networks that have the ability to transmit data, voice, and video, or any combination of these services over the same networks. Converged networks are considered modern networks compared to traditional networks, where only dedicated services were provided on the networks. That has been the reason why we have existing networks such as telephone networks for transmitting voice, broadcast networks for transmitting video, and computer networks for transmitting data.

To understand the growing complexity of networks, let's compare the classic phone devices of many decades ago with today's smartphones. Obviously, the great potential that the smartphones offer compared to the classic phones makes this comparison sound naive; however, it is worth mentioning the fact that while the classic phones have used a dedicated voice communication network that understandably must have been less complex, by contrast the smartphones use a more complex communication network. That is because today’s communications networks, from frontend devices to backend devices, are various vendor technologies, resulting in more complexity when it comes to network scaling, upgrading, or patching.

As explained earlier, the converged network integrates data, voice, and video into a single network. This is achieved thanks to the technologically advanced equipment and the TCP/IP protocol. Thus, it can be said that the elements of converged networks are a convergent device and a converged service. An example of a convergent device is the multiplexer (as in Figure 1.26) that, at its input, merges multiple communication signals into a single signal at its output. For the converged service, it can be said that it is a service that provides voice, data, and video signals in a single network, thus providing services for all modes of communication:

Cisco's three-layered architecture helps defining the enterprise networks by simplifying the process of designing a reliable, highly-redundant, and scalable hierarchical inter-network. The three layers of Cisco architecture are as follows:

• Access layer, as the name indicates, is the layer in which network services are accessed. This layer mainly consists of computers, servers, hubs, layer 2 switches, access points, and other network end devices. A LAN network can be considered as an access layer analogy.
• Distribution layer is the middle layer that plays the role of the bridge by interconnecting the access layer and the core layer. This layer mainly uses layer 3 switches and routers. Extended LANs that form the MAN can be considered as a distribution layer analogy.
• Core layer is a fast and highly redundant network that is managed by core switches and routers. It is a backbone of the corporate network that enables the packet's movement between distribution-layer devices in different segments of the network. A WAN network can be considered as a core layer analogy.

We live in the Internet of Things (IoT) era in which the internet dictates the way we live and work. Therefore, things that were only science fiction a few years ago have started to become a reality. Thus, the overwhelming development of technology has transformed our world into an ever-changing environment. This necessarily requires everyone to adapt to this new reality. Some of the current trends in computer networks include the following:

• Improved security is becoming the topmost priority of enterprise networks. That is due to the fact that the number of users is growing more and more, and with that, more sophisticated have become the cyber criminals attacks.
• Increased bandwidth is ranked by analysts as enterprises second priority, right after the security. That is due to continuously increasing demands for traffic, thus putting the networks under pressure as they carry traffic.
• Software-defined networks (SDNs) continue to increase in popularity, especially by enterprises. That has to do with the convergence nature of SDNs, which multiplex data over multiple physical links, thus providing better performance than dedicated communication networks.
• Video communication, besides having made the distance communication between individuals more appealing, has enabled great opportunities for online collaboration and entertainment.
• Online collaboration, including video communication, brings people together on a common project. In addition to businesses, more and more of this trend is being embraced by educational institutions and individuals.
• Bring your own devices (BYODs) is a network trend that enables users to use their personal equipment to access business data. Obviously, that enables freedom, flexibility, and more opportunities for end users.
• Cloud computing, other than changing the way we access and store data, is reshaping the internet too. From businesses to individuals, cloud computing provides on-demand services to any device, anywhere in the world, securely and economically.

We summarize the chapter with the following points:

