Window (16-bit)— A parameter used for flow control. The window defines the range of sequence numbers beyond the last acknowledged sequence number that the sending machine is free to transmit without further acknowledgment.
Checksum (16-bit)— A field used to check the integrity of the segment. A receiving computer performs a checksum calculation based on the segment and compares the value to the value stored in this field. TCP and UDP include a pseudo-header with IP addressing information in the checksum calculation. See the discussion of the UDP pseudo-header later in this hour.
Urgent Pointer (16-bit)— An offset pointer pointing to the sequence number that marks the beginning of any urgent information.
Options— Specifies one of a small set of optional settings.
Padding— Extra zero bits (as needed) to ensure that the data begins on a 32-bit boundary.
Data— The data being transmitted with the segment.