KC 11
How fast is that wireless technology? Use the pulldown menus below to match the approximate transmission rate with the the wireless technology that achieves that rate. Of course, sender/receiver distance, noise and other factors determine actual transmission speed, so "your mileage may vary" (YMMV). 802.11 ax 5G cellular 4G LTE 802.11 ac 4G LTE 802.11 g Bluetooth
14 Gbps 10 Gbps 3.5 Gbps hundreds of Mbps 54 Mbps 2 Mbps
What is the purpose of RTS (request to send) and CTS (clear to send) frames in WiFi (802.11) networks? Select one or more of the answers below. [Hint: check two answers below].
A CTS that is sent allows a receiver to force other nodes (other than the intended sender who sent the RTS) to refrain from transmitting, thus allowing the sender who sent the RTS to then transmit a frame with less likelihood of a collision. RTC/CTS frames helps nodes in a wireless network mitigate the effects of the hidden terminal problem.
What is the purpose of a beacon frame in WiFi (802.11) networks?
A beacon frame allows an access point to advertise its existence, and the frequency channel it is operating on, to devices that want to connect to an access point.
In 4G LTE cellular systems, what is an International Mobile SubscriberIdentity (IMSI)?
Assigned by a mobile carrier network to a device, when the device attaches to the radio access network, serving a similar link-layer role as MAC addresses in a wired network.
Why does the WiFi (802.11) link-layer frame have three addresses? [Note: WiFi actually has four MAC addresses in the frame, but we're only focusing here on the three widely used ones].
Because both the access point that will relay this frame to the intended link-layer receiving host or router interface, as well as that intended destination host or router interface need to be specified.
Why are link-layer ACKs used in WiFi (802.11) networks? [Hint: check two of the boxes below].
Because of the hidden terminal problem, a node that is transmitting and hears no collisions still doesn't know if there was a collision at the receiver. Wireless links are noisier than wired links, and so bit level errors are more likely to occur, making link-layer error recovery more valuable that in less-noisy wired links.
Which of the following statement are true about the Bluetooth protocol?
Bluetooth uses TDM, FDM, polling, error detection and correction, and has sleep modes to conserve device power. Pretty sophisticated for a consumer technology!
Which of the following statements is true about the link-level service of reliable data transfer (using ACKs) in WiFi (802.11) networks and in 4G cellular networks?
Both WiFi and LTE provide link-level reliable data transfer.
What is meant when we say that a network of devices is operating in "infrastructure mode"?
Devices communicate with each other and to the larger outside world via a base station (also known as an access point).
Which of the following statements about the characteristics of wireless links are true?
Path loss refers to the decrease in the strength of a radio signal as it propagates through space. The bit error rate (BER) of a wireless channel increases as the signal-to-noise ratio (SNR) increases. ? The "hidden terminal problem" happens when A sends to B over a wireless channel, and an observer, C (that can be even closer to A than B), does not detect/receive A's transmission because of physical obstacles in the path between A and C. Multipath propagation occurs when portions of the electromagnetic wave reflect off objects and the ground taking paths of different lengths between the sender and a receiver, and thus arriving at the receiver at slightly different points in time.
Which of the following statement are true about the 802.11 (WiFi) MAC protocol?
The 802.11 MAC protocol performs collision avoidance. That is, an 802.11 sender and receiver can use approaches such as RTS/CTS, inter-frame spacing, and explicit acknowledgments to try avoid, rather than detect, colliding transmissions from another node.
