Information Technology Reference
In-Depth Information
TABLE 13.1
Colored Tokens for Modeling PIndex
States (Colors)
Description
Free
The node is free and able to process a message.
Dead
The node is dead; its position in the PG is vacant for joining nodes.
Busy
The node is busy processing a message, but will place a message
in its buffer.
Leaving
The node will leave soon; it will not accept any more messages but
will complete the ones in its buffer. It will also tell its PG and
referencing nodes to update their TECs.
Search request
The node is sending a search request; the receiving node responds
and forwards it according to the PIndex search algorithm.
Query response
The node is sending a response back, to any form of query.
Join requests
The node is requesting to join a PG (receiving); if space is vacant it
will join, otherwise the request is forwarded to a neighboring PG.
Contact updates
The node is updating its TEC replacing its existing contacts with
new ones; done when a node has newly joined a PG.
Resource updates
The node is updating its resource information, and informs the
nodes in its PG to do the same along with nodes in its TEC.
“execute stage” consuming the required node and message usage from
their respective places. Finally after the delayed transition (relative to the
job) and the condition that the buffer is empty, the token can be transited
to the “end” place.
13.5
In this section, we simulate PIndex under a large network population to
give an insight into the performance and behavior of PIndex. A descrip-
tion of the simulated conditions is given followed by their results.
PIndex Evaluation Using Colored Petri Nets
13.5.1
Simulation Conditions
Having implemented the PIndex CPN model, simulations were performed
under varying network conditions, while keeping the node i ring rates
(search, update, leaving, failure, and joining) and their probabilities
(i ring and failure) constant. The rates used in the PIndex simulator were
spread over a Poisson distribution, while the probabilities were spread
over a normal distribution. The rates used in the simulations for search,
update, leave, failure, and join rates were respectively 4, 20, 0.33, 0.16, and
0.5 per second. It is noted that the search and update rates were used
for each PG, while the remaining rates were for the whole PIndex network.
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