The document discusses MAC layer protocols, specifically CSMA/CD and CSMA/CA. CSMA/CD is used for wired networks and works by having nodes listen to check if the medium is free before transmitting. If a collision is detected, transmission stops and resumes after a backoff time. CSMA/CA is used for wireless networks and aims to avoid collisions through the use of request to send, clear to send, and acknowledgement frames exchanged between nodes, rather than detecting collisions. Both protocols reduce collisions compared to simple CSMA, but CSMA/CA is less efficient and cannot completely solve collisions in wireless networks due to issues like hidden terminals.

1. MAC Layer protocols
MAC (Media Access Control)

2. Presenter :
KAZIM HUSSAiN
BS IT 15-102
BZU MULTAN
COURSE INSTRUCTOR :
DR. AMIR HUSSAIN

3. Protocols of MAC Layer :
1- CSMA/CD
2- CSMA/CA
What is CSMA(carrier sense multiple access)??
It reduced the chances of collision.
It works on principle “sense before send”
Advantages :
 Fairly simple to implement
 Functional scheme that works
Disadvantage :
It can’t eliminate the collision permanently .

4. CSMA/CD(carrier sense multiple
access/collision detection) :
=> It is wired network
=>Listen the medium until if it is free?
=> If it is free then start talking , and be careful
someone else can talk during this period
=> I f collision occur then , stop and talk after back off
time

5. Advantages :
1- It detect collision within a short time .
2- More efficient than a simple CSMA.
3- It request node for transmission before sending any frame.
4- If collision occur then it send frame again at free time.
5- CSMA/CD is beneficial , because it avoid from a wasteful
transmission.

6. Disadvantages :
1- It can’t reduce the possibility of collision between two nodes
2-Not much efficient to detect a collision
3- Inappropriate for large networks
4-limited to 2500 meters , after this distance collision can’t detected

8. CSMA/CA(carrier sense multiple
access/collision avoidance)
1- It was invented for wireless networks
2- It avoid from collision
3- It uses three stages to avoid from collision
IFS (Interface space )
Contention window
Acknowledgement
4-It use RTS= Request to send
5- It use CTS= clear to send
6-its similar to CSMA, but instead of sending packets control frame are
exchanged

9. CTS and RTS??
RTS
CTS
Defer

10. Advantage of CSMA /CA:
1- When data is large then it reduce the collision chances
2- It avoid from hidden terminal collision
3- It control packets and send these packets to whom receiver wants to
send
Disadvantages :
1- It is less efficient than a CSMA/CD
2- It can’t solve the problem of MAC Layer in wireless networks
3- Its difficult to avoid from collision in wireless networks