Slotted Aloha

Question

Let N station share 60 kbps of slotted aloha channel. Frame size is 1024 bits which are send at every 40 seconds. The value of N is ?

Comments

Is it 863?

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is aloha in syllabus?

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I think flow and access control are in syllabus.

Answer 1

Given Bandwidth (B) = 60 Kbps = 60*10³

Bitrate for each host (b) = 1024/40 = 25.6 b/s

 

In slotted ALOHA, Number of stations N = (0.368 * Bandwidth) / Bitrate of each station.

= (0.368 * 60*10³) / 25.6

= 862.5 stations

 

Comments

Can u explain how u got the formula ?

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anyone who knows the correct answer please post it.this question is leading to many confusions

Answer 2

The maximum throughput for Slotted aloha is $36.8$%, $0.368$
Hence, effective bandwidth $= 0.368*60kbps=22.08 kbps$
Bits per second outputted by each station $= 1024/40 = 25.6 bps = 25bps$

N station outputs 25 bits on a channel which has the effective B.W of 23.16 kbps
So, 
   $  (22.08*10^3)/25 = 22080/25= 883.2$, So 883 stations
 

Comments

Maximum throughout is 0.368 not 0.386 so answer is wrong..

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@Prabhu thanks, i corrected my solution.

Answer 3

throughput of slotted aloha=(efficiency of slotted aloha)*(bandwidth of the channel)........(1)

throughput of slotted aloha=(number of stations in slotted aloha)*(throughput of each stations)...(2)

so from 1 and 2

(number of stations in slotted aloha)*(throughput of each stations)=(efficiency of slotted aloha)*(bandwidth of the channel)

where the efficiency of slotted aloha is 36.8% or 0.368......