Suppose you are asked to design a new reliable byte-stream transport protocol like TCP. This protocol, named myTCP, runs over a 100 Mbps network with Round Trip Time of 150 milliseconds and the maximum segment lifetime of 2 minutes. Which of the following is/are valid lengths of the Sequence Number field in the myTCP header?

To prevent sequence number wrap-around while old packets might still be in the network, the sequence number wrap-around time must be greater than the Maximum Segment Lifetime (MSL).

1. Data generation rate:

   $$\text{Bandwidth} = 100\text{ Mbps} = \frac{100 \times 10^6}{8}\text{ bytes/sec} = 1.25 \times 10^7\text{ bytes/sec}$$

2. Maximum Segment Lifetime (MSL):

   $$\text{MSL} = 2\text{ minutes} = 120\text{ seconds}$$

3. Total bytes transmitted during MSL:

   $$\text{Data transferred} = 120 \times 1.25 \times 10^7 = 1.5 \times 10^9\text{ bytes}$$

4. Minimum sequence number space required:

   $$2^N \ge 1.5 \times 10^9$$

   Since $2^{30} \approx 1.0737 \times 10^9$ and $2^{31} \approx 2.147 \times 10^9$, we require:

   $$N \ge 31\text{ bits}$$

Therefore, any field length greater than or equal to $31$ bits is valid. Hence, 32 bits (B), 34 bits (C), and 36 bits (D) are valid sequence number lengths.