TCP previous segment lost: Each TCP segment carries a byte counter and a length, e.g. "Here is the data, starting at byte number 1425765, for 1000 bytes, i.e. until 1426764." You would normally expect the next packet to say "Here is data starting at byte number 1426765, for 1000 bytes." But if you receive instead a segment that purports to start at 1427765, then you must have lost a segment somewhere. There is a hole in your data stream.
TCP acked lost segment: When the destination receives segment 1426765 for 1000 bytes, it can send an acknowledgement. Actually, it sends ACK 1427765, to say that it is OK so far, and it is expecting 1427765. I think this message means that the destination send an acknowledgement apparently for a segment that the analyser never saw. If you are getting this message, the destination knows more about the data stream than your analyser does. Maybe packets are going down more than one path, and the analyser is not seeing all of them. Or it could be a bug in the destination.
Maybe there is a different interpretation of the message: that a segment had arrived out of the correct sequence, been recovered, and had finally been ACKed. You will have to look in the analyser documentation to be sure. (Although knowing the standard of most technical documentation, it will probably say "This message means that TCP acked a lost segment" ;-( )
Kevin Dorrell
Luxembourg
