Re: [chrony-dev] SW/HW timestamping on Linux

[Denny Page <dennypage@xxxxxx>]

Miroslav,

There is no correction necessary. The speed change itself does not have any impact because the transmission time is symmetrical.

Given host A on a 1Gb link and host B on a 100Mb link:

  A -> Switch transmission time 754ns

  Switch -> B transmission time 7540ns

  Total time 8294ns

  B -> Switch transmission time 7540ns

  Switch -> transmission time 754ns

  Total time 8294ns

The propagation delay is symmetrical.

Unless there are a backlog of packets on one of the involved ports, the switch has zero impact on accuracy.

Denny

On Nov 21, 2016, at 00:30, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:

In your case you will still need to have some correction for the extra
delay due the switch in the 100mbit->1gbit direction and I suspect
switches in general will be the biggest trouble when trying to get the
best accuracy.