Question

Question 3 (25 points): 1) (1pt) Explain briefly and in your own words why collision is an issue in random access protocols but not in controlled access protocols. 2) (2pts) Explain briefly and in your own words why collision is an issue in random access protocols but not in channelization protocols. 3) (2pts) What happens if there is a collision during the handshaking period? 4) (5pts) Give 2 reasons that CSMA/CD cannot be used in a wireless LAN? 5) (5pts) What are the three strategies used in CSMA-CA to avoid collisions? 6) (5pts) Explain the hidden station problem? Explain briefly how to resolve it in your own words and by drawing a figure? 7) (5pts) Explain the exposed station problem? Explain briefly how to resolve it in your own words and by drawing a figure?

Answer 1

1)In a random access method access is based on contention. In a controlled access method,
either a central authority or other stations control the access. in Random access methods administration overhead is less. The controlled access method are collision free.
In controlled access protocol the stations interact with each other by providing authentication.But in random access the station will transfer data whenever it have the data to send,there is no any authentications among the stations which are in interaction.

2)In channelization protocol the available bandwidth is divided between the stations.The major adventage is that if a staion does not have the data to send,then the allocated channel will remains idle.That's why the collision is not issue in the channelization protocol.In random protocol the station will send the data whenever it have the data to send,that's why the possibility of the collision is high in random protocol.

4)

a)Wireless transceivers can't send and receive on the same channel at the same time, so they can't detect collisions
b)Terminals are actually connected to the medium, and do experience real time what is going on. In wireless it would exceed the capacity of the cell, plus there would be configurations of terminals which each could see the base station, but which couldn’t see each other (near/far effect)

5)  

1.InterFrame Space-It is the time which the station waits when the station find the channel busy.
2.Contention Window-It is the time which is devided into number of slots.the station will select one of the slot from the devided list to sent frame.
3.Acknowledgement-The positive acknowledgements and time-out timer can help guarantee a successful transmission of the frame.