Project ForgeComputer Networks
Transport Protocols & IP Addressing
GATE 2018
Hard
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 ____.
34 seconds(± 1 accepted)
Explanation
TCP sequence numbers wrap around after the full 32-bit space, 2³² bytes. At 1 Gbps = 1.25×10⁸ bytes/sec, the time to cycle through the full sequence space (and return to reusing 1234) is 2³²/1.25×10⁸ = 4,294,967,296/125,000,000 ≈ 34.36 seconds ≈ 34 seconds.
Source: GATE CS 2018 (2018)
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