Example Model

• Model timeShared from Law's textbook:
  • time-shared computer with N terminals
    • 
  • terminals send jobs with random computing time
  • jobs processed by single CPU in time-slices with round-robin scheduling
  • job completed → new job created after random waiting time
  • stops after NJ finished jobs
  • outputs average response time, queue length, CPU utilization
• Transaction-based approach:
  • jobs are modeled by entities
    • entities have attributes (startTime, serviceTime)
    • implemented as struct variables
  • handling of entities with four new atomics
    • 
  • am_adddata
    • adds a set of new attributes to each incoming entity
    • changes non-entity input to entity (conserving value as attribute)
  • am_writedata
    • changes value of an entity attribute
    • may use values from other attributes
    • changing function defined by arbitrary Matlab command
  • am_readdata
    • outputs value of an attribute from the input entity
  • am_deletedata
    • deletes a set of attributes
  • some atomics read parameter from entity attribute (server, distribute)
• Important new components:
  • server with exponentially distributed service times
    • coupled model using entities with attribute tS
    • 
  • N-server
    • serves up to N incoming entities, each with its own service time
    • atomic with complicated behaviour
    • e.g. several concurrent incoming and outgoing entities
    • NSA-DEVS → concurrent outgoing entities separated by infinitesimal time
• Complete model:
  • coupled models for Terminals and CPU straight forward
  • example output
    •