Which of the following is a 16-bit field that identifies the source port number of the application
program in the host that is sending the segment?

A.
Sequence Number

B.
Header Length

C.
Acknowledgment Number

D.
Source Port Address

Explanation:

Source Port Address is a 16-bit field that identifies the source port number of the application

program in the host that is sending the segment.
Answer option C is incorrect. This is a 32-bit field that identifies the byte number that the sender of
the segment is expecting to receive from the receiver.
Answer option B is incorrect. This is a 4-bit field that defines the 4-byte words in the TCP header.
The header length can be between 20 and 60 bytes. Therefore, the value of this field can be
between 5 and 15.
Answer option A is incorrect. This is a 32-bit field that identifies the number assigned to the first
byte of data contained in the segment.