1. LAN Performance From Stallings text on LANs

2. CSMA/CD What is the maximum utilization possible for n nodes?

3. Determine Optimal Behavior of Each Node 1.Calculate probability of one node transmitting. 2.Optimize that probability with respect to N (it is a function of N). 3.Calculate expected number of contention cycles prior to a successful transmission. 4.Calculate efficiency.

4. Probability of ONE node transmitting P is the probability of each node transmitting 1-P is the probability that a node does not transmit Success is marked by the occurrence of one tranmission in conjunction with n-1 nodes refraining Probability each node transmitting Step 1

5. Maximize A with respect to P Step 2

6. So… the maximum value of A is

7. Probability of ONE node transmitting Estimate the length of the contention interval! Step 3

8. Therefore: Maximum utilization is Step 4

9. Results

10. Token Ring

11. a<1 and n nodes a is the fraction of the frame which can exist on the link OR the “time” it will take for the head to propagate back to the sender a/n is the time required to propagate from one node to the next node (time to pass the token) IF the token is released immediately after xmit:

12. a>1 and n nodes More than one frame fits. Head does not return to sender before xmit completes If sender needs the leading edge before forwarding the token: If sender needs the trailing edge before forwarding the token:

13. Asymptotic Token Ring Behavior as

14. See graphs