6.Carrier Sense Multiple Access

CSMA/CD (Carrier Sense Multiple Access/Collision Detect):

            

CSMA/CD (Carrier Sense Multiple Access/Collision Detect)

                      

                                  

1.If computer A wants to communicate over the multi-access medium then, it will sence the carrier/medium i.e cable.

2.It will check wheather,there is any communication on same medium is going on i.e sensing carrier.

3.If there any communication is going on then computer A will wait else if it is found medium as free then it will start to send data on medium and communication will continue.

4.If at a same time computer A and computer D sensed carrier and found that medium is free then both are send their data at a same time at that time collision between both data will occur.

5.So because of collision packet or data gets corrupted and sent to all computers then they will detect collision.

  

How collision is detected:

Because of every frame cyclic redundancy check bit is added.

If collision occurs then FCS,CRC and DATA gets separated then computer will detect that collision has occurred.  

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance):

1.When collision gets detected and  all device gets corrupt data then all devices will goes in Integral Wait State.

2.Which device is near the collision that device is first goes in Integral Wait State.

3.In Integral Wait State that device can not transmit any data.

4.which device first went in Integral Wait State that device will first came out from the Integral Wait State.

5.then by the preference all device will get a chance to send the data,this technique is known as collision avoidance.