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

Christopher J. Holland msnews at microsoft.com
Fri Aug 1 19:11:30 UTC 2003


If you have a few seconds, please visit my web site.

http://24.25.205.51/Project_TCPIP/Project_NTP/Project_NTP.htm
I did a packet Sniff of NTP and I am trying to come up with the values
that the NTP Client Program shows.

Some how, they are coming up with these values for T1,T2,T3 & T4.
Delta (Running Fast): 2.330172 seconds
Round Trip Time 130 ms

No matter what Values I plug in for T1,T2,T3 & T4, they
don't come out to the expect values.

NTP (Client to Server)
0B 00 00 00 (Flags)
00 00 00 00 (Root Delay)
00 00 00 00 (Root Dispersion)
00 00 00 00 (Reference Identifier)
00 00 00 00 00 00 00 00 (Reference Timestamp)
00 00 00 00 00 00 00 00 (Originate Timestamp)
00 00 00 00 00 00 00 00 (Receive Timestamp)
C2 D4 F4 D5 90 62 4D D2 (Transmit Timestamp)

NTP (Server to Client)
0C 01 00 F0 (Flags) (Version 1, Mode 4, Stratum Primary Ref, Poll
0)(Precision -16 (0.01526 ms)
00 00 00 00 (Root Delay)(0.00)
00 00 00 16 (Root Dispersion) (0.34 ms)
43 44 4D 41 (Reference Identifier) (CDMA)
C2 D4 F4 CE 45 41 63 77 (Reference Timestamp)
C2 D4 F4 D5 90 62 4D D2 (Originate Timestamp)
C2 D4 F4 D3 4C 6E 19 B9 (Receive Timestamp)
C2 D4 F4 D3 4C 91 E2 15 (Transmit Timestamp)

Converting to Decimal Notation
C2 D4 F4 CE 45 41 63 77 (Reference Timestamp) (14039115105183032183)
C2 D4 F4 D5 90 62 4D D2 (Originate Timestamp T1) (14039115136508251602)
C2 D4 F4 D3 4C 6E 19 B9 (Receive Timestamp T2) (14039115126778239417)
C2 D4 F4 D3 4C 91 E2 15 (Transmit Timestamp T3) (14039115126780584469)

Still Stuck on T4. Perhaps it is the original Transmit Time Stamp, or the
Original Reference TimeStamp,
??? T4 = C2 D4 F4 D5 90 62 4D D2 (Originate Timestamp)
(14039115136508251602)
??? T4 = 00  00 00  00  00 00 00 00 (Reference TimeStamp)
??? T4 = C2 D4 F4 CE 45 41 63 77 (Reference Timestamp)
(14039115105183032183)


 (T4 as the Reference Timestamp)










d = 2.330172 seconds







t = 130 ms (Not equal to)



 (T4 as the Originate Timestamp)











d = 2.330172 seconds (Maybe???)





t: := -9.729 x 10^9



t = 130 ms (Not equal to)



Thanks,
> As I understand it, when you ask a server for the time the server fills in
> T2 and T3, and you as the client fill in fields T1 and T4.  You need to
> keep a copy of T1 yourself, because the server may replace the T1 value by
> the time at which it got its last update (I paraphrase).
  T1 is the Reference Time Stamp, which is all 00's
  T4 is the originating Time Stamp.
> So you can make
> a first-order estimate of the server's sanity looking at the new value of
> T1 when the packer returns.  By manipulating your saved T1, T2, T3 and T4,
> you can get the round-trip delay and clock offset.
>
> The key thing is that (your copy of) T1 and T4 are completed by the client
> using its timeframe, and the server does T2 and T3 using the server's
> timeframe.  The copy of T1 in the return packet is overwritten by the
> server.


Thanks for your help,
"David J Taylor" <david-taylor at blueyonder.co.uk> wrote in message
news:hcxWa.59$pi1.964809 at news-text.cableinet.net...
> "Christopher J. Holland" <msnews at microsoft.com> wrote in message
> news:PSwWa.97$It3.109169 at twister.socal.rr.com...
> > 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
>
> As I understand it, when you ask a server for the time the server fills in
> T2 and T3, and you as the client fill in fields T1 and T4.  You need to
> keep a copy of T1 yourself, because the server may replace the T1 value by
> the time at which it got its last update (I paraphrase).  So you can make
> a first-order estimate of the server's sanity looking at the new value of
> T1 when the packer returns.  By manipulating your saved T1, T2, T3 and T4,
> you can get the round-trip delay and clock offset.
>
> The key thing is that (your copy of) T1 and T4 are completed by the client
> using its timeframe, and the server does T2 and T3 using the server's
> timeframe.  The copy of T1 in the return packet is overwritten by the
> server.
>
> (I'm not an expert so I hope I've got this right!).
>
> Cheers,
> David
>
>


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