ALOHA: ALOHA is a system for coordinating and arbitrating access to a shared communication Networks channel. It was developed in the 1970s by Norman Abramson and his colleagues at the University of Hawaii. The original system used for ground based radio broadcasting, but the system has been implemented in satellite communication systems.

1. LOHA
LOHA

2. WHAT IS MAC
?• When nodes are connected with
a shared line ,called
multipoint.
•We need many protocol to handle
shared link.
•All of these protocol belong to a
sub layer in a data link layer called
media access
control (MAC).

5. No station is superior to
another station.
Transmission is random
among station.
That’s why this method is
known as random access
method.
Random access protocol

7. WHAT IS ALOHA ?
•Aloha means "Hello".
• ALOHA is a system for
coordinating to a shared
communication networks
channel.
•It is random access method.

8. Types of
ALOHA
Pure
ALOHA
Slotted
ALOHA

9. PURE ALOHA
•It is original ALOHA.
•It sends frame whenever it has
frames.
•There is possibility of collision in
it.
•If acknowledgement is not
received within specified time,it
resends data.

10. Pure ALOHA

11. Slotted ALOHA
•Slotted ALOHA was invented to
improve the efficiency of pure
ALOHA developed by Roberts
in 1972.
• In slotted ALOHA, the time of
the shared channel is divided
into discrete intervals called
slots.
•In slotted ALOHA, there is still a

12. Slotted ALOHA

13. PURE ALOHA VS SLOTTED ALOHA
Pure ALOHA
 It is less efficient.
 Pure Aloha is a
Continuous time
system.
 Pure ALOHA
doesn't check
whether the
channel is busy.
 More efficient.
 slotted Aloha is a
non continuous
time system.
 slotted ALOHA
checks whether the
channel is busy.
Slotted ALOHA

14. Reference
•Data communication and networking,
By Forouzon
• www.slideshare.com
•www.computernotes.com