[ntp:questions] long linear network, time accuracy, and ntp strata

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Tue Oct 19 14:15:24 UTC 2010


Miernik, Jerzy (Jerzy) wrote:
> Unruh and Terje, thank you for replying.
>
> What if we complicated networking somewhat, such that at times node50
> acquires GPS capability while node1 may looses it? Actually, to make
> the problem general, any one node (possibly only one) may have GPS
> and remain at an extremity of the network, where indeed the traffic
> between 'outer' nodes must be routed through all other 48 nodes
> forming a chain of 49 hops. So, sometimes node2 may have GPS too,
> like this:
>
> Node2 --- node3 --- node1 --- node4 --- .... --- node49 --- node50
> GPS
>
> Or nodes node1, node2, node3, node4 have GPS in some kind of a
> 'normal' network of four, with a long tail (like in a kite) of 46
> nodes attached to one of the four.
>
> How best could we write ntp.conf, to synchronize time in such special
> networks?

In that case it is equally easy:

You can use the exact same ntp.conf for every machine:

server node1 iburst
server node2 iburst
server node3 iburst
server node4 iburst

# HW ref clock line for any server which has one connected:
server 127.127.x.y ...

This works because NTP is intelligent enough to detect that you 
configure a server to use itself as a reference, so this line will be 
disregarded on those four potential GPS hosts.

The refclock line must either be commented out (on node5..50) or you'll 
have to softlink the relevant symbolic device, i.e.

/dev/gps0 -> /dev/tty0

on all of them.

Terje
-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"




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