Q4] (20 Marks): Give the reason of each of the following: i. Layered architecture is required for data communication models. ^ ii. Multiple-access protocol is needed to access the link in the shared networks iii. The frame header for a wireless LAN, IEEE 802.11, has four address fields. iv. For slotted ALOHA, the vulnerable time-T while in pure ALOHA, vulnera time=2*T frame frame