1. CIS 235: Networks Fall, 2007 Western State College Computer Networks Fall, 2007 Prof Peterson

2. CIS 235: Networks Fall, 2007 Western State College A state machine is a restricted computational process. It is allowed to only remember one thing: the current state (a finite number). At each state, the machine observes an input and makes a transition to a new state. We write states in circles, transitions with arcs between circles, and input values as labels on these arcs. Inside each circle is a state name. We’ll only deal with machines in which there is only one possible transition in each state.

3. CIS 235: Networks Fall, 2007 Western State College Protocols are often described using state machines. We need to be able to read these state machines as if they were java code. EvenOdd 1 1 0 0

4. CIS 235: Networks Fall, 2007 Western State College Here’s an O-O state machine: class StateMachine { public int state; public StateMachine(int state) { this.state = state; }

5. CIS 235: Networks Fall, 2007 Western State College public void nextState(int input) { switch (state) { case 0: switch (input) { case 0: state = 0; break; case 1: state = 1; break; } case 1: switch (input) { case 0: state = 1; break; case 1: state = 0; break; }}

6. CIS 235: Networks Fall, 2007 Western State College  You have to encode the state and input as some sort of Java type. This is a perfect place for enumerations.  You can also place actions on the transitions or states. These are often represented a pieces of code on the arcs in a state diagram.  State machines can talk to each other by observing each others state and calling each others transition function.

7. CIS 235: Networks Fall, 2007 Western State College StateMachine s = new StateMachine(0); s.nextState(0); s.nextState(1); s.nextState(0); System.out.print(s.state);

8. CIS 235: Networks Fall, 2007 Western State College What sort of delays do a satellite link introduce? Why? What is the difference between circuit switching and packet switching? What is a “reservation”? What is “best effort”? What is an “end to end connection”? What is FDM? TDM? How are these used in current communication systems? What is bandwidth?

9. CIS 235: Networks Fall, 2007 Western State College  What is a “silent period”?  Why might circuit switching give better quality of service? What is the main drawback?  What is a “wrapper”?  What is a packet? Are packets really atomic?  What is “store and forward”?  What is a buffer / queue?  What is packet loss? How does packet loss manifest itself?