CCENT/CCNA: ICND1 100-105 Certification Guide: Learn computer network essentials and enhance your networking skills by obtaining the CCENT certification

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.

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:

Figure 1.2. Personal Area Network (PAN)

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:

Figure 1.3. Metropolitan Area Network (MAN)

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:

Figure 1.4. Wide Area Network (WAN)

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

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):

Figure 1.5. Bus physical topology

Ring

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:

Figure 1.6. Ring physical topology

Star

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:

Figure 1.7. Star physical topology

Extended star

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:

Figure 1.8. Extended star physical topology

Hierarchical

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:

Figure 1.9. Hierarchical physical topology

Mesh

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:

Figure 1.10. Mesh physical topology

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:

Figure 1.11. Logical topology

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 ashared printer in the role of the resource provider, and the PC and laptop in the role of resourcerequesters.

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 ahost. 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 nodeon 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):

Figure 1.12. Network interface card (NIC)

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:

Figure 1.13. Storage area network (SAN)

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:

Figure 1.14. Stack of Cisco switches

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:

Figure 1.15. Stack of Cisco routers

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:

Figure 1.16. Cisco firewall

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 wirelessaccess 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):

Figure 1.17. Stack of access points (APs)

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.

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:

Figure 1.18. Peer-to-peer computer 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. 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:

Figure 1.19. Client/server computer network

The WindowsServer (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. TheNew 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:

Figure 1.20. Login screen in Windows Server 2016

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:

Figure 1.21. Login screen in SUSE Linux Enterprise Server 11

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:

Figure1.22. Login screen in macOS X Server

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.

Figure 1.23. UTP cable

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 cableInternet Service Providers (ISP) for transferring data and video signal:

Figure 1.24. Coaxial cable

Fibreoptic, 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:

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:

Figure 1.25. Fibre optic cable

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.

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 contrastthe 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:

Figure 1.26. Orthogonal Frequency Division Multiplexing (OFDM) multiplexing technique used in DSL Wireless Router

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: