Understanding Radio Profiles
Radio profiles contain configuration information for radios. A single Radio profile can be applied to many radios that share a common configuration. This topic describes Radio profile configuration concepts. To create, assign, or delete a Radio profile, see Creating and Managing a Radio Profile.
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All wireless radios continually scan for other RF transmitters. While 802.11b/g radios scan in the 2.4-GHz to 2.4835-GHz spectrum, 802.11a radios scan in the 5.15-GHz to 5.85-GHz spectrum. There are two scanning methods, passive scanning and active scanning. By default, radios perform both types of scans on all channels allowed by the country of operation. (The country of operation is the regulatory domain set during initial access point deployment.)
While both types of scanning are on by default, active scanning is done only on channels on which local government regulations allow it to transmit. Channels that are not authorized for unlicensed use and channels that require radar detection with dynamic frequency selection (DFS) are excluded from active scanning.
For more information, about scanning see Understanding Wireless Scanning.
The electromagnetic spectrum includes all possible frequencies of electromagnetic radiation. Wireless communication uses unlicensed radio bands where different types of devices (microwave ovens, cordless phones, video surveillance cameras for example) might emit radio signals that interfere with Wi-Fi service. Spectral analysis detects and reports on radio transmissions in the frequency bands used by Wi-Fi equipment. For more information, about scanning see Understanding Wireless Scanning and Monitoring the RF Spectrum of a Radio.
Dynamic Frequency Selection (DFS) Channels
The regulatory bodies of most countries now allow many 5-GHz (802.11a) channels that are assigned for use by radar systems to be used for by 802.11 wireless networking, provided there is no radar operating in the vicinity of the wireless network deployment. To use these channels, the wireless access point must implement radar detection and immediately vacate any channel on which radar is active. This requirement is referred to as Dynamic Frequency Selection (DFS). To accomplish this, a DFS mechanism was created to have unlicensed devices detect the presence of a radar system on the device channel and, if the level of the radar is above a certain threshold, vacate that channel and select an alternate channel.
When you deploy an access point, you must configure the correct country of operation to ensure compliance with local government regulations. Failing to do so might cause harmful interference to other systems. In certain countries, such as the United States, access point models are country-specific and will not operate if you configure a different country of operation. Since the corresponding DFS requirements for each available country of operation are programmed into the access point, you do not have to specifically configure the DFS channels. All you need to do is enable DFS in a Radio profile and the appropriate channel avoidance will be implemented.
RFID Asset Tracking
RFID stands for Radio-Frequency Identification. RFID tracking devices consist of transponders, capable of carrying as much as 2,000 bytes of data, with an attached antenna. These devices provide a unique identifier for the object they are attached to.
There are various kinds of RFID, such as the card readers on the doors at companies—the Juniper Networks wireless system does not support those kinds of RFIDs. Juniper Networks access points are capable of reading 802.11 RFID tags that chirp short 802.11 messages periodically, for example AeroScout tags. Because the RFID tag must be scanned by an access point radio to retrieve the identifying information, you must configure RFID scanning in a Radio profile. Then the information can be scanned by access points in that Radio profile and fed to a transceiver to interpret the information.
RFID tags replace traditional barcode solutions for inventory and tracking, and provide the following advantages:
You can track items without climbing ladders, crawling under furniture, or having to be in the direct line of sight of tracked items.
Most things can be tracked, including people.
The time it takes to conduct a complete inventory is significantly reduced, while the accuracy of the data is greatly increased.
The time it takes to locate an asset, for example an expensive medical device, is greatly reduced.
WMM Power Save
The receiver portion of an 802.11 radio consumes considerable battery power if it is left on all the time. WMM Power Save enables mobile devices to minimize the length of time a receiver is fully powered on, thereby extending extend battery life. With WMM Power Save, the same amount of data can be transmitted in fewer frames in a shorter time, while allowing the Wi-Fi device to preserve power in a low-power, dozing state in between transmissions. To take advantage of WMM Power Save functionality, both the Wi-Fi client and access point must use WMM Power Save. In addition, the applications used also need to support WMM Power Save to inform the client of the requirements of the traffic they generate. WMM is a required feature for 802.11n capable devices—almost all modern Wi-Fi devices support it.
For more information about WMM Power Save, see Understanding WMM Power Save and WLAN Client Battery Life.
Countermeasures are actions used by controllers and access points to thwart rogue devices attempting to use your network. You can also apply countermeasures to suspect devices. Countermeasures are enabled in a Radio profile and take place automatically when an access point discovers a device.
Countermeasures cannot be configured with Network Director Release 1.0. Use the MSS CLI to configure countermeasures.
Limiting Client Power
In Radio profiles, you can limit the maximum power level allowed on clients that associate to your access points. Then, when a client associates with an access point, the access point transmits the maximum power level setting allowed in that country to the client. Clients automatically configure their power to match the access point requirements.
802.11n Channel Width
802.11n channels can be either 40 MHz or 20 MHz wide if you use the 5-GHz radio band. See Understanding Wireless Radio Channels for more information and for instructions to indicate a 40 MHz channel width.
Automatic Channel Tuning
Channel auto-tuning automatically makes channel tuning decisions for access point radios based on the RF data gathered by access points. Channel auto-tuning is configured in a Radio profile and constantly operates on all access point radios by default. For more information about automatic channel tuning, see Understanding Adaptive Channel Planner.
Automatic Power Tuning
The amount of power an access point uses affects the coverage area of the access point. The higher the power level, the larger the coverage area of an access point. Usually, you want your access points to cover all areas with minimal overlap. With automatic power tuning, which is controlled by the Radio profile, access points adjust the power levels of radios automatically, based on the power levels of all neighboring access points. For more information about automatic power tuning, see Understanding Auto Tune Power Policy for Wireless Radios.
IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN) computer communication in the 2.4-GHz and 5-GHz frequency bands. For more information about IEEE 802.11, see Understanding the IEEE 802.11 Standard for Wireless Networks.
Long and Short Preamble Length
The preamble is part of the IEEE 802.11b physical layer specification. Specifically, the preamble is a data header section that contains information the access point and clients need when both sending and receiving packets.
In general, use the short preamble type in high network traffic areas, and use the long preamble to provide more reliable communication in noisy (high interference) networks.
Note that all 802.11b devices must support the long preamble format, but can also optionally support the short preamble. Because the short preamble is default, if an 802.11b device has trouble communicating with other 802.11b devices, try using the long preamble.