IEEE 80211 general questions Summarize and describe the basi

IEEE 802.11 general questions Summarize and describe the basic functions in the IEEE 802.11 Physical layer (PHY) and Data Link Control layer (DLC). How do IEEE 802.11 stations test for a free channel? Explain the purpose of the Medium Access Control (MAC) timing parameters Short InterFrame-Space (SIFS), Point (coordination function) Interframe Space (PIFS), and Distributed (coordination function) Interframe Space (DIFS). Explain why they should be carefully chosen. Why has a station at least to wait one DIFS prior to transmission? Explain the function of the Network Allocation Vector (NAV)? Compare the IEEE 802.11 infrastructure and ad hoc mode according to their architecture, services, and MAC functions. Discuss the suitability of using CSMA/CD (collision detection) and CSMA/CA (collision avoidance) in Wireless Local Area Networks (WLANs). Provide examples where these methods are inefficient.

Solution

A.Physical Layer-It is layer 1 in OSI model.Basically it deals with the physical connectivity between devices for data   transmission.It converts the data into bits for transmitting through physical media.

Data Link Layer-It is the 6th layer in OSI madel .It is the middle man Betweeen Network Layer and Physical layer.It is responsible for converting Packets into Frames and deframes datagram packets and transfer to Network layer.It also check error and correct it.

D.The Network Allocation Vector is a virtual carrier-sensing mechanism used with wireless network protocols .The stations listening on the wireless medium read the Duration field and set their NAV, which is an indicator for a station on how long it must defer from accessing the medium.The NAV may be thought of as a counter, which counts down to zero at a uniform rate. When the counter is zero, the virtual CS indication is that the medium is idle; when nonzero, the indication is busy. The medium shall be determined to be busy when the STA is transmitting.

F.CSMA/CD(Collision Detection) and CSMA/CA(Collision Avoidance) are using for making the network media free of jam by sensing the traffic and avoid the jam.When carrier sense multiple access detect a jam in the media it sends a halt message to all the stations for random period of time then after the random period of time stations again start sending signals.On a network that uses CSMA/CD, when a system wants to send data to another system, it first checks to see whether the network media is free. It must do this because each piece of network media used in a LAN can carry only one signal at a time. If the sending node detects that the media is free, it transmits, and the data is sent to the destination.Collision detection works by detecting fragments of the transmission on the network media that result when two systems try to talk at the same time. The two systems wait for a randomly calculated amount of time before attempting to transmit again. This amount of time a matter of milliseconds is known as back off .