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 ?

Answer 2

The maximum throughput for Slotted aloha is 36.8%, 0.386
Hence, effective bandwidth = 0.386*60kbps=23.16 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, 
     (23.16*10^3)/25 = 23160/25= 926.4, So 926 stations