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

David L. Mills mills at udel.edu
Fri Aug 1 19:51:01 UTC 2003

```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
> Transmit Timestamp      T3   time reply sent by server
>
> 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
>>>Transmit Timestamp T3 = (Packet) Transmit Timestamp
>>>Destination Timestamp T4 =  The destination timestamp is scarfed by the
>>>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,
>>>>
>>>>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
>>>>>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
>>>>>>>    Transmit Timestamp      T3   time reply sent by server
>>>>>>>
>>>>>>> The roundtrip delay d and local clock offset t are defined as
>>>>>>>
>>>>>>>
>
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>>>>>>>    |
>
> |
>
>>>>>>>    |                   Reference Timestamp (64)
>
> |
>
>>>>>>>    |
>
> |
>
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>>>>>>>    |
>
> |
>
>>>>>>>    |                   Originate 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
>>>>>>>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
>>>>>>>    Transmit Timestamp      T3   time reply sent by server
>>>>>>>
>>>>>>> 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)
>
> |
>
>>>>>>>    |
>
> |
>
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>>>>>>>    |
>
> |
>
>
> |
>
>>>>>>>    |
>
> |
>
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>>>>>>>    |
>
> |
>
>>>>>>>    |                    Transmit Timestamp (64)
>
> |
>
>>>>>>>    |
>
> |
>
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>