Explain virtual-circuit switching vs datagram forward and the benefits of each

1) Explain virtual-circuit switching vs datagram forward and the benefits of each:

2) Explain the characteristics of ATM and the benefits provided by fixed-size cells:

3) Explain OFDM and how it operates. Alternately, you can explain the Shannon-Hartley theorem on the maximum data that can be transmitted over bandwidth.

4) Explain multi-path interference. Feel free to provide diagrams and examples of how systems may overcome this type of interference (for example multiple antennas, etc.).