[ntp:questions] Re: Question about RFC-2030 SNTP Version4

Christopher J. Holland msnews at microsoft.com
Fri Aug 1 21:40:47 UTC 2003


Hi,

It took me a while to find it, but this is the Link.
http://www.eecis.udel.edu/~mills/database/brief/arch/arch.pdf
Slide 7 show the same formulas.
I really don't want to get too deep into understand the theory behind the
formulas.
I would just like to calculate the answers, so they look like the NTP Client
Program does.
I thought I could just plug in the Received Packet Values and come up with
Delta and
Round trip. Unfortunately, it isn't working out that way. So, maybe someday
I will come back
and understand it.

Thanks
"David L. Mills" <mills at udel.edu> wrote in message
news:bgegb8$fvk$1 at dewey.udel.edu...
> Christopher,
>
> Please see Slide 7 in the NTP Archetecture briefing on the NTP Project
> page linked from www.ntp.org. Disregard "scarfed" as casual abuse of the
> English patois most widely known as millspeak. I'm too old to change my
> dirty rotten ways.
>
> Dave
>
> Christopher J. Holland wrote:
> > What is T4?
> > What does scarfed mean?
> >
> > The roundtrip delay d and local clock offset t are defined as
> >
> > Originate Timestamp     T1   time request sent by client
> > Receive Timestamp       T2   time request received by server
> > Transmit Timestamp      T3   time reply sent by server
> > Destination Timestamp   T4   time reply received by client
> >
> > d = (T4 - T1) - (T3 - T2)     t = ((T2 - T1) + (T3 - T4)) / 2.
> >   a.. C2 D4 F4 CE 45 41 63 77 (Reference Timestamp)
(14039115105183032183)
> >   b.. C2 D4 F4 D5 90 62 4D D2 (Originate TimeStamp T1)
> > (14039115136508251602)
> >   c.. C2 D4 F4 D3 4C 6E 19 B9 (Receive Timestamp T2)
(14039115126778239417)
> >   d.. C2 D4 F4 D3 4C 91 E2 15 (Transmit Timestamp T3)
(14039115126780584469)
> > Delta
> >
> >   a.. d = (14039115105183032183 - 14039115136508251602) -
> > (14039115126780584469 - 14039115126778239417)
> >   b.. d = (-31325219419) - (2345052)
> >   c.. d = 2.330172 seconds
> > Round Trip
> >
> >   a.. t = ((14039115126778239417-14039115136508251602) +
> > (14039115126780584469-14039115105183032183)) /2
> >   b.. t = ((-9730012185) + (21597552286)) /2
> >   c.. t = 130 ms
> >
> > Thanks
> > "David L. Mills" <mills at udel.edu> wrote in message
> > news:bgdu55$ao2$1 at dewey.udel.edu...
> >
> >>Christopher,
> >>
> >>How did you come to the conclusion the destination timestamp is zero?
> >>That would require your onboard clock to be zero as well.
> >>
> >>Dave
> >>
> >>Christopher J. Holland wrote:
> >>
> >>>Hi,
> >>>
> >>>Ok, then this is the correct way.
> >>>Originate Timestamp T1 = (Packet) Originate Timestamp
> >>>Receive Timestamp T2 = (Packet) Receive Timestamp
> >>>Transmit Timestamp T3 = (Packet) Transmit Timestamp
> >>>Destination Timestamp T4 =  The destination timestamp is scarfed by the
> >>>                                             receiver of  that packet,
> >>>making the total of four timestamps.
> >>>
> >>>So, does scarfed  mean that the Destination TimeStamp is 0?
> >>>
> >>>
> >>>TIA,
> >>>"David L. Mills" <mills at udel.edu> wrote in message
> >>>news:bgd0ed$qhc$1 at dewey.udel.edu...
> >>>
> >>>
> >>>>Christopher,
> >>>>
> >>>>The originate, receive and transmit timestamps are in the packet
header
> >>>>you receive. The destination timestamp is scarfed by the receiver of
> >>>>that packet, making the total of four timestamps. You may wish to
light
> >>>>up the architecture briefing at the NTP project page linked from
> >>>>www.ntp.org.
> >>>>
> >>>>Dave
> >>>>
> >>>>Christopher J. Holland wrote:
> >>>>
> >>>>
> >>>>
> >>>>>Hi,
> >>>>>
> >>>>>Thanks, but that isn't what I was asking. You already pointed it out.
> >>>>>I was just lucky to join the list when you did post it.
> >>>>>
> >>>>>I am trying to relate T1,T2,T3 & T4 to the Packet Structure.
> >>>>>
> >>>>>***** Is this the correct way? *******************************
> >>>>>Originate Timestamp T1 = (Packet) Reference Timestamp
> >>>>>Receive Timestamp T2 = (Packet) Originate Timestamp
> >>>>>Transmit Timestamp T3 = (Packet) Receive Timestamp
> >>>>>Destination Timestamp T4 = (Packet) Transmit Timestamp
> >>>>>
> >>>>>***** Is this the correct way? *******************************
> >>>>>Originate Timestamp T1 = (Packet) Originate Timestamp
> >>>>>Receive Timestamp T2 = (Packet) Receive Timestamp
> >>>>>Transmit Timestamp T3 = (Packet) Transmit Timestamp
> >>>>>Destination Timestamp T4 = (Then where do I get this value? is it the
> >>>>>Reference Timestamp?)
> >>>>>**********************************************
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>>>    Timestamp Name          ID   When Generated
