[ntp:questions] Re: Asymmetric lines

John Pettitt jpp at cloudview.com
Sat Feb 5 03:11:29 UTC 2005



Richard B. Gilbert wrote:

> John Pettitt wrote:
>
>>
>> Hi all
>>    I just put up a stratum 1 server (FreeBSD using the GPS18 with 
>> PPS) on the end of a very asymmetric line (6000 kbps down 608 kbps 
>> up).   When I look on the local machine 
>> (gatekeeper.no-such-agency.net) I see this:
>>
>> ntpq> pe
>>     remote           refid      st t when poll reach   delay   
>> offset  jitter
>> ============================================================================== 
>>
>> *GPS_NMEA(0)     .GPS.            0 l    8   16  377    0.000    
>> 0.003   0.002
>> LOCAL(0)        73.78.73.84      5 l    1   64  377    0.000    
>> 0.000   0.002
>> +[stratum1-a]    .GPS.            1 u   29   64  377   21.147    
>> 2.068   9.112
>> +[stratum2-b]    .CDMA.           1 u   51   64  377   17.442    
>> 2.019   6.896
>> +time.sr.sonic.n 63.192.96.10     2 u   37   64  377   10.896    
>> 0.891   0.579
>>
>>
>> note: names of the stratum 1 servers edited
>>
>> However when I look from one of my other boxes 
>> (eschelon.no-such-agency.net in a server farm connected by multiple 
>> OC12's) I see
>>
>> ntpq> pe
>>     remote           refid      st t when poll reach   delay   
>> offset  jitter
>> ============================================================================== 
>>
>> LOCAL(0)        73.78.73.84      5 l   57   64  377    0.000    
>> 0.000   0.002
>> *gatekeeper.no-s .GPS.            1 u  777 1024  377   21.392   
>> -1.933   0.098  <- my S1 server
>> +[stratum1-a]    .GPS.            1 u  791 1024  377    7.456   
>> -1.524   0.421
>> +[stratum1-b]    .CDMA.           1 u  789 1024  377    3.446   
>> -1.171   0.216
>>
>>
>> Again the names of the stratum 1's edited but they are the same 
>> servers as above.
>>
>> So I'm seeing a 2ms offset on the box itself and about 600ms from the 
>> outside world.     I probably wouldn't care about this except that 
>> the offset seems to be stopping ntpd on my S1 from backing off it's 
>> poll intervals (it's been stuck at 64 for 12 hours).
>>
>> I seem to recall an asymmetric fudge patch being discussed but I 
>> can't find it.  Does anybody have a copy?  (or other suggestions for 
>> tweaking the setup)
>>
>> John
>> P.S. both gatekeeper and eschelon are part of pool.ntp.org
>
>
> I don't see the 600ms!   Gatekeeper differs from its reference clock 
> by 3 microseconds and from its upstream network servers by  1 -- 2 
> milliseconds.   Eschelon is seeing a -1.9 millisecond offset from 
> gatekeeper and -1 to -1.5 millisecond offsets from its upstream 
> networks servers.   What am I missing?
>
Typo 600us not 600ms - (it's been one of those days) - the 600us being 
as viewed from Eschelon - I guess I'm just being pick but it would be 
really nice if my S1 actually matched everybody elses :)

John




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