As you can see in the table below, the RTT values (laboriously) measured off the RTT graph are in fact nothing more than the "time since last packet" of the next outgoing packet.
TCVAL and TCSECR values (which I have checked OK with Windump)  are ignored.
 
Packet    time since    TCVAL TSECR        Graph
            last packet                                    RTT value
315    0.250100        9290        7407    in    .189
316    0.189288        7456        9290    out   
317    0.218539        9361        7413    in    .22
318    0.220896 
 
True RTT values are several seconds.      
       
 
On downloads with timestamp disabled, the RTT graph also shows this time to next outgoing packet.
 
I'm using Windows 95, TCP1323=2, Ethereal set up file 0.9.8 downloaded 14 dec, and winpcap 3 0 a4.
Can anybody help?
 
Roger
 

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