Outstanding. Thanks Gilbert!
Mike Dross
mdross@xxxxxxxxxxxxxxxxxx
www.wright-weather.com
On May 12, 2011, at 12:06 PM, Gilbert Sebenste <sebenste@xxxxxxxxxxxxxxxxxxxxx>
wrote:
> Hello everyone,
>
> The issue which is causing the 1 and 2 frame packet drops
> from NOAAport for Linux kernels is/was this...
>
> http://www.linuxinsight.com/proc_sys_net_ipv4_ipfrag_max_dist.html
>
> 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):
>
> http://noaaport.admin.niu.edu:8025
>
> 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...
>
> http://www.novra.com/Website/Novra_Support.html
>
> 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: http://weather.admin.niu.edu **
> *******************************************************************************
>
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