Lecture in Wireless LANs

(Last Updated On: December 8, 2017)
Review of Wireless LANs

Definition of Terms

  • The IEEE 802.11 standard for wireless LANs defines two services: basic service set (BSS) and extended service set (ESS). An ESS consists of two or more BSSs; each BSS must have an access point (AP).
  • A BSS without an AP is called an ad hoc network; a BSS with an AP is called an infrastructure network.
  • The basic service set (BSS) is the building block of a wireless LAN.
  • An extended service set (ESS) is made up of two or more BSSs with APs. In this case, the BSSs are connected through a distribution system, which is usually a wired LAN.
  • The physical layer methods used by wireless LANs include frequency-hopping spread spectrum (FHSS), direct sequence spread spectrum (DSSS), orthogonal frequency-division multiplexing (OFDM), and high-rate direct sequence spread spectrum (HR-DSSS).
  • FHSS is a signal generation method in which repeated sequences of carrier frequencies are used for protection against hackers.
  • One bit is replaced by a chip code in DSSS.
  • OFDM specifies that one source must use all the channels of the bandwidth.
  • The orthogonal frequency-division multiplexing (OFDM) method for signal generation in a 5-GHz ISM band is similar to frequency division multiplexing (FDM), with one major difference: All the subbands are used by one source at a given time. Sources contend with one another at the data link layer for access.
  • HR-DSSS is DSSS with an encoding method called complementary code keying (CCK).
  • The wireless LAN access method is CSMA/CA.
  • The access method used in the distributed coordination function (OCF) MAC sublayer is CSMAICA.
  • The access method used in the point coordination function (PCF) MAC sublayer is polling.
  • The network allocation vector (NAV) is a timer used for collision avoidance.
  • Network Allocation Vector (NAV) forces other stations to defer sending their data if one station acquires access. In other words, it provides the collision avoidance aspect. When a station sends an RTS frame, it includes the duration of time that it needs to occupy the channel. The stations that are affected by this transmission create a timer called a NAV.
  • The MAC layer frame has nine fields. The addressing mechanism can include up to four addresses.
  • Wireless LANs use management frames, control frames, and data frames.
  • IEEE 802.11 defines several physical layers, with different data rates and modulating techniques.
  • The CTS frame in CSMA/CA handshake can prevent collision from a hidden station.
  • Bluetooth is a wireless LAN technology that connects devices (called gadgets) in a small area.
  • A Bluetooth network is called a piconet. Multiple piconets form a network called a scatternet.
  • A Bluetooth network consists of one primary device and up to seven secondary devices.
  • The Bluetooth radio layer performs functions similar to those in the Internet model’s physcial layer.
  • The Bluetooth baseband layer performs functions similar to those in the Internet model’s MAC sublayer.
  • A Bluetooth network consists of one master device and up to seven slave devices.
  • A Bluetooth frame consists of data as well as hopping and control mechanisms. A frame is one, three, or five slots in length with each slot equal to 625 µs.
  • A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneously.
  • In multiple-secondary communication, the primary sends on the even-numbered slots; the secondary sends on the oddnumbered slots.

Basic service sets (BSSs)

Basic service sets (BSSs)

Extended service sets (ESSs)

Extended service sets (ESSs)

CSMA/CA flowchart

CSMA/CA flowchart

Physical layers

Physical layers

Industrial, scientific, and medical (ISM) band

Industrial, scientific, and medical (ISM) band

Piconet

Piconet

Scatternet

Scatternet

Bluetooth layers

Bluetooth layers

Layer comparison of Bluetooth and the Internet model

  • Radio layer → Internet physical layer
  • Baseband layer → MAC sublayer of Internet data link layer
  • L2CAP layer → LLC sublayer of Internet data link layer

Note: You can proceed to take the multiple choice exam regarding this topic. Wireless LANs – Set 1 MCQs

List of Data Communications Lectures

credit: Behrouz A. Forouzan©2014 www.PinoyBIX.org
Lecture in Wireless LANs
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