Re: [ldm-users] NOAAport DVB-S2 primary packet drop issue SOLVED!

Outstanding. Thanks Gilbert!

Mike Dross

On May 12, 2011, at 12:06 PM, Gilbert Sebenste <sebenste@xxxxxxxxxxxxxxxxxxxxx> 

> Hello everyone,
> The issue which is causing the 1 and 2 frame packet drops
> from NOAAport for Linux kernels is/was this...
> It's a dynamic kernel tuning parameter for the network stack.  Here's the
> specifics:
> :  *"Redhat noticed in our latest test that we had a number of fragments
> :  dropped after timeout.  The number lost matched almost exactly with the
> :  number of frames reported lost by acq_stats.  They gave us a new kernel
> :  parameter to try modifying: net.ipv4.ipfrag_max_dist.  The default value
> :  is 64.  I increased it to 4096 per Redhat's suggestions and the lost
> :  frames reported by acq_stats immediately stopped."*
> But wait...I learned this morning that there's a way to get even better
> results tuning this parameter!
> Put this in your Linux system /etc/sysctl.conf file (or wherever it is
> located in your system):
> net.ipv4.ipfrag_max_dist = 0
> And then type this as user root:
> sysctl -w net.ipv4.ipfrag_max_dist=0
> THAT solves everything. Big or small, the packets get through!
> I am not losing ANY packets now. ZERO! Yippee!
> Credit for this fix goes to Raytheon, RedHat, and NOAA for their 
> collaborative effort. Now, if you are using another OS, you
> may need to fine-tune this parameter. Set it to zero, or in some
> cases, you may need to set it to 8192 if zero doesn't work for
> you. 4096 wasn't good enough for my CentOS/RHEL 2.6.18 kernel.
> I still dropped a few of the largest data chunks being sent across
> when it was set at 4096.
> The DVB-S2 issue isn't completely over yet. They still need to raise the 
> power back up another 5-6 dB from the bird (SES-1) to get it to where it was 
> before. For testing purposes, it was OK with a 3.7 meter dish.
> Here, have a look at what happened when a 55 dBZ cell producing 3/4" hail 
> passed over and south of our dish, directly in the path of the satellite,
> just before 8Z (3 AM CDT) this morning (the data for today will disappear at 
> 0Z this evening):
> Also...for those of you running npstats, which makes those neat graphs and 
> charts, author Jose Nieves is coming out with a fix shortly so that the
> signal strength will be seen if it drops below 60%.
> What is good about all of this happening is that the signal from NOAA is
> clean as a whistle. Interference, and any uplink issues which you could
> get away with under a DVB-S broadcast, is gone. I lost about 30 packets of
> data in 12 hours after changing the parameter above to 4096, but again,
> now it's zero. And I anticipate, barring thunderstorms, sun outages,
> etc...that many days I will have perfect reception, as will many of you.
> And with 5 days until the end of the original dual illumination was
> scheduled...if they really had to or wanted to...NOAA could dump the
> DVB-S broadcast and switch over to the new one.
> Finally, do NOT forget to update the firmware on your Novra S-300!
> I repeat...that's a must-do. Your reception, and most importantly,
> having the unit crash with subpar or no reception depends on you
> upgrading that immediately. Click here, and go to the bottom of the
> page to get the file...
> Also, for you Unix junkies, download and install CMCS on that same page,
> so you can administer it remotely. You'll be glad you did...
> Gilbert
> *******************************************************************************
> Gilbert Sebenste                                                     ********
> (My opinions only!)                                                  ******
> Staff Meteorologist, Northern Illinois University                      ****
> E-mail: sebenste@xxxxxxxxxxxxxxxxxxxxx                                  ***
> web:                                      **
> *******************************************************************************
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