free estadisticas Saltar al contenido

Difference between pure ALOHA and grooved ALOHA

febrero 10, 2020

Pure ALOHA and Slotted ALOHA are both random access protocols, implemented on the MAC (Medium Access Control) layer, a sublevel of Data Link Layer. The purpose of the ALOHA protocol is to determine which concurrent station should have the next chance to access the multi-access channel at the MAC level. The main difference between Pure ALOHA and Slotted ALOHA is that the time in Pure Aloha continues while the time in Slotted ALOHA is fair.

Let us discuss the other differences between Pure ALOHA and Slotted ALOHA in the comparison table.

Comparative chart

Basis for comparison Pure ALOHAS channeled ALOHA
IntroducedIntroduced by Norman Abramson and his colleagues at the University of Hawaii in 1970.Introduced by Roberts in 1972.
Frame transmissionThe user can transmit the data frame whenever the station has the data to transmit.The user must wait until the next boot to transmit the data frame.
TimeIn Pure ALOHA time continues.In Slotted ALOHA the discrete time.
Transmission successfulThe probability of successful transmission of the data frame: S = G * and ^ -2GThe probability of successful transmission of the data frame: S = G * and ^ -G
SynchronizationTime not synchronized globally.The weather here globally synchronized.
ThroughputThe maximum throughput occurs in G = 1/2 that 18%.The maximum throughput occurs in G = 1, which is 37%.

Definition of pure ALOHA

Pure ALOHA was introduced by Norman Abramson and his associates to the University of Hawaii in the early 1970s. Pure ALOHA allows all stations to transmit data whenever data needs to be sent. When each station transmits data without checking whether the channel is free or not, there is always the possibility of collision of data frames. If the acknowledgment arrived for the received frame, then ok or if the two frames collide (Overlap), they are damaged.

If a damaged frame, the stations wait for a random amount of type and retransmit the frame until it transmits correctly. The waiting time of each station must be random and must not be the same just to avoid collision of the frames again and again. Pure ALOHA throughput maximized when frames are of uniform length. The formula for calculating the throughput of Pure ALOHA S- = G * and ^ -2G, the maximum throughput when G = 1/2 that 18% of the total transmitted data frames.

Definition of grooved ALOHA

After the pure ALOHA of 1970, Roberts introduced another method to improve the capacity of Pure ALOHA, which is called Slotted ALOHA. He proposed dividing time into discrete intervals called time intervals. Each time interval corresponds to the length of the frame. Unlike Pure ALOHA, Slotted ALOHA does not allow you to transmit data whenever the station has the data to send. The ALOHA slot causes the station to wait until the next time slot and allow each data frame to be transmitted in the new time slot.

Synchronization can be achieved in ALOHA grooves with the help of a special station that emits a pip at the beginning of each time slot like a clock does. The formula for calculating the throughput of Slotted ALOHA S = G * and ^ -G, the maximum throughput when G = 1 that 37% of the total transmitted data frames. In ALOHA Slots, 37% of the empty time slot, 37% of successes and 26% of collision.

Key differences between pure ALOHA and grooved ALOHA

  1. Pure ALOHA was introduced by Norman and his associates to the University of Hawaii in 1970. On the other hand, Slotted ALOHA was introduced by Roberts in 1972.
  2. In pure ALOHA, every time a station has the data to send, it transmits it without waiting while, with an ALOHA slot, a user waits for the next time slot to be transmitted.
  3. In pure ALOHA the continuous time while in Slotted ALOHA the discrete time is divided into slots.
  4. In pure ALOHA the probability of successful transmission S = G * and ^ -2G. On the other hand, in ALOHA with slit the probability of a successful transmission S = G * and ^ -G.
  5. The sender and receiver time in pure ALOHA not globally synchronized while the sender and receiver time in ALOHA slit globally synchronized.
  6. The maximum throughput occurs in G = 1/2 that 18% while the maximum throughput occurs in G = 1 that 37%.

Conclusion:

ALOHA grooved somewhat better than pure ALOHA. Since the probability of collision lower in ALOHA with notch compared to ALOHA is pure because the station waits for the next time interval which allows to pass the frame in a previous time band and avoids the collision between the frames.


Rate this post