RANDOM ACCESS PROTOCOL IN COMMUNICATION

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

• 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

 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

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

 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

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.

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

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

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

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 .

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 .

Principle of Aloha without collision

Principle of Aloha with collision

VULNERABLE TIME FOR PURE
ALOHA PROTOCOL

FRAMES IN SLOTTED ALOHA
NETWORK

VULNERABLE TIME FOR
SLOTTED ALOHA PROTOCOL

Simulated Performance of Pure
ALOHA

Simulated Performance of Slotted
ALOHA

Efficiency of Slotted v/s Pure Aloha

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 .

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

Disadvantages of ALOHA
 Collisions
 Idle slots
 Clock synchronization

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 ’ .

Space / Time Model of Collision in
CSMA

 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

 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

Flow Chart of 1-Persistence
Channel Busy ?

Simulation Performance of 1-
Persistence

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

 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

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

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

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

THANK YOU ALL & HAVE
A NICE DAY

RANDOM ACCESS PROTOCOL IN COMMUNICATION

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