[ldm-users] NOAAport transition update...

As you know, this has been very messy. As far as I can tell,
using a 3.8 meter dish (12 foot), I am getting good
reception until I get some rain, then it goes downhill
from our dish 60 miles west of Chicago.

But...obviously, there's the packet capture issue.
Jose Nieves, UNIDATA and many others (including NOAA,
of course) have had major reception issues due to the
"burstiness" of the data. With high data bursts,
substantial amounts of data are lost. Not by the
Novra receiver, but by the operating system.

Consider the following:


That's a summary of what Jose Nieves has done so far,
and as you can see, it's dramatic. He's used the
LDM and NOAAport software from UNIDATA, as well as
his own nbsp ingester, and, by using different
kernels and OS's, it really makes a huge difference.
Using CentOS and Debian, you get a lot of packet drops
with the 2.6.18* kernel. I have really been banging my head
since my Novra tells me I am getting NO packet loss,
and yet I'm seeing tons of dropped packets in my logs.
I've struggled to understand that the issue is at the
software level, and not necessarily at the hardware level.

This is also what NOAA is dealing with right now. If you have a Novra S-300, now would be the time to test to see if you can get the feed without dropping packets. NOTE: Your C/N should be 9 or higher for perfect reception,but even though mine is ~12.5, it guarantees NOTHING. No packet drops doesn't mean you aren't losing a ton of data, as NOAA and myself are after it's passed on to the computer/server. It is speculated that the 2.6.18 Linux kernels can't handle the data burstiness. The uplink is now fine, albeit lower in power than what I'd like to see.

Gilbert Sebenste                                                     ********
(My opinions only!)                                                  ******
Staff Meteorologist, Northern Illinois University                      ****
E-mail: sebenste@xxxxxxxxxxxxxxxxxxxxx                                  ***
web: http://weather.admin.niu.edu                                      **

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