If you do have any fiber optic equipment handy, go ahead and identify it now, based

Understanding Wired and Wireless Networks | 59 When it comes to interference, a cable itself can be its worst enemy. Generally, fiber optic cables are not affected by EMI, because they are inherently light based, not electricity based. Although a fiber optic cable will still produce a type of electromagnetic radiation, the cable is not traditionally affected by EMI in the same way copper-based cables are. However, if a fiber run is installed improperly, it can give strange results when it comes to the data signal. Exact installation rules must be followed including proper termination, specific radii for turns, avoiding bunching, and so on. Improper installation results in the signal becoming “bent,” which causes data loss. Chromatic dispersion is also a factor, as opposed to attenuation on twisted-pair cables. If the light is refracted too often, again, the signal will degrade. Fiber optic cable in general is the most secure cable, allows for the longest runs, and offers data transfer rates that are equal to or greater than twisted-pair cable. However, due to the com- plexity of installation, cost, and so on, fiber optic cable is not usually a first choice for all of the individual client computer runs. Instead, it is used for backbone connections; switch con- nections at the top of hierarchical star topologies, and other high-bandwidth or long-distance applications. CERTIFICATION READY How do you identify wireless devices? 1.4 ■ Comprehending Wireless Networks Wireless networks are everywhere. There are wireless networks for computers, handheld devices, wide-area connections, and more. Chances are you have used a wireless network in the past. In order to install and troubleshoot wireless networks, you must understand the basics of wireless communications and have knowledge of the devices, standards, frequencies, and security methods. THE BOTTOM LINE Table 3-3 continued C ABLING S TANDARD M EDIUM M AXIMUM D ISTANCE 1000BASE-BX10 Single-mode fiber 10 km 10GBASE-SR Multi-mode fiber 26–82 meters 10GBASE-LR Single-mode fiber 10–25 km 10GBASE-LRM Multi-mode fiber 220 meters 10GBASE-ER Single-mode fiber 40 km Identifying Wireless Devices Wireless devices might allow for central connectivity of client computers and handheld devices. Or, they might offer an extension of connectivity to a pre-existing wireless network and could be used to connect entire local area networks to the Internet. In addition, some wireless devices can be connected directly to each other in a point-to-point fashion. By far the most well-known wireless device is the wireless access point WAP. This device quite often also acts as a router, firewall, and IP proxy. It allows for the connectivity of various wireless devices such as laptops, PDAs, handheld computers, and so on. It does so by making connections via radio waves on specific frequencies. Client computers and handheld devices must use the same frequency in order to connect to the WAP. In the following exercise, we will identify wireless access points, wireless network adapters, and wireless bridges and repeaters. 60 | Lesson 3 EXAMINE WIRELESS DEVICES GET READY. To examine wireless devices, perform these steps: 1. Execute a Bing search in the images section for the term “wireless access point.” Take a look at some of the various types of WAPs and their connections.

2. Examine Figure 3-7. This displays the front LED panel of a common wireless access

point. Notice there is a green LED for the WLAN connection. WLAN is short for wire- less local area network; the LED tells us that wireless is enabled on this device. This particular device also acts as a 4-port switch; these ports are labeled “Ethernet,” and two of them have green-lit LEDs, which means that computers are physically con- nected to those ports and are active. Finally, the “Internet” LED is lit, which is the physical connection from the WAP to the Internet. Although a WAP by itself is just a wireless transmitter, usually with a single port to connect to the LAN, multifunction network devices like these are very common in small networks and home offices. Figure 3-7 Wireless access point

3. Execute a Bing search in the images section for the term “wireless network adapter.”

Examine the results. Wireless network adapters allow for connectivity between a desktop computer or laptop and the wireless access point. They come in many shapes and sizes, including USB, PC Card, ExpressCard, and, of course, as an internal PCI or PCI Express adapter card for a personal computer. Most laptops today have built- in wireless network adapters, which are basically a chip on a circuit board with an antenna attached.

4. Access the Internet and execute searches on various wireless manufacturers’ Web sites

to find out about the latest wireless access points and network adapters they offer. Write down your results for each of the following manufacturers’ fastest access points and network adapters: • www.d-link.com • http:home.cisco.comen-USwireless • http:www.netgear.com • http:www.belkin.com

5. Execute a Bing search in the images section for the term “wireless repeater.” Examine

the results. A wireless repeater is used to extend the coverage of a wireless network. Due to the fact that most WLANs only have a range of about 100 feet or so depending on the standard, wireless repeaters are often needed to extend that signal further. They can be wired to the access point, but more often than not, they are placed on the perimeter of the existing wireless network area. Understanding Wired and Wireless Networks | 61 6. Execute a Bing search in the images section for the term “wireless bridge.” Examine the results. A wireless bridge is similar to a wireless repeater, but the bridge can con- nect different 802.11 standards together; this is known as bridge mode. 7. Access a wireless access point simulator. We use the D-link DIR-655 emulator later in this lesson. Take a look at the following link now, and login to the DIR-655 Device UI emulator to become acquainted with its interface. There is no password: http:support.dlink.comemulatorsdir655 Table 3-4 IEEE 802.11 WLAN standards IEEE 802.11 S TANDARD D ATA T RANSFER R ATE M AX . F REQUENCY 802.11a 54 Mbps 5 GHz 802.11b 11 Mbps 2.4 GHz 802.11g 54 Mbps 2.4 GHz 802.11n 600 Mbps 300 Mbps typical 5 GHz andor 2.4 GHz CERTIFICATION READY How do you identify wireless networking standards? 1.4 Identifying Wireless Networking Standards In order to set up a functional wireless LAN, a network administrator has to know several wireless standards, as well as ways to secure the wireless network transmissions. A wireless LAN WLAN is a network composed of at least one WAP and at least one com- puter or handheld device that can connect to the WAP. Usually these networks are Ethernet based, but they can be based off other networking architectures. In order to ensure com- patibility, the WAP and other wireless devices must all use the same IEEE 802.11 WLAN standard. These standards are collectively referred to as 802.11x not to be confused with 802.1X, and they are defined by the data link layer of the OSI model. The term “WLAN” is often used interchangeably with Wi-Fi. However, Wi-Fi refers to a trademark created by the Wi-Fi Alliance. Wi-Fi products and technologies are based on the WLAN standards. These WLAN standards dictate the frequency or frequencies used, speed, and so on. Table 3-4 shows the most common standards and their maximum data transfer rate and frequency. In the United States, 802.11b and g have 11 usable channels, starting with channel 1 centered at 2.412 GHz and ending with channel 11 centered at 2.462 GHz. This is a smaller range than some other countries use. Many of the channels in a WLAN overlap. To avoid this, organizations may put, for example, three separate WAPs on channels 1, 6, and 11, respectively. This keeps them from overlapping and interfering with each other. If two WAPs on channels 4 and 5 are in close proximity to each other, there will be a decent amount of interference. It’s also wise to keep WLAN WAPs away from Bluetooth devices and Bluetooth access points, because Bluetooth also uses the 2.4 GHz frequency range. It should go without saying that compatibility is key. However, many WAPs are backward compatible. For example, an 802.11g WAP might also allow 802.11b connections. Perhaps it even allows 802.11a connections, which would be an example of wireless bridging. But generally, companies are looking for the fastest compatible speed possible from all of their wireless networking equipment—and today, that means 802.11n. 802.11n is superior to older WLAN standards in the following ways: • Multiple-Input Multiple-Output MIMO: This means that wireless devices can have more antennas, up to four maximum.