GSPN REPRESENTATION OF PHASE-TYPE DISTRIBUTIONS - Modelling with Generalised Stochastic Petri Nets - page 166

Table 7.5: Specification of the transitions of the Central Server Model of
Fig. 7.10

transition rate semantics transition weight priority ECS

TERM 0.1 infinite-server getCPU 1 1 1

T 1−2 3.0 infinite-server stopI 1 1 1

T 3 3.0 infinite-server getDISK 1 1 2

DISK 0.8 infinite-server complete 1 1 3

INT 1.0 infinite-server I/O 9 1 3

CPUbusy 1.0 infinite-server returnW 1 1 4

returnI 1 1 5

stopW 1 1 6

t 1 1 1 6

t 2 1 1 6

Table 7.6: Initial marking of the Central Server Model of Fig. 7.10

place initial marking

think 6

CPUidle 1

DISKidle 1

noINT 1

p 4 1

p control 1

and 7.11, respectively. In both cases, a structural analysis of the resulting
GSPN systems shows that immediate transitions stopW, t 1 , and t 2 belong
to the same ECS. Although not very likely, the possibilities for these three
transitions to be in apparent conflict exist and corresponding weights must
be assigned during the specification of the model. In practice, any assign-
ment of weights to these transitions works, since transitions t 1 and t 2 are
mutually exclusive due to the presence of only one token in place p control and
since transitions t 1 and t 2 only test the presence of tokens in place useCPU
so that their firings do not disable transition stopW when place grabCPU
is marked.
The GSPN systems of Figs. 7.3, 7.10, and 7.11 can now be considered as
different representations of the same problem that can be used for different
purposes: the original GSPN system of Fig. 7.3 can be used for a quali-