Subject: npmps-04bis

From: [email-masked]
Date: Fri, 22 Dec 2000 12:42:28 +0200

Dear IPPMers,

please find attached the version -04bis of the npmps draft. Thanks to Al &
Glenn for comments. The following changes to -04 have been made:

- I got rid of the the spurious month names due to Emacs' case-insensitive
search & replace algorithm. Indeed, these JUNE have caused some confusion.
- I implemented Al's refinement into 4.6. and added some more text into incT
error bullet pt. The section now reads

   The description of any specific measurement method should include an
   accounting and analysis of various sources of error or uncertainty.
   The Framework document [1] provides general guidance on this point, 
   but we note here the following specifics related to periodic
   streams and delay metrics:

   +  Error due to variation of incT. The reasons for this can be e.g.
      uneven process scheduling, possibly due to CPU load.
   +  Errors or uncertainties due to uncertainties in the clocks of the
      MP(Src) and MP(Dst) measurement points.
   +  Errors or uncertainties due to the difference between 'wire time'
      and 'host time'.

Earlier during the e-mail thread, Al commented that also real sources of
periodic streams may (and do) exhibit variation in transmission times. This
is true, but incorporation of intentional deviations from periodic behaviour
into the actual measurement metrics would result in a quite complex
construct. Basically, a (public domain) source should be cited for
definitive research results on "typical" variations due to O/S or
application. This should then be mapped into a corresponding metrics
description and so forth.

Thus, I find it a bit difficult to justify adding a mention of real
application behaviour in this context. In my view, the goal should be that
incT is (for practical purposes) negligible.

Season's greetings,

	Vilho

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 Vilho Räisänen                           
 [email-masked]                 
 Senior research engineer                 
 Nokia Research Center, Helsinki, Finland 
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