Classing Queues
    
      - Classing:
        
          - a group of entities are called to the front
            of the queue
            
              - entities have fixed classes (1, 2, 3, ...)
 
              - operator calls for a class number   
 
              - corresponding entities move to the front of the
                queue
 
              - relative order inside class members and among
                other entities remains
 
            
           
          - examples
            
              - boarding of a plane ("now all passengers of rows
                10 - 15")
 
              - routing of network packets ("now all packets of a
                given video file")
 
              - loading of a truck ("now all boxes of a given
                size")
 
            
           
        
       
      - Benchmark task:
        
          - reference model + classing (both versions)
 
          - one global operator
 
          - benchmark fixes operator behaviour and assignment of
            classes
 
          - problem
            
              - how to change the ordering in a queue dynamically