[ntp:questions] Re: Clock accuracy & auto setting : digital television does a crap job of providing time services...
larson at w6yx.stanford.edu
Thu Apr 27 04:24:11 UTC 2006
In article <e2p993$qim$2 at gnus01.u.washington.edu> "Max Power" <mikehack at u.washington.edu> writes:
>In North America, the FM RDS time service is of very low quality.
>In Europe (I understand) this is not the case with RDS.
>Stations running RDS should be mandated by law to provide a quality
>service -- based on transmitter power and coverage area.
>Over time RDS's time service should be uniform.
>DRM (on MW and SW) time service is of a lower quality than RDS -- but could
>be upgraded with a specialized "80 bit" NTP-UNIX time packet.
>ATSC and DVB-T (& DVB-H/M) need a uniform ~"80 bit"...~"128 bit" time packet
>service that is well thought out.
>Futureproofing is important, so probably 128 bits or more is preferable.
128 bits? What do you want - to specify the time of the heat death of the
universe (long after our sun dies) to nanosecond resolution, then be able to
tell the time of the death of the next universe (if there is one)?
64 bit NTP is probably quite adequate, and definitely enough bits if
one doesn't insist on the NTP nanosecond precision.
However, the time information doesn't need to be NTP, or IP based.
By the way, NTP is not a part of unix.
Presently, the analog TV stations transmitting time don't even seem
to consider it worth keeping the clocks set accurately -- some use a
PC's clock, with no external source to deal with its drift.
The time sent with ATSC seems to be random as well. Some stations
seem to have gone ahead with DST, but the only way to get the program
data to be correct is to manually force (and set) the receiver to use
local standard time.
Of course, not using UTC is astoundingly stupid -- folks who live next
to a time zone boundary are out of luck if some stations are on each side.
However, counting on broadcasters to get the time right is a fantasy.
They cannot even get their program guide information correct in the data
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