perfSONAR User Q&A and Other Discussion

[Andrew Lake <>]

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: 
>>> 
>>> 
>> 
>