Key characteristics of Classical Aloha:
* Pure Aloha: A simple and decentralized protocol where each station transmits data packets whenever it has data to send, without coordinating with other stations.
* Contention-based: Stations compete for access to the shared channel, potentially leading to collisions where packets overlap and become unusable.
* Random access: Stations transmit data randomly, without a specific schedule or reservation.
* Limited throughput: The collision probability increases with the number of stations, significantly impacting network efficiency.
How it works:
1. A station with data to send prepares a packet and sends it to the shared channel.
2. If another station is transmitting simultaneously, a collision occurs, and the packets are corrupted.
3. Stations detect collisions and retransmit their packets after a randomly chosen delay to avoid another collision.
Advantages:
* Simplicity: Easy to implement and manage.
* Decentralized: No central authority required for network operation.
* Flexibility: Can adapt to varying traffic loads.
Disadvantages:
* Low efficiency: High collision probability, especially with heavy traffic.
* Limited throughput: Difficult to achieve high data transfer rates.
* No guarantee of delivery: Packets can be lost due to collisions.
Evolution of ALOHA:
* Slotted Aloha: A modification of Classical Aloha where time is divided into fixed-length slots, and stations only transmit at the beginning of a slot. This reduces the probability of collisions.
* Carrier Sense Multiple Access (CSMA): A more advanced protocol where stations listen to the channel before transmitting, reducing the chance of collisions.
Legacy of Classical Aloha:
Classical Aloha, despite its limitations, laid the foundation for modern packet-switching networks. It introduced key concepts like contention-based access, random access, and collision detection, which are still used in today's wireless networks.