dB (17 dBm = 50 mW)
subtract 3 more (14 dBm = 25mW)
Content 6.5 Implementing Wireless LANs 6.5.10 Effective Isotropic Radiated Power EIRP of a transmitter is the power that the transmitter appears to have if it were an isotropic radiator (if the antenna radiated equally in all directions). By virtue of the gain of a radio antenna (or dish), a beam is formed that preferentially transmits the energy in one direction. The EIRP is estimated by adding the gain (of the antenna) and the transmitter power (of the radio). Transmit power is rated in dBm or mW: EIRP = transmitter power + antenna gain – cable loss Radio equipment has output limits that are given as EIRP and must not be exceeded. Different countries have different standards. Check with the authorities in the country of installation to determine the maximum EIRP. The FCC and ETSI uses EIRP for power limits in regulations for 2.4-GHz and 5-GHz WLANs. RF energy is carried between the antennas and the radio equipment through a coaxial cable. An antenna cable introduces signal loss in the antenna system for both the transmitter and receiver. Loss of signal strength is directly proportional to the length of the cable segment. As the diameter of the cable increases, signal loss is decreased, but at a much higher purchase cost. As signal frequency increases (higher numbered channel), signal loss increases. To reduce signal loss, minimize the cable length and use only low-loss or ultralow-loss antenna cables to connect radio devices to antennas. Radio output is measured in dBm. Figure shows the dBm ratings for Cisco Aironet Wireless equipment and the resulting EIRP when this equipment is used with a 6-dBi patch antenna and the FCC maximum of 36 dBm for multipoint wireless links. The maximum EIRP allowed by the FCC for a Part 15 2.4-GHz device in the United States is 36 dBm. The standards are different for specific point-to-point systems. However, this class is focused on WLANs that would be considered point-to-multipoint solutions, so the maximum EIRP must not exceed 36 dBm, and the maximum gain on an antenna must not exceed 16 dBi, unless installed by a professional installer. The highest gain antenna approved for Cisco’s 2.4-GHz frequency band is the 21-dBi Parabolic Dish Antenna. Figure shows the ETSI standards. The following is an excerpt from the document ETSI EN 300 328-1 V1.2.2 (2000-07): The effective radiated power is defined as the total power of the transmitter. The effective radiated power shall be equal to or less than 20 dBm (100 mW) EIRP. This limit shall apply for any combination of power level and intended antenna assembly. To stay in the limit of the EIRP in Europe, you have to reduce the conducted power of the Aironet devices when you use antennas with more than 3-dBi gain. Figure summarizes the EIRP limits for 2.4-GHz and 5-GHz WLANs in FCC and ETSI regulation domains. The following is an excerpt from FCC Title 47 Section 15.407:
Content 6.6 Implementing Wireless LANs 6.6.1 Configuring Wireless WLANs You can configure an autonomous access point using any of the following: The WLAN configuration requires an IP address on the access point, except for the serial console. The IP address on an autonomous access point can be set using a DHCP server or the CLI via the serial console. You can find the IP address of the access point in the following ways:
Content 6.6 Implementing Wireless LANs 6.6.2 Role of Autonomous Access Points in a Radio Network The Cisco Aironet 1100, 1200, and 1300 Series autonomous access points and bridges can perform the following different functions in a WLAN network, which allows for flexible use of the wireless equipment: The Cisco Aironet 1100 Series does not support bridge mode. The 1100 Series access points can be used as workgroup bridges. Root devices accept associations from non-root devices. Only non-root devices can initiate connections, such as clients to root devices. Therefore, it is important to configure the role of the device. Access point and bridging can be combined in one device with two radios (2.4 and 5 GHz).
Content 6.6 Implementing Wireless LANs 6.6.3 Autonomous Access Point Configuration via the Web Browser Figure shows the homepage of an autonomous access point, which is displayed when you connect to the access point. You can access configuration options from the menu on the left. You can return to the homepage at any time by clicking Home on the menu. The homepage provides a summary of the access point and bridge status, including the following: You can configure the basic parameters of the access point on the Express Setup page. These parameters may be set for either of the access point’s radio interfaces or as follows: