Question about the sequence number and next sequence number

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If packet's Sequence Number and Next Sequence Number are equal that means the packet contains no data (TCP segment length = 0) in other words this is "pure ACK".

If you see such packet somewhere in the middle of a trace - this is unidirectional data transfer.

Keep in mind also 1 is not absolute Seq.n, but relative. If you want to spot real Seq.n you have to disable Relative Sequence numbers option in TCP dissector.