User's Manual

AR24027 Operator’s Manual (rev E)
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4.3.7 Maximum Permissible Exposure (MPE) Limitations
The installer must mount all transmit antennas so as to comply with the limits for human exposure to
radio frequency (RF) fields per paragraph 1.1307 of the FCC Regulations . The FCC requirements
incorporate limits for Maximum Permissible Exposure (MPE) in terms of electric field strength,
magnetic field strength, and power density.
Antenna installations must be engineered so that MPE is limited to 1 mW/cm
2
, the more stringent
limit for "uncontrolled environments". The table below specifies the minimum distance that must be
maintained between the antenna and any areas where persons may have access, including rooftop
walkways, sidewalks, as well as through windows and other RF-transparent areas behind which
persons may be located.
Minimum Distance calculation to
avoid Antenna Radiation Hazard (exposure of 1 mW/cm
2
)
Antenna Gain (dBi): 9 18 24
Max. Output Power
23 23 23
MPE safe distance (cm)
11* 28* 63*
*NOTE: For fixed location transmitters, the minimum separation
distance is 2 m, even if calculations indicate a lower MPE distance.
4.4 Ethernet Bridging
The AR24027 operates as an Ethernet bridge. As a bridge, the AR24027 runs in “promiscuous mode”,
i.e., it examines all the Ethernet packets that are flowing in the local LAN. Since these Ethernet
packets contain a “source” and “destination” address, the radio quickly learns the addresses of all the
“local” stations connected to the LAN (all the “source” addresses of packets flowing in the LAN are
local).
Each AR24027 periodically transmits the information about the local Ethernet addresses to all other
radios. Therefore every AR24027 holds an Ethernet table that includes one entry for every Ethernet
address connected to any of the LANs (this table can be examined with the “show ethernet”
command).
With this information on hand, each AR24027 examines the destination address of every Ethernet
packet in the local LAN and makes one of the following decisions:
1. If the destination address is for a “local” station, discard the packet.
2. If the destination address is connected to a remote radio, queue that packet to be forwarded
through the appropriate RF port.
3. If the destination address is unknown, “flood” the packet into the network. The packet will show
up at every LAN connected to any radio in the network.
Each AR24027 has capacity to store 500 entries in its Ethernet table. Entries are erased after a certain
amount of time to allow for stations to be moved between LANs and not show up in two distinct