1. Learning Objectives
After interacting with this Learning Object, the learner will be able to:
Explain the process of collision detection in CSMA/CD

2. Protocols (Contention Based and Contention Free)
Contention-based (random access)
ALOHA
CSMA (Carrier Sense Multiple Access)
IEEE
Contention-free
FDMA
TDMA
CDMA

3. Contention Free Protocols

4. Polling Protocol:
The polling protocol is a master node. It is used for eliminate collisions.
It is used to surveys each of the nodes and transfer certain maximum number of data frames.
If received message from the master node, then each node will ready to transfer data otherwise, master node sends message asking it to send its data.
One node completed successfully then start another transaction by using master node.
It is a round-robin fashion technique. The master node is used to polls each node in a cyclic manner.

5. Token Passing Protocol:
The Token passing protocol is not a master node.
It is used to transfer data in some fixed order.
If any node have the token the send its data. If it is not received destination node then search to go for next node and transfer it.
The main disadvantage is, if any node fails then entire transfer data will be crashed.

6. Resource Reservation Protocol (RSVP)
is a transport layer[1] protocol designed to reserve resources across a network for quality of service (QoS) using the integrated services model. RSVP operates over an IPv4 or IPv6 and provides receiver-initiated setup of resource reservations for multicast or unicast data flows. It does not transport application data but is similar to a control protocol, like Internet Control Message Protocol (ICMP) or Internet Group Management Protocol (IGMP). RSVP is described in RFC 2205.

7. 1 2 3 4 5 Definitions of the components/Keywords:
CSMA/CD is Carrier Sense Multiple Access / Collision Detection : - Carrier Sense – the ability of a network card to sense or detect communication on the network - Multiple Access – states that in that network there are multiple stations that could access the network at the same time - Collision Detection – the method needed for detecting a collision
Carrier Sense Multiple Access/Collision Detect (CSMA/CD) is the protocol for carrier transmission access in Ethernet networks.
Carrier-sense multiple access with collision detection describes how the Ethernet protocol regulates communication among nodes
On Ethernet, any station can send a frame at any time. Each station senses whether the medium is idle and therefore available for use. If it is, the station begins to transmit its first frame. If another station also tries to transmit at the same time, a collision occurs and the frames are discarded and then a jamming signal is sent throughout the network in order to notify all stations of the collision. Each station then waits for a random period of time and retries. If another collision occurs, the time intervals from which the random waiting time is selected are increased step by step. This is known as exponential back off. The stations retry until successful transmission of the frame.
CSMA/CD is specified in the IEEE standard. 1 2 3 4 5 7

8. 1 2 3 4 5 Definitions of the components/Keywords:
The jam signal is a signal that carries a 32-bit binary pattern sent by a data station to inform the other stations that they must not transmit.
Transmit – The stations (nodes) sends the frames to other stations (nodes)
Carrier Sense – The stations (nodes) listen to the medium if it is idle for transmission
Back off – After collision occurs, a jam signal is sent to notify all stations of the collision. After the jam signal is sent, the stations (nodes) wait for a random period of time called Back off period
The flow chart for CSMA/CD protocol is :
given in the next slide 2 3 4 5

10. 1 Master Layout 1 2 3 4 5 Give a box to enter position of stations
Give values from 1 to 99 to select for the station and the gap between the stations must be 15 or above
Give STOP and CLEAR buttons
Give a box to enter Frame size and default size will be 150 5

11. 3 Step 1: 1 2 4 5 Instruction for the animator
Text to be displayed in the working area (DT)
Show the black Line ranging from 0 to 100 and the details of the colors as given above
The text in DT should appear initially on the screen
Minimum 2 stations should be created and maximum 4 stations allowed
Minimum distance between two stations should be equal to or above 15
After creating stations, click on any square box (representing station) 5

12. 3 Step 2: 1 2 4 5 Instruction for the animator
Text to be displayed in the working area (DT)
When the user selects ‘Add station’ , show a square box at that particular position
The text in DT of previous slide should be shown 5

13. 3 Step 3: 1 2 4 5 When single station transmits
Instruction for the animator
Text to be displayed in the working area (DT)
When the user clicks any square box then show a green line
The text in DT should appear in parallel to the figures
Station 2 is transmitting 5
** All the coming slides are given as examples but the actual position of the boxes and their states follow according to the square boxes selected by the user and the procedure depends on the algorithm given in the 5th slide.

14. 3 Step 4: 1 2 4 5 When single station transmits
Instruction for the animator
Text to be displayed in the working area (DT)
When the user clicks any square box then show a green line
The text in DT should appear in parallel to the figures
Station 3 is transmitting 5

15. 3 Step 5: 1 2 4 5 When 2 stations transmit at a time
Instruction for the animator
Text to be displayed in the working area (DT)
When the user clicks any two square boxes one after the other immediately then show a redlines (indicating collision)
The text in DT should appear in parallel to the figures
Station 2 is transmitting
Station 3 is backing off due to collision 5

16. 3 Step 6: 1 2 4 5 When 3 stations transmit at a time
Instruction for the animator
Text to be displayed in the working area (DT)
When the user clicks any three square boxes one after the other immediately then show a redlines (indicating collision)
The text in DT should appear in parallel to the figures
Station 1 is sensing
Station 2 is backing off due to collision
Station 3 is backing off due to collision 5

17. Questionnaire 1
1.A node wants to send a packet over a wireless LAN. What will CSMA/CD protocol do if the channel is idle?
Answers:
a) Sense the channel and sends the packet immediately if it is idle
b) Sense the channel and sends the packet if it is still idle after a random period of time after the jam signal is sent
c) both a and b
d) either a or b 2 3 4 5

18. Questionnaire 1
2. A node wants to send a packet over a wireless LAN. What will CSMA/CD protocol do if the channel is busy?
Answers:
a) waits until the channel is idle and sends the packet immediately
b) waits until the channel is idle and sends the packet if it is idle even after the jam signal is sent
c) both a and b
d) either a or b 2 3 4 5

19. 4 Questionnaire 1 2 3 5 3. What is the jam signal sent for? Answers:
a) To stop transmission for a random back off time
b) To avoid further collision
c) To inform all other nodes that there is a collision
d) All the above 2 3 4 5

20. Questionnaire 1
4. After a jam signal is sent, which of the below event happens?
Answers:
a) Nodes send packet immediately
b) Nodes wait for a random period of time
c) a and b
d) a or b 2 3 4 5

21. Questionnaire 1
5. What is purpose of CSMA/CD protocol in wireless LAN?
Answers:
a) Create different size of packets
b) Detect collision of packets
c) Avoid collision of packets
d) All the above 2 3 4 5

22. CSM
CSMA/CD Vs CSMA
"In CSMA/CD the source stop transmission as soon as it detects the collision.
While in CSMA the frame is transmitted even though the collision has occurred. 

23. CSM
◆ Send as soon as channel is idle ◆ Problem: blocked senders all try to send at once

24. CSM
P-persistent CSMA
This is an approach between 1-persistent and non-persistent CSMA access modes. When the transmitting node is ready to transmit data, it senses the transmission medium for idle or busy. If idle, then it transmits a frame with probability p. If busy, then it senses the transmission medium continuously until it becomes idle, then transmits with probability p. If the node does not transmit (the probability of this event is 1-p), it waits until the next available time slot. If the transmission medium is still not busy, it transmits again with the same probability p.

25. CSM
P-persistent CSMA

26. Links for further reading
Reference websites:
llision_detection
Books:
COMPUTER NETWORKS –
Andrew S. Tanenbaum