[smokeping-users] The Smoke

[Chris Wilson]

Hi Thomas,

On Thu, 11 Feb 2010, Thomas Klein wrote:

> For every round of measurement smokeping sends several packets. It then 
> sorts the different round trip times and selects the median, (ie. the 
> middle one). This means when there are 10 time values, value number 5 is 
> selected and drawn. The other values are drawn as successively lighter 
> shades of gray in the background (smoke).
> 
> How can i find out what the smoke will look for such example values 
> where the median will be always 5?
> 
> Nr. 	Val1 	Val2 	Val3 	Val4 	Val5
> 1 	1 	1 	5 	4 	1

sort the values:

1 1 1 1 4 5
1-1 light
  1-1 medium
    1-1 dark with green bar on the media
      1-4 medium
        4-5 light

Note that 1-1 is invisible, so you will have a green bar at 1, with some 
medium smoke above that (1-4) and light smoke from 4-5. It will look 
pretty smoky.

> 2 	2 	2 	5 	5 	1

sort the values:

1 2 2 2 5 5

1-2 light
  2-2 medium
    2-2 dark with green bar
      2-5 medium
        5-5 light

median green bar at 2, a little light smoke below, lots of medium smoke 
above.

> 3 	3 	5 	5 	5 	1

sort the values:

1 3 3 5 5 5 

1-3 light
  3-3 medium
    3-5 heavy with green bar
      5-5 medium
        5-5 light

2 intervals of light and 2 of medium smoke below the median (5?), little 
or no smoke above.

> I have noted that my latency measurements tend to have more smoke above 
> the median measurement than below and wonder what this does mean and how 
> to interprete the graphs.

None of the pings will ever arrive with less than some minimum time 
(because of the speed of light) and most will be just a little above it 
(if you have good equipment and it's not overloaded), so the mean and 
median are just above the minimum. There is no maximum, however, and 
occasionally packets will get delayed quite significantly, and this shows 
as a lot of light smoke above the median (and eventually a change in the 
median if enough packets are delayed).

Cheers, Chris.
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