Subject: [ntpwg] NTP Follow-up packet details

From: "STUART VENTERS" <[email-masked]>
Date: Thu, 13 Nov 2008 09:25:28 -0600

Dave,

I'd like to understand your plan for NTP follow up timestamping.

 (On the ntp.org it appears that the details are still to be worked out.)

It appears that for a simple server to client time transfer,
    the following rules might cover it:

1) If the client receives a server packet with T3 < T2,
      then the server is using follow-up timestamping.
       (Which means that the T3 value is not for this transaction,
          but rather for the previous on in this session.)

2) A session is identified at by a unique set of
        server IP address and UDP port,
   and client IP address and UDP port.

3) Since we are only trying to transfer time to the client,
     the client doesn't need an accurate value for T1 in it's request packet,
       so we don't need follow-up for T1.

Are these rules reasonable / inline with what you were thinking?

Regards,

Stuart

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From: "David L. Mills" <[email-masked]>
Date: Thu, 13 Nov 2008 23:19:56 +0000

Stuart,

See the white paper http://www.eecis.udel.edu/~mills/onwire.html on the 
NTP project page. The interleaved options have been implmeneted and 
tested in thedevelopment version. See the xleave option on the server 
documentation page.

In the current code the interleaved modes avoid the message digest 
latency as well as the output queuing delays. However, for the most 
precise performance the drivers, in particular the ethernet driver 
interface code needs to be modified. For the best performance hardware 
timestamps would be required and the interleaved code can handle that if 
available.

***: The department has disabled access to our campus news server, so I 
can't read the newsgroup. I have no explanation why staff did that and 
they don't answer my mail. At last for the present, you should copy my 
campus mailbox [email-masked].

Dave