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Re: NTp sources that work in a datacenter (was Re: Is latencyequivalent to RTT?)

  • From: Henk Uijterwaal (RIPE-NCC)
  • Date: Wed May 14 11:14:53 2003

On Wed, 14 May 2003, Steve Francis wrote:

> [email protected] wrote:
> > I assume that it's fairly common for people to have Solaris or Linux
> > boxes
> >
> >in every PoP to do measurements. In that case, the difficulty isn't in
> >measuring one-way latency, it's in synchronizing the time on all the
> >servers. And with fairly cheap GPS and CDMA clocks that is a lot
> >easier/cheaper than it once was.
> >
> But what GPS clock can you install in a datacenter? AFAIK, they all
> require roof (or at least window) access in order to install the
> antenna. (At least, all the GPS based ntp servers I've looked at do).

Half the sky is sufficient, so if you have a window that can open, you are
usually fine.  Just stick the receiver outside the window.

> Is that not true of CDMA servers?

No, they work inside buildings if there is not too much interference.  An
advantage of these units is that they work whereever a CDMA phone works,
so it really easy to check.   We have 2 CDMA units installed in
data-centers and they just work.

> How have others solved this issue? (Short of owning their datacenters.)

For GPS:  There are units on the market that can work with 250m of regular
CAT5 cable between GPS receiver and PC, if the building has structured
wiring, get permission to access the roof, then use the existing wiring to
reach the computer room.  Getting permission to access the roof is the
tricky part.


Henk Uijterwaal                             Email: [email protected]
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That problem that we weren't having yesterday, is it better? (Big ISP NOC)