GATE CS 2018 Q25 — Transport Layer: Flow Control, Congestion Control, UDP, TCP, Sockets

To find the minimum time before a TCP sequence number can be reused (wrap-around time), we need to calculate how long it takes to consume the entire TCP sequence number space.

1. TCP Sequence Number Space

TCP sequence numbers are represented using a 32-bit field. Since TCP assigns a sequence number to every byte of data transmitted, the total sequence number space is:

2. Transmission Rate

The given bandwidth is $1\text{ Gbps} = 10^9\text{ bits per second}$.

Converting this rate into bytes per second:

3. Wrap-around Time Calculation

The time $T$ required to consume the entire $2^{32}$ sequence space is:

4. Rounding

• Rounding $34.36$ to the closest integer gives $34$.
• If we approximate $2^{32} \approx 4.3 \times 10^9$ or use other minor approximations, the result can be slightly higher, which is why the range 34 to 35 is accepted.