Let's say there are two host A and B, and host A sends data to host B and host B only sends ack segement(I know TCP is full-duplex but in this scenario, only A sends data to B, B only sends ack to A).

so when B receives data from A, B will prepair an ack segment and send it back to A. My questions is,

Q1-Is the Data field empty in this ack segement?

Q2- is the sequence number field in the ack segement empty like 0000...000, or a special bit pattern to indicate null? enter image description here

1 Answer 1


Q1: Yes, the data field may be empty when there's nothing to send.

Q2: The sequence number remains the same for pure ACK segments to indicate that no data has been sent. The sequence numbers for each direction are synchronized at initial connection and increased when data is send in that direction to indicate the data's position in the virtual stream.

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