[ntp:questions] NTP over multicast sat link with no return channel

Danny Mayer mayer at ntp.isc.org
Sat Apr 8 02:19:16 UTC 2006


juliansomers at googlemail.com wrote:
> Hello!
> 
> I have a number of linux machines to which I send multicast data over a
> one-way dvb satellite link.
> 
> In addition to this dvb 'forward channel', these machines are able to
> connect to the internet via a satellite phone 'return channel'. I am
> currently running ntpd on them to sync the clock when they do connect
> via sat-phone. But as the sat-phone sessions are brief and irregular,
> this is not reliable enough. Sometimes months go by without any two-way
> traffic.
> 
> In my dreams, I am able to set the clocks with a multicast time signal
> over the one-way DVB channel, which is available at all times.
> 
> As far as I can tell, I can't use ntpd for this, as it won't work
> unless there can be a two-way conversation between client and server. I
> hope I am mistaken.
> 
> Is there any way it can be done?
> 
> Many thanks for your time,
> 
> Julian

Normally you could use broadcastclient novolley but you can't do that
with multicast even though there is no major difference between the two
because it's not implemented for multicast. It's something that we may
consider adding if it makes sense. I'm not sure that it makes sense to
use broadcastclient here.

YOu also have the issue of known asymmetry which you might need to take
account of.

Danny



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