Re: 20050724: Questions about LDM 6.4

Gilbert,

> To: General Support <address@hidden>
> From: Gilbert Sebenste <address@hidden>
> Subject: Questions about LDM 6.4
> Organization: NIU
> Keywords: 200507242026.j6OKQHjo017074 LDM-6.4

The above message contained the following:

> Now that 6.4 is out,

I almost wish that it wasn't. :-)  I managed to release it the evening
of the day before the LDM training-workshop so that I could use the
attendees as guinea pigs. :-)  The web-pages still aren't up-to-snuff
and now I have to answer support-email.  :-)

Such is life.  Please bear with me.

> I have questions. From the UNIDATA GFORGE website:
> 
> "Automatic switching between primary and alternate transfer-mode by 
> downstream LDM-s."
> 
> Suppose I have the following 4 scenarios:
> 
> 1. Site 1 (primary) has bandwidth issues and so is behind in sending me 
> data (say, HRS). Site 2 (alternate) has no issues and is fine. This 
> means that my LDM will automatically switch to site 2 for data, assuming, 
> of course, that I have site 2 as an an alternate feed.

That's correct.  Make sure that the REQUEST entries for site 1 and site 2
have the same feedtype and pattern.

> Question: Can I use more than 1 alternate for a particular feed,

Yes.

> and how does that work?

Just add another entry with the same feedtype and pattern.  For any
given feedtype/pattern pair, the first entry will be the initial primary
one and the other will initially be alternates.

This brings up an important point: feedtpe/pattern pairs in REQUEST
entries should either be identical to those of other entries or
completely disjoint (i.e., feedtype/pattern pairs should never
"overlap").

> 2. Site 1's upstream site goes down, so site 1's LDM is up, but since they 
> didn't specify a working alternate, no data is coming from them. Site 2 
> is unaffected because it gets its data from a different upstream source 
> that is working fine.
> 
> Question: Will the LDM automatically switch to site 2 if I have site 2 
> specified as an alternate?

Yes.

> 3. Site 1 is completely down; it's Internet connection is toast.
> Site 2 is fine. Question: Will the LDM switch over to site 2 
> automatically if I have site 2 specified as an alternate?

Yes.

> 4. Site 1 is down; site 2's LDM is up but no data is coming from it, and a 
> site 3 is fine. Assuming I can specify 2 alternates, will the LDM 
> automatically switch to site 3, assuming I have a second alternate?

Yes.

> How many alternates can I have? How many are practical?

No limit on the number of alternative, upstream LDM-s is imposed by the
LDM system.  At some point, however, the bandwidth used by the
COMINSOON messages from the alternate sites will exceed the bandwidth
used by the primary site.  Three or four upstream LDM-s for any given
feedtype/pattern pair is probably a reasonable upper-limit.

> *******************************************************************************
> Gilbert Sebenste                                                     ********
> (My opinions only!)                                                  ******
> Staff Meteorologist, Northern Illinois University                      ****
> E-mail: address@hidden                                  ***
> web: http://weather.admin.niu.edu                                      **
> Work phone: 815-753-5492                                                *
> *******************************************************************************

Regards,
Steve Emmerson

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