ALOHA is a simple communications scheme where each transmitter sends data whenever it has a frame to send. There are two versions: Pure Aloha, where time is continuous and not synchronized, and stations transmit whenever they have data; and Slotted Aloha, where time is divided into slots and stations can only transmit at slot boundaries. Pure Aloha was introduced in 1970 at the University of Hawaii to connect users to a central computer using low-cost radio equipment. The maximum throughput of Pure Aloha is 18% of the total transmitted frames.

1. PRESENTED BY,
Pratistha Singh

2. Points To Consider:
1. What is ALOHA?
2. Basic Idea Behind Aloha
3. Version Of Aloha
4. What is Pure Aloha?
5. History of Pure Aloha
6. Procedure for Pure Aloha
7. Analysis Of Pure Aloha

3.  Aloha refers to a simple communications scheme in
which each source (transmitter) in a network sends
data whenever there is a frame to send.
 In a wireless broadcast system or a half-duplex two-
way link, Aloha works perfectly.
1. What is ALOHA?

4. 2. Basic Idea Behind
Aloha

5. 3. Versions Of Aloha
ALOHA
PURE
ALOHA
SLOTTED
ALOHA
Original Version Of Aloha Modified Version Of Aloha

6. 4. What is Pure Aloha?
 In Pure Aloha the station transmits frames whenever
they have data to be send.
 The time is continuous and is not globally
synchronized.

8.  Introduced by Norman Abramson and his associates
at the University of Hawaii in 1970.
 The goal was to use low cost commercial radio
equipment to connect users of Oahu and other
Hawaiian islands with a central time sharing computer.
5. History of Pure Aloha

9. 6. Procedure for Pure Aloha

10.  For successful transmission we can consider frames to be of same
length and the channel to be noise-less.
 Here,
 Tf is the frame time.
G is the average number of total frames transmitted per Tf.
S is number of successful transmission.
 The throughput of the Pure ALOHA is S=G*e^-2G.
 The maximum throughput i.e., S=0.184 when G=(1/2) which is 18%
of the total transmitted data frames.
Here, e^-2G is the probability of successful transmission.
7. Analysis Of Pure Aloha