1. Please state the five layers of the network protocol stack. 2. Consider the following local area network (the port numbers in the figure refer to switch ports): Switch 1 Switch 2 Port 1 Port 3 Port 3 Port 1 Node A Node D Port 2 Port 2 Node B Node Assume the layer-2 forwarding tables are initially empty. The following forwarding events happen in the order as they are listed. Assume Event 2 happens right after Event 1 so that none of the forwarding table entries will timeout. Event 1: B sends a frame to A Event 2: D sends a frame to B Please illustrate the switch forwarding tables after each event: Switch l's table after event 1: Switch 2's table after event 1: Switch 1's table after event 2: Switch 2's table after event 2