Knowledge checks

A beacon frame allows a mobile device to signal that it is ready to receive a frame.

A beacon frame allows a node with a directional antenna to aim the antenna towards the beacon point to maximize the quality of the send and receive signal.

A beacon frame allows a mobile node to determine the direction in which it should move in order to obtain an increasing signal strength.

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.

Hearing a receiver ACK, all other stations will stop transmitting.  This reduces collisions.

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.

The sender can used the differences in the signal strength in an ACK to infer whether the receiver is moving towards, or away from, the sender

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.

Because there may be two hosts or routers that are possible destinations for this link-layer frame and we need to identify which of these is the intended receiver.

Because the sender of this frame can be either the access point or a link-layer host or router interface, and we need to identify which of these two is the sender.

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.

RTC/CTS frames allow a sender to gather CTS frames from all other network nodes, so that it knows it can then send without collisions.

A CTS  allows a receiver to let the sender (who sent that RTS) know that it (the receiver) has enough buffers to hold a frame transmitted by that sender

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.

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.

The 802.11 MAC protocol performs carrier sensing.  That is, it listens before transmitting and will only transmit if the channel is sensed idle.

The 802.11 MAC protocol performs collision detection.  That is, an 802.11 sender will listen to the channel while it is transmitting, and stop transmitting when it detects a colliding transmission from another node.

Bluetooth uses TDM, FDM, polling, error detection and correction, and has sleep modes to conserve device power.  Pretty sophisticated for a consumer technology!

Bluetooth transmits all frames in the same frequency band.

Bluetooth networks have a centralized controller that serves to coordinate the various client devices in a Bluetooth piconet.

Bluetooth transmission rates can be as high as in WiFi networks.