[chrony-users] Support for PTP transparent clocks

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

The latest code in git now supports PTP corrections provided by
one-step end-to-end unicast transparent clocks. It should allow
chronyd to reach the same or possibly even better performance as
a typical PTP client with full on-path PTP support.

The server needs to have HW timestamping and NTP-over-PTP enabled:

hwtimestamp *
ptpport 319

and the client also needs to enable the new extension field F324:

hwtimestamp *
ptpport 319
server a.b.c.d port 319 xleave minpoll 0 maxpoll 0 extfield F323 extfield F324

If you compile chronyd with the --enable-debug option and start it with
"-d -d", you can check for these messages:

ntp_io.c:536:(NIO_UnwrapMessage) Unwrapped PTP->NTP len=104 corr=0.000003016
ntp_core.c:1708:(apply_net_correction) Applied correction rx=0.000004600 tx=0.000004848 dur=0.000001584

If the reported correction in the first message is nonzero, there are
working PTP transparent clocks between the client and server.

In my tests it works well with the IES3110-8TF-R switch. Thanks to
James for recommending it.

Here is a list of switches with the required PTP support I received
from FS.COM. If you can test some of these switches or any other
switches claiming one-step E2E unicast TC support from other vendors,
please let us know.

IES3100-8TF IES3100-8TF-P
IES3110-24TF IES3110-8M12
IES3110-8TF IES3110-8TF-P IES3110-8TF-R IES3110-8TFM-P IES3110-8TFP-R
IES5100-24TS-P
S5800-48F4SR S5800-48F4SR-DC S5800-48F4SR-PE 
S5850-24S2C S5850-24S2C-DC S5850-24S2C-PE  
S5850-48B8C S5850-48B8C-DC S5850-48B8C-PE  
S5850-48S8C S5850-48S8C-DC S5850-48S8C-PE
S8550-32C S8550-32C-DC S8550-32C-PE
S5850-48S6Q-R S5850-48S6Q-R-DC S5850-48S6Q-R-PE (MA license required)

-- 
Miroslav Lichvar


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