p. 319

3 LAN

LAN (Local Area Network) is a network that is set up in a narrow area (or premise). This section provides an insight into the devices and techniques that are used to construct a LAN.

3 - 1 Basic Techniques of a LAN

A LAN is constructed by connecting the computers and peripheral equipment in a company and premise with a private line. The construction of a LAN has the following merits.

(1) Wired LAN

A wired LAN is connected by using a communication line (i.e., cable), and supports the IEEE 802.3 standard. An IEEE 802.3 LAN is also called Ethernet, and is represented by the following symbolic notation. For example, 10BASE5 is a baseband LAN which has a transmission speed of 10 Mbps and uses a coaxial cable with a cable length of 500 m. · 1 question

p. 320

In a wired LAN, the three types of media (i.e., cables) that are described below are used for connecting devices. Moreover, a LAN module (e.g., a LAN adapter, a NIC (Network Interface Card), as a standard installation or an additional installation) is used for connecting the PC to LAN.

p. 321

(2) Wireless LAN

A wireless LAN is connected by using electromagnetic waves or infrared rays, and supports the IEEE 802.11a/b/g/n standards (at present, IEEE 802.11n, which uses a frequency band of 2.4 GHz/5 GHz, and has a maximum communication speed of 600 Mbps is the main standard). Since a wireless LAN does not use cables, the layout can be changed easily, and as long as there are no obstacles, communication can be performed even at a distance of 50 to 100 meters. When a wireless LAN is used, a user connects the terminal to a wireless LAN access point. At this time, the wireless LAN sets an access point identifier SSID (Service Set IDentifier), or a network identifier ESSID (Extended SSID), which is an extended edition of SSID, in order to identify the wireless LAN access point. By making this setting, only the devices having the same SSID or ESSID are identified as the appropriate users (or devices), and therefore unauthorized use (or access) is prevented. However, since it is difficult to secure safety only through this method, it is necessary to examine sufficient security measures. In addition, a wireless LAN can even be connected to a wired LAN and the Internet through a wireless LAN access point. (Generally, this method is often used.)