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

Maarten Wiltink maarten at kittensandcats.net
Sat Nov 20 14:58:24 UTC 2004

"Karapetkov, Stefan H" <stefan.karapetkov at siemens.com> wrote in message
news:mailman.9.1100911842.54146.questions at lists.ntp.isc.org...

> I am looking for a reliable network time server to provide
> Date and Time to our SIP telephones.

You are posting this as the _manufacturer_ of these telephones?
That's great - there have been parties before you who simply
"borrowed" other people's existing services without notice or
permission. The results were not pretty.

You could put up a few of your own public servers, suitably spread
out, or strike a deal with somebody who already does. Various ISPs,
Akamai, Apple, Red Hat, or even Microsoft.

> 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.

Is the polling interval configurable, and what is the default?

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

NTP servers always send only GMT (UTC, really) time. (I say NTP because
SNTP mostly means that a client restricts itself to a subset of NTP.)

> 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.

Traffic is UDP, to remote port 123, in a simple query-response pattern.
Firewalls should generally have no problems allowing inside-initiated

In enterprise settings, it would be reasonable to expect internal NTP
servers that could be used, so the telephones stay inside the firewall.
When deploying more than a few dozen of these devices (depending on the
polling interval), traffic considerations alone probably warrant internal
NTP service.

Maarten Wiltink

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