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[Datastream #AYJ-610338]: Level 2 radar delay intentional?

Hi Gilbert,

re: Level II latencies

> Right now, I am uniformly 7 minutes behind.
> 
> Mar 09 06:01:25 pqutil INFO:     1742 20060309060124.767 NEXRAD2 160013
> L2-BZIP2/KHDX/20060309055948/160/13
> Mar 09 06:01:25 pqutil INFO:    18089 20060309060124.648 NEXRAD2 424017
> L2-BZIP2/KSJT/20060309060009/424/17
> Mar 09 06:01:25 pqutil INFO:    44887 20060309060123.890 NEXRAD2 312019
> L2-BZIP2/KGRR/20060309055953/312/19
> Mar 09 06:01:25 pqutil INFO:     9074 20060309060124.742 NEXRAD2 989061
> L2-BZIP2/KARX/20060309055647/989/61
> Mar 09 06:01:25 pqutil INFO:     7388 20060309060125.015 NEXRAD2 635047
> L2-BZIP2/KRGX/20060309055826/635/47
> Mar 09 06:01:25 pqutil INFO:    29890 20060309060124.989 NEXRAD2 12026
> L2-BZIP2/KEAX/20060309055918/12/26
> Mar 09 06:01:25 pqutil INFO:    19138 20060309060124.972 NEXRAD2 819006
> L2-BZIP2/KLCH/20060309055951/819/6
> Mar 09 06:01:25 pqutil INFO:     8916 20060309060125.097 NEXRAD2 804015
> L2-BZIP2/KTWX/20060309060026/804/15
> Mar 09 06:01:25 pqutil INFO:    14192 20060309060125.080 NEXRAD2 52042
> L2-BZIP2/KGRB/20060309055601/52/42
> Mar 09 06:01:25 pqutil INFO:    13277 20060309060125.252 NEXRAD2 273032
> L2-BZIP2/KDAX/20060309055924/273/32
> 
> Level 3 data is beating this by 5-6 minutes.

Five things:

- the latencies your listing is showing are on the order of a second not 7
  minutes. Remember that latency is time received minus the time the product
  was created.

- I believe that the time included in the header of the Level II product
  is not the time that the volume scan finished or even the time when
  the piece of the volume scan finished.  I _think_ (but am not positive)
  that it is more like the time the volume scan began.

- A full volume scan takes on the order of 5 minutes to complete

- we know that the NWS is _NOT_ introducing a delay into the relay of the
  Level II data.  The have been working diligently to get the data out
  of the NEXRADs and to the toplevel relay nodes (IRaDS, Purdue, the MAX,
  and the ERC) as fast as possible.  For the record, we know this because
  Steve Emmerson has been asked on occasion to logon to the LDM machine
  at several NEXRADs to troubleshoot some problem.  It is our observation
  that the process by which data is injected into the LDM does not have
  any buffering.  In fact, the NWS' design is to not even try to relay
  data if it is more than 15 minutes old (meaning that the LDM queue
  on the NEXRAD LDM is very small).

- any toplevel Unidata relay can verify that the products being relayed to
  them are not being delayed by the toplevel relay by using:

  notifyme -vxl- -f NEXRAD2 -h toplevel_LevelII_relay

You can verify that there is no latency being introduced in the sequence of
relays to yourself by using the 'topology' links in the real time statistics
pages.  When a site's upstream host is reporting latency statistics, one
can click on the upstream hostname listed in the 'topology' link page
and see the differential latency from that indicated host to its immediate
upstream.

One last comment.  There are still some NEXRADs/LDMs at NEXRADs where the
system clock is not properly maintained.  This inaccuracy will manifest itself
in continuous latencies for that particular NEXRAD in the realtime statistics
plots.  I realize that this is not what you are referring to, but I wanted
to add it here "for the record".

Cheers,

Tom
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Ticket Details
===================
Ticket ID: AYJ-610338
Department: Support Datastream
Priority: Normal
Status: Closed