This document summarizes Carrier Sense Multiple Access (CSMA) techniques for digital data communication systems. It describes four CSMA access modes: 1-Persistent, Non-Persistent, P-Persistent, and O-Persistent. It also discusses CSMA protocol modifications like CSMA with Collision Detection (CSMA/CD), CSMA with Collision Avoidance (CSMA/CA), and Virtual Time CSMA (VTCSMA). Applications of different CSMA techniques are provided. At the end, it mentions including a MATLAB code sample for CSMA/CD.

1. BTM509 Digital Data Communication Systems
KOCAELI UNIVERSITY
Graduate School of
Natural and Applied Sciences
Prepared By: Mohammed ABUIBAID
Email: m.a.abuibaid@gmail.com
Submitted to: Dr. Halil YİĞİT
Electronic and Communication Engineering
Carrier Sense Multiple Access
AcademicYear
2015/2016

2. Presentation Outline
1. Introduction to CSMA
2. CSMA access modes
3. CSMA Protocol Modifications
4. MATLAB code of CSMA/CD

3. Introduction video
CSMA Access Modes
- 1-Persistent
- Non-Persistent
- P-Persistent
- O-Persistent
CSMA Protocol Modifications
- CSMA with collision detection
- CSMA with collision avoidance
- Virtual time CSMA
CSMA/CD & CSMA/CA made simple – Youtube

4. CSMA access modes
 1-Persistent : an aggressive transmission algorithm
 Non-Persistent : a non aggressive transmission algorithm
 P-Persistent : an approach between 1-persistent and non-persistent
 O-Persistent: Each node is assigned a transmission order by a supervisory node

5. 1-Persistent CSMA access mode
 In case of a collision, the sender waits for a random period of time and attempts
to transmit again unconditionally (i.e. with probability=1).
 1-persistent CSMA is used in CSMA/CD systems including Ethernet.

6. Non-Persistent CSMA access mode
 This approach reduces collision, results in overall higher medium throughput
but with a penalty of longer initial delay compared to 1–persistent.

7. P-Persistent CSMA access mode
 P-Persistent CSMA is used in CSMA/CA
systems including Wi-Fi and other
packet radio systems.

8.  Each node is assigned a transmission order by a supervisory node.
 When the transmission medium goes idle, nodes wait for their time slot in
accordance with their assigned transmission order.
 The node assigned to transmit first transmits immediately.
 The node assigned to transmit second waits one time slot (but by that time the first node
has already started transmitting).
 Nodes monitor the medium for transmissions from other nodes and update their
assigned order with each detected transmission (i.e. they move one position closer to the
front of the queue).
O-Persistent CSMA access mode

9. O-Persistent CSMA access mode
 O-Persistent CSMA is used by CobraNet, LonWorks and the controller area network.
It is used for the automation of various functions
within buildings such as lighting and HVAC, …etc.
It is used in large audio installations such as
convention centers, stadiums, airports, … etc.

10. CSMA Protocol Modifications:
 CSMA/CD: improves CSMA performance by terminating transmission as soon
as a collision is detected.
 CSMA/CA: improves CSMA performance by reducing the incidence of collision.
 VTCSMA : improves CSMA performance by avoiding collision generated by
nodes transmitting signals simultaneously.

11. CSMA/CD : CSMA with Collision Detection
CSMA Procedure Collision Detected Procedure

12. CSMA/CD Applications
 CSMA/CD was used in now obsolete shared media Ethernet variants
(10BASE5, 10BASE2) and in the early versions of twisted-pair Ethernet
which used repeater hubs.
10BASE2

13. CSMA/CD Applications
 Modern Ethernet networks, built with switches and full-duplex
connections, no longer need to utilize CSMA/CD because each collision
domain is now isolated.
 CSMA/CD is still supported for
backwards compatibility and for
half-duplex connections.

14. CSMA with Collision Avoidance
Collisions are avoided by three
strategies:
 Inter-frame space
 The contention window
 Acknowledgments

15. CSMA/CA Applications
 GNET -
 Apple's LocalTalk
 802.11 RTS/CTS
 IEEE 802.15.4 (Wireless PAN)
 NCR WaveLAN
 HomePNA
 Bus networks
 ITU-T G.hn standards ( G.9960)

16. VTCSMA : Virtual time CSMA
 Designed to avoid collision generated by nodes transmitting signals simultaneously.
 It used mostly in hard real-time systems (such as mission-critical applications)
 It uses two clocks at every node, a virtual clock VC and a real clock RC which tells "real time".
 When the transmission medium is sensed to be busy, the VC freezes.
 When the transmission medium is free, VC is reset.
 Calculating VC runs faster than RC when channel is free
 VC is not initiated when the transmission medium is busy.

17. MATLAB Code

18. Mohammed Abuibaid
Live & Breathe Wireless