Question

1. In the IEEE 802.3 Ethernet standard, the MAC layer represents the physical layer specification, while the LLC layer describes the data link layer specification.

True

False

2. What is true regarding the IEEE 802.11 WLAN standard?

a. to avoid the crowded ISM spectrum, 802.11 requires the use of licensed frequency channels

b. both centralized and decentralized access methods are available in the 802.11 standard

c. WLAN communications can only be accomplished using an AP

d. there is no method available to prevent data collisions over unguided medium

3. For IEEE 802.11 WLANs, what is a reason why DSSS (direct sequence spread spectrum) and OFDM (orthogonal frequency division multiplexing) are used?

a. FDM is preferred, but DSSS and OFDM are cheaper and easier to implement

b. OFDM is resilient in RFI environments and is spectrally efficient

c. the use of PN codes with DSSS means that a centralized network is established that is free from data collisions

d. Neither DSSS nor OFDM are used in WLANs

4. IEEE 802.15 Bluetooth is a standard that implements a centralized access method.

True

False

Answer 1

Solution:   

1. In the IEEE 802.3 Ethernet standard, the MAC layer represents the physical layer specification, while the LLC layer describes the data link layer specification.

a) True

b) False

Explanation: MAC layer and LLC layer are part of Data Link Layer (layer 2).

Physical layer is different from MAC. It is layer 1.

IEEE 802.3 defines standard for MAC layer.

2. What is true regarding the IEEE 802.11 WLAN standard?

a) to avoid the crowded ISM spectrum, 802.11 requires the use of licensed frequency channels

b) both centralized and decentralized access methods are available in the 802.11 standard

c) WLAN communications can only be accomplished using an AP

d) there is no method available to prevent data collisions over unguided medium

Explanation :

a) False. In the US, 802.11a and 802.11g devices may be operated without a license.

b) Channel access in PCF (Point coordination function) mode is centralized. Channel access in DCF (Distributed Coordination Function (DCF) is decentralized. It uses CSMA/CD protocol. IEEE 802.3 supports both PCF and DCF. Hence option b is true.

c) False. Wireless ad-hoc networks communicate without using access points (AP)

d) False. Data collision is prevented using an algorithm known as Multiple Access with Collision Avoidance (MACA)

3. For IEEE 802.11 WLANs, what is a reason why DSSS (direct sequence spread spectrum) and OFDM (orthogonal frequency division multiplexing) are used?

a) FDM is preferred, but DSSS and OFDM are cheaper and easier to implement

b) OFDM is resilient in RFI environments and is spectrally efficient

c) the use of PN codes with DSSS means that a centralized network is established that is free from data collisions

d) Neither DSSS nor OFDM are used in WLANs

Explanation :

DSSS and OFDM are used to reduce interference. All other options are incorrect.

4. IEEE 802.15 Bluetooth is a standard that implements a centralized access method.

  a) True

b) False

Explanation: Bluetooth uses a master/slave architecture and it is centralized access method.