Mac protocol and IEEE 802.11 ppt..

 Mac protocol and IEEE 802.11

Men Accessories on the Table

 What is MAC protocol? 

• Medium access control.
• It is a part of data link layer and directly invokes physical layer protocol.
•Enforces discipline in access of shared channel
when multiple nodes contend to access to channel.

Properties MAC protocol?

• Channel utilization is maximum.
• Capable of supporting several types of traffic.
• Equipment failure or change in N/W condition
[Robust in nature].

MAC issues

• Difficult to implement collision detection scheme.

•Issues of hidden and exposed terminals makes MAC protocol inefficient.

Hidden terminal problem 

• A communicate with B , C cannot receive A.
• C communicate with B, C sense a “ free ” medium and starts transmitting.
•Colllision at B, when A cannot receive collision and continues with its transmitting to B,
• A is hidden from C and vice versa.

Exposed terminal problem 

• B sends to A, C wants to send to another terminal.
• C sense carrier is busy.
• C postpone its transmission until it detects the medium is idle again.
•But A is outside the radio range of C waiting is not necessary.
• C is exposed to B.


IEEE 802.11

• Family of WLANs.
•It is a standard that specifies the physical or MAC layer adapted.
• Define separate standard for infrastructure based and adhoc network.
•It is the set of technology guidelines for implementing wi-fi.
• Frequency : 2.4 GHz

Infrastruture based mode of IEEE 802.11

• Helps in providing wi-fi hotspot for internet access.

•Multiple access point are connected to form distribution N/W.

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