Chapter 14 Wireless LANs

Chapter 14 of Data Communications and Networking by Behrouz A. Forouzan, titled "Wireless LANs", focuses on the technologies, standards, and functionalities of wireless LANs. Here are detailed notes from the chapter:

1. Introduction to Wireless LANs

• Wireless LANs (WLANs) are increasingly common in various environments, including campuses, offices, and public spaces.

• Two major technologies for WLANs are covered in this chapter: IEEE 802.11 (also called wireless Ethernet) and Bluetooth, a technology for small wireless LANs.

2. IEEE 802.11

• IEEE 802.11 is the primary standard for wireless LANs, covering both the physical and data link layers.

2.1. Architecture

• The IEEE 802.11 standard defines two types of services:

  1. Basic Service Set (BSS):

     • Consists of stationary or mobile wireless stations and an optional access point (AP).

     • Ad hoc Network: A BSS without an AP. Stations communicate directly with each other.

     • Infrastructure Network: A BSS with an AP, where the AP acts as a hub for communication between stations.

  2. Extended Service Set (ESS):

     • Consists of two or more BSSs connected via a distribution system (usually a wired LAN).

     • Stations in an ESS can communicate through APs connected to the distribution system.

2.2. MAC Sublayer

• The MAC layer controls how stations access the shared medium. IEEE 802.11 defines two MAC protocols:

  1. Distributed Coordination Function (DCF):

     • Uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) for accessing the medium.

     • Unlike CSMA/CD in wired LANs, WLANs use CSMA/CA due to the difficulty of detecting collisions in a wireless environment.

  2. Point Coordination Function (PCF):

     • Uses polling to control access to the medium. The AP polls stations to give them permission to send data, avoiding collisions.

2.3. Addressing Mechanism

• IEEE 802.11 uses a flexible addressing mechanism with up to four addresses:

  • Address 1: Destination station or AP.

  • Address 2: Source station.

  • Address 3: Intermediate AP.

  • Address 4: Used only when communicating across multiple APs.

2.4. Frame Types

• Management Frames: Used for connection establishment and maintenance between stations and APs.

• Control Frames: Help in accessing the channel and ensuring reliable communication.

• Data Frames: Carry the actual data being transmitted.

2.5. Physical Layer

• The IEEE 802.11 standard supports several physical layers, each with different data rates and modulation techniques:

  • 802.11a: Operates in the 5 GHz band using OFDM (Orthogonal Frequency-Division Multiplexing) with data rates up to 54 Mbps.

  • 802.11b: Operates in the 2.4 GHz band using DSSS (Direct Sequence Spread Spectrum) with data rates up to 11 Mbps.

  • 802.11g: Similar to 802.11a but operates in the 2.4 GHz band and supports backward compatibility with 802.11b.

3. Bluetooth

• Bluetooth is a short-range wireless technology designed for communication between devices (e.g., phones, computers, peripherals).

• Bluetooth networks are ad hoc, meaning devices spontaneously form networks called piconets.

3.1. Piconet and Scatternet

• A piconet consists of a master device and up to seven active slave devices.

• Multiple piconets can form a scatternet, where devices can participate in multiple piconets simultaneously.

3.2. Bluetooth Layers

• Bluetooth has its own set of layers, with the Logical Link Control and Adaptation Protocol (L2CAP) responsible for multiplexing, segmentation, reassembly, and quality of service (QoS).

4. Key Features of WLANs

• Mobility: Stations in WLANs can move between networks, with three types of mobility defined:

  1. No-transition mobility: Stationary or moving within a single BSS.

  2. BSS-transition mobility: Moving between BSSs within an ESS.

  3. ESS-transition mobility: Moving between ESSs, though IEEE 802.11 does not guarantee continuous communication during such moves.

5. Summary

• The IEEE 802.11 standard provides the foundation for modern wireless LANs, offering flexibility in addressing, medium access, and physical layer configurations.

• Bluetooth serves as a complementary technology, offering short-range communication solutions for connecting small devices.

These detailed notes provide an in-depth understanding of the technologies and functionalities behind wireless LANs as described in Chapter 14 of the book【7:0†source】【7:1†source】【7:4†source】.