Networks Chapter 7 Review Questions – Study Guide, Revision Notes, and
Practice Questions
What are the differences between the following types of wireless channel impairments: path
loss, multipath propagation, interference from other sources? - ✔✔Path loss: decreasing in
strength of signal
- due to the attenuation of the electromagnetic signal when it travels through matter. or over
long distance
- receives weak signal instead of original signal
Multipath Propagation: receiver receives signal from multiple paths of different lengths
- occurs from portions of electromagnetic spectrum reflecting off objects and ground, taking
paths of different lengths between a sender and receiver
- results in blurring of the received signal
Interference: superposing of 2 or more signals with same frequency
- occurs when the other source is also transmitting in the same frequency range as the wireless
network.
- results in original transmitted signal merging with noise signal, so altered signal is received
What does it mean for a wireless network to be operating in "infrastructure mode"? If the
network is not in infrastructure mode, what mode of operation is it in, and what is the
difference between that mode of operation and infrastructure mode? - ✔✔- Infrastructure
Mode: each wireless host is connected to the larger network via a base station (access point).
Routing, address assignment, etc. are provided by the networks they are connected.
- If not operating in infrastructure mode, a network operates in ad-hoc mode
- Ad-hoc Mode: wireless hosts have no infrastructure with which to connect. In the absence of
such infrastructure, the hosts themselves must provide for services such as routing, address
assignment, DNS-like name translation, and more.
, What are the four types of wireless networks identified in our taxonomy in Section 7.1 ? - ✔✔-
Single hop, infrastructure-based
- Single hop, infrastructure-less
- Multi-hop, infrastructure-based
- Multi-hop, infrastructure-less
As a mobile node gets farther and farther away from a base station, what are two actions that a
base station could take to ensure that the loss probability of a transmitted frame does not
increase? - ✔✔- Increasing the transmission power
- Reducing the transmission rate
Describe the role of the beacon frames in 802.11. - ✔✔Beacon frames permit nearby wireless
stations to discover and identify the AP.
True or false: Before an 802.11 station transmits a data frame, it must first send an RTS frame
and receive a corresponding CTS frame. - ✔✔False
Why are acknowledgments used in 802.11 but not in wired Ethernet? - ✔✔- in wireless LAN,
the frame may not reach the destination season mainly due to high bit error rates of wireless
channels. The 802.11 MAC protocol uses ACK schemes to deal with it.
- In wired Ethernet, bit error rate is very negligible and transmission is very reliable, so ACKs are
not required.
True or false: Ethernet and 802.11 use the same frame structure. - ✔✔False
Describe how the RTS threshold works. - ✔✔- RTS threshold is the value that can be set by any
wireless station to stop using the RTS/CTS sequence for the packets that have frames shorter
than this value.
- This ensures that RTS/CTS mechanism is used only for large frames.
Practice Questions
What are the differences between the following types of wireless channel impairments: path
loss, multipath propagation, interference from other sources? - ✔✔Path loss: decreasing in
strength of signal
- due to the attenuation of the electromagnetic signal when it travels through matter. or over
long distance
- receives weak signal instead of original signal
Multipath Propagation: receiver receives signal from multiple paths of different lengths
- occurs from portions of electromagnetic spectrum reflecting off objects and ground, taking
paths of different lengths between a sender and receiver
- results in blurring of the received signal
Interference: superposing of 2 or more signals with same frequency
- occurs when the other source is also transmitting in the same frequency range as the wireless
network.
- results in original transmitted signal merging with noise signal, so altered signal is received
What does it mean for a wireless network to be operating in "infrastructure mode"? If the
network is not in infrastructure mode, what mode of operation is it in, and what is the
difference between that mode of operation and infrastructure mode? - ✔✔- Infrastructure
Mode: each wireless host is connected to the larger network via a base station (access point).
Routing, address assignment, etc. are provided by the networks they are connected.
- If not operating in infrastructure mode, a network operates in ad-hoc mode
- Ad-hoc Mode: wireless hosts have no infrastructure with which to connect. In the absence of
such infrastructure, the hosts themselves must provide for services such as routing, address
assignment, DNS-like name translation, and more.
, What are the four types of wireless networks identified in our taxonomy in Section 7.1 ? - ✔✔-
Single hop, infrastructure-based
- Single hop, infrastructure-less
- Multi-hop, infrastructure-based
- Multi-hop, infrastructure-less
As a mobile node gets farther and farther away from a base station, what are two actions that a
base station could take to ensure that the loss probability of a transmitted frame does not
increase? - ✔✔- Increasing the transmission power
- Reducing the transmission rate
Describe the role of the beacon frames in 802.11. - ✔✔Beacon frames permit nearby wireless
stations to discover and identify the AP.
True or false: Before an 802.11 station transmits a data frame, it must first send an RTS frame
and receive a corresponding CTS frame. - ✔✔False
Why are acknowledgments used in 802.11 but not in wired Ethernet? - ✔✔- in wireless LAN,
the frame may not reach the destination season mainly due to high bit error rates of wireless
channels. The 802.11 MAC protocol uses ACK schemes to deal with it.
- In wired Ethernet, bit error rate is very negligible and transmission is very reliable, so ACKs are
not required.
True or false: Ethernet and 802.11 use the same frame structure. - ✔✔False
Describe how the RTS threshold works. - ✔✔- RTS threshold is the value that can be set by any
wireless station to stop using the RTS/CTS sequence for the packets that have frames shorter
than this value.
- This ensures that RTS/CTS mechanism is used only for large frames.
