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Re: 20030919: Re: Request for information re: LDM

This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.

  • Subject: Re: 20030919: Re: Request for information re: LDM
  • Date: Mon, 22 Sep 2003 09:12:45 -0600
Janet,

>Date: Mon, 22 Sep 2003 07:05:09 -0600
>From: Linda Miller <address@hidden>
>To: Janet S Gibson <address@hidden>
>Subject: 20030919: Re: Request for information re: LDM

The above message contained the following:

> > I am guessing that LDM transfers data via text based files.  Is that
> > correct

The LDM system deals with finite-length data-products.  It is irrelevant
whether or not the products are text-based (most of the data we
distribute is, in fact, binary).

> > or how does it deal with the marshalling/unmarshalling problem?
> > It also looks like LDM is built upon an RPC architecture.  Is this
> > correct?

The LDM component responsible for data-product transmission and
reception is based on ONC RPC technology; consequently, the data is
transmitted in a cannonical (XDR) form with the RPC layers handling
the marshalling and unmarshalling.

> > One of the problems I am trying to solve is a remote radar which
> > produces real-time data which needs to be displayed and analyzed on a
> > beam by beam basis in real-time at high data rates.  Is LDM a good match
> > for the data transfer part of this problem?

The LDM should be a good match.  In order to answer your question
definitively, however, I would need to know the following:

    1.  What corresponds to a data-product?
    
    2.  What size is it?

    3.  How often are these data-products generated?
    
    4.  How good is the communications link between the two computers?
        (I suggest running some ftp(1)-based tests).

One of our computers is currently transmitting about 1.2 megabits per
second of CONDUIT data via the LDM (that's well over a terabyte of data
per day).

> > How would this data be
> > integrated into my display and analysis packages?

A "decoder" would have to exist at the downstream LDM.  It would be
responsible for disposing of your data-products, which it would read from
standard input.

> > We are moving all of
> > our radar systems to PC Windows.  What plans are there for migrating LDM
> > in that direction?  When could we rely on its delivery?

There are no plans for porting the LDM system to Windows.  Depending on
the speed of the computer, you could probably run the LDM under a UNIX
emulator, however.

> > Janet S. Gibson
> >
> > N.O.A.A. R/ET6
> > 325 Broadway
> > Boulder, CO 80305
> >
> > phone: 303-497-6148
> > fax: 303-497-6181
> > email: address@hidden

Regards,
Steve Emmerson
LDM Developer