| Re: [chrony-users] Getting time synchronization offset from chronyd |
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William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ unruh@xxxxxxxxxxxxxx
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On Thu, 16 Jul 2020, Hal Murray wrote:
g.morand@xxxxxxxx said:
I only need to know that the system is not too much away from the actual time
(<= 1 second). I use *iburst* so that it gets quickly synchronized at
startup. I don't need much precision, that is why I use big sync intervals.
We are using the GSM network, where every MB costs, I know NTP is not much
but there is no small economy.
If network traffic is important, have you considered dropping chrony and
piggypacking whatever you need for time on other traffic?
That of course does not change the size of the packets sent/received.
And usually traffic is charged per byte, not per connection.
Fortunately ntp packets are not that big (something like 80 bytes).
The downside is that you have to become a time/NTP expert. You are half way
there already.
Do you actually need time on the IoT device? Can you use the time on the
server? That is, rather than sending a message that says "X happened at T0",
send a message that says "X just happened" and let the server fill in the
time. Or "X happened Y seconds ago" if you want to batch several events.
Are you using UDP? TCP? TLS? ...
TLS needs sane time for certificate checking.
With UDP, you have to do your own retransmissions. If timing is important,
you need to include some sort of ID in each packet so you can tell an expected
response from a long delayed response to a previous request.
I believe ntp protocol uses TCP.
Also the packets contain time information, so one can figure out when they
were sent by looking at the time information.
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