Self doubt

Question

In CSMA CD:
 

1) Before starting transmission of frame station sense COMPLETE carrier or only its connection point ? 
     

     example :  if D is transmitting frame to E WIll A sense carrier as idle or busy
 

2) Lets take At time t = 5  Station A wants to send frame to B and Station D wants to send frame to E .

     WIll it be possible    simultaneously ?

      Does detecting channel idle by two stations ALWAYS imply collision will happen ?
 

     
 

Answer 1

1) When some node is transmitting it will send a high impedance signal in the whole network result in A sensing the carrier as busy.

2) Yup, it will create a collision. To get it resolved we use the method known as exponentially back off algorithm.

Waiting time = (0 to 2^k - 1) * propagation time (where k is the no. of time the collision had happened till that moment)