ack and delay ack

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Dear all,

I watched the video and know windows will ack every two packets, and Linux would ack two full MSS packets (dealy ack).

But I found my remote servers will ack every two packets or three packets (sometimes) when received when the client was moving data to the server. And sometime the server will also ack one packet when received data from the client but not always.

The client MSS is 1250, and the remote server MSS is 1350.

Please advise how to explain it and any document I can read to understand it?

Thank you! codec