Time Management and Nullmessages

[Christian Stenzel]

Hello all,

for the preparation of my talk in Magdeburg I've read some
publications dealing with CERTI. My main resource is 
ftp://ftp.cert.fr/pub/siron/.

As I read in  ftp://ftp.cert.fr/pub/siron/02F-SIW-018.pdf 
the time synchronization relies on the original Nullmessage-algorithm 
of Chandy and Misra, also called CMB-algorithm. 

There a nullmessage is a promise not to generate
any message with a lower timestamp then tnow+lookahead. Nullmessages
are generated after each increment of the simulation clock (I suppose 
after each TAR resp. NER, if no "normal" message is available).

As I think to know this algoritm do not allow something like a 
zero-lookahead. When using zero-lookahead, normally it should lead to 
an infinite synchronization loop. Also depends the performance of the 
distributed simulation highly on the value of the lookahead and 
with it on knowledge depending on the concrete simulation model. 
Small lookaheads generate much more nullmessages and network traffic.

I've done no experiments concerning zero-lookahead and CERTI yet, so
 perhaps anyone of you had. This matter directly influences the TARA
and the NERA service, I suppose.

As I know protocols like Deadlock Detection and Recovery (Chandy, Misra)
or synchronous variants can handle zero lookahead.

So the question is if I could use zero-lookahead with CERTI. 


-- 
Psssst! Schon vom neuen GMX MultiMessenger gehört?
Der kann`s mit allen: http://www.gmx.net/de/go/multimessenger