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 pediatrician's office. We assume that there is a pediatrician and a nurse and that we have three kinds of patients:

Patients that see first the nurse then the pediatrician
Patients that only see the nurse
Patients that only see the pediatrician

Thus the situation is as described in the following queueing network:


         SWITCH1  ----+       +--+  SWITCH2
 INPUT ---->x----->||||------>|  |---->x---------------------->x-----> OUTPUT
            |     ----+       +--+     |                       ^
            |     QUEUE1     SERVER1   |                       |
            v                (nurse)   v    ----+     +--+     |
            x------------------------->x---->||||---->|  |---->x
                                            ----+     +--+
                                           QUEUE2     SERVER2
                                                   (pediatrician)

where SERVER1 is the nurse and SERVER2 is the pediatrician. QUEUE1 and QUEUE2 are, respectively, waiting rooms for the nurse and for the pediatrician.

The pediatrician's office is open from INITTIME to FINTIME.
Jobs arrive to the INPUT randomly, say, with interarrival time uniformly distributed in the time interval AMIN..AMAX.
At SWITCH1 the patients may go to the nurse with probability R1 (of course, with probability 1-R1 they go to the pediatrician).
At SWITCH2 the patients that are done with the nurse will go to the OUTPUT with probability R2 (of course, they will go to the pediatrician with probability 1-R2).
When patients get to a server (nurse or pediatrician), if the server is free the patients move directly to the server; otherwise they wait in the queue of that server until their turn to move to the server arrives.
Jobs are serviced at a server for a random amount of time, uniformly distributed, say, in the interval S1MIN..S1MAX and S2MIN..S2MAX respectively at the nurse and the pediatrician.
At FINTIME the simulation terminates, that is, we do not consider further the patients that are being serviced or that are waiting in the queues.

The user is asked at run time for:

a seed for the random number generator
the values of INITTIME, FINTIME, AMIN, AMAX, R1, R2, 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 patient into the system, the start of a job at a server (nurse or pediatrician), and the completion of a job at a server] [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 - start time of simulation].
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].
For each kind of user, compute the Average and Maximum Response Time for the whole system

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 January 19 and it is due February 10 by 5pm. Be sure to receive a message back from the TA confirming that he has received the homework.

ingargiola@cis.temple.edu