SNTP server + ntpd 4.2.4 client - NTP

This is a discussion on SNTP server + ntpd 4.2.4 client - NTP ; Unruh wrote: > SNTP is a client protocol, not a server, according to RFC. You keep saying that. Which RFC are you referring to? > We have absolutely no idea what you are running on all your machines. You > ...

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Thread: SNTP server + ntpd 4.2.4 client

  1. Re: SNTP server + ntpd 4.2.4 client

    Unruh wrote:

    > SNTP is a client protocol, not a server, according to RFC.


    You keep saying that. Which RFC are you referring to?

    > We have absolutely no idea what you are running on all your machines. You
    > never told us. This was an assumption based on the weird conditions you
    > stated. It really really helps if you give information when you ask for
    > help so that the help may actually be helpful. Tell us what your system is,
    > what "SNTP program" you are using as the server, what the other client
    > machines on the lan are running.


    The only client is an x86 PC running Linux 2.6.22.1-rt9 (i.e. with
    real-time extensions) and ntpd 4.2.4p0@1.1472.

    The server is an embedded device (HEOL-T101) with a GPS receiver and a
    Fast Ethernet port. I have no idea what operating system runs on the
    device; there might not even be an OS. The manufacturer claims the
    device implements SNTPv4 instead of the full NTP.

    ( http://www.heoldesign.com/index.php?id=58 )

    I plan to connect the two systems with a cross-over Ethernet cable.
    The round-trip time between the two systems would be 80-85 Ás.

    > If you attach a GPS PPS receiver to one of your boxes (the server) and you
    > use a reasonable client then yes you can expect much better than 100 Ás
    > accuracy on your net-- assuming it is not overloaded and the machines are
    > not overloaded with disk activity.


    The GPS receiver is inside the embedded device, which will serve time
    over its Ethernet port.

    Considering the answers I've been given by you and by others in this
    thread, I believe there is a good chance that the setup outlined above
    will work.

  2. Re: SNTP server + ntpd 4.2.4 client

    Noob writes:

    >Unruh wrote:


    >> SNTP is a client protocol, not a server, according to RFC.


    >You keep saying that. Which RFC are you referring to?


    >> We have absolutely no idea what you are running on all your machines. You
    >> never told us. This was an assumption based on the weird conditions you
    >> stated. It really really helps if you give information when you ask for
    >> help so that the help may actually be helpful. Tell us what your system is,
    >> what "SNTP program" you are using as the server, what the other client
    >> machines on the lan are running.


    >The only client is an x86 PC running Linux 2.6.22.1-rt9 (i.e. with
    >real-time extensions) and ntpd 4.2.4p0@1.1472.


    >The server is an embedded device (HEOL-T101) with a GPS receiver and a
    >Fast Ethernet port. I have no idea what operating system runs on the
    >device; there might not even be an OS. The manufacturer claims the
    >device implements SNTPv4 instead of the full NTP.


    Just looked it up. A bit bizarre-- power over the ethernet? The ethernet
    has no power supply capability. Do you mean that you have to supply the
    device with 60V running on one of the unused ethernet cable lines? Sounds
    noisy to me.

    The GPS timing claimed is 40ns, but the timestamp is only 10usec. How much
    does this thing cost? Are you really in a situation where this is a better
    solution than say a cheap Garmin 18LVC?




    >( http://www.heoldesign.com/index.php?id=58 )


    >I plan to connect the two systems with a cross-over Ethernet cable.
    >The round-trip time between the two systems would be 80-85 Ás.


    >> If you attach a GPS PPS receiver to one of your boxes (the server) and you
    >> use a reasonable client then yes you can expect much better than 100 Ás
    >> accuracy on your net-- assuming it is not overloaded and the machines are
    >> not overloaded with disk activity.


    >The GPS receiver is inside the embedded device, which will serve time
    >over its Ethernet port.


    >Considering the answers I've been given by you and by others in this
    >thread, I believe there is a good chance that the setup outlined above
    >will work.


    YOu have not told us what the requirements are, so what "will work" is
    is unclear. Yes, I am sure it will discipline your computer's clock.
    probably to better than ms accuracy.



  3. Re: SNTP server + ntpd 4.2.4 client

    Unruh wrote:

    > Just looked it up. A bit bizarre-- power over the ethernet? The ethernet
    > has no power supply capability. Do you mean that you have to supply the
    > device with 60V running on one of the unused ethernet cable lines? Sounds
    > noisy to me.



