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TCP Flow and Congestion Control

GATE CSE 2018 · Q25

NAT1 markMedium

Time

Consider a long-lived TCP session with an end-to-end bandwidth of 1 Gbps (=109= 10^9 bits-per-second). The session starts with a sequence number of 1234. The minimum time (in seconds, rounded to the closest integer) before this sequence number can be used again is _______.

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Solution

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Official answer: 34

TCP Flow and Congestion Control

TCP sequence numbers are 32 bits wide and count bytes of data.

  1. Total sequence numbers available:

    232 sequence numbers=232 bytes2^{32} \text{ sequence numbers} = 2^{32} \text{ bytes}
  2. Total data in bits before sequence number wrap-around:

    Total bits=232×8=4,294,967,296×8=34,359,738,368 bits\text{Total bits} = 2^{32} \times 8 = 4{,}294{,}967{,}296 \times 8 = 34{,}359{,}738{,}368 \text{ bits}
  3. Transmission rate (bandwidth):

    Bandwidth=109 bits/second\text{Bandwidth} = 10^9 \text{ bits/second}
  4. Wrap-around time:

    T=232×8109=34,359,738,368109≈34.3597 secondsT = \frac{2^{32} \times 8}{10^9} = \frac{34{,}359{,}738{,}368}{10^9} \approx 34.3597 \text{ seconds}

Rounding to the closest integer gives 34.

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This TCP Flow and Congestion Control previous year question is Q25 of the GATE CSE 2018 paper. Find more GATE CSE PYQs on TCP Flow and Congestion Control in Computer Networks, or browse all GATE CSE PYQs.

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TCP Flow and Congestion Control in GATE CSE

TCP Flow and Congestion Control has 23 GATE CSE PYQs across 21 papers from 2012 to 2026. This is the only 1-mark NAT question among them, and GATE CSE 2018 has 2.

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GateAI solution cardGATE CSE 2018 · Q25 · NAT

Consider a long-lived TCP session with an end-to-end bandwidth of 1 Gbps (= 109 bits-per-second). The session starts with a sequence number of 1234. The minimum time (in seconds, rounded to the closest integer) before this sequence number can be used again is …

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