Recapping TCP

Transmission Control Protocol (TCP) was first defined in RFC 675, and the v4 specification came out in RFC 793. TCP provides:

• Connection-oriented setup and tear-down of TCP sessions
• The service sends and receives a stream of bytes, not messages, and guarantees that all bytes received will be identical with bytes sent and in the correct order
• Reliable, in-order delivery, uses sequence number to recover from data that is damaged, lost, duplicated, or delivered out of order by the Internet communication system
• Flow control prevents the receiver's buffer space from overflowing
• Congestion control (as defined in RFC 5681) algorithms are: slow start, congestion avoidance, fast retransmit, and fast recovery
• Multiplexing; every TCP conversation has two logical pipes; an outgoing and incoming pipe

TCP header fields

Each TCP segment has a 20-byte header with optional data values, as shown in the following screenshot displaying a TCP frame in the Wireshark Packet Details pane:

The following...