    You have no PoE devices in your environment? Phones over twisted pair? No
    APs? Cool! :-)

    The thing that strikes me as odd about this device is that it *doesn't*
    support NTP. If you are building a time appliance, why would you scrimp on
    the code and deny your customers NTP?


    --
    Peter Laws / N5UWY
    National Weather Center / Network Operations Center
    University of Oklahoma Information Technology
    plaws@ou.edu
    -----------------------------------------------------------------------
    Feedback? Contact my director, Craig Cochell, craigc@ou.edu. Thank you!

  4. Re: SNTP server + ntpd 4.2.4 client

    Unruh wrote:

    > Just looked it up. A bit bizarre-- power over the ethernet? The ethernet
    > has no power supply capability. Do you mean that you have to supply the
    > device with 60V running on one of the unused ethernet cable lines? Sounds
    > noisy to me.
    >

    I believe it is a relatively new, but very real, standard. The power is
    transmitted as a phantom between two pairs. In one variation, they are
    the pairs used for normal, 10baseT. I gather one reason is that there
    are exemptions in electrical codes for ELV power feeds as part of
    datacommunication systems, whereas a normal feed would require a
    formally qualified (not just competent) electrician.

    The feed is 48V DC. I'm not 100% sure that counts as ELV, but it is the
    same as most analogue telephone systems.

    The apparent source specification is IEE 802.3-2005, although I haven't
    gone to source.

    As the power is common mode with respect to the signals, the noise
    should not be excessive.

  5. Re: SNTP server + ntpd 4.2.4 client

    I use PoE every day -- it powers the outdoor antennae that connects to
    my wireless ISP (distance of about 5 miles). I have gotten up to
    3000kb/s over this link (which is slightly higher than what I'm paying
    for). So, whatever you are debating here, PoE is almost certainly *not*
    the problem.


    David Woolley wrote:
    > Unruh wrote:
    >
    >
    >> Just looked it up. A bit bizarre-- power over the ethernet? The ethernet
    >> has no power supply capability. Do you mean that you have to supply the
    >> device with 60V running on one of the unused ethernet cable lines? Sounds
    >> noisy to me.
    >>
    >>

    > I believe it is a relatively new, but very real, standard. The power is
    > transmitted as a phantom between two pairs. In one variation, they are
    > the pairs used for normal, 10baseT. I gather one reason is that there
    > are exemptions in electrical codes for ELV power feeds as part of
    > datacommunication systems, whereas a normal feed would require a
    > formally qualified (not just competent) electrician.
    >
    > The feed is 48V DC. I'm not 100% sure that counts as ELV, but it is the
    > same as most analogue telephone systems.
    >
    > The apparent source specification is IEE 802.3-2005, although I haven't
    > gone to source.
    >
    > As the power is common mode with respect to the signals, the noise
    > should not be excessive.
    >


  6. Re: SNTP server + ntpd 4.2.4 client

    andy.helten@dot21rts.com (Andy Helten) writes:

    >I use PoE every day -- it powers the outdoor antennae that connects to
    >my wireless ISP (distance of about 5 miles). I have gotten up to
    >3000kb/s over this link (which is slightly higher than what I'm paying
    >for). So, whatever you are debating here, PoE is almost certainly *not*
    >the problem.


    OK, learn something new every day! I do agree that it is weird that they
    would have put SNTP on that thing rather than NTP.

    How much did it cost?




    >David Woolley wrote:
    >> Unruh wrote:
    >>
    >>
    >>> Just looked it up. A bit bizarre-- power over the ethernet? The ethernet
    >>> has no power supply capability. Do you mean that you have to supply the
    >>> device with 60V running on one of the unused ethernet cable lines? Sounds
    >>> noisy to me.
    >>>
    >>>

    >> I believe it is a relatively new, but very real, standard. The power is
    >> transmitted as a phantom between two pairs. In one variation, they are
    >> the pairs used for normal, 10baseT. I gather one reason is that there
    >> are exemptions in electrical codes for ELV power feeds as part of
    >> datacommunication systems, whereas a normal feed would require a
    >> formally qualified (not just competent) electrician.
    >>
    >> The feed is 48V DC. I'm not 100% sure that counts as ELV, but it is the
    >> same as most analogue telephone systems.
    >>
    >> The apparent source specification is IEE 802.3-2005, although I haven't
    >> gone to source.
    >>
    >> As the power is common mode with respect to the signals, the noise
    >> should not be excessive.
    >>


  7. Re: SNTP server + ntpd 4.2.4 client

    The web page http://www.heoldesign.com/index.php?id=58 twice
    refers to NTP ("High Precision PG NTP Micro Server"; "The
    HEOL-T101 NTP server...") and twice refers to SNTP
    ("compliant with SNTP protocol"; "Timing Ethernet protocol:
    SNTP V4").

