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This chapter describes the procedures for configuring the bridge's radio network.
Here's what you'll find in this chapter:
From the Configuration Radio menu, you can configure the radio network.
Navigation: Main > Configuration > Radio
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Caution Changes to radio parameters take effect immediately. If your Telnet or browser session is accessing the bridge over a radio link, you might lose the session because the bridge might no longer be associated to an Access Point on the network. If this happens, it may be necessary to change the Access Point's radio parameters to reestablish the radio link. You can also use a crossover cable to attach the bridge to the Ethernet port on a PC to configure it. |
This string functions as a password for the bridge to join the radio network. The bridge must supply a matching SSID in order to associate to an Access Point.
The Rates option sets the list of data rates at which the bridge will be allowed to send and receive radio packets. The rate may be configured as an inclusive range (1 to 11) or as an individual rate (11).
The Basic_rates option determines the rate every radio node in the cell must support. If the basic rate is not supported, the bridge is not allowed to associate. The lowest basic rate controls the rate at which all multicast and broadcast packets are transmitted. The highest basic rate controls the bit rate at which the management packets are transmitted.
Use the Radio IEEE 802.11 menu to configure RTS/CTS and encryption parameters.
Navigation: Main > Configuration > Radio > I80211
The Rts parameter determines the minimum-size transmitted packet that will use the RTS/CTS protocol. The value typed must range from 0 to 2400 bytes. The default is 2048.
This protocol is most useful in infrastructures where the mobile nodes roam so far that the nodes on one side of the cell cannot hear the transmission of the nodes on the other side of the cell.
When the transmitted packet is equal to or larger than the RTS threshold, an RTS packet is sent. The destination node must respond with a CTS packet before the originator can send the real data packet. A node at the far end of a cell detects the RTS to/from the bridge or the CTS to/from the bridge. The node will detect how long to block its transmitter to allow the real packet to be received by the bridge. The RTS and CTS are small and, if lost in a collision, they can be retried more quickly and with less overhead than if the whole packet must be retried.
The disadvantage of using RTS/CTS is that for each data packet you transmit that is larger than the threshold size, you must transmit and receive another packet and thereby reduce throughput.
Wired Equivalent Privacy (WEP) is an optional IEEE 802.11 feature that provides data confidentiality equivalent to a wired LAN without crypto techniques to enhance privacy. WEP makes the wireless LAN link in a system only as secure as the wired link.
Navigation: Main > Configuration > Radio > I80211 > Privacy
It is important that you execute steps in the following order:
Step 2 Choose 4-Transmit to set the transmit key.
Step 3 Choose 2-Auth to set the authentication mode.
Step 4 Choose 1-Encryption to turn on encryption.
The Encryption option sets encryption parameters on all data packets except association packets and some control packets. Options are off, on, mixed on, or mixed off. The Access Point must also have encryption active and a key set properly. The following is an explanation of each option:
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Caution If you select on or mixed on as the WEP category and you are configuring the bridge through its radio link, you will lose connectivity to the bridge if the WEP key is set incorrectly. Be sure the WEP key you set exactly matches the WEP key used on your wireless LAN. |
The Auth parameter determines which method of authentication the system will use. Options are open or shared_key. The Open setting, which is the default, allows any Access Point, regardless of its WEP settings, to authenticate and then attempt to communicate with the bridge. The Shared_key setting instructs the bridge to send a plain-text, shared-key query to any Access Point attempting to communicate with the bridge. The shared-key setting can leave the bridge open to a known-text attack from intruders, and it is therefore not as secure as the open setting.
This value establishes the WEP key the bridge will use to receive packets. The value must match the key used by the Access Point. The key consists of up to 10 hexadecimal characters for 40-bit encryption, or 26 hexadecimal characters for 128-bit encryption. The hexadecimal characters may be any combination of 0-9, a-f, or A-F.
Follow these steps to set Key:
Step 2 Type the number (1-4) of the key the bridge will use and press Enter.
Step 3 Type the key (10 or 26 characters) and press Enter.
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Caution The WEP key you use to transmit data must be set to exactly the same value on your Access Point and your bridge. |
This value establishes the WEP key the bridge will use to transmit packets. Many users elect to use the same key as above. If a different key is chosen, a matching key must be established on the Access Point.
Follow these steps to set Transmit key:
Step 2 Type the number (1-4) of the key the bridge will use and press Enter.
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Note Only one WEP key can be used at a time to transmit. |
The Linktests option tests the transmission quality between bridge nodes and other nodes on the radio network as well as individual node radio performance.
A link test sends special control packets to a specified destination, which in turn echoes the packets back to the source. Each control packet sent has a sequence number that allows the sender to know whether packets were lost on the way to the destination or on the way back to the source node.
Navigation: Main > Configuration > Radio > Linktests
The Strength option sends a packet once per second to the parent Access Point. This packet is echoed back to the bridge, which records and displays the RF signal strength associated with that particular node.
This feature can be used to quickly verify the link to each radio partner or signal strength can be monitored while aligning directional antennas between two nodes. As the antennas are moved, the signal strength can be monitored to achieve maximum value.
The Align option breaks the association with the Access Point and starts monitoring beacons from all Access Points within radio range. Press any key to stop the test.
This test provides a continuous readout of radio signal parameters between the Access Point and the bridge to which it is associated. Display parameters include signal strength, signal quality, number of hops to the backbone, load, and the number of clients associated to the Access Point. Use the test to align directional antennas or to optimize bridge location and orientation.
