What is a TCP segment and its main header fields?

• A. A TCP segment includes a header with Source Port, Dest Port, Sequence Number, Acknowledgment Number, Data Offset, Flags, Window, Checksum, Urgent Pointer, Options, plus the data payload.
• B. A TCP segment contains only IP addresses and payload.
• C. A TCP segment is identical to a UDP datagram.
• D. A TCP segment includes Ethernet MAC addresses.

Answer: (A)

TCP segments carry data with reliability and in-order delivery between two endpoints. The main header fields include Source Port and Destination Port to identify the communicating processes, followed by the Sequence Number used to order segments and the Acknowledgment Number used to confirm receipt. The Data Offset indicates how long the header is (since options can extend it), and the Flags convey control signals for the connection (like SYN, ACK, FIN). The Window size provides flow control, telling the sender how much data can be sent before waiting for an acknowledgment. The Checksum offers error detection for the segment, Urgent Pointer handles any urgent data, and Options allows optional features. The Data payload is the actual application data carried by the segment. These elements together define a TCP segment at the transport layer, distinguishing it from other protocols.

Channels like UDP don’t include this kind of sequencing, acknowledgments, and flow control, and the header fields are different. Ethernet MAC addresses belong to the data-link layer, not the TCP segment header, so they aren’t part of the TCP header.