[time-nuts] time-nuts Digest, Vol 99, Issue 111

Magnus Danielson magnus at rubidium.dyndns.org
Sat Oct 27 14:14:11 UTC 2012


Dear Jacques,

On 10/25/2012 11:17 AM, Jacques Tiete wrote:
> Hello Magnus,
>
> I know what you're talking about, I'm working for a company specialized in
> broadcasting (from studio's to stations to satellites...) and in this
> world correct
> timing is paramount, we live by the 1/25 second rythm and even less if you
> have to sync on a line in the image ;-).
> Some time ago we were instaling a complete TV station and had huge problems
> with image stability and also especially the correct starting time of a
> clip or transmission.
> Nobody wants to start his newsreel at eg. 20:00:05;23... it must be
> 20:00:00;00
> We were looking into this and noticed that the customers servers (Win!)
> where
> synced by SNTP, this is plain c..p!
> Have a look @
> http://technet.microsoft.com/en-us/library/cc773013(WS.10).aspx
> Especially where it says:
> */"Important
> The W32Time service is not a full-featured NTP solution that meets
> time-sensitive /*
> */application needs and is NOT SUPPORTED by Microsoft as such. For more
> information, /*
> */see Microsoft Knowledge Base article 939322, Support boundary to
> configure the /*
> */Windows Time service for high-accuracy environments."/*
>
> Also have a look @ http://support.microsoft.com/kb/939322
> It says:
> */"We do not guarantee and we do not support the accuracy of the W32Time
> service /*
> */between nodes on a network. The W32Time service is not a full-featured
> NTP solution/*
> */that meets time-sensitive application needs. The W32Time service is
> primarily /*
> */designed to do the following:/*
> */Make the Kerberos version 5 authentication protocol work.
> Provide loose sync time for client computers.
> The W32Time service cannot reliably maintain sync time to the range of 1
> to 2 seconds. /*
> */Such tolerances are outside the design specification of the W32Time
> service."/*
>
> So it is... 1 to 2 seconds....!!!!!!!!

These are very valuable references, many thanks for bringing them to my 
attention.

> Our video playout servers are decent super stable units that use heaps
> of Xilinx FPGA's
> for coding/decoding videostreams supervised by a mil-spec VXworks OS, it
> uses the
> so-called LTC for synchronising the playout, implemented mostly in
> hardware so
> I did not suspect our machines. I did install a new TCG (TimeCode
> Generator) where
> I also had heaps of problems with, I did debug the stuff together with
> the manufacturer's
> R&D and finally got a perfectly synced station AND a Stratum-1 NTP
> (everything in
> double with automatic failover, a requirement for a TV-station). (Thanks
> to lurking for
> years as a genetically predispositioned Time-Nut, my father was a
> watchmaker...So I
> knew more or less what a was talking about and could prove things thanks
> to my TBolt etc.)
> Then I did install Meinberg NTP-client on every Win machine and all was
> suddenly
> perfectly running, everybody happy!
> This also solved some frequent file versioning problems for storing
> different versions of
> videoclips especially in a mixed Win/Lin environment where Linux proved
> to be the
> more logical/strict way of implementation.

This is a valuable experience to share. Many thanks!

> Another thing, being considered as the local video timenut a colleague
> called me from
> Saudi Arabia where he was having timing problems on two locations spaced
> 700km. apart
> where he had funny image jumps at the exact same time, both stations
> were synced by
> each the same TCG with GPS option (same as above), could the americans
> jam the GPS
> signals over there, somebody heard about this? It could be a real
> problem for us, we
> may need to use another method for station timing (Rb maybe, with some
> regular syncing
> etc.)

There are geographical areas where you have higher risk of being the 
indirect target, yes.

> Sorry for my long message but I don't often send timenut mail and this
> is a good example
> of some real-life timenutting ;-)

Then you should share me of your experience. :) This was a very nice post.

> I also have here a nice BeagleBone mini Linux board resting, where I
> would want to install
> a FreeBSD image on and implement a NTP with a promising GPS board from
> Adafruit,
> something for the long and cosy winter evenings... :-)

So many nice projects. :)

Have a BeagleBone lying around here somewhere. Putting a GPS onto it 
would be a great project. :)

Cheers,
Magnus




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