What is the Difference Between Pure Aloha and Slotted Aloha?
Aloha was developed in 1970 at the university of Hawaii. As an improvement to pure Aloha which is lan-based protocol, Slotted Aloha was introduced in the year 1972. Slotted Aloha is divided into discrete intervals ‘slot’ that corresponds to the frame.
Before we jump into understanding the difference between Pure Aloha and Slotted Aloha, we need to understand what aloha in computer networks is. Let us get started away with the topic.
Table of Contents
Difference between Pure Aloha and Slotted Aloha
Both pure and slotted aloha are the types of aloha. While Pure aloha is used when the data is available to send over a channel at stations. Slotted aloha overcomes the issues with pure aloha.
| Parameter | Pure Aloha | Slotted Aloha |
| Time Slot | Stations can transmit data at anytime | Stations transmit data only at the beginning of time slot |
| Time | Continuous and not globally synchronized | Discrete and globally synchronized |
| Vulnerable time | 2×Tt | Tt |
| Maximum efficiency | 18.4%. | 36.8%. |
| Number of collisions | No reduction | Reduces to half |
What is Aloha?
Aloha is a data link layered multiple access lan-based protocol. It describes the way in which multiple terminals can access without any conflict or interference. The protocol operates within the medium access control sublayer of an OSI model. Aloha allows the streaming of several data that originates from multiple nodes that are transferred through the multi-point transmission channel.
About Pure Aloha
While discussing the types of Aloha, the first one is Pure Aloha. It is a network protocol that is used for data transmission in computer networks. As one of the first protocols, it enabled communication among computers over a shared communication channel. Here, the computer transmits the data as soon as they have it without awaiting acknowledgement from the receiver.
When two computers simultaneously transmit the data, a collision will occur, and the data gets lost. Now, the transmitting computer waits for a random amount of time before making an attempt to transmit again so that there is no collision. The random wait time is then determined by the backoff algorithm. The following are the techniques used in Pure Aloha:
- Step 1: Nodes transmit the frames whenever data is available for sending.
- Step 2: Whenever two or multiple nodes simultaneously transmit data, the chance of collision is there and frames get destroyed.
- Step 3: Sender expects an acknowledgement from the receiver.
- Step 4: In case the acknowledgement is not received within a timeline, sender node assumes that frame has been destroyed.
- Step 5: In case the frame gets destroyed by a collision, node will have to wait for a random amount of time and then, send it again. Here, the waiting time is random to avoid multiple collisions between frames.
- Step 6: When the period of time-out passes, each station must wait for a random amount of time before resending the frame. This randomness helps in avoiding more collisions.
Explore networking and hardware courses
What is the formula of efficiency of Pure Aloha?
The formula for pure ALOHA is:
where ‘g’ is the avg number of frames generated during the transmission of one frame. The symbol ‘e’ represents the base of the natural logarithm which is equal to 2.71828.
About Slotted Aloha
The slotted aloha overcomes the possibility of the frame hitting in the pure Aloha. Unlike pure Aloha, Slotted Aloha does not allow data transmission whenever the station wants to send it. When a station wants to send the frame to a shared channel, the frame can only be sent in the beginning of slot.
Every slot has been allotted with only one frame. When the station fails to send the data, it waits till the next slot. However, the possibility of collision is there when two stations try to send a frame at the start of the time slot. Slotted Aloha increases the channel utilization by reducing the frequency of collisions. It also increases the delay for users since they have to wait for next time slot for transmitting the frame.
Advantages of Slotted Aloha
The following are the advantages of Slotted Aloha :
- Efficiency: By dividing time into the discrete slot, the computer transmits data only during the assigned slot. This prevents any collisions and thus improves the overall efficiency of the network.
- Increased throughput: As slotted aloha reduces any collisions and network congestion, it helps in achieving higher throughput than any other networking protocols.
- Reduces Network Congestion: It is an important type of aloha that prevents simultaneous data transmission from multiple computers. This leads to collisions and waste of network bandwidth.
Disadvantages of Slotted Aloha
The following points indicate the disadvantages of Slotted Aloha:
- The high collision rate in the case of slotted Aloha results in a high packet loss rate that can negatively impact the overall performance of the network.
- The maximum throughput is concentrated to only 18.4% of the network capacity. This makes it difficult for networks that have high data transfer requirements.
- It is not suitable for large networks consisting of large numbers of devices. The probability of collisions increases as the channel congestion and collisions increase with the number of devices.
- Slotted aloha does not prioritize some types of data packets, which may lead to the delays in the transmission of critical information.
Related Reads:
Read Later
FAQs
What are the differences between pure and slotted aloha systems?
In Pure Aloha, the station transmits the data whenever it is available at arbitrary times. For slotted aloha, a station needs to wait at the start of the next slot to transmit.
Why is Slotted ALOHA considered more efficient than Pure ALOHA?
Slotted ALOHA is considered more efficient than Pure ALOHA due to its structured approach to data transmission. In Slotted ALOHA, time is divided into discrete slots, and data transmission is synchronized to these slots. This reduces the likelihood of collisions, as transmissions only occur at the beginning of a time slot. As a result, Slotted ALOHA has a higher throughput, making it more efficient. Slotted ALOHA is considered more efficient than Pure ALOHA due to its structured approach to data transmission. In Slotted ALOHA, time is divided into discrete slots, and data transmission is synchronized to these slots. This reduces the likelihood of collisions, as transmissions only occur at the beginning of a time slot. As a result, Slotted ALOHA has a higher throughput, making it more efficient.
Where do we use Slotted Aloha?
Slotted Aloha is used is communication networks.
Jaya is a writer with an experience of over 5 years in content creation and marketing. Her writing style is versatile since she likes to write as per the requirement of the domain. She has worked on Technology, Fina... Read Full Bio
Top Picks & New Arrivals
