perfSONAR User Q&A and Other Discussion

[Jianan Wang <>]

Hi Alan, Andrew,

Thanks for providing me all these information. The threshold adjustment 
works perfectly for me!


On 4/8/2014 2:52 PM, Andrew Lake wrote:
> Hi,
>
> Well I stand corrected :) Ignore the first part of my email and see the 
> second half for how to adjust the thresholds accordingly.
>
> Thanks,
> Andy
>
>
> On Apr 8, 2014, at 2:19 PM, Alan Whinery 
> <>
>  wrote:
>
> > On 4/8/2014 3:43 AM, Andrew Lake wrote:
> > > Hi,
> > >
> > > A negative latency value means NTP is not synchronized. It does NOT
> > > mean latency is under a millisecond by itself. In real terms, it
> > > means a packet arrived to the destination before it was sent, which
> > > isn't possible unless the clocks are wrong. I would recommend
> > > correcting the clocks if at all possible rather than changing the
> > > thresholds.
> > A negative latency value does not mean that NTP is not synchronized.
> >
> > When the actual path latency is similar in magnitude to typical NTP
> > drift, synchronized clocks can show negative latency even though NTP is
> > properly synchronized. Between two hosts on a LAN, where latency is less
> > than a millisecond, and NTP is synchronized with only network peers (no
> > hardware clocks), negative latency results in owamp tests will probably
> > be unavoidable, because clock drift will be on the order of at least a
> > millisecond. It may be that temperature control and mature filters can
> > do better, but the way to ensure the necessary clock accuracy for
> > one-way latency on ~ 1 ms paths is to add hardware clocks to each node.
> >
> > it looks like Jianan already understood this, but you may have missed
> > his meaning of "on a LAN".
> >
> > > That being said, the thresholds in maddash are completely
> > > configurable. Under the checks section you can adjust the "command"
> > > option with the thresholds you want. Changing the -c and -w options
> > > to something containg the negative values will do what you want. For
> > > example -c "-15:15" -w "-10:10" will make it red if it falls outside
> > > the range -15 ms to 15 ms, yellow if its outside the range -10 ms to
> > > 10 ms and green if it is in between -10ms and 10 ms. The notations is
> > > standard nagios notation so you can do other fancy things with the
> > > ranges if you are familiar with that but the above should do the
> > > trick.
> > >
> > > Hope that helps, Andy
> > >
> > >
> > > On Apr 7, 2014, at 1:05 PM, Jianan Wang 
> > > <>
> > >  wrote:
> > >
> > > > Hi Everyone,
> > > >
> > > > I have a question about having Maddash display alarming red colour
> > > > while the latency value is minus. This maddash is operated on a
> > > > LAN, so there could be some minus latency issue from NTP
> > > > synchronization precision. Apparently the minus latency means the
> > > > latency is under milisecond, which should indicate the network is
> > > > pretty good, so I just wonder if I could tweak the Maddash to have
> > > > latency values lower than zero display green instead of red.
> > > >
> > > >
> > > > Thanks.
> > > >
> > > > -- Jianan Wang Department of Electrical and Computer Engineering,
> > > > Duke University Department of Optical Engineering, ZJU  Information
> > > > Engineering Qizhen Leadership School, ZJU Tel:(1) 919-937-4582
> > > > Email: