A. To indicate the beginning of a three-way handshake B. To reassemble the segments into the correct order C. To identify the numbers of the data packets that can be sent without acknowledgment D. To track the different conversations crossing the network at the same time
TCP refers to the Transmission Control Protocol. This has to do with the traffic on the network and with TCP it can go in different directions. UDP is very similar to TCP in that it controls the conversations among the networks.
However, the difference between the two is that UDP which stands for User Datagram Protocol is easier and is not connected compared to the TCP. Both systems control how messages are sent and received on the Internet.
However, with UDP it is not connected so that once the message or packet is sent, it is over. TCP and UDP have port numbers attached to them and the purpose for having these port numbers is to track the different conversations crossing the network at the same time.
The main purpose of TCP/UDP port numbers is to track the different conversations crossing the network at the same time. Hence, the correct option is D.
Both TCP/UDP port numbers are mainly used by the application layer protocols of IP (Internet Protocol) model to transfer bits, called packets over the internet. These are widely used protocols over the internet.