[ntp:questions] Re: NTP, Mac OS X & Cisco 837

Richard B. Gilbert rgilbert88 at comcast.net
Wed Apr 13 15:24:15 UTC 2005


viz wrote:

>
>On 13/4/05 3:34 AM, in article 870o51de9734hu62ua88lq5kamdvgb48an at 4ax.com,
>"Brian Inglis" <Brian.Inglis at SystematicSW.Invalid> wrote:
>
>  
>
>>On Tue, 12 Apr 2005 20:10:21 +1000 in comp.protocols.time.ntp, viz
>><viz at REMOVEBLOCK.pacific.net.au> wrote:
>>
>>    
>>
>>>Description: Newbie (to NTP) wanting to set up NTP on a Mac G5, and to have
>>>it act as a broadcast server for a Cisco 837 router running SNTP. Mac ver
>>>10.3.8; NTP ver 4.1.1, Cisco 837 ver 12.3(2)XC2
>>>
>>>Problem: Cannot get my Mac to synch with Sydney located timeservers
>>>130.155.98.13 or 130.155.98.1
>>>      
>>>
>>Check out servers at:
>>http://ntp.isc.org/bin/view/Servers/WebHome
>>
>>This seems to be the only public access secondary server in Sydney:
>>http://ntp.isc.org/bin/view/Servers/NtpTpgComAu
>>there's another in Canberra:
>>http://ntp.isc.org/bin/view/Servers/AnimalGoldwebComAu
>>and you should contact the admins of these sites before use;
>>and there's also a public access pool server (currently in Melbourne):
>>au.pool.ntp.org
>>    
>>
>
>Hmmm might have to use the Melbourne one... I thought that there were
>geographical (distance) issues with ntp servers? The longer the distance the
>less accuracy?
>
>/viz
>
>  
>
Not exactly!  The potential error in transmitting the time from server 
to client via NTP is one half the round trip delay;  for a twenty 
millisecond round trip delay, the error could be anywhere from zero to 
ten milliseconds.  The physical length of the path between server and 
client and the speed of light determine a minimum delay.  There are, 
however, other causes of delay; e.g. every  hub, switch, and router the 
packet passes through adds some delay.

I believe that the major cause of error is asymmetry in the delays 
applying to the request and reply halves of the transaction.



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