<P> While IP handles actual delivery of the data, TCP keeps track of' segments' - the individual units of data transmission that a message is divided into for efficient routing through the network . For example, when an HTML file is sent from a web server, the TCP software layer of that server divides the sequence of file octets into segments and forwards them individually to the IP software layer (Internet Layer). The Internet Layer encapsulates each TCP segment into an IP packet by adding a header that includes (among other data) the destination IP address . When the client program on the destination computer receives them, the TCP layer (Transport Layer) re-assembles the individual segments and ensures they are correctly ordered and error - free as it streams them to an application . </P> <P> Transmission Control Protocol accepts data from a data stream, divides it into chunks, and adds a TCP header creating a TCP segment . The TCP segment is then encapsulated into an Internet Protocol (IP) datagram, and exchanged with peers . </P> <P> The term TCP packet appears in both informal and formal usage, whereas in more precise terminology segment refers to the TCP protocol data unit (PDU), datagram to the IP PDU, and frame to the data link layer PDU: </P> <P> Processes transmit data by calling on the TCP and passing buffers of data as arguments . The TCP packages the data from these buffers into segments and calls on the internet module (e.g. IP) to transmit each segment to the destination TCP . </P>

Which of the following is not a field in a control frame