he Autho- rization Key (AK) Update Protocol is used. The SS is responsible for maintaining valid keys. There are two active AKs with overlapping lifetimes at all times. A reauthoriza- tion process is done periodically. The AK lifetime is 7 days and the grace time timer is 1 hour. Figure 13.19 is the Traffic Encryption Key (TEK)-Finite State Machine (FSM) Transition Matrix. And Figure 13.20 is the (orization) finite state machine (FSM) transition matrix. Data encryption is based on DES ion CBC mode with IV derived from the frame number. Hooks are defined for other, stronger algorithms such as AES. Two simultaneous keys with overlapping and offset lifetimes allow for uninterrupted service. The rules REVIEW EXERCISES for key usage are as follows: AP: encryption (older key), decryption (both keys); AT: encryption (newer key) decryption (both keys). The key sequence number is carried in the MAC header. Only the MAC PDU payload (including subheaders) is encrypted. The management messages are unencrypted. REVIEW EXERCISES 1. Names three ways one might consider for configuring a metropolitan area net- work (MAN). 2. Which of the three ways of configuration would you use if re-siting nodes was not an option or requirement and the data rate on the backbone was > 54 Mbps. 3. Give two ways we can augment the capacity of a fiber-optic cable lay. Can you think of a third one? 4. Why would we want a ring network for the fiber option with automatic protection switching? 5. Give 3 unique differences in the WLAN arena between IEEE 802. 11a and 802.11b. 6. What is the main function of AP in an 802.11 configuration. 7. How would one define an "ad hoc" network? 8. What access protocol is used on IEEE 802.11. Suppose a node with traffic to send heard someone else on the medium. What action is taken? 10. What are the steps taken, in sequence, when a node has a packet to transmit? 11. The IEEE 802.15 standard goes by two common names. What are they? Roughly, what kind of maximum operational range can I expect from a WPAN transmitter? 13