• The internet is the network of the networks.
• A computer network is a group of computers connected to each other in order to share resources.
• Usually, the resources can be data, network services, and peripheral devices.
• The fundamental requirement for designing a computer network is that there must be two or more computers:
  • A PAN is defined as a computer network that is used to connect and transmit data among devices located in a personal area, usually utilizing Bluetooth or Wi-Fi to interconnect devices
  • A LAN usually covers the floor of the building, several floors of the building, an entire building, or even a few buildings that are close to one another
  • A MAN represents a group of LANs interconnected within the geographical boundary of the town or city
  • A WAN is a computer network that covers a wide geographic area using dedicated telecommunication lines such as telephone lines, leased lines, or satellites
• The intranet is considered to be the private network of an organization where employees can access network services.
• The extranet can be thought of as an intranet with a controlled access.
• Physical topology presents ordering, arrangement, and placement of the physical parts of a computer network, such as computers, peripheral devices, cables for data transmission, and network equipment:
  • Bus is the physical topology in which computers, peripheral and network devices are connected through the bus that mainly consists of coaxial cable.
  • Ring is the physical topology in which computers, peripheral and network devices form a closed cycle that takes the shape of a ring network where each device is connected to each other.
  • Star is the physical topology in which computers and peripheral and network devices are connected independently with a central device.
  • Extended star is the physical topology in which computers, peripheral and network devices are connected into two or more star topology networks, and then the central components (that is switches) are interconnected over a bus.
  • Hierarchical is the physical topology that represents a combination of star and bus topologies.
  • Mesh is the physical topology in which each computer is connected with every computer to form the network.
• Logical topology represents the logical aspect of the computer network.
• In logical topology, it is the logical paths that are used to carry electric or light signals from one computer to another, or from one network node to another node.
• Clients are computers that request the resources in a computer network.
• Servers are network components that provide resources to clients. Servers too have an active role.
• A host is any device with an IP address that requests or provides networking resources to any other host or node on the network.
• A node is any device that can generate, receive, and transmit the networking resources on the computer network.
• A network interface is a component-like network card or LAN port on network equipment that enables clients, servers, peripheral devices, and network equipment to get connected and communicate with each other.
• Peripheral devices are printers, scanners, SAN, and any other peripheral device that provides resources to clients either through a LAN or as a shared device on a network.
• Applications and shared data are virtual network components that represent applications and files shared on the network that are usually provided by servers.
• Hubs and switches are acting as central components (in Ethernet communication technology) of the computer network to enable interconnection and communication between clients, servers, and peripheral devices.
• Routers are a computer network component that enables routing of the data (that is, packets) from an LAN to the internet, and vice versa.
• The computer network architecture represents the computer network design that allows the computer network components to communicate with one another:
  • Peer-to-peer is a computer network in which the participating computers do not play the predefined roles in the network, but instead they change roles from client to server and vice versa, based on the actual activity on the network.
  • Client/server 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.
• NOSs are software that are capable of managing, maintaining, and providing resources in the network.
• In metallic mediums, copper wires in twisted pairs and coaxial cables transmit electrical impulses.
• In glass mediums, fibre optic cable transmits pulses of light.
• In air mediums, waves and rays from the electromagnetic spectrum transmit signals in different frequencies.
• Twisted pairs is a cable that contains four twisted pairs of copper with a total of eight wires, each with a specified color.
• Coaxial is a copper cable presented in two forms: thin coaxial with the length up to 185 m, and thick coaxial with the length up to 500 m.
• Fibre optic is a cable made up of glass through which the light is transmitted:
  • Single mode utilizes only one light, and can reach the length from 40 km to 60 km
  • Multimode utilizes multiple lights, and can reach the length from 2 km to 3 km
• Infrared and Bluetooth are wireless technologies for transmission of data over short distances.
• Radio waves, or otherwise known as electromagnetic radiation, uses electromagnetic waves with the longer spectrum of wavelengths than infrared rays.
• Satellite technology uses a wide spectrum of wavelengths and frequencies.
• The converged networks, known also as triple play services networks, are networks that have the ability to transmit data, voice, and video, or any combination of these services over the same networks:
  • A convergent device is the multiplexer that, at its input, merges multiple communication signals into a single signal at its output
  • A converged service is a service that provides voice, data, and video signals in a single network, thus providing services for all modes of communication
• Cisco's three-layered hierarchical model helps define the enterprise networks by simplifying the process of designing a reliable, highly redundant, and scalable hierarchical internetworks:
  • Access layer, as the name indicates, is the layer in which network services are accessed.
  • Distribution layer is the middle layer that plays the role of the bridge by interconnecting the access layer and the core layer.
  • Core layer is a fast and highly redundant network that is managed by core switches and routers.
• We live in the IoT era in which the internet dictates the way we live and work.

1. A computer network is a group of computers connected to each other in order to share resources. (True | False)
2. _________________ represents a group of LANs interconnected within the geographical boundary of the town or city.
3. Which of the following are the layers of Cisco's three-layered hierarchical model? (Choose two):
   1. Access
   2. Services
   3. Peripheral
   4. Core
4. The converged networks, known also as triple play services networks, are networks that don't have the ability to transmit data, voice, and video, or any combination of these services over the same networks. (True | False)
5. _________________ is a cable that contains four twisted pairs of copper with a total of eight wires, each with a specified color.
6. Which of the following are fibre optic modes?
   1. Single
   2. Dual
   3. Triple
   4. Multi
7. The computer network architecture represents the computer network design that allows the computer network components to communicate with one another. (True | False)
8. _________________ are a computer network component that enables routing of the data (that is, packets) from LAN to the internet, and vice versa.
9. Which of the following are types of computer networks? (Choose two)
   1. PAN
   2. DAS
   3. NAS
   4. LAN
10. In logical topology, it is the logical paths that are used to carry electric or light signals from one computer to another, or from one network node to another node. (True | False)

11. _________________ is the physical topology in which computers and peripheral and network devices are connected independently with a central device.
12. Which of the following represent the physical topologies? (Choose all that apply)
    1. Bus
    2. Ring
    3. Star
    4. All of the above
13. The intranet is considered to be the public network of an organization where employees can access network services. (True | False)
14. _________________ is defined as a computer network that is used to connect and transmit data among devices located in a personal area, usually utilizing Bluetooth or Wi-Fi to interconnect devices.
15. Which of the following represent the network architectures? (Choose two)
    1. Peer-to-peer
    2. Client/server
    3. Storage area network (SAN)
    4. Network-attached storage (NAS)
16. The computer network architecture represents the computer network design that allows the computer network components to communicate with one another. (True | False)
17. _________________ is the network of the networks.
18. Which of the following are network mediums? (Choose all that apply)
    1. Metallic
    2. Glass
    3. Air
    4. All of the above