7. For the client-server application over TCP: ( 3 marks) a. Why must the server program be executed before the client program? b. For the client-server application over UDP, why may the client program be executed before the server program? 8. What is the difference between MAIL TO : in SMTP and To : in the mail message itself? (1 marks) 9. Explain the main problem with the Network Address Translation. (2 marks) 10. Suppose that the UDP receiver computes the Internet checksum for the received UDP segment and finds that does not match the value carried in the checksum field. Can the receiver be absolutely certain that bit errors have occurred? Explain by giving example of binary numbers. ( 2 marks) 11. What is meant by destination-based forwarding? How does this differ from generalized forwarding? (2 marks) 12. Give an example showing why a network operator might want one class of packets to be