Question

(networking):if Host A wants to deliver a 12 bits segment to host B, and the sequence number of the previous bit sent is 82:

a)assuming that the segment reached its destination - what would be the serial number sent in the confirmation?

b)assuming that the confirmation was lost. how would the TCP protocol recover from the loss?

c)assuming that host B wanted to transmit data just after receiving the segment in the original question, is it possible to know what would be the serial number of the segment that will be sent?

Answer 1

a) Each bit is given one sequence number and sequence number of a segment is the sequence number of first bit of the segment.
It is given that sequence number of the previous bit sent is 82. So, now receiver wants to get bit with sequence number 83. So it sends serial number 83 in confirmation.

b) Every time a packet is sent a timer is started. If confirmation is reached to sender within that timer then the timer stops. But if the confirmation does not reach and the timer times out. Then the segment is retransmitted when the receiver receives the duplicate segment, it understands that confirmation must have got lost. So it discards the duplicate segment and resends the confirmation.

c) The starting serial number is selected randomly from a list of possible sequence numbers. So starting serial number cannot be known as it is selected randomly.

Hope this helps
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Thank You!!