GateAI
Data Link Layer

GATE CSE 2021 Set 2 · Q54

NAT2 marksEasy

Time

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 (=106= 10^6 bits 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 \underline{\hspace{1.5cm}}.

Your answerNumerical answer

Enter a value to check

Solution

Step-by-step verified solution

Official answer: 135 (±5) (±5)

Data Link Layer

Given:

  • Frame length, L=1000 bitsL = 1000\text{ bits}

  • Channel transmission rate, R=1 Mbps=106 bpsR = 1\text{ Mbps} = 10^6\text{ bps}

  • Frame transmission time, Tfr=LR=1000106=10−3 s=1 msT_{\text{fr}} = \frac{L}{R} = \frac{1000}{10^6} = 10^{-3}\text{ s} = 1\text{ ms}

  • Aggregate arrival rate, λ=1000 frames/second\lambda = 1000\text{ frames/second}

The offered load GG per frame transmission time is:

G=λ×Tfr=1000×10−3=1G = \lambda \times T_{\text{fr}} = 1000 \times 10^{-3} = 1

For Pure ALOHA, the probability of a successful transmission is given by:

Psuccess=e−2G=e−2×1=e−2≈0.135335P_{\text{success}} = e^{-2G} = e^{-2 \times 1} = e^{-2} \approx 0.135335

The throughput in frames per second (S′S^{\prime}) is:

S′=λ×Psuccess=1000×e−2≈1000×0.135335=135.335S^{\prime} = \lambda \times P_{\text{success}} = 1000 \times e^{-2} \approx 1000 \times 0.135335 = 135.335

Rounding to the nearest integer gives 135 (acceptable range: 130 to 140).

Try the question first, then check your work.

Think the official key or this write-up is wrong?

Report error or challenge

Examiner trap

The misconception this question tests

This Data Link Layer previous year question is Q54 of the GATE CSE 2021 Set 2 paper. Find more GATE CSE PYQs on Data Link Layer in Computer Networks, or browse all GATE CSE PYQs.

Free diagnostic

Where do you stand for GATE?

Take the 20-minute diagnostic: the 3 topics that cost you the most marks, and a rank range. Or sit 5 related Data Link Layer PYQs now with no account.

One GATE CSE PYQ every morning

An official question by email at 7 AM IST, with a link to its verified solution. Unsubscribe in one click.

Data Link Layer in GATE CSE

Data Link Layer has 27 GATE CSE PYQs across 17 papers from 2013 to 2026. 12 of them are 2-mark NAT questions like this one, and GATE CSE 2021 Set 2 has 2.

How GATE tests Data Link Layer

More from GATE CSE 2021 Set 2

Share this solution

A plain-text card for WhatsApp or Telegram study groups.

GateAI solution cardGATE CSE 2021 Set 2 · Q54 · NAT

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 (= 106 bits 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 1.5cm.

Topic-wise GATE CS PYQs with verified steps

Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.