1. Give a short answer to the following topics:

• Are all the layers necessary? If so, according to what criteria we may devise the number of layers?
• Why do LANs tend to use broadcast networks? Why not use networks consisting of multiplexers and switches?
• What are the advantages and disadvantages of the current approaches in packet-switching?

2. A university computer science department has 3 Ethernet segments, connected by two transparent bridges into a linear network. One day, the network administrator quits and is hastily replaced by someone from the computer center, which is a token ring shop. The new administrator, noticing that the ends of the network are not connected, quickly orders a new transparent bridge and connects both loose ends to it, making a closed ring. What happens next. Explain your answer.

3. Let's assume the following situation: In principle, we may have two acknowledgment strategies when a file is transferred between two computers. One is to segment the file into packets, that are individually acknowledged by the receiver, but the file transfer as a whole is not acknowledged. In the other one, packets are not acknowledged individually, but the entire file is acknowledged when it arrives. Discuss these two approaches in terms of pros and cons.