0
32kviews
Compare between pure ALOHA and Slotted ALOHA.

Mumbai University > Electronics and Telecommunication > Sem 6 > Computer Communication and Telecom Network

Marks: 5M

Year: Dec 2015

2 Answers
0
443views
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 enter image description here Frames in Slotted ALOHA enter image description here
0
127views
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
Please log in to add an answer.