GATE | GATE-CS-2014-(Set-3) | Question 65

Every host in an IPv4 network has a 1-second resolution real-time clock with battery backup. Each host needs to generate up to 1000 unique identifiers per second. Assume that each host has a globally unique IPv4 address. Design a 50-bit globally unique ID for this purpose. After what period (in seconds) will the identifiers generated by a host wrap around?
(A) 128
(B) 64
(C) 256
(D) 512

Answer: (C)

Explanation: Wrap-around time is nothing but in how many seconds will all the hosts generate all IDs possible. (i.e. TOTAL_IDS / NO. OF IDS PER SEC).

Total IDs possible with 50-bit is 2^50.

One host generating 1000 identifiers per sec. So all hosts will generate 2^32 * 1000 —-> 2^32 * 2^10—–> 2^42 unique IDs.

If we Divide them, we get answer (i.e. 2^50/2^42=2^8)

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