Nagetive frame time that is collected from PAA and WireShark

Unanswered Question
May 29th, 2008

Question of reading packages in Ethereal/Wireshak, that were collected from PAA:

When a read or write command comes in --- the first SCSI request package and the last SCSI complete package has high possibility not in the same capture file, especially when the capture file is not big.

Then I will see: [time from Exchange First: -5.763400000 seconds]

Does that mean total complete time is 5.7634 seconds???

I went back to 5-6 seconds from that frame, but could not find the first frame. So I was wondering maybe -5.7634 seconds does not really mean it. Do I need to do some kind of math to find the first request frame in previous files???

I have this problem too.
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plowden Tue, 06/03/2008 - 06:36

A negative time here could also mean two different fiber channel exchanges (SCSI command sequences) used the same originator exchange ID (OX_ID) and WireShark is getting confused. It's not against the standards for a device to use the same OX_ID, so this is not an issue with the PAA or the integrity of the packets. One way to tell Exchanges apart is to look at the receiver exchange ID (RX_ID). It's likely the RX_ID for a frame from the receive will be different for two different exchanges where the OX_ID is the same.


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