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

Christopher J. Holland msnews at microsoft.com
Fri Aug 1 16:49:51 UTC 2003

```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
> >>>>>
> >>>>>
> >>>>>
> >>>>
> >>>
> >
> >
>

```