Homework 1: Discrete-Event Simulation

Hints, Partial solution, Suggested format of Log File, Directions for mailing homework to Lab Instructor,

Write in C a program to do the discrete-event simulation of a system representing a CPU and a Disk. The situation is as described in the following queueing network:

                
                
         SWITCH1    ----+       +--+           SWITCH2
 INPUT ---->x------->||||------>|  |------------->x--------> OUTPUT
            ^       ----+       +--+              |
            |       QUEUE1     SERVER1            |
            |                   (CPU)             |
            |          +--+          +----        v  
            x----------|  |<---------||||<--------+
                       +--+          +----
                     SERVER 2       QUEUE2                          
                      (DISK)

where SERVER1 is the CPU and SERVER2 is the Disk. QUEUE1 and QUEUE2 are, respectively, the buffers for requests to the CPU and to the Disk..

The system operates from INITTIME to FINTIME.
Jobs arrive to the INPUT randomly, say, with interarrival time uniformly distributed in the time interval AMIN..AMAX.
At SWITCH1 a job goes to the CPU if it is free, otherwise it waits on QUEUE1. When a job arrives to the CPU it executes for a random time uniformely distributed in the interval S1MIN .. S1MAX.
At SWITCH2 the jobs will have probability SIGMA of going to OUTPUT and (1 - SIGMA) of going to the Disk.
A job going to the Disk will wait in QUEUE2 if the disk is busy. Otherwise it goes to the Disk where it will stay for a random time uniformly distributed in the interval S2MIN .. S2MAX.
When a job is done at the Disk it goes back to the CPU. Notice that a job may go quite a few times around the loop CPU .. Disk.
At FINTIME the simulation terminates, that is, we do not consider further the jobs that are being serviced or that are waiting in the queues.

The user is asked at run time to specify:

a seed for the random number generator
the values of INITTIME, FINTIME, AMIN, AMAX, SIGMA, S1MIN, S1MAX, S2MIN, S2MAX
the name of a log file where will be logged each significant event [the significant events are , the arrival of a new job into the system, the start of a job at a server (CPU or Disk), the completion of a job at a server, and the end of the simulation (FINTIME)] [Here is the suggested format for the log file.]

Determine:

The average and the maximum size of each Queue.
The Utilization of each Server [= time-the-server-is-busy / total-time; where total-time = time of termination of the simulation( = FINTIME) - start time of simulation(= INITTIME)].
The Average and Maximum Response Time at each Server [or Turn-Around Time = Time a job completes service at the Server - Time that job arrived at that server and queue].
The Average and Maximum Response Time for the whole system (time when a job exits the system minus its arrival time)

Run the program a number of times with different values for the parameters and random seed. Examine in correspondence the utilizations and queue sizes. If for a given choice of parameters by changing the random seed we obtain utilization and size values that are stable [i.e. do not change much, say, change at most 10%], then we have a good simulation.

This homework is assigned on September 5 and it is due September 27 by 5pm. Mail the homework to the TA. Be sure to receive within 24 a message back from the TA confirming reception of the homework. If you do not receive the reply from the TA contact by email both the instructor and the TA.

ingargiola@cis.temple.edu