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.