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Revision 16 as of 2005-01-25 20:21:52
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Revision 17 as of 2005-03-13 22:10:44
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IEEE 802.11 sends network packets from the sending host to one (["Unicast"]) or more (["Multicast"]/["Broadcast"]) receiving hosts.

Wi-Fi (WLAN, IEEE 802.11)

Wi-Fi, or IEEE 802.11, is the standard for wireless LANs, or WLANs. The abbreviation Wi-Fi stands for Wireless Fidelity, and resembles the Hi-Fi acronym. It represents a whole collection of protocols within the same family of Ethernet and Token Ring.

It is specified by [http://standards.ieee.org/getieee802/802.11.html various IEEE 802.11 specifications].

IEEE 802.11 sends network packets from the sending host to one (["Unicast"]) or more (["Multicast"]/["Broadcast"]) receiving hosts.

The 802.11 protocols specify a wireless shared network, which means that the maximum bandwidth is only available to one user at a time.

  • 802.11 (2MBit/s 2.4GHz) First generation of WLAN equipment; allows 1 and 2 Mbps.
  • 802.11b (11MBit/s 2.4GHz) Second generation of WLAN equipment, and the first generation to receive widespread use; allows 1, 2, 5.5 and 11 Mbps.
  • 802.11a (54MBit/s 5GHz)
  • 802.11g (54MBit/s 2.4GHz)

Some additional 802.11 standards are:

  • 802.11i (Security WPA1 and WPA2) No change to data rate. Improvement in security.
  • 802.11e (Quality of service)

History

XXX - add a brief description of 802.11 history

Protocol dependencies

  • 802.11 is the lowest software layer, so it only depends on hardware.

Example traffic

One ICMP Ping Request and response session from Station(STA1 to station(STA2) via Access point(AP)BR ICMP ECHO requestBR

  • ICMP Echo request (802.11 data packet with source STA1, Destination STA2, To DS bit set) This packet is transmitted from STA1 and recieved by APBR

  • ACK(802.11 control packet, dest STA1) This packet is transmitted by AP and recieved by STA1 BR

  • ICMP Echo request (802.11 data packet with source STA1, Destination STA2, From DS bit set) This packet is transmitted by AP and recieved by STA2.BR

  • ACK(802.11 control packet Dest AP) This packet is sent to AP by STA2 to acknowledge reciept of the Echo request packet.

ICMP ECHO ResponseBR

  • ICMP Echo response(802.11 data packet with source STA2, Destination STA1, To DS bit set) This packet is transmitted from STA2 and recieved by APBR

  • ACK(802.11 control packet, dest STA2) This packet is transmitted by AP and recieved by STA2BR

  • ICMP Echo response (802.11 data packet with source STA2, Destination STA1, From DS bit set) This packet is transmitted by AP and recieved by STA1.BR

  • ACK (802.11 control packet Dest AP) This packet is sent to AP by STA1 to acknowledge reciept of the Echo response packet.

XXX - Add example traffic here (as Ethereal screenshot).

Ethereal

The 802.11 dissector is fully functional.

Note that whether you can capture 802.11 traffic, whether the traffic will look like Ethernet traffic or 802.11 traffic, and whether you can capture non-data traffic (management frames, control frames) depend on the operating system on which you're capturing, the version of that operating you're using, the type of 802.11 network adapter you're using, and the version of the driver for that adapter, and the version of libpcap you're using. See [http://www.ethereal.com/media.html the Ethereal Supported Capture Media page] and [http://www.ethereal.com/faq.html#raw_80211_sniff the Ethereal FAQ item on capturing raw 802.11 traffic], and the FAQ items below it on 802.11 capture support on particular operating systems, for more details.

Preference Settings

(XXX add links to preference settings affecting how 802.11 is dissected).

Example capture file

XXX - Add a simple example capture file. Keep it short, it's also a good idea to gzip it to make it even smaller, as Ethereal can open gzipped files automatically.

Display Filter

A complete list of 802.11 display filter fields can be found in the [http://www.ethereal.com/docs/dfref/w/wlan.html display filter reference]

  • Show only the 802.11-based traffic:

     wlan 

    Show only the 802.11-based traffic to and from 802.11 MAC address 08:00:08:15:ca:fe:

     wlan.addr==08.00.08.15.ca.fe 

Capture Filter

  • Capture only the 802.11-based traffic to and from 802.11 MAC address 08:00:08:15:ca:fe:

     wlan host 08:00:08:15:ca:fe 

Note that older versions of libpcap won't support "wlan" - you might have to use "ether" or "link" on those versions. (Those versions won't support capturing raw 802.11 traffic, and might not support 802.11 capture at all.)

Discussion

Should most of the content be moved to the WLAN page, and only Wi-Fi described here (pointing to the WLAN page)? AFAIK, Wi-Fi is only a conformance issue, but not the protocol itself, or am I wrong here? - Ulf Lamping

As far as I can tell, WLAN is a concept and Wi-Fi refers to a given WLAN technology, namely based on the IEEE 802.11 protocol family. You'll find articles today about another technology, Wi-Max. I'd put pointers from the WLAN page to Wi-fi and to a new page Wi-Max (or WiMax). - Olivier Biot

Wi-Fi (last edited 2015-04-16 11:15:32 by EnderWiggin)