Navigation: Main > Configuration > Radio > Linktests > Multicast
The time displays in milliseconds. Each packet contains the time it was sent. When a packet is received by the source, the time difference indicates the round-trip time. Longer times indicate full bandwidth of either the processor or the radio.
The signal strength and quality parameters report on the radio signal at the time the packets are received at each end. Signal strength and quality are expressed in decibels referenced to an input signal of one milliwatt of power (dBm) and as a percentage of full power.
The Unicast option tests the path between the bridge and any other Cisco Aironet node in the wired or radio network. The packets are sent with the same error recovery as normal user data, so round-trip times indicate the infrastructure throughput and congestion.
Navigation: Main > Configuration > Radio > Linktests > Unicast
The time displays in milliseconds. Each packet contains the time it was sent. When a packet is received by the source, the time difference indicates the round- trip time. Longer times indicate full bandwidth of either the processor or the radio.
The signal strength and quality parameters report on the radio signal at the time the packets are received at each end. Signal strength and quality are expressed in decibels referenced to an input signal of one milliwatt of power (dBm) and as a percentage of full power.
If the path to the target node was over the radio, the report displays the total number of radio retries necessary to complete the test. A large number of retries indicates radio interference problems.
The Remote option runs a multicast link test between a remote bridge node associated in the infrastructure and its parent Access Point. You will be prompted for the address of the bridge node in order to make a broadcast request. The two remote nodes will run the link test and return the results, which display to the operator locally.
Navigation: Main > Configuration > Radio > Linktests > Remote
The Destination option indicates the target node address for the link test. You may type an infrastructure address or the string any. If you select any, the bridge directs the test to the Access Point to which the unit is associated. If you type an infrastructure address, it may only be used for the remote or unicast link tests.
The Size and Count options indicate the size and number of packets to be sent. The default values are 100 packets of 512 bytes each. Both the size and the count can be changed. The packet size can be set from 30 to 1450 bytes and the count of the number of packets to transmit can be set from 1 to 999 packets.
When running the link test, use the highest data bit rate possible to test the reliability of your data bit rate and frequency combination. The more packets you send and the larger the packet size, the more accurate the test.
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Note Multiple large packets increase test time. |
The Rate option allows you to force the link test to transmit packets at only one of the allowed rates, or you can select auto to use the highest allowed rate and rate-shift if necessary.
During an automatic link test, the three indicators on the bridge turn green in a cyclic pattern to indicate that a test is in progress. At the end of the test, the indicators are set to a steady pattern for 4 seconds to indicate the test results. The particular pattern that is displayed depends on the percentage of packets lost during the test as shown in Table 4-1.
Radio | Status | Ethernet | % of Packets Lost | Quality |
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The Autotest procedure helps determine the placement of bridges. For example, at each prospective location, an installer could cycle the power on the bridge and watch the indicator displays for the results of the link test. As the test begins to fail, the installer could determine the radio range to the infrastructure and adjust the location accordingly.
The Continuous option continuously repeats the link tests. If the value for the parameter is zero, the tests are not repeated; otherwise, the value determines the delay (in seconds) between tests.
The extended radio parameters are not normally modified, but some may have to be changed when certain situations arise.
Navigation: Main > Configuration > Radio > Extended
The Parentid parameter controls the address with which the bridge associates. If the value is set to any, the bridge associates with its best choice of parent based on signal quality and load. If the value is set to a specified infrastructure address, the bridge only associates to the Access Point assigned that address.
If the Parent_timeout option is set to on, the lost bridge makes only one attempt to re-associate to the parent Access Point. If the bridge does not find the requested parent, the bridge stops searching and associates to the best Access Point. If the Parent_timeout is set to off, the bridge only attempts to re-associate to the parent Access Point.
The Count_retry option establishes a particular level of radio performance by controlling the RF packet retry level. If the retry count is reached, the retry process on this particular packet is stopped. The bridge is disassociated from the Access Point and then begins scanning for a new parent Access Point.
The Count_retry range is 8 to 64. The default setting is 64. Reduce the retry count field if the bridge is mobile and you want to change from Access Point to Access Point very quickly after moving out of range. In non-mobile applications, lowering this parameter could help if there were sources of temporary interference. It would cause the bridge to retry at a later time.
If there has been no traffic between the bridge and its parent for the specified amount of time, the bridge sends a special refresh packet to ensure that the parent is still reachable. The value may be set from 5 to 150 tenths of a second. Leave the default value unless the bridge is mobile and needs to quickly verify that it has moved out of range (faster than once every 15 seconds).
The Diversity option is not available for bridge models with one captured antenna. For bridge models with two removable antennas, the default setting is on.
The Power parameter reduces the power level of the radio transmitter down from the maximum allowed by the regulatory commission.
The Fragment parameter determines the largest packet size that may be transmitted. Packets that are larger than this size will be broken into pieces that are transmitted separately and rebuilt on the receiving side.
If there is a lot of radio interference or collisions with other nodes, the smaller lost packets can be retried faster and with less impact on the airwaves. The disadvantage is that if there is limited interference, long packets take more time to transmit due to the extra packet overhead and acknowledgments for the fragments.
Set the fragment size between 256 and 2048 bytes. Default fragment size is 2048.
The Options feature is reserved for future system improvements.
Posted: Wed Aug 9 14:16:38 PDT 2000
Copyright 1989-2000©Cisco Systems Inc.