[ntp:questions] What exactly does "Maximum Distance Exceded" mean?

Danny Mayer mayer at ntp.org
Tue Mar 17 03:26:02 UTC 2009

Joseph Gwinn wrote:
> In article <rZidnbLPV6C-nSLUnZ2dnUVZ_o-WnZ2d at giganews.com>,
>  "Richard B. Gilbert" <rgilbert88 at comcast.net> wrote:
>> Joseph Gwinn wrote:
>>> In article <49BDC52B.20808 at ntp.org>, mayer at ntp.org (Danny Mayer) wrote:
>>>> Joseph Gwinn wrote:
>>>>>>> The FAQ has to be the place for such explanations.
>>>>>> I'm not sure if this qualifies as an FAQ as I don't recall that it has 
>>>>>> come up before.  FAQ stands for Frequently Asked Questions.
>>>>> RAQ then?  Rarely Asked Questions
>>>>> Seriously, I can't believe that I'm the only person in history to be 
>>>>> perplexed by these status codes, and those little three-word summaries 
>>>>> are a bit telegraphic.
>>>>> Joe Gwinn
>>>> You aren't the only one. These questions have been asked before by a
>>>> number of people. In fact I had to look at this at one point when I was
>>>> getting these codes. Of course I just looked at the source code and
>>>> never looked for documentation.
>>> My fundamental point is that expecting a significant part of the NTP 
>>> user base to read the code simply does not scale, for a host of reasons.
>>>> I will tell you that this is a combination of bits so it's not just a
>>>> number. Each bit represents a test code that failed so you have quite a
>>>> bit to look at.
>>> Just for curiosity, how many semicolons are there in the NTPv3 and NTPv4 
>>> codebases?  My impression is that each is about 20,000 or 30,000, but I 
>>> don't know why or where I got the number.
>>> Joe Gwinn
>> I once did a "line count" of the entire NTP codebase.  70,000 lines!
> Oof!  I had no idea it was that large.  There is the reason why, out of 
> millions of users, very few will ever read the code.  Even 20,000 lines 
> would stop most people.  It would take at least a year of study to 
> become reasonably familiar with the code.  In the 1970s I did such 
> things for a living, but no longer would I be able to spend that much 
> time on any one thing.  
> Hmm.  In the 1970s, I worked on an embedded realtime program consisting 
> of ~60,000 lines of assembly code running on a midicomputer, a SEL 
> 32/85.  The big innovation was when we went to Fortran.
> Joe Gwinn

This probably includes all of the refclocks and the Windows code so YMMV.


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