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[LDM #ZJU-572512]: Darn that LDM! ;-)

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  • Subject: [LDM #ZJU-572512]: Darn that LDM! ;-)
  • Date: Thu, 03 Nov 2011 15:18:17 -0600
Gilbert,

> Check this out...from NWS Central Region Headquarters...
> 
> 497
> NOUS73 KBCQ 032050
> ADMCRH
> 
> TO: ALL
> FROM: CRH
> SUBJECT: OC3 cutover follow up
> 
> ********** PLEASE SHARE WITH ENTIRE STAFF **********
> 
> 
> ***PLEASE SHARE WITH STAFF***
> 
> ALL,
> 
> THE OC3 CUTOVER PROBLEMS EXPERIENCED TODAY WERE A RESULT OF
> MTU ISSUES ON WFO/RFC ROUTERS AND LDM APPLICATION SOFTWARE.
> THE MTU AFFECTED PACKET TRANSFER RATES THAT DIRECTLY
> IMPACTED THE WAY CERTAIN WEB PAGES LOAD. THE LDM SOFTWARE
> WAS OVER RUNNING THE LOCAL WFO/RFC BANDWIDTH AS IT IS A
> SMART APPLICATION THAT AUTOMATICALLY DOES TCP CONGESTION
> CONTROL, WHICH SAW THE NEW OC3 AS A LARGE PIPE AND KEPT
> SENDING MORE DATA, WHICH IN TURN CHOKED THE LOCAL WFO/RFC
> BANDWIDTH, RESULTING IN RSYNC FAILURES AND SLOW DOWNLOAD
> SPEEDS. WE HAVE RATE LIMITED LDM HERE AT CRH ON THE OPSNET
> FIREWALL AND HAVE BEEN RUNNING SUCCESSFULLY. WE WILL
> CONTINUE TO MONITOR AND ADJUST AS NECESSARY TOMORROW.
> 
> IF YOUR SITE HAS ANY ISSUES OVERNIGHT WITH RSYNC, PLEASE
> CONSULT YOUR LOCAL IT STAFF AND IF NEEDED, OPEN A TICKET
> WITH OPSNET. PLEASE DO NOT OPEN A TICKET WITH NIDS UNLESS
> DIRECTED.
> 
> THANKS FOR YOUR PATIENCE AND ASSISTANCE DURING THIS MAJOR
> TRANSITION.
> 
> STEVE

Well, that explains the email we just received from them.

> ?
> ---
> 
> Hey, they admit it's a smart application. I fully agree! :-)

So do I. :-)

Actually the problem isn't the LDM. The problem is caused by the interaction of 
a TCP connection and its congestion algorithm with the lack of implementation 
of the Early Packet Discard algorithm in routers.

> *******************************************************************************
> Gilbert Sebenste                                                     ********
> (My opinions only!)                                                  ******
> Staff Meteorologist, Northern Illinois University                      ****
> E-mail: address@hidden                                  ***
> web: http://weather.admin.niu.edu                                      **
> Twitter: http://www.twitter.com/NIU_Weather                            **
> Facebook: http://www.facebook.com/niu.weather                           *
> *******************************************************************************

Regards,
Steve Emmerson

Ticket Details
===================
Ticket ID: ZJU-572512
Department: Support LDM
Priority: Normal
Status: Closed