While opening a TCP connection, the initial sequence number is to be derived…
2009
While opening a TCP connection, the initial sequence number is to be derived using a time-of-day(ToD) clock that keeps running even when the host is down. The low order 32 bits of the counter of the ToD clock is to be used for the initial sequence numbers. The clock counter increments once per millisecond. The maximum packet lifetime is given to be 64s. Which one of the choices given below is closest to the minimum permissible rate at which sequence numbers used for packets of a connection can increase?
- A.
0.015/s
- B.
0.064/s
- C.
0.135/s
- D.
0.327/s
Attempted by 25 students.
Show answer & explanation
Correct answer: B
Given:
The time-of-day clock increments once per millisecond → 1000 ticks per second.
Maximum packet lifetime (MSL) = 64 seconds.
Reasoning:
Over the 64 s maximum packet lifetime the clock advances: 64 s × 1000 ticks/s = 64,000 ticks.
To avoid reuse or ambiguity of sequence numbers within that lifetime, the minimum permissible rate at which sequence numbers used for packets of a connection must increase is the number of seconds in the lifetime divided by the tick rate, i.e. 64 / 1000.
Calculation: 64 ÷ 1000 = 0.064 per second
Conclusion: The value closest to the minimum permissible rate is 0.064/s.