Appendix D Wireless LANs
ZyWALL USG 50-H User’s Guide
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Antenna Overview
An antenna couples RF signals onto air. A transmitter within a wireless device sends an RF
signal to the antenna, which propagates the signal through the air. The antenna also operates in
reverse by capturing RF signals from the air.
Positioning the antennas properly increases the range and coverage area of a wireless LAN.
Antenna Characteristics
Frequency
An antenna in the frequency of 2.4GHz (IEEE 802.11b and IEEE 802.11g) or 5GHz (IEEE
802.11a) is needed to communicate efficiently in a wireless LAN
Radiation Pattern
A radiation pattern is a diagram that allows you to visualize the shape of the antenna’s
coverage area.
Antenna Gain
Antenna gain, measured in dB (decibel), is the increase in coverage within the RF beam width.
Higher antenna gain improves the range of the signal for better communications.
For an indoor site, each 1 dB increase in antenna gain results in a range increase of
approximately 2.5%. For an unobstructed outdoor site, each 1dB increase in gain results in a
range increase of approximately 5%. Actual results may vary depending on the network
environment.
Antenna gain is sometimes specified in dBi, which is how much the antenna increases the
signal power compared to using an isotropic antenna. An isotropic antenna is a theoretical
perfect antenna that sends out radio signals equally well in all directions. dBi represents the
true gain that the antenna provides.
Types of Antennas for WLAN
There are two types of antennas used for wireless LAN applications.
• Omni-directional antennas send the RF signal out in all directions on a horizontal plane.
The coverage area is torus-shaped (like a donut) which makes these antennas ideal for a
room environment. With a wide coverage area, it is possible to make circular overlapping
coverage areas with multiple access points.
• Directional antennas concentrate the RF signal in a beam, like a flashlight does with the
light from its bulb. The angle of the beam determines the width of the coverage pattern.
Angles typically range from 20 degrees (very directional) to 120 degrees (less directional).
Directional antennas are ideal for hallways and outdoor point-to-point applications.
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Страница 280: ...Chapter 16 ALG ZyWALL USG 50 H User s Guide 280...
Страница 286: ...Chapter 17 IP MAC Binding ZyWALL USG 50 H User s Guide 286...
Страница 287: ...287 PART III Firewall Firewall 289...
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Страница 304: ...Chapter 18 Firewall ZyWALL USG 50 H User s Guide 304...
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Страница 313: ...Chapter 19 IPSec VPN ZyWALL USG 50 H User s Guide 313 Figure 238 VPN IPSec VPN VPN Connection Edit IKE...
Страница 356: ...Chapter 21 SSL User Screens ZyWALL USG 50 H User s Guide 356...
Страница 358: ...Chapter 22 SSL User Application Screens ZyWALL USG 50 H User s Guide 358...
Страница 368: ...Chapter 24 L2TP VPN ZyWALL USG 50 H User s Guide 368...
Страница 394: ...Chapter 25 L2TP VPN Example ZyWALL USG 50 H User s Guide 394...
Страница 395: ...395 PART V Application Patrol Application Patrol BWM 397...
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Страница 421: ...421 PART VI Anti X ADP 423...
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Страница 429: ...Chapter 27 ADP ZyWALL USG 50 H User s Guide 429 Figure 359 Profiles Traffic Anomaly...
Страница 432: ...Chapter 27 ADP ZyWALL USG 50 H User s Guide 432 Figure 360 Profiles Protocol Anomaly...
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Страница 462: ...Chapter 29 Addresses ZyWALL USG 50 H User s Guide 462...
Страница 474: ...Chapter 31 Schedules ZyWALL USG 50 H User s Guide 474...
Страница 484: ...Chapter 32 AAA Server ZyWALL USG 50 H User s Guide 484...
Страница 506: ...Chapter 34 Certificates ZyWALL USG 50 H User s Guide 506...
Страница 510: ...Chapter 35 SSL Application ZyWALL USG 50 H User s Guide 510...
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Страница 568: ...Chapter 38 Logs ZyWALL USG 50 H User s Guide 568 Figure 464 Maintenance Log Log Setting Edit System Log...
Страница 584: ...Chapter 40 Diagnostics ZyWALL USG 50 H User s Guide 584...
Страница 586: ...Chapter 41 Reboot ZyWALL USG 50 H User s Guide 586...
Страница 596: ...Chapter 43 Product Specifications ZyWALL USG 50 H User s Guide 596...
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Страница 636: ...Appendix A Log Descriptions ZyWALL USG 50 H User s Guide 636...
Страница 640: ...Appendix B Common Services ZyWALL USG 50 H User s Guide 640...
Страница 646: ...Appendix C Importing Certificates ZyWALL USG 50 H User s Guide 646...