4. TCP sequence numbers and ACK numbers (20 points). Hosts A and B are communicating over a TCP connection, and Host B has already received from A all bytes up through byte 2000. Suppose Host A then sends two segments back-to-back to Host B, with 1000 and 500 bytes of data in the first and second segments, respectively. In the first segment, the sequence number is 2001 (for simplicity, we assume the sequence number starts from 0, although it typically starts with a random number in practice), the source port number is 50002, and the destination port number is 80. Host B sends an ACK to A whenever it receives a segment from A. a. (6 points) In the second segment from A to B, what is the sequence number, source port number, and destination port number? b. (6 points) Suppose the first segment arrives at B earlier than the second segment. In the ACK for the first arriving segment from B to A, what is the ACK number, source port number, and destination port number? c. (4 points) Now suppose the second segment arrives at B earlier than the first segment (i.e., the two segments arrive out of order). In the ACK for the first arriving segment from B to A, what is the ACK number? d. (4 points) Now suppose the first segment is lost and the second segment arrives at B. In the ACK for the arriving segment from B to A, what is the ACK number?