Re: Clocking Sources (was NTp sources that work in a datacenter (was Re: Is latency equivalentto RTT?))
The desire for everyone to have a timing source that is tracable to a Cesium clock comes from the SONET standard. If you tie two SONET networks together, if they both don't have timing that's tracable to a Stratum 1 (PRS) source, they'll drift at the points where they interconnect and PSE (Positive Stuff Event) and NSE (Negative Stuff Event) errors will be the result. This is BAD BAD BAD for the voice networks that are provisioned over SONET.
BITS and SONET systems do not carry time-of-day information. It's only frequency. Sonet/GR253C SDH/G811 stratum-1 is 1x10-11 that will give you one pointer update every 72 days. But you can do one pointer-update every two frames... -P (you do stuffing on PDH systems)
This seems like a good time to put in a plug for the pool.ntp.org NTP servers. This is collection of public ntp servers provided by individuals and ISP's placed in a round-robin DNS system. The goal is to provide the general public with a list of NTP servers that they can use without abusing the stratum 1 servers. If you can provide an NTP server to the pool, it would be greatly appreciated. The bandwidth and CPU usage of an NTP server is quite low so you can easily provide NTP services to hundreds or even thousands of users. If you create default NTP setups and you don't have good default NTP servers to use, feel free to use pool.ntp.org for one or more of your NTP sources. (You should have at least 3 NTP sources, although using more than three doesn't usually help much.) For more information, see: http://fortytwo.ch/time/ -wayne
ns1.mainelinesys.com Curtis On Sun, 1 Jun 2003, wayne wrote:
This seems like a good time to put in a plug for the pool.ntp.org NTP servers. This is collection of public ntp servers provided by individuals and ISP's placed in a round-robin DNS system. The goal is to provide the general public with a list of NTP servers that they can use without abusing the stratum 1 servers.
If you can provide an NTP server to the pool, it would be greatly appreciated. The bandwidth and CPU usage of an NTP server is quite low so you can easily provide NTP services to hundreds or even thousands of users.
If you create default NTP setups and you don't have good default NTP servers to use, feel free to use pool.ntp.org for one or more of your NTP sources. (You should have at least 3 NTP sources, although using more than three doesn't usually help much.)
For more information, see:
-wayne
-- -- Curtis Maurand mailto:curtis@maurand.com http://www.maurand.com
Peter Lothberg wrote:
The desire for everyone to have a timing source that is tracable to a Cesium clock comes from the SONET standard. If you tie two SONET networks together, if they both don't have timing that's tracable to a Stratum 1 (PRS) source, they'll drift at the points where they interconnect and PSE (Positive Stuff Event) and NSE (Negative Stuff Event) errors will be the result. This is BAD BAD BAD for the voice networks that are provisioned over SONET.
BITS and SONET systems do not carry time-of-day information. It's only frequency.
Sonet/GR253C SDH/G811 stratum-1 is 1x10-11 that will give you one pointer update every 72 days. But you can do one pointer-update every two frames...
-P
(you do stuffing on PDH systems)
I reread my post and I didn't think I mentioned TOD information being a part of the BITS/SONET requirements. BUT, most if not all BITS systems that have a GPS component will also provide an NTP feed derived from the almanac and TOD information provided by the satellites. That's true of the Datum and the Symmetricom products and I'm pretty sure of the Larus products as well. -Richard
participants (4)
-
Curtis Maurand -
N. Richard Solis -
Peter Lothberg -
wayne