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802.11 Protocol Overview

If the 802.11b verses 802.11a and 802.11g dialog is confusing you, do not worry, it is confusing. This page as an overview of what it all means for those who are curious or interested. If you are not interested and simply want to know what to buy, we recommend a radio that supports the 802.11n (draft 2) protocol. Check out the card list from the Cisco Systems site.

The Basics:

In order for two devices to communicate, their radios must speak the same language or protocol. WiFi radios can use a variety of IEEE protocols to communicate, known as 802.11b, 802.11g, and 802.11a, and 802.11n. The 802.11b protocol operates in the 2.4 Ghz frequency range and has a maximum speed of 11Mbps. The 802.11g protocol operates in the 2.4 Ghz frequency range and has a maximum speed of 54Mbps. The 802.11a protocol operates in the 5.8 Ghz frequency range and has a maximum speed of 54Mbps. The 802.11n protocol can work in both the 2.4 Ghz and the 5.8 Ghz frequency ranges.

The Details:

Some devices have multiple radios or radios that speak more than one protocol. In order for two devices to communicate they must agree on a protocol to use based on the capabilities of *both* devices. That is, they must both be speaking the same protocol in order to communicate. The table below shows a chart of the different combinations of protocols used by client and access point devices deployed on campus.

Access Point Protocol Capabilities
  b/g a/b/g a/b/g/n
b 11 11 11
b/g 54(g) 54(g) 54(g)
a 0* 54(a) 54(a)
a/b 11 54(a) 54(a)
a/b/g 54(g) 54(a or g) 54(a or g)
a/b/g/n 54(g) 54(a or g) 300**

The top row of the table above shows the combinations of the protocols that different access point radios on campus use. The left column has five combinations of protocols which reflects the variety that client devices might posess.

Client radios choose the protocol they wish to use based on the capabilities of the client and the access points that are in range of the client, as well as the signal strength and noise. The chart represents the way most radio drivers are configured to choose a protocol, and the maximum speed in Mbps that the radio can operate. Actual speeds will be lower due to the following variables:

  • Protocol overhead
  • Client's distance to an access point
  • Volume of usage on an access point
  • Radio interference and barriers

* 802.11a only devices will not get a signal in some areas of campus, including all outdoor areas. An 802.11a only radio is not recommended for this reason.

** 802.11n data rates are only available using WPA authentication.

802.11b Low Data Rates Disabled

We have disabled the lowest data rates (1 & 2 Mbps) supported by the 802.11b protocol on all indoor access points. This was done as a performance improvement to prevent clients from remaining associated at lower data rates when there is higher quality coverage by an access point available. Clients associating at low data rates have the ability to greatly reduce the performance of all users and access points within range of their radio. While nearly all users will see improved performance because of this change, there are a few clients which are only capable of associating at these low rates. These clients, such as the Nintendo Wii, will not be able to associate with campus access points and should look for alternatives such as wired ethernet.


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This page last modified: Feb 13, 2017 at 03:48 PM EST
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