    Giving the manufacturer the benefit of the doubt, I would
    infer that it is a genuine NTP server, and that the packets
    sent over the wire comply with RFC 4330 (SNTP v4), which is
    the most recent RFC to be published on the subject of NTP
    and its relatives. As the RFC states, "The NTP and SNTP
    packet formats are the same".

    Paul

  8. Re: SNTP server + ntpd 4.2.4 client

    Unruh wrote:

    > Noob wrote:
    >
    >> Unruh wrote:
    >>
    >>> SNTP is a client protocol, not a server, according to RFC.

    >>
    >> You keep saying that. Which RFC are you referring to?



    Apparently, you forgot to answer this question ;-)


    >> The only client is an x86 PC running Linux 2.6.22.1-rt9 (i.e. with
    >> real-time extensions) and ntpd 4.2.4p0@1.1472.

    >
    >> The server is an embedded device (HEOL-T101) with a GPS receiver and a
    >> Fast Ethernet port. I have no idea what operating system runs on the
    >> device; there might not even be an OS. The manufacturer claims the
    >> device implements SNTPv4 instead of the full NTP.

    >
    > Just looked it up. A bit bizarre -- power over the ethernet? The ethernet
    > has no power supply capability.


    Engineers do all sorts of crazy things.

    http://en.wikipedia.org/wiki/Power_over_Ethernet

    Anyway, I didn't plan on using that feature.

    > The GPS timing claimed is 40ns, but the timestamp is only 10usec. How much
    > does this thing cost?


    Over 1000 euros (!!) AFAIU.

    > Are you really in a situation where this is a better
    > solution than say a cheap Garmin 18LVC?


    I've already told my boss several times about the GPS18LVC. I'm not
    sure why he ignores my request to test a unit.

    Reference to self:
    https://buy.garmin.com/shop/shop.do?pID=223&pvID=796

    The HEOL-T101 comes with a very stable XO (OCXO perhaps?) accurate
    within +/- 30 ppb. How much does such an XO cost?

    Does the GPS18LVC provide an oscillator to serve time even when there
    are not enough satellites in sight?

    >> Considering the answers I've been given by you and by others in this
    >> thread, I believe there is a good chance that the setup outlined above
    >> will work.

    >
    > You have not told us what the requirements are, so what "will work" is
    > is unclear. Yes, I am sure it will discipline your computer's clock.
    > probably to better than ms accuracy.


    My goal was clearly stated in my original message: Will the new setup
    provide better accuracy than the current setup.

  9. Re: SNTP server + ntpd 4.2.4 client

    On Mar 18, 1:05*pm, Unruh wrote:

    > Just looked it up. A bit bizarre-- power over the ethernet? The ethernet
    > has no power supply capability. Do you mean that you have to supply the
    > device with 60V running on one of the unused ethernet cable lines? Sounds
    > noisy to me.


    http://en.wikipedia.org/wiki/Power_over_Ethernet

    It's very common in VoIP environments, and environments with wireless
    access points. We use PoE to power both at our Chicago office; no
    "wall warts" needed. PoE switches cost about 30% more per port than
    non-PoE switches, depending on manufacturer.

  10. Re: SNTP server + ntpd 4.2.4 client

    Paul.Croome@softwareag.com wrote:

    > Giving the manufacturer the benefit of the doubt, I would
    > infer that it is a genuine NTP server, and that the packets
    > sent over the wire comply with RFC 4330 (SNTP v4), which is
    > the most recent RFC to be published on the subject of NTP
    > and its relatives. As the RFC states, "The NTP and SNTP



    That makes more sense. That's what we get for believing the marketers ... :-)

    PoE clock box, eh? Hmmmm. Not a bad idea ...

