RANDOM ACCESS PROTOCOL IN COMMUNICATION

In random access ,each station has right to send the data. However , if more than one station tries to send ,collision will occur .To avoid this collision , protocols came into existence.

In random access method , no stations are superior & none is assigned the control over the other .

When a station has a data to send , it uses a procedure defined by a protocol whether to send or not .

1. RANDOM ACCESS PROTOCOL IN COMMUNICATION BY : AMOGHA.A.K . ELECTRICAL AND ELECTRONICS ENGINEERING DEPARTMENT

2. Introduction Problem Statement History Need for Random access Functions What is ALOHA & CSMA ? Flow Chart Simulated Graphs Advantages Limitations Applications Future Scope Conclusion References Contents

3. In random access ,each station has right to send the data. However , if more than one station tries to send ,collision will occur .To avoid this collision , protocols came into existence. In random access method , no stations are superior & none is assigned the control over the other . When a station has a data to send , it uses a procedure defined by a protocol whether to send or not . Introduction

4. When 2 users transmit the data packets at the same time , collision occurs & these packets are destroyed . To avoid this , random access protocol has been adopted . Problem Statement

5. The development of ALOHA network commenced in 1968 at the University of Hawaii by Norman Abramson. It became operational in 1971 . During 1980’s the frequencies were assigned for mobile medium . In 1985, frequencies were made available for WIFI facilities . History of ALOHA

6. Need For Protocol When two computers are connected via single connection , the data collision takes place . Hence to avoid , a set of rules & regulations are needed which are called the protocols.

7. Describes the rules that govern the transmission of data over the communication network. Provides a method for orderly and efficient exchange of data between the sender and the receiver. Functions of Protocol

8. ALOHA is for coordinating & accessing to share communication in network channel. It is the simplest collision resolution protocol . What is ALOHA ?

9. 1.Pure Aloha: This is the original version of Aloha . 2.Slotted Aloha: This is the modified version of pure Aloha. Types of Aloha

10. What is Pure Aloha ? Whenever a station has a data , it transmits. When 2 or more stations transmit data at same time , there is a collision .Hence, the sender waits a random amount of time & then re-transmit the data again . The waiting time is random , otherwise the same packet will collide again .

11. What is Slotted Aloha ? Slotted ALOHA was invented to improve the efficiency of pure ALOHA as collisions in Pure ALOHA are very high . In slotted ALOHA , the time is divided into discrete intervals called slots . Station can send a frame only at the beginning of the slot & only one frame is sent in each slot .

12. Principle of Aloha without collision

13. Principle of Aloha with collision

14. FRAMES IN PURE ALOHA NETWORK

15. VULNERABLE TIME FOR PURE ALOHA PROTOCOL

16. FLOW CHART FOR PURE ALOHA

17. FRAMES IN SLOTTED ALOHA NETWORK

18. VULNERABLE TIME FOR SLOTTED ALOHA PROTOCOL

19. FLOW CHART FOR SLOTTED ALOHA

20. Simulated Performance of Pure ALOHA

21. Simulated Performance of Slotted ALOHA

22. Efficiency of Slotted v/s Pure Aloha

23. Comparison between Pure & Slotted Aloha The chances of collisions are more in Pure ALOHA as compared to Slotted ALOHA . Slotted ALOHA is more efficient as compared to Pure ALOHA .

24. Advantages of ALOHA Packet contention technique Single active node can continuously transmit at full rate . Highly decentralized Simple protocol

25. Disadvantages of ALOHA Collisions Idle slots Clock synchronization

26. What is CSMA ? CSMA protocol was developed to overcome the problem found in ALOHA i.e. to minimize the chances of collision to improve the performance . CSMA is a network access method used on shared network topologies . It is based on the principle of ‘carrier sense ’ .

27. Space / Time Model of Collision in CSMA

28. Vulnerable Time in CSMA

29. If the channel is idle, station transmits the frame, if busy senses the channel after random time. This protocol reduces the chance of collision but longer delays. It is a non - aggressive transmission algorithm. Non- Persistence

30. This protocol is called 1 – Persistence because the station transmits with probability of 1. When it finds the channel idle without any collision , station continuously sense the channel until it becomes free. It is an aggressive transmission algorithm. 1 - Persistence

31. Flow Chart of Non-Persistent

32. Flow Chart of 1-Persistence Channel Busy ?

33. Simulation of Non-Persistence

34. Simulation Performance of 1-Persistence

35. Out of these 2-types of CSMA it is found that Non-persistence CSMA performs the best. Summary of CSMA

36. Low-data-rate tactical satellite communications networks by military forces. In subscriber-based satellite communications networks. Mobile telephony call setup Set-top box communications In the contactless RFID technologies. Applications

37. Research is to be made to avoid any security breach & improvement in packet delivery efficiency . Future Scope

38. Conclusions Computer networks & protocols have changed the humans working & communication. The digital network is empowering us for future.

39. References www.My reading room/aloha protocol.com Protocol – oriented programming , Jon Hoffman www.searchnetworking.techtarget.com  ALOHA Random Access that Operates as a Rateless Code domir Stefanovi´c , Member, IEEE, Petar Popovski , Senior Member, IEEE 7-Aug,2013 Throughput Analysis of Wireless Relay Slotted ALOHA Systems with Network Coding Daisuke Umehara , Tomoya Hirano, Satoshi Denno , and Masahiro Morikura Graduate School of Informatics, Kyoto University Yoshida- honmachi , Sakyo- ku , Kyoto 606-8501, Japan-IEEE -2016 http://users.cs.cf.ac.uk/Dave.Marshall/Internet/node41.html

40. THANK YOU ALL & HAVE A NICE DAY