(left the host)
              +------ acked_byte        +---sent_bytes
              |                         |
	      v                         v 
+++++++++++++++++++++++++++++++++++++++++
|p1-----|p2------|p3-----|p4------|-----|
       ^                ^
       |                |
       |                +-----p3.ack.last_byte
       |
       +--- p1.ack.last_byte




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