Computer-Networks

Question 25

Consider a network using the pure ALOHA medium access control protocol, where each frame is of length 1,000 bits. The channel transmission rate is 1 Mbps (= 10⁶bits per second). The aggregate number of transmissions across all the nodes (including new frame transmissions and retransmitted frames due to collisions) is modelled as a Poisson process with a rate of 1,000 frames per second. Throughput is defined as the average number of frames successfully transmitted per second. The throughput of the network (rounded to the nearest integer) is _________.

135

Computer-NetworksSliding-Window-ProtocolGATE 2021 CS-Set-2Video-Explanation

Question 25 Explanation:

1 frames takes = Tt = L / B.w. => 1000 / 10^6 = 1 millisec

1000 frame Tt = 1000 x 1 millisec = 1 sec

In 1 sec, 1000 frames sends, which is 1 millisec per frame.

So, G = 1

Efficiency of Pure Aloha (η) = G x e^-2G

where G = Number of requests per time slot willing to transmit.

e = Mathematical constant approximately equal to 2.718

So, η = 1 x 2.718(^{-2 x 1)} = 0.1353

Therefore, In 1 sec1000 frames = 0.1353 x 1000 = 135.3(closest integer) =>135

Throughput => 135

Correct Answer: A

Question 25 Explanation:

1 frames takes = Tt = L / B.w. => 1000 / 10^6 = 1 millisec

1000 frame Tt = 1000 x 1 millisec = 1 sec

In 1 sec, 1000 frames sends, which is 1 millisec per frame.

So, G = 1

Efficiency of Pure Aloha (η) = G x e^-2G

where G = Number of requests per time slot willing to transmit.

e = Mathematical constant approximately equal to 2.718

So, η = 1 x 2.718(^{-2 x 1)} = 0.1353

Therefore, In 1 sec1000 frames = 0.1353 x 1000 = 135.3(closest integer) =>135

Throughput => 135

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