11.1 TCP/IP Transport Layer  
  11.1.7 Transmission Control Protocol (TCP)  
Transmission Control Protocol (TCP) is a connection-oriented Layer 4 protocol that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack. In a connection-oriented environment, a connection is established between both ends before the transfer of information can begin. TCP is responsible for breaking messages into segments, reassembling them at the destination station, resending anything that is not received, and reassembling messages from the segments. TCP supplies a virtual circuit between end-user applications.

The protocols that use TCP include:

  • FTP (File Transfer Protocol)
  • HTTP (Hypertext Transfer Protocol)
  • SMTP (Simple Mail Transfer Protocol)
  • Telnet

The following are the definitions of the fields in the TCP segment:

  • Source port – Number of the calling port
  • Destination port – Number of the called port
  • Sequence number – Number used to ensure correct sequencing of the arriving data
  • Acknowledgment number – Next expected TCP octet
  • HLEN – Number of 32-bit words in the header
  • Reserved – Set to zero
  • Code bits – Control functions, such as setup and termination of a session
  • Window – Number of octets that the sender is willing to accept
  • Checksum – Calculated checksum of the header and data fields
  • Urgent pointer – Indicates the end of the urgent data
  • Option – One option currently defined, maximum TCP segment size
  • Data – Upper-layer protocol data

 

Web Links

TCP

http://www.webopedia.com/TERM/T/TCP.html