Assume that the bandwidth for a TCP connection is 1048560 bits /sec. Let α be…
2015
Assume that the bandwidth for a TCP connection is 1048560 bits /sec. Let α be the value of RTT in milliseconds (rounded off to the nearest integer) after which the TCP window scale option is needed. Let β be the maximum possible window size with window scale option. Then the values of α and β are
- A.
63 milliseconds, 65535 x 2^14
- B.
63 milliseconds, 65535 x 2^16
- C.
500 milliseconds, 65535 x 2^14
- D.
500 milliseconds, 65535 x 2^16
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Correct answer: C
Key idea: the bandwidth–delay product must not exceed the native 16-bit TCP window (65535 bytes).
Step 1: Maximum unscaled window = 65535 bytes.
Step 2: RTT threshold α = (65535 bytes × 8 bits/byte) / 1,048,560 bits/s = 524,280 / 1,048,560 = 0.5 s = 500 milliseconds.
Step 3: Window scale allows a left-shift up to 14, so maximum scaled window β = 65535 × 2^14 = 1,073,725,440 bytes (≈ 1.07 GB).
Answer: α = 500 milliseconds; β = 65535 × 2^14 (1,073,725,440 bytes).
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