Basics of Wi-Fi Study Notes

By BYJU'S Exam Prep

Updated on: September 25th, 2023

WiFi stands for Wireless Fidelity. WiFi is the marketing name for IEEE standard 802.11. It is a standard for both Level 1 (physical) and Level 2 (data link) of a wireless data transmission protocol. It is primarily a local area networking (LAN) technology designed to provide in-building broadband coverage.

Current WiFi systems support a peak physical-layer data rate of 54 Mbps and typically provide indoor coverage over a distance of 100 feet.
WiFi offers remarkably higher peak data rates than do 3G systems, primarily since it operates over a larger 20 MHz bandwidth, but WiFi systems are not designed to support high-speed mobility.
WiFi interfaces are now also being built into a variety of devices, including personal data assistants (PDAs), cordless phones, cellular phones, cameras, and media players.
WiFi is Half Duplex: All WiFi networks are contention-based TDD systems, where the access point and the mobile stations all vie for use of the same channel. Because of the shared media operation, all Wi-Fi networks are half duplex.
There are equipment vendors who market Wi-Fi mesh configurations, but those implementations incorporate technologies that are not defined in the standards. Channel Bandwidth: The Wi-Fi standards define a fixed channel bandwidth of 25 MHz for 802.11b and 20 MHz for either 802.11a or g networks.
Wi-Fi – IEEE Standards: The 802.11 standard is defined through several specifications of WLANs. It defines an over-the-air interface between a wireless client and a base station or between two wireless clients.
  • 802.11 − This pertains 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 − This is an extension to 802.11 that pertains to wireless LANs and goes as fast as 54 Mbps in the 5-GHz band. 802.11a employs the orthogonal frequency division multiplexing (OFDM) encoding scheme as opposed to either FHSS or DSSS.
  • 802.11b − The 802.11 high rate WiFi is an extension to 802.11 that pertains to wireless LANs and yields a connection as fast as 11 Mbps transmission (with a fallback to 5.5, 2, and 1 Mbps depending on strength of signal) in the 2.4-GHz band. The 802.11b specification uses only DSSS. Note that 802.11b was actually an amendment to the original 802.11 standard added in 1999 to permit wireless functionality to be analogous to hard-wired Ethernet connections.
  • 802.11g − This pertains to wireless LANs and provides 20+ Mbps in the 2.4-GHz band.

Wi-Fi Concepts: There are two general types of Wi-Fi transmission: DCF (Distributed Coordination Function) and PCF (Point Coordination Function). DCF is Ethernet in the air. It employs a very similar packet structure, and many of the same concepts. There are two problems that make wireless different then wired.

  • The hidden substation problem.
  • High error rate.

These problems demand that a DCF Wi-Fi be a CSMA/CA network (Collision Avoidance) rather than a CSMA/CD network (Collision Detect). The results are the following protocol elements,

  • Positive Acknowledgement. Every packet sent is positively acknowledged by the receiver. The next packet is not sent until receiving a positive acknowledgement for the previous packet.
  • Channel clearing. A transmission begins with a RTS (Request to Send) and the destination or receiver responds with a CTS (Clear to Send). Then the data packets flow. For the channel is cleared by these two messages.
  • Channel reservation: Each packet has a NAV (Network Allocation Vector) containing a number X. The channel is reserved to the correspondents (the sender and receiver of this packet) for an additional X milliseconds after this packet. Once you have the channel, you can hold it with the NAV. The last ACK contains NAV zero, to immediately release the channel.


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