(20 pts) Consider an ensemble of seven stations:

S_(1)-S_(7)

placed in a 3-dimensional space with widely\ varying geographic distances between them. Stations

S_(1)

and

S_(2)

are very closely spaced (with just\

4ft

separation) - and so are

S_(4)

and

S_(5)

. Some stations have a separation beyond the wireless range\ of

600ft

, while others are within the wireless range (though not close to each other). Out-of-rang\ situations arise because the signal strength decays exponentially w.r.t. the distance

d

from sender (i.e.,\ signal strength is proportional to

(1)/(d^(2))

). Consider a scenario of

S_(1)

trying to transmit its packet to

S_(2)

,\

S_(3)

trying to transmit its packet to

S_(4)

, and

S_(5)

trying to transmit its packet to

S_(6)

. Figure 3 illustrates\ the within-range and out-of-range stations in this scenario, which leads to some but not all stations\ overhearing the signals sent. In a context of this partial overhearing of signals, explain the following:\ A: The dilemma faced by the MAC-layer of various stations

S_(1)-S_(7)

in deciding to transmit or not\ transmit their ready packets - which is a case of the "hidden-station" and "exposed-station"\ problems in wireless networks

^(8)

.\ B: How the RTS-CTS hand-shake protocol between a sender and receiver (as provided in IEEE-802.11)\ alleviates the "hidden-station" and "exposed-station" problems.\ 2-dimensional planar view of wireless nodes (placed over a 3-dimensional space)\ wireless range:

600ft

\ [beyond this distance, signals\ are too weak to be sensed]\ distance between stations are shown

7. (20 pts) Consider an ensemble of seven stations: S1S7 placed in a 3-dimensional space with widely varying geographic distances between them. Stations S1 and S2 are very closely spaced (with just 4ft separation) - and so are S4 and S5. Some stations have a separation beyond the wireless range of 600ft, while others are within the wireless range (though not close to each other). Out-of-rang situations arise because the signal strength decays exponentially w.r.t. the distance d from sender (i.e., signal strength is proportional to d21 ). Consider a scenario of S1 trying to transmit its packet to S2, S3 trying to transmit its packet to S4, and S5 trying to transmit its packet to S6. Figure 3 illustrates the within-range and out-of-range stations in this scenario, which leads to some but not all stations overhearing the signals sent. In a context of this partial overhearing of signals, explain the following: A: The dilemma faced by the MAC-layer of various stations S1S7 in deciding to transmit or not transmit their ready packets - which is a case of the "hidden-station" and "exposed-station" problems in wireless networks 8. B: How the RTS-CTS hand-shake protocol between a sender and receiver (as provided in IEEE-802.11) alleviates the "hidden-station" and "exposed-station" problems. 2-dimensional planar view of wireless nodes (placed over a 3-dimensional space) distance between stations are shown Figure 3: Placement of wireless nodes in a geographic area