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 .
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 .
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
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 ’ .
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
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