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<TITLE>Packet loss calculations in Smokeping</TITLE>
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<P><FONT SIZE=2 FACE="Arial">Chris, I will attempt to clarify some of your points, but first:</FONT>
</P>
<P><FONT SIZE=2 FACE="Arial">I have no control over the disclaimer. It is added automatically to all outgoing mail by the companies mail gateway. Legal will do what they are required to do, I apologize in advance, but it's going to be on anything I send.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">></FONT> <FONT SIZE=2 FACE="Courier New">This is actually an RRD question, at least in part, which is not specific to Smokeping </FONT>
<BR><FONT SIZE=2 FACE="Courier New">>(Smokeping may be feeding the wrong data to rrdtool).</FONT>
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<P><FONT SIZE=2 FACE="Arial">Agreed. (Yes, I think it is).</FONT>
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<P><FONT SIZE=2 FACE="Arial">></FONT> <FONT SIZE=2 FACE="Courier New">There are NO lost pings in the above record, i.e. all ten pings have values rather than </FONT>
<BR><FONT SIZE=2 FACE="Courier New">> being NAN.</FONT>
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<P><FONT SIZE=2 FACE="Arial">There are never any NAN values that I have found in the actual latency fields, regardless of the number of lost pings. To me this means that any attempt at having rrdtool calculate an accurate packet loss value is doomed from the start. Looks to me like rrdtool is attempting to calculate all latency values.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">></FONT> <FONT SIZE=2 FACE="Courier New">Perhaps this row which you give as an example was not really filled in at all, but</FONT>
<BR><FONT SIZE=2 FACE="Courier New">> interpolated between the previous and next rows? Alternatively, you do not say whether</FONT>
<BR><FONT SIZE=2 FACE="Courier New">> this record is a primary data point (PDP) or one of the archives. </FONT>
</P>
<P><FONT SIZE=2 FACE="Courier New">Here is another example. Notice by the time stamps that these are PDP's:</FONT>
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<P><FONT SIZE=2 FACE="Courier New">1171260000: NaN 0.0000000000e+00 4.0000000000e-03 3.0780843433e-03 3.0780843433e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03</FONT></P>
<P><FONT SIZE=2 FACE="Courier New">1171260300: NaN 9.2099200000e+00 4.0000000000e-03 3.0000000000e-03 3.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03</FONT></P>
<P><FONT SIZE=2 FACE="Courier New">1171260600: NaN 2.3430822667e+00 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03 3.9949136000e-03</FONT></P>
<P><FONT SIZE=2 FACE="Courier New">1171260900: NaN 0.0000000000e+00 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03 4.0000000000e-03</FONT></P>
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<P><FONT SIZE=2 FACE="Courier New">Seems to me, that in the case of a packet loss situation within a single poll, it is up to Smokeping to feed actual data from all 10 polls to rrdtool, even if one or more or all of the polls are timeouts. I'll leave the details of that to the developers of SmokePing, however I would count the number of ping requests that are lost and use that value for loss, rather than have rrdtool try to calculate it. Having rrdtool calculating averages to fill in the holes within a single rrd record seems to me to be a very bad approach for calculating loss data (although a good thing for interface traffic data). In the case of a completely missed poll (due to a system restart or some such event), then I would have no problem with interpolation being used for latency values.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">></FONT> <FONT SIZE=2 FACE="Courier New">Also, the loss value is not exactly 5 because of this interpolation and summarisation, and</FONT>
<BR><FONT SIZE=2 FACE="Courier New">> because RRD stores floating point numbers rather than exact ones.</FONT>
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<P><FONT SIZE=2 FACE="Arial">I would have no problem with a packet loss value of 8.5 or 9.5. However, as the example above clearly shows, we really have no idea of the actual numer of packets lost and therefore the actual packet loss for this event. Since we are using Smokeping data for outage reporting, it is very important to us the loss data be an accurate reflection of the loss on the network.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Thanks, Vern</FONT>
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