Compare between pure ALOHA and Slotted ALOHA.

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written 8.3 years ago by

teamques10 ★ 68k

Pure ALOHA	Slotted ALOHA
The original ALOHA protocol is called pure ALOHA.	Slotted ALOHA was invented to improve the efficiency of pure ALOHA.
A simple version pure ALOHA, does not require Slots.	Slotted ALOHA requires slot synchronization.
The idea is that each station sends a frame whenever it has a frame to send.	Force the station to send only at the beginning of the time slot.
However, since there is only one channel to share, there is the possibility of collision between frames from different stations.	If multiple nodes transmit, node detect collision Slotted.
It does not require global time synchronization.	It does require global time synchronization
Pure ALOHA has a vulnerable time of 2 x Tfr This is so because there is no rule that defines when the station can send.	In slotted ALOHA we divide the time into slots of Tfr.
Throughput is reduced by one half i.e. S = (1/2e).	The throughput for slotted ALOHA is S =: G x e-G.
Frames in Pure ALOHA	Frames in Slotted ALOHA

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	Pure Aloha	Slotted Aloha
Basic	In pure aloha, data can be transmitted at any time by any station.	In slotted aloha, data can be transmitted at the beginning of the time slot.
Time	In Pure Aloha, time is continous and is not globally syncronized.	In Slotted Aloha, time is discrete and is globally syncronized.
Vulnerable time	In Pure Aloha vulnerable time = 2 x Tt.	In slotted Loha vulnerable time = Tt.
Maximum efficiency	Maximum efficiency = 18.4%.	Maximum efficiency = 36.8%.
Number of collisions	It does not decrease the number of collisions to half.	Slotted aloha enhances the efficiency of pure aloha.It reduces the number of collisions to half.
Successful transmission	Probability of the successful transmission of the frame is S = G * e-2G	Probability of the successful transmission of the frame is S = G * e-G

Pure Aloha

Slotted Aloha

Basic

In pure aloha, data can be transmitted at any time by any station.

In slotted aloha, data can be transmitted at the beginning of the time slot.

Time

In Pure Aloha, time is continous and is not globally syncronized.

In Slotted Aloha, time is discrete and is globally syncronized.

Vulnerable time

In Pure Aloha vulnerable time = 2 x Tt.

In slotted Loha vulnerable time = Tt.

Maximum efficiency

Maximum efficiency = 18.4%.

Maximum efficiency = 36.8%.

Number of collisions

It does not decrease the number of collisions to half.

Slotted aloha enhances the efficiency of pure aloha.It reduces the number of collisions to half.

Successful transmission

Probability of the successful transmission of the frame is S = G * e-2G

Probability of the successful transmission of the frame is S = G * e-G