[ntp:questions] Re: Reliable SNTP server for commercial use

Danny Mayer mayer at gis.net
Mon Nov 22 04:33:49 UTC 2004

"Karapetkov, Stefan H" <stefan.karapetkov at siemens.com> wrote in message news:<mailman.9.1100911842.54146.questions at lists.ntp.isc.org>...
> Hello, 
> 		I am looking for a reliable network time server to provide
> Date and Time to our SIP telephones. 
> 		The SIP telephones support Simple Network Time Protocol and
> provide options to configure an IP address or DNS name of the SNTP server as
> well as time offset. Based on this configuration, the SIP telephone will
> contact the time server periodically and synchronize its internal Date and
> Time which is displayed in idle state. 
Any ntp server will provide sntp protocol support. sntp is basically a
subset of ntp.

> 		The time server should preferably send GMT time and the SIP
> phone user will be able to set the time offset.

ntp/sntp only know about UTC and nothing else.

> 		Any suggestions will be appreciated.

If you are inside a corporate network then you really want to have
number of internal  ntp servers running that the SIP phones can
connect to and leave it to the ntp servers to get the correct time.
Those ntp servers can be set up as usual to get their time from
either a clock module or the internet with the appropriate
confuration of the firewall.  These ntp servers cannot be set
up for anycast as it will be unable to distinguish between to
different server using the same address. Make sure that any ntp
server gets its time only from those providers that have authorized
them to query that time source.

It's much more important that the system on which you are running
the SIP server get acccurate time since it needs to communicate
with othe SIP Servers. I don't remember if the protocol requires
that two servers agree on the time or what accuracy is required.

> 		Since the time server is on the Internet while the SIP
> telephones can be installed in enterprise networks, please comment on the
> SNTP ability to traverse firewalls.
As long as you open UDP/123 port in the firewall for queries
from inside out and allow the replies back in, it will have no problem
traversing the firewalls.


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