    --
    Peter Laws / N5UWY
    National Weather Center / Network Operations Center
    University of Oklahoma Information Technology
    plaws@ou.edu
    -----------------------------------------------------------------------
    Feedback? Contact my director, Craig Cochell, craigc@ou.edu. Thank you!

  11. Re: SNTP server + ntpd 4.2.4 client

    On 2008-03-19, Noob wrote:

    > Does the GPS18LVC provide an oscillator to serve time even when there
    > are not enough satellites in sight?


    No. You'll have to pay (much) more than $70-$80 if you want a good
    hold-over oscillator.

    --
    Steve Kostecke
    NTP Public Services Project - http://support.ntp.org/

  12. Re: SNTP server + ntpd 4.2.4 client

    Steve Kostecke wrote:
    > On 2008-03-19, Noob wrote:
    >
    >
    >>Does the GPS18LVC provide an oscillator to serve time even when there
    >>are not enough satellites in sight?

    >
    >
    > No. You'll have to pay (much) more than $70-$80 if you want a good
    > hold-over oscillator.
    >


    With something like 27 NAVSTAR (GPS) satellites aloft, there should
    almost always be seven or eight above the horizon. Satellites more than
    ten degrees above the horizon are preferred!

    I've never used the GPS18LVC (I have a Motorola M12+T) but if you know
    your exact location you only need one satellite to get the time. There
    are four equations in four unknowns (lattitude, longitude, elevation,
    and time). Not knowing any of these variables, you need four
    satellites. Once you know your location a single satellite is
    sufficient to solve for time.


  13. Re: SNTP server + ntpd 4.2.4 client

    Richard B. Gilbert wrote:

    > With something like 27 NAVSTAR (GPS) satellites aloft, there should
    > almost always be seven or eight above the horizon. Satellites more than
    > ten degrees above the horizon are preferred!
    >
    > I've never used the GPS18LVC (I have a Motorola M12+T) but if you know
    > your exact location you only need one satellite to get the time. There
    > are four equations in four unknowns (lattitude, longitude, elevation,
    > and time).


    ITYM latitude.

    > Not knowing any of these variables, you need four satellites.


    The Wikipedia article was an entertaining read.
    http://en.wikipedia.org/wiki/GPS#Calculating_positions

  14. Re: SNTP server + ntpd 4.2.4 client


    >Does the GPS18LVC provide an oscillator to serve time even when there
    >are not enough satellites in sight?


    No.

    --
    These are my opinions, not necessarily my employer's. I hate spam.


  15. Re: SNTP server + ntpd 4.2.4 client


    >I've never used the GPS18LVC (I have a Motorola M12+T) but if you know
    >your exact location you only need one satellite to get the time. There
    >are four equations in four unknowns (lattitude, longitude, elevation,
    >and time). Not knowing any of these variables, you need four
    >satellites. Once you know your location a single satellite is
    >sufficient to solve for time.


    That works only if you have appropriate software. The GPS-18 LVC
    doesn't have that sort of software.

    --
    These are my opinions, not necessarily my employer's. I hate spam.


  16. Re: SNTP server + ntpd 4.2.4 client

    Noob writes:

    >Unruh wrote:


    >> Noob wrote:
    >>
    >>> Unruh wrote:
    >>>
    >>>> SNTP is a client protocol, not a server, according to RFC.
    >>>
    >>> You keep saying that. Which RFC are you referring to?



    >Apparently, you forgot to answer this question ;-)


    As I just wrote, I was wrong. I was misremembering the rfc. Sorry for the
    misinformation.



    >> The GPS timing claimed is 40ns, but the timestamp is only 10usec. How much
    >> does this thing cost?


    >Over 1000 euros (!!) AFAIU.


    Ah, yes, that was exactly what I guessed ( see previous post). Sheesh.


    >> Are you really in a situation where this is a better
    >> solution than say a cheap Garmin 18LVC?


    >I've already told my boss several times about the GPS18LVC. I'm not
    >sure why he ignores my request to test a unit.


    >Reference to self:
    >https://buy.garmin.com/shop/shop.do?pID=223&pvID=796


    >The HEOL-T101 comes with a very stable XO (OCXO perhaps?) accurate
    >within +/- 30 ppb. How much does such an XO cost?


