IEEE 802.11 for WLAN

IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base version of the standard IEEE 802.11-2007 has had subsequent amendments. These standards provide the basis for wireless network products using the Wi-Fi brand.The 802.11 family consists of a series of over-the-air modulation techniques that use the same basic protocol. The most popular are those defined by the 802.11b and 802.11g protocols, which are amendments to the original standard.
802.11 and 802.11x refers to a family of specifications developed by the IEEE for wireless LAN (WLAN) technology. 802.11 specifies an over-the-air interface between a wireless client and a base station or between two wireless clients. 802.11 technology has its origins in a 1985 ruling by the U.S. Federal Communications Commission that released the ISM band for unlicensed use.Vic Hayes, who held the chair of IEEE 802.11 for 10 years and has been called the “father of Wi-Fi” was involved in designing the initial 802.11b and 802.11a standards within the IEEE.

There are several specifications in the 802.11 family:

  • 802.11 — applies to wireless LANs and provides 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS).
  • 802.11a — an extension to 802.11 that applies to wireless LANs and provides up to 54-Mbps in the 5GHz band. 802.11a uses an orthogonal frequency division multiplexing encoding scheme rather than FHSS or DSSS.
  • 802.11b (also referred to as 802.11 High Rate or Wi-Fi) — an extension to 802.11 that applies to wireless LANS and provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1-Mbps) in the 2.4 GHz band. 802.11b uses only DSSS. 802.11b was a 1999 ratification to the original 802.11 standard, allowing wireless functionality comparable to Ethernet.
  • 802.11e — a wireless draft standard that defines the Quality of Service (QoS) support for LANs, and is an enhancement to the 802.11a and 802.11b wireless LAN (WLAN) specifications. 802.11e adds QoS features and multimedia support to the existing IEEE 802.11b and IEEE 802.11a wireless standards, while maintaining full backward compatibility with these standards.
  • 802.11g — applies to wireless LANs and is used for transmission over short distances at up to 54-Mbps in the 2.4 GHz bands.
  • 802.11n — 802.11n builds upon previous 802.11 standards by adding multiple-input multiple-output (MIMO). The additional transmitter and receiver antennas allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity through coding schemes like Alamouti coding. The real speed would be 100 Mbit/s (even 250 Mbit/s in PHY level), and so up to 4-5 times faster than 802.11g.
  • 802.11r –  802.11r, also called Fast Basic Service Set (BSS) Transition, supports VoWi-Fi handoff between access points to enable VoIP roaming on a Wi-Fi network with 802.1X authentication.
  • 802.1X — Not to be confused with 802.11x (which is the term used to describe the family of 802.11 standards) 802.1X is an IEEE standard for port-based Network Access Control that allows network administrators to restricted use of IEEE 802 LAN service access points to secure communication between authenticated and authorized devices.
802.11 network standards
802.11
protocol
Release Freq.
(GHz)
Bandwidth
(MHz)
Data rate per stream
(Mbit/s)
Allowable
MIMO streams
Modulation Approximate indoor range Approximate outdoor range
(m) (ft) (m) (ft)
Jun 1997 2.4 20 1, 2 1 DSSS, FHSS 20 66 100 330
a Sep 1999 5 20 6, 9, 12, 18, 24, 36, 48, 54 1 OFDM 35 115 120 390
3.7[A] 5,000 16,000[A]
b Sep 1999 2.4 20 5.5, 11 1 DSSS 35 115 140 460
g Jun 2003 2.4 20 6, 9, 12, 18, 24, 36, 48, 54 1 OFDM, DSSS 38 125 140 460
n Oct 2009 2.4/5 20 7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2[B] 4 OFDM 70 230 250 820[8]
40 15, 30, 45, 60, 90, 120, 135, 150[B] 70 230 250 820[8]
ac (DRAFT) Nov. 2011 5 80 433, 867 8
160 867, 1.73 Gbit/s, 3.47 Gbit/s, 6.93 Gbit/s

Current 802.11 standards define “frame” types for use in transmission of data as well as management and control of wireless links.

Frames are divided into very specific and standardized sections. Each frame consists of a MAC header, payload and frame check sequence (FCS). Some frames may not have the payload. The first two bytes of the MAC header form a frame control field specifying the form and function of the frame. The frame control field is further subdivided into the following sub-fields:

  • Protocol Version: two bits representing the protocol version. Currently used protocol version is zero. Other values are reserved for future use.
  • Type: two bits identifying the type of WLAN frame. Control, Data and Management are various frame types defined in IEEE 802.11.
  • Sub Type: Four bits providing addition discrimination between frames. Type and Sub type together to identify the exact frame.
  • ToDS and FromDS: Each is one bit in size. They indicate whether a data frame is headed for a distribution system. Control and management frames set these values to zero. All the data frames will have one of these bits set. However communication within an IBSS network always set these bits to zero.
  • More Fragments: The More Fragments bit is set when a packet is divided into multiple frames for transmission. Every frame except the last frame of a packet will have this bit set.
  • Retry: Sometimes frames require retransmission, and for this there is a Retry bit which is set to one when a frame is resent. This aids in the elimination of duplicate frames.
  • Power Management: This bit indicates the power management state of the sender after the completion of a frame exchange. Access points are required to manage the connection and will never set the power saver bit.
  • More Data: The More Data bit is used to buffer frames received in a distributed system. The access point uses this bit to facilitate stations in power saver mode. It indicates that at least one frame is available and addresses all stations connected.
  • WEP: The WEP bit is modified after processing a frame. It is toggled to one after a frame has been decrypted or if no encryption is set it will have already been one.
  • Order: This bit is only set when the “strict ordering” delivery method is employed. Frames and fragments are not always sent in order as it causes a transmission performance penalty.

source: wikipedia

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Posted on March 15, 2012, in System Networking and tagged , , , . Bookmark the permalink. Leave a comment.

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