![VISVESVARAYA TECHNOLOGICAL UNIVERSITY
BELAGAVI – 590018
GOVERNMENT ENGINEERING COLLEGE,
KUSHALNAGARA 571234
Department of Electronics And Communication Engineering
SUBJECT: Computer Communication Network [21EC53]
TOPIC : Slotted Aloha and CSMA
PRESENTED BY;
Akshatha M
USN:4GL21EC002
PRESENTED TO;
PROF.Roopa](https://image.slidesharecdn.com/akshatha-240323101046-6709e7e8/85/SLOTTED-ALOHA-and-pure-aloha-are-the-category-of-aloha-1-320.jpg)
SLOTTED ALOHA and pure aloha are the category of aloha
- 1. VISVESVARAYA TECHNOLOGICAL UNIVERSITY BELAGAVI – 590018 GOVERNMENT ENGINEERING COLLEGE, KUSHALNAGARA 571234 Department of Electronics And Communication Engineering SUBJECT: Computer Communication Network [21EC53] TOPIC : Slotted Aloha and CSMA PRESENTED BY; Akshatha M USN:4GL21EC002 PRESENTED TO; PROF.Roopa
- 2. INDEX MULTIPLE Access protocol Aloha Pure Aloha Slotted aloha CSMA protocol Types of CSMA protocol
- 3. Multiple Access Protocol Random Access Protocols Controlled Access Protocols Channelization Protocols
- 4. ALOHA What is aloha? Aloha is a random access protocol. It was actually designed for WLAN but it is also applicable for shared medium In this, mulyiple stations can transmit data at the same time and can hence lead to collision & data being garbled TYPES Pure Aloha Slotted Aloha
- 5. PURE ALOHA
- 6. SLOTTED ALOHA It was developed just to improve the efficiency of pure aloha as the chances for collision in pure aloha are high. The time of the shared channel is divided into discrete time intervals called slots. Sending of data is allowed only at the beginning of these slots. If a station misses out the allowed time, it must wait for the next slot. This reduces the probability of collision.
- 7. Vulnerable Time= Frame Transmission Time Throughput = G x e^-G; Where G is the number of stations wish to transmit in the same time. Maximum Throughput = 0.368 gor G=1.
- 9. PURE ALOHA V/S SLOTTED ALOHA Pure Aloha Slotted Aloha Any Station can transmit the data at any time. Any station can transmit the data at the beginning of any time slot. The time is continuous and not globally synchronized. The time is discret and globally synchronized. Vulnerable time in which collision may occur=2 x Tfr Vulnerable time in which collision may occur = Tfr Probability of successful transmission of data packet =G x e^-2G Probability of successful transmission of data packet=G x e^-G Maximum efficiency=18.4%(occurs at G=1/2) Maximum efficiency = 36.8% (occurs at G=1) Main advantage: Simplicity in implementation. Main advantage : It reduces the number of collisions to half and doubles the efficiency of pure aloha
- 10. CSMA PROTOCOL • CSMA Stands for Carrier Sense Multiple Access. • To minimize the chance of collision and, therefore, increase the performance, the CSMA method was developed. • Principle of CSMA :”Sense before transmit” or “listen before talk”. • Carrier busy = Transmission is taking place. • Carrier idle = No transmission currently taking place. • The possibility of collision still exist because of propagation delay; a station may sense the medium and find it idle,only because the first bit sent by another station has not yet been received.
- 11. Space /time model of collision in CSMA
- 12. Vulnerable time in CSMA
- 13. What are the types of CSMA? 1-persistent CSMA • The 1-persistent method is simple and straightforward. • In this method, after the station finds the line idle, it sends its frame immediately with probability 1. • This method has the highest chance of collision because two or more stations may find the line idle Nonpersistent • In the nonpersistent method, a station that has a frame to send senses the line. • If the line is idle, it sends immediately. • If the line is not idle, it waits a random amount of time and then senses the line again. • The nonpersistent approach reduces the chance of collision • This method reduces the efficiency of the network
- 14. p-Persistent • The p-persistent method is used if the channel has time slots with a slot duration equal to or greater than the maximum propagation time. • It reduces the chance of collision and improves efficiency. • In this method, after the station finds the line idle it follows these steps: • 1. With probability p, the station sends its frame. 2. With probability q = 1 − p, the station waits for the beginning of the next time slot and checks the line again. a. If the line is idle, it goes to step 1. b. If the line is busy, it acts as though a collision has occurred and uses the backoff procedure.
- 15. Behaviour of three persistence methods
- 16. Flow diagrams of three persistence methods
- 17. THANK YOU