(Last Updated On: December 8, 2017)
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)
Extended service sets (ESSs)
Industrial, scientific, and medical (ISM) band
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