Suppose Host A sends three TCP segments back to back to Host

Suppose Host A sends three TCP segments back to back to Host B over a TCP connection. The first segment has sequence number 80; the second has sequence number 120, and the last one has sequence number 160; a. How much data is in the first segment? b. Suppose that the first segment is received by B and an ACK is received by A. If the second segment is lost but the third segment arrives at B. In the next acknowledgment that Host B sends to Host A, what will be the acknowledgment number?

Solution

a. the first segment has 39 bytes data (120 is the first byte in the next segment, so bytes 80 to 119 is transmitted)

b. the acknowledgement number from B will remain at 120 since it is expecting byte number 120 and receives an out of order packet.