computer networks - sequence number

Question

Suppose a TCP connection uses a fifteen bit clock to generate starting sequence numbers. The clock ticks for each 0.1 sec and each tick generate a sequence number. The lifetime of a packet 60 sec. If 300 sequence numbers are used by packets for each minute, what is the time for resynchronization of clock?

1.  3261.6 sec
2.  4261.6 sec
3.  5361.6 sec
4.  6433.6 sec

Answer 1

Each tick of the clock generates one sequence number in 0.1 sec

we have 15 bit clock

so, no. of sequences generated by clock = 2^15 =32768 sequence numbers

which will take 0.1 * 32768 =3276.8 sec by clock

now Lifetimeof the packet is 60 sec and in 60 sec it can eat 300seq numbers so it eats one seq no. in (60/300) =0.2 sec

now to finish 32768 seq no. it will take

0.2*32768

=6553.6 sec . but answer is not matching:(

approx. it is close to option (4)

can u plz tell the answer...

Comments

answer is option D

but can you pls explain what is menat by "what is the time for resynchronization of clock?" and have you taken into consideration that packet lifetime is 60 sec??

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and whts the use of finding that clock will take 3276.8 sec to generate sequence number??

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re-synchronization means :

when clock is ticking one by one it must be synchronised with the time when packet is eating sequence number one by one, due to synchronisation only I considered that if packet can use one seq no. in 0.2 second then to finish all the sequence no. of clock it needs 6553.6sec time

yes I am considering 60 sec as lifetime of the packet,till 60 second our message will be alive and after that we can use the same sequence number as long as wrap around time>lifetime of the packet

here wrap around time is 0.1 * 32768 =3276.8 sec > 60sec so all the 32768 seq no. can be used in 6553.6 sec

available sequence no. is more than enough..once all the 32768 seq no. is finished, clock will again tick from the start and resynchronise with the packet time