Throughput of Pure ALOHA
The probability of successful transmission (S) can be derived from the probability that no other packets are sent during the vulnerable time period. This is given by:
What is the full form of ALOHA?
The full form of ALOHA is Advocates of Linux Open-source Hawaii Association.
Maximum Throughput of Pure ALOHA
The maximum throughput occurs when G=0.5
Smax=0.5 × e-1 ≈ 0.184
This means the maximum throughput of Pure ALOHA is approximately 18.4%. In other words, only about 18.4% of the time is used for successful transmissions, and the rest is lost due to collisions.
What is ALOHA and its type?
ALOHA is a basic method for sending data over a shared network. It was created to manage how data is transmitted and to deal with collisions when two devices send data at the same time.
There are two types of ALOHA:
What is the use of ALOHA?
ALOHA is used to transmit data over a public network channel.
Pure aloha v/s slotted aloha
Now, let's see the comparison chart between pure aloha and slotted aloha. We are comparing both terms on the basis of characteristics to make the topic more clear and understandable.
From the above discussion, it can be said that slotted aloha is somewhat better than pure aloha. It is because there is less possibility of collision in slotted aloha.
So, that's all about the article. Hope it will be helpful and informative to you.
Throughput of Pure ALOHA
Let 𝑇 be the frame time, i.e. the time required for 1 frame to be transmitted.
Let G be the number of transmission attempts per frame time.
The probability that 𝑘 frames are generated during the frame time is given by the Poisson distribution−
$$P(k)=\frac{G^k e^{-G}}{k!}$$
From this we can say that the probability that 0 frames are generated ( 𝑘k = 0 ) during the frame time is $e^{-G}$.
In case of pure ALOHA, the vulnerable time period so that collision does not occur between two frames is equal to two frame times, i.e. 2T𝑇. In 2T time,average number of transmission attempts is 2G.
The probability that 0 frames are initiated in the vulnerable time period will be −
The throughput, 𝑆, is calculated as the number of transmission attempts per frame time, 𝐺, multiplied by the probability of success, 𝑃(0).
Frequently Asked Questions on Pure ALOHA – FAQs
Key Features of Pure ALOHA
For more details please refer Derive the efficiency of Pure ALOHA protocol and Differences between Pure and Slotted Aloha article.
Pure ALOHA is an early and simple method for sending data over a shared network, where devices transmit whenever they have data to send. It doesn’t check if the channel is free, leading to frequent collisions when two devices send data at the same time. This results in a maximum efficiency of about 18.4%, meaning many transmissions are lost due to these collisions.
ALOHA is a medium access control (MAC) protocol for transmission of data via a shared network channel. Using this protocol, several data streams originating from multiple nodes are transferred through a multi-point transmission channel. There are two types of ALOHA protocols – Pure ALOHA and Slotted ALOHA.
In pure ALOHA, the time of transmission is continuous. Whenever a station has an available frame, it sends the frame. If there is collision and the frame is destroyed, the sender waits for a random amount of time before retransmitting it.
After transmitting a frame, a station waits for a finite period of time to receive an acknowledgement. If the acknowledgement is not received within this time,the station assumes that the frame has been destroyed due to collision and resends the frame.
A collision occurs if more than one frame tries to occupy the channel at the same time. The situation is depicted in the following diagram−