> >>>>>>>    ------------------------------------------------------------
> >>>>>>>    Originate Timestamp     T1   time request sent by client
> >>>>>>>    Receive Timestamp       T2   time request received by server
> >>>>>>>    Transmit Timestamp      T3   time reply sent by server
> >>>>>>>    Destination Timestamp   T4   time reply received by client
> >>>>>>>
> >>>>>>> The roundtrip delay d and local clock offset t are defined as
> >>>>>>>
> >>>>>>>
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>    |
> >
> > |
> >
> >>>>>>>    |                   Reference Timestamp (64)
> >
> > |
> >
> >>>>>>>    |
> >
> > |
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>    |
> >
> > |
> >
> >>>>>>>    |                   Originate Timestamp (64)
> >
> > |
> >
> >>>>>>>    |
> >
> > |
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>    |
> >
> > |
> >
> >>>>>>>    |                    Receive Timestamp (64)
> >
> > |
> >
> >>>>>>>    |
> >
> > |
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>    |
> >
> > |
> >
> >>>>>>>    |                    Transmit Timestamp (64)
> >
> > |
> >
> >>>>>>>    |
> >
> > |
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>TIA,
> >>>>>Thanks,
> >>>>>"David L. Mills" <mills at udel.edu> wrote in message
> >>>>>news:bgbbil$be4$1 at dewey.udel.edu...
> >>>>>
> >>>>>
> >>>>>
> >>>>>>Christopher,
> >>>>>>
> >>>>>>Please take a number. You are somewhere in the list of thirty-odd
> >
> > folks
> >
> >>>>>>who have found and reported that typo
> >>>>>>
> >>>>>>     d = (T4 - T1) - (T3 - T2)     t = ((T2 - T1) + (T3 - T4)) / 2.
> >>>>>>(Correct Formula)
> >>>>>>
> >>>>>>The correction is on file at the IETF. A draft update to RFC-2030
with
> >>>>>>this correction and much new material is in review.
> >>>>>>
> >>>>>>Dave
> >>>>>>
> >>>>>>Christopher J. Holland wrote:
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>>Hi,
> >>>>>>>
> >>>>>>>I managed to decipher the 32 Bit Time to YYYY/MM/DD/HH//MM/SS
format.
> >>>>>>>Is there an RFC to tell you how to do that?
> >>>>>>>Now, I am trying to figure out how to calculate Round Trip delay
and
> >>>>>
> >>>>>Offset.
> >>>>>
> >>>>>
> >>>>>
> >>>>>>>I'm not sure which fields are which?
> >>>>>>>Good thing I popped on this list at this time. I still had the old
> >>>>>>>conversion formula!
> >>>>>>>
> >>>>>>>
> >>>>>>>Does
> >>>>>>>Originate Timestamp T1 = (Packet) Reference Timestamp
> >>>>>>>Receive Timestamp T2 = (Packet) Originate Timestamp
> >>>>>>>Transmit Timestamp T3 = (Packet) Receive Timestamp
> >>>>>>>Destination Timestamp T4 = (Packet) Transmit Timestamp
> >>>>>>>
> >>>>>>>or does
> >>>>>>>Originate Timestamp T1 = (Packet) Originate Timestamp
> >>>>>>>Receive Timestamp T2 = (Packet) Receive Timestamp
> >>>>>>>Transmit Timestamp T3 = (Packet) Transmit Timestamp
> >>>>>>>Destination Timestamp T4 = (Then where do I get this value? is it
the
> >>>>>>>Reference Timestamp?)
> >>>>>>>
> >>>>>>>
> >>>>>>>    Timestamp Name          ID   When Generated
> >>>>>>>    ------------------------------------------------------------
> >>>>>>>    Originate Timestamp     T1   time request sent by client
> >>>>>>>    Receive Timestamp       T2   time request received by server
> >>>>>>>    Transmit Timestamp      T3   time reply sent by server
> >>>>>>>    Destination Timestamp   T4   time reply received by client
> >>>>>>>
> >>>>>>> The roundtrip delay d and local clock offset t are defined as
> >>>>>>>
> >>>>>>>    d = (T4 - T1) - (T2 - T3)     t = ((T2 - T1) + (T3 - T4)) / 2.
> >>>>>
> >>>>>(Wrong
> >>>>>
> >>>>>
> >>>>>
> >>>>>>>Formula)
> >>>>>>>    d = (T4 - T1) - (T3 - T2)     t = ((T2 - T1) + (T3 - T4)) / 2.
> >>>>>>>(Correct Formula)
> >>>>>>>
> >>>>>>>
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>    |
> >
> > |
> >
> >>>>>>>    |                   Reference Timestamp (64)
> >
> > |
> >
> >>>>>>>    |
> >
> > |
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>    |
> >
> > |
> >
> >>>>>>>    |                   Originate Timestamp (64)
> >
> > |
> >
> >>>>>>>    |
> >
> > |
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>    |
> >
> > |
> >
> >>>>>>>    |                    Receive Timestamp (64)
> >
> > |
> >
> >>>>>>>    |
> >
> > |
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>    |
> >
> > |
> >
> >>>>>>>    |                    Transmit Timestamp (64)
> >
> > |
> >
> >>>>>>>    |
> >
> > |
> >
> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >
> >>>>>>>Thanks for your help
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>
> >>>
> >
> >
>





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