The Components of a Network

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The Components of a Network

Put simply, a network is a collection of machines that have been linked together both physically and through software components to facilitate communication and sharing of information among them. By this definition, a network might be as simple as the computers shown in Figure 2.1. In fact, Figure 2.1 shows the simplest kind of network that can be created: two machines connected by a piece of coaxial cable. This example is deceptively simple and hides a fairly complex arrangement of pieces that must work together to enable these two machines to communicate.

Look at Figure 2.2, which shows each of the components, both hardware and software, required to enable communication between these two machines.

Observe that the first requirement for a network is a physical connection. A number of communication methods can be used to establish a physical connection: 10Base-T Ethernet, 10Base-2 Ethernet, Token Ring, FDDI, and others. Each connection type has pros and cons in terms of ease of installation, maintenance, and expense (see Table 2.1). The following table reflects some generalizations about each type of media as a means to connect computers together. Unless you plan to run a wireless network, you need some kind of physical connection between machines for transferring data back and forth.

The second requirement for a network is appropriate hardware, such as a network card in the machine that acts as the interface to the network. The hardware provides the appropriate connection the machine needs to communicate with other machines across the wire. Physical networks can have different connection methods, depending on what has been installed. For example, if the physical network consists of coaxial cable, a BNC connector attaches the machines to the network; whereas if the physical network uses unshielded twisted-pair cabling, RJ-45 connectors connect the machines to the network. It is very difficult to connect an unshielded twisted pair network card to a network that uses coaxial cable and vice versa. Conversion devices and intermediary pieces can be purchased to allow for this kind of mixing, but you’re generally better off buying a network card that supports your physical media inherently. This prevents an additional source of error when troubleshooting network connection problems.

Some network cards support multiple connection types for easy implementation. Naturally, a network card in the machine requires machine resources, including interrupts and memory addresses. These features need to be available for the network card to function.

Your third requirement in setting up a network is to install a network protocol. A network protocol is software installed on a machine that determines the agreed-upon set of rules for two or more machines to communicate with each other. One common metaphor used to describe different protocols is to compare them to human languages.

Think of a group of people in the same room who know nothing about each other. In order for them to communicate, this group has to determine what language to speak, how to handle identifying each other, whether to make general announcements or have private conversations, and so on. If machines are using different protocols, it is equivalent to one person speaking French and another person speaking Spanish. Machines that have different protocols installed are not able to communicate with each other. Common protocols in the Microsoft family include: NetBEUI (NetBIOS Extended User Interface), NWlink (NDIS compliant version of Novell’s IPX/SPX), DLC (Data Link Control), AFP (Appletalk File Protocol), and TCP/IP (Transmission Control Protocol/Internet Protocol).

The fourth and final key to the networking equation is having an operating system that is network-aware. Examples of operating systems that are network-aware include Windows NT, Windows 95, Windows for Workgroups, DOS, Unix, and Novell. Most operating systems are network-aware, but until now almost all applications were written to ask for local resources (hard drives) on the machine. Applications have only recently become fully network-aware and still generally use local drives to access resources.

Because applications still use local drives, it falls upon the operating system to be able to redirect (thus the name of the redirector) local resource requests to other machines out on the network. Figure 2.3 illustrates why you map or connect network drives to virtual local drives. The operating system knows the resources are on another machine, but the applications do not. In Figure 2.3, the application thinks that drive x: is actually on the local machine. The operating system is responsible for acting on behalf of the application when a resource on the network is requested. Here the I/O manager redirects the save request from the application and sends it to the network redirector. To have a network, your operating system must have the appropriate networking components installed, otherwise the operating system cannot utilize resources that reside over a network connection.

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