MAC in Detail

MAC Address : 

                           

                                               The solution to the media access problem with WLANs is to use the carrier sense multiple access with collision avoidance (CSMA/CA) algorithm. The collision avoidance part minimizes the statistical chance that collisions could occur. However, CSMA/CA does not prevent collisions, so the WLAN standards must have a process to deal with collisions when they do occur. Because the sending device cannot tell if its transmitted frame collided with another frame, the standards all require an acknowledgment of every frame. 

Each WLAN device listens for the acknowledgment, which should occur immediately after the frame is sent. If no acknowledgment is received, the sending device assumes that the frame was lost or collided, and it resends the frame.

The following list summarizes the key points about the CSMA/CA algorithm, omitting some of the details for the sake of clarity:

Step 1 Listen to ensure that the medium (space) is not busy (no radio waves currently are being received at the frequencies to be used).

Step 2 Set a random wait timer before sending a frame to statistically reduce the chance of devices all trying to send at the same time.

Step 3 When the random timer has passed, listen again to ensure that the medium is not busy. If it isn’t, send the frame.

Step 4 After the entire frame has been sent, wait for an acknowledgment.

Step 5 If no acknowledgment is received, resend the frame, using CSMA/CA logic to wait for the appropriate time to send again.