Simulation of Telephone System

1. Simulation of Telephone System Lost-Call System Objective of simulation will be to process given number of call to determine processed, completed, blocked and busy call.

2. FROM TO LENGTH LINES NEXT CALL LINKS ARRIVAL TIME CALLS IN PROGRESS TO FROM END CLOCK CALL COUNTERS PROCESSED COMPLETED BLOCKED BUSY Fig (a) : - System State - 1

3. Fig (a), records the state of the system at time 1027 • There are two activities causing events: • New calls can arrive • Existing calls can finish

4. As shown in fig(a), there are 3 future events: • The call between lines 2 and 5 is due to finish at time 1053 • The call between lines 4 and 7 is due to finish at time 1075 • New call is due to arrive at time 1057

5. First step= scan the next potential event • In this case, the next potential event is 1053. The clock is updated. • Second step= Select the Activity that is to cause event • In this case, the activity is to disconnect the call. • Third step= Test whether the potential event can be executed • Fourth step= Change records to reflect the effects of the event • The call is shown to be disconnected by setting 0 for lines 2 and 5, reducing the number of links in use by 1, and removing the finished call from the call-in-progress table

6. Fifth and final step= Gather statistics of simulation output • Counters are set aside to record the number of processed, completed, blocked and busy calls. • With the disconnection of a call processed and completed call counts are increased by 1 • The state of the system then appears as shown in fig(b)

7. FROM TO LENGTH LINES NEXT CALL LINKS ARRIVAL TIME CALLS IN PROGRESS TO FROM END CLOCK CALL COUNTERS PROCESSED COMPLETED BLOCKED BUSY Fig (b) : - System State - 2

8. FROM TO LENGTH LINES NEXT CALL LINKS ARRIVAL TIME CALLS IN PROGRESS TO FROM END CLOCK CALL COUNTERS PROCESSED COMPLETED BLOCKED BUSY Fig (c) : - System State - 3

9. FROM TO LENGTH LINES NEXT CALL LINKS ARRIVAL TIME CALLS IN PROGRESS TO FROM END CLOCK CALL COUNTERS PROCESSED COMPLETED BLOCKED BUSY Fig (d) : - System State - 4

10. Typically, the simulation will run until a given number of calls has been processed or certain time has elapsed

11. Delayed Calls • Telephone system modified so that call which is not connected are not lost • Instead they wait until they are connected • Happens to messages in switching system that has store and forward capability

12. FROM TO LENGTH NEXT CALL LINES ARRIVAL TIME LINKS DELAYED CALLS TO FROM LENGTH CLOCK CALLS IN PROGRESS TO FROM END CALL COUNTERS PROCESSED COMPLETED BLOCKED BUSY Fig (e) : - System State – 3A

13. System moves through the first 2 states exactly as before • State of the system at time 1057, when the call from line 1 has arrived, now appears as shown in fig(e), which is labelled as system state-3A • Same as state 3, shown in fig(c), except that it now shows the delayed call • When a call is completed, it is necessary to check the delayed call list to see if a waiting call can be connected • The next event, however is arrival of call from line 3 at time 1063 which is going to line 6. The system goes to state-4A

14. FROM TO LENGTH NEXT CALL LINES ARRIVAL TIME LINKS DELAYED CALLS TO FROM LENGTH CLOCK CALLS IN PROGRESS TO FROM END CALL COUNTERS PROCESSED COMPLETED BLOCKED BUSY Fig (f) : - System State – 4A

15. FROM TO LENGTH NEXT CALL LINES ARRIVAL TIME LINKS DELAYED CALLS TO FROM LENGTH CLOCK CALLS IN PROGRESS TO FROM END CALL COUNTERS PROCESSED COMPLETED BLOCKED BUSY Fig (g) : - System State – 5A

16. Thankyou!