$1.$ Suppose that a Web server runs in Host C on port $80.$ Suppose this Web server uses persistent connections, and is currently receiving requests from two different Hosts, A and B$.$ Are all of the requests being sent through the same socket at Host C$?$ If they are being passed through different sockets, do both of the sockets have port $80?$ Discuss and explain $(20$ points$).$

$2.$ Explain briefly how TCP protocol works in terms of connection setup and tear down. $(20$ points$)$

$3.$ What are the differences between TCP Tahoe and TCP Reno? $(20$ points$)$

$4.$ Host A and B are communicating over a TCP connection, and Host B has already received from A all bytes up through byte $126.$ Suppose Host A then sends two segments to Host B back$-$to$-$back. The first and second segments contain $80$ and $40$ bytes of data, respectively. In the first segment, the sequence number is $127,$ the source port number is $302,$ and the destination port number is $80.$ Host B sends an acknowledgment whenever it receives a segment from Host A $(20$ points$).$