MAC (Multiple Access Controll) Protocols
CSMA (Carrier Sense Multiple Access) Improvement: Start transmission only if no transmission is
ongoing 1-Persistance, P-Persistance, Non-Persistance
CSMA/CD (CSMA with Collision Detection)
Improvement: Stop ongoing transmission if a collision is detected
CSMA/CA (CSMA with Collision Avoidance)
Improvement: Wait a random time and try again when carrier is quiet. If still quiet, then transmit
Question 1: Consider two scenario mentioned below and find out, which
scenario results more serious loss of bandwidth because of collision. Explain
your answer with technical justification.
1: Very small cable length with very very long packet size
2: Very large cable length with too small packet size.
Question 2: A system is following CSMD/CA technique. Find out the time
span in which a collision may occur. Packetor frame Time, Contention Period,
Idle Period…?
Serious Drawback of CSMA/CD or CSMA/CA:
When medium is too long and frames or packets are too sort.
The time when a frame or packet gets collide, we might have transmitted other frames.
Solution is “Collision Free Protocol” called as “Reservation Protocol” or “Bit-Map Protocol”.
1. System reserve a slot before transmission.
2. Time is divided into contention period and packets/frame period.
3. Suppose we have “N” Station , then we will be having N slots in contention period.
4. Each station willing to send, will put “1” into it’s slot, and reserve its time for transmission.