Questions and Answers
What is the main focus of the first section of Chapter 15?
Comparing wired and wireless networks
Which technology is discussed as a personal area network in Chapter 15?
Bluetooth
In Chapter 15, what is the main topic of discussion regarding the IEEE 802.11 Project?
Architecture of the LAN
According to Chapter 15, where can wireless LANs typically be found?
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What is one of the unique features of wireless LANs highlighted in Chapter 15?
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Which section of Chapter 15 briefly describes and compares different protocol layers?
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What does the term WiFi refer to in wireless LAN?
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What is a BSS without an AP called according to the text?
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Which IEEE 802.11 station type can move from one ESS to another within the network?
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What does the MAC sublayer DCF stand for in IEEE 802.11?
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What is depicted in Figure 15.4 of the standard?
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Which types of services are defined in the IEEE 802.11 standard architecture?
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What is a key characteristic of wireless LANs that may not apply to wired LANs?
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Why does the CSMA/CD algorithm not work in wireless LANs?
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Which IEEE standard is specifically designed for wireless LANs?
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What prevents collision detection in wireless LANs?
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Which characteristic is negligible or ignored in wired LANs but significant in wireless LANs?
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What is one factor that makes CSMA/CD ineffective in wireless LANs?
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Study Notes
Wireless LANs
- Wireless communication is one of the fastest-growing technologies with increasing demand for connecting devices without cables.
- Wireless LANs can be found in college campuses, office buildings, and public areas.
Comparison of Wired and Wireless LANs
- Wired LANs have a physical backbone, whereas wireless LANs do not.
- Wired LANs use a wired medium, whereas wireless LANs use the air as the medium.
- In wired LANs, the connection is point-to-point, whereas in wireless LANs, the connection is point-to-multipoint.
Characteristics of Wireless LANs
- Attenuation: signal reduction with distance.
- Interference: signals from other devices can interfere with the wireless signal.
- Multipath Propagation: signals can arrive at the receiver via different paths.
- Error: bits can be altered during transmission.
Access Control in Wireless LANs
- CSMA/CD algorithm does not work in wireless LANs due to:
- Wireless hosts cannot send and receive at the same time.
- Hidden station problem prevents collision detection.
- Distance between stations can be great.
IEEE 802.11 Project
- IEEE 802.11 is a wireless LAN standard covering physical and data-link layers.
- Also known as wireless Ethernet or WiFi (in some countries).
Architecture of IEEE 802.11
- Defines two kinds of services: Basic Service Set (BSS) and Extended Service Set (ESS).
- BSS without an AP is called an ad hoc network; BSS with an AP is called an infrastructure network.
Station Types in IEEE 802.11
- Station with no-transition mobility: stationary or moving only inside a BSS.
- Station with BSS-transition mobility: can move from one BSS to another within one ESS.
- Station with ESS-transition mobility: can move from one ESS to another.
MAC Sublayer in IEEE 802.11
- Defines two MAC sublayers: Distributed Coordination Function (DCF) and Point Coordination Function (PCF).
- CSMA/CA (Collision Avoidance) is used to avoid collisions.
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