Networking.docx
Transcript
Network Types The local area network (LAN) was created to connect computers in a single office or building. Expanding upon that, a wide area network (WAN) includes networks outside the local environment and can also distribute resources across great distances. Generally, it’s safe to think of a WAN...
Network Types The local area network (LAN) was created to connect computers in a single office or building. Expanding upon that, a wide area network (WAN) includes networks outside the local environment and can also distribute resources across great distances. Generally, it’s safe to think of a WAN as multiple, disbursed LANs connected together. Today, LANs exist in many homes (wireless networks) and nearly all businesses. WANs are fairly common too, as businesses embrace mobility and more of them span greater distances. Historically, only larger corporations used WANs, but many smaller companies with remote locations now use them as well. 313 Having two types of network categories just didn’t feel like enough, so the industry introduced three more terms: the personal area network, the metropolitan area network, and the wireless mesh network. The personal area network (PAN) is a very small-scale network designed around one person within a very limited boundary area. The term generally refers to networks that use Bluetooth technology. On a larger scale is the metropolitan area network (MAN), which is bigger than a LAN but not quite as big as a WAN. The most recent designation created is the wireless mesh network (WMN). As the name indicates, it’s a wireless network, and it uses what’s known as a mesh topology. We’ll cover both of those concepts in more detail later in this chapter. It is important to understand these concepts as a service professional because when you’re repairing computers, you are likely to come in contact with problems that are associated with the computer’s connection to a network. Understanding the basic structure of the network can often help you solve a problem. LANs The 1970s brought us the minicomputer, which was a smaller version of large mainframe computers. Whereas the mainframe used centralized processing (all programs ran on the same computer), the minicomputer used distributed processing to access programs across other computers. As depicted in Figure 6.1, distributed processing allows a user at one computer to use a program on another computer as a backend to process and store information. The user’s computer is the frontend, where data entry and minor processing functions are performed. This arrangement allowed programs to be distributed across computers rather than be centralized. This was also the first time network cables rather than phone lines were used to connect computers. Figure 6.1 Distributed processing By the 1980s, offices were beginning to buy PCs in large numbers. Portables were also introduced, allowing computing to become mobile. Neither PCs nor portables, however, were efficient in sharing information. As timeliness and security became more important, floppy disks were just not cutting it. Offices needed to find a way to implement a better means to share and access resources. This led to the introduction of the first type of PC local area network (LAN): ShareNet by Novell, which had both hardware and software components. LANs simply link computers in order to share resources within a closed environment. The first simple LANs were constructed a lot like the LAN shown in Figure 6.2. Figure 6.2 A simple LAN 314 After the introduction of ShareNet, more LANs sprouted. The earliest LANs could not cover large distances. Most of them could only stretch across a single floor of the office and could support no more than 30 computers. Furthermore, they were still very rudimentary and only a few software programs supported them. The first software programs that ran on a LAN were not capable of being used by more than one user at a time. (This constraint was known as file locking.) Nowadays, multiple users often concurrently access a program or file. Most of the time, the only limitations will be restrictions at the record level if two users are trying to modify a database record at the same time. WANs By the late 1980s, networks were expanding to cover large geographical areas and were supporting thousands of users. Wide area networks (WANs), first implemented with mainframes at massive government expense, started attracting PC users as networks went to this new level. Employees of businesses with offices across the country communicated as though they were only desks apart. Soon the whole world saw a change in the way of doing business, across not only a few miles but across countries. Whereas LANs are limited to single buildings, WANs can span buildings, states, countries, and even continental boundaries. Figure 6.3 shows an example of a simple WAN. Figure 6.3 A simple WAN 315 The networks of today and tomorrow are no longer limited by the inability of LANs to cover distance and handle mobility. WANs play an important role in the future development of corporate networks worldwide. PANs The term PAN is most commonly associated with Bluetooth networks. In 1998, a consortium of companies formed the Bluetooth Special Interest Group (SIG) and formally adopted the name Bluetooth for its technology. The name comes from a tenth-century Danish king named Harald Blåtand, known as Harold Bluetooth in English. (One can only imagine how he got that name.) King Blåtand had successfully unified warring factions in the areas of Norway, Sweden, and Denmark. The makers of Bluetooth were trying to unite disparate technology industries, namely computing, mobile communications, and the auto industry. Although the most common use of a PAN is in association with Bluetooth, a PAN can also be created with other technologies, such as infrared. Current membership in the Bluetooth SIG includes Microsoft, Intel, Apple, IBM, Toshiba, and several cell phone manufacturers. The technical specification IEEE 802.15.1 describes a wireless personal area network (WPAN) based on Bluetooth version 1.1. The first Bluetooth device on the market was an Ericsson headset and cell phone adapter, which arrived on the scene in 2000. While mobile phones and accessories are still the most common type of Bluetooth device, you will find many more, including wireless keyboards, mice, and printers. Figure 6.4 shows a Bluetooth USB adapter. Figure 6.4 Bluetooth USB adapter We cover Bluetooth in more detail in Chapter 8, “Installing Wireless and SOHO Networks.” Also, if you want to learn more about Bluetooth, you can visit www.bluetooth.com. One of the defining features of a Bluetooth WPAN is its temporary nature. With traditional Wi-Fi, you need a central communication point, such as a wireless router or access point to connect more than two devices together. (This is referred to as infrastructure.) Bluetooth networks are formed on an ad hoc basis, meaning that whenever two Bluetooth devices get close enough to each other, they can communicate directly with each other—no316central communication point is required. This dynamically created network is called a piconet. A Bluetooth-enabled device can communicate with up to seven other devices in one piconet. Two or more piconets can be linked together in a scatternet. In a scatternet, one or more devices would serve as a bridge between the piconets. MANs For those networks that are larger than a LAN but confined to a relatively small geographical area, there is the term metropolitan area network (MAN). A MAN is generally defined as a network that spans a city or a large campus. For example, if a city decides to install wireless hotspots in various places, that network could be considered a MAN. One of the questions a lot of people ask is, “Is there really a difference between a MAN and a WAN?” There is definitely some gray area here; in many cases they are virtually identical. Perhaps the biggest difference is who has responsibility for managing the connectivity. In a MAN, a central IT organization, such as the campus or city IT staff, is responsible. In a WAN, it’s implied that you will be using publicly available communication lines, and there will be a phone company or other service provider involved. WMNs Wireless networks are everywhere today. If you use your smartphone, tablet, or laptop to look for wireless networks, chances are you will find several. Wireless clients on a network typically access the network through a wireless access point (WAP). The WAP may connect wirelessly to another connectivity device, such as a wireless router, but more likely uses a wired connection to a router or switch. (We’ll talk about all of these devices later in the chapter.) The key defining factor of a mesh network topology is that it has multiple redundant connections. If one fails, another is available to take its place. Therefore, a wireless mesh network is one that uses wireless but has multiple redundant connections to help ensure that communication runs smoothly. While mobility is a key feature of wireless networking, the key infrastructure that wireless clients connect to is generally not mobile. It makes it a lot harder to connect to a hot spot if you don’t know where it will be today! In order to implement a WMN, the access points and other wireless infrastructure must support it. A WMN is then managed through a cloud-based network controller, which allows the administrator to enable, configure, and monitor the network remotely.
