00:01
We're asked to construct a finite state machine for a restricted telephone switching system that implements the following rules.
00:09
We're told the only calls to the telephone numbers 0, 911, and the digit 1, followed by 10 -digit telephone numbers that begin with 212.
00:23
We're going to go through.
00:38
Sorry.
00:38
I mean, in the digit one followed by 10 -digit telephone numbers that begin with 212 -80 -866 -867 and 888 are sent to the network.
00:54
All those strings of digits are going to be blocked by the system, and the user is going to hear an error message.
01:03
So, assume the possible inputs are the 10 digits.
01:12
Now let s0 be the start state.
01:56
Let s1 be the state representing a successful call.
02:10
So a call that goes through to the network.
02:15
And therefore it follows that there's not going to be any outputs from s1.
02:25
Now, from s0 we have the inputs of 2, 3, 4, 5, 6, 7, or 8.
02:57
So if we put in those inputs, then the machine goes back to s0.
03:10
And we'll output an error message for the user.
03:36
Now suppose that the input is zero at the state s0, then we're going to move to state s1, and we're going to output that zero is sent to the network.
04:24
Now, suppose that we input 9 at s0, then we're going to move to state s2, with no output.
05:27
Now, suppose that input 1 at s2, then we'll move to state s3 with no output...