    >Does the GPS18LVC provide an oscillator to serve time even when there
    >are not enough satellites in sight?


    For a little while. But even with a bad off the shelf computer, the
    internal crystal is probably good for 200ppb, and if it is temp controlled,
    better than that.



    >>> Considering the answers I've been given by you and by others in this
    >>> thread, I believe there is a good chance that the setup outlined above
    >>> will work.

    >>
    >> You have not told us what the requirements are, so what "will work" is
    >> is unclear. Yes, I am sure it will discipline your computer's clock.
    >> probably to better than ms accuracy.


    >My goal was clearly stated in my original message: Will the new setup
    >provide better accuracy than the current setup.


    I misremember your current setup. But from operating a 18LVC on one
    computer distributed to a bunch around the department at a university, I am
    getting what looks like 10us accuracy on most of the machines-- not all. It
    depends on the machine load, network load, etc.
    On a machine querying that server over an ordinary telephone ADSL I am
    getting about 200usec accuracy ( with a 100usec offset in quiet ADSL times)
    Since I seem to recall that you were currently getting about 10ms accuracy,
    yes, almost anything will give you better accuracy than that.

    IF your machine runs linux then you will get better accuracy if you use
    chrony than if you use ntp ( by a factor of 2-3).(chrony is an ntp
    implimentation but with a very different clock discipline algorithm than is
    used by ntp). If you computer that you are trying to control is temperature
    controlled and has a constant work load, both will probably be about the
    same, but if the temp fluctuates due for example to changing work loads,
    then chrony does a much better job of tracking those fluctuations.



    What accuracy do you need?



  17. Re: SNTP server + ntpd 4.2.4 client

    "Richard B. Gilbert" writes:

    >Steve Kostecke wrote:
    >> On 2008-03-19, Noob wrote:
    >>
    >>
    >>>Does the GPS18LVC provide an oscillator to serve time even when there
    >>>are not enough satellites in sight?

    >>
    >>
    >> No. You'll have to pay (much) more than $70-$80 if you want a good
    >> hold-over oscillator.
    >>


    >With something like 27 NAVSTAR (GPS) satellites aloft, there should
    >almost always be seven or eight above the horizon. Satellites more than
    >ten degrees above the horizon are preferred!


    >I've never used the GPS18LVC (I have a Motorola M12+T) but if you know
    >your exact location you only need one satellite to get the time. There
    >are four equations in four unknowns (lattitude, longitude, elevation,
    >and time). Not knowing any of these variables, you need four
    >satellites. Once you know your location a single satellite is
    >sufficient to solve for time.



    Yes, but the internals of the receiver are not available to the user. Thus
    the 18LVC uses a minimum of 4 since it is quite possible that it is
    moving-- it is designed for OEM truck operations. Thus the 18LVC claim, if
    I recall correctly, that it needs 4 If less than 4 for a few 10s of seconds
    it stops delivering a PPS. On the other hand, as you say, if you have any
    view of the sky at all, that should not be a problem.


  18. Re: SNTP server + ntpd 4.2.4 client

    David Woolley wrote:

    >>> It's a violation of NTP, so the result will only be compliant as an
    >>> SNTP client.

    >> What is a violation of NTP?

    >
    > NTP clients must use NTP servers, not SNTP ones.
    >


    No, That is not correct. NTP clients can use SNTP servers. See the draft
    NTPv4 spec, section 14, for details.

    Danny

  19. Re: SNTP server + ntpd 4.2.4 client

    Noob wrote:
    > Unruh wrote:
    >
    >> AFAIK, SNTP is a CLIENT protocol, not a server. That is why it
    >> is called Simple.

    >
    > Is section 6 in RFC 4330 a figment of my imagination then?
    >
    > http://tools.ietf.org/html/rfc4330#section-6


    That is correct. It's not called CNTP.

    Danny

  20. Re: SNTP server + ntpd 4.2.4 client

    Harlan Stenn wrote:
    > David> NTP clients must use NTP servers, not SNTP ones.
    >
    > I do not believe this is true.
    >


    Correct.

    > The problem is one might want to *know* that the SNTP server is actually
    > talking to a refclock, or more generally, that the SNTP "instance" is
    > playing by the rules.
    >


    There is no way to ensure that. Furthermore there is nothing in the
    protocol which allows you to differentiate between the two. This is
    really a non-starter.

    Danny

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