The Transmission Control Protocol (TCP) is a connection-oriented reliable protocol. It provides a reliable transport service between pairs of processes executing on End Systems (ES) using the network layer service provided by the IP protocol.
TCP providing reliable data transfer to FTP over an IP network using Ethernet
TCP is stream oriented, that is, TCP protocol entities exchange streams of data. Individual bytes of data (e.g. from an application or session layer protocol) are placed in memory buffers and transmitted by TCP in transport Protocol Data Units (for TCP these are usually known as "segments"). The reliabel, flow-controlled TCP service is much more complex than UDP, which only provides a Best Effort service. To implement the service, TCP uses a number of protocol timers that ensure reliable and synchronised communication between the two End Systems.
For most networks approximately 90% of current traffic uses this transport service. It is used by such applications as telnet, World Wide Web (WWW), ftp, electronic mail. The transport header contains a Service Access Point which indicates the protocol which is being used (e.g. 23 = Telnet; 25 = Mail; 69 = TFTP; 80 = WWW (http)). The port numbers associated with these services generally have the same value as those used for UDP services (a full list of all port numbers is provided in the reference at the end of this page).
UDP (and description of how ports work)
Example Packet Decodes
TCP is defined by a number of RFCs published by the Internet Society.
Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
Clark, D., "Window and Acknowledgement Strategy in TCP", RFC 813, July 1982.
Jacobson, V., Braden, R., and D. Borman, "TCP Extensions for High Performance", RFC 1323, May 1992.
Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP Selective Acknowledgment Options", RFC 2018, October 1996.
Touch, J., "TCP Control Block Interdependence", RFC 2140, April 1997.
Allman, M., Paxson, V., and W. Stevens, "TCP Congestion Control", RFC 2581, April 1999.
Floyd, S., Mahdavi, J., Mathis, M., and M. Podolsky, "An Extension to the Selective Acknowledgement (SACK) Option for TCP", RFC 2883, July 2000.
Paxson, V. and M. Allman, "Computing TCP's Retransmission Timer", RFC 2988, November 2000.
Allman, M., Balakrishnan, H., and S. Floyd, "Enhancing TCP's Loss Recovery Using Limited Transmit", RFC 3042, January 2001.
Allman, M., Floyd, S., and C. Partridge, "Increasing TCP's Initial Window", RFC 3390, October 2002.
Allman, M., "TCP Congestion Control with Appropriate Byte Counting (ABC)", RFC 3465, February 2003.
Blanton, E., Allman, M., Fall, K., and L. Wang, "A Conservative Selective Acknowledgment (SACK)-based Loss Recovery Algorithm for TCP", RFC 3517, April 2003.
Ludwig, R. and M. Meyer, "The Eifel Detection Algorithm for TCP", RFC 3522, April 2003.
Floyd, S., "HighSpeed TCP for Large Congestion Windows", RFC 3649, December 2003.
Blanton, E. and M. Allman, "Using TCP Duplicate Selective Acknowledgement (DSACKs) and Stream Control Transmission Protocol (SCTP) Duplicate Transmission Sequence Numbers (TSNs) to Detect Spurious Retransmissions", RFC 3708, February 2004.
Floyd, S., "Limited Slow-Start for TCP with Large Congestion Windows", RFC 3742, March 2004.
Floyd, S., Henderson, T., and A. Gurtov, "The NewReno Modification to TCP's Fast Recovery Algorithm", RFC 3782, April 2004.
Bhandarkar, S., Reddy, A., Allman, M., and E. Blanton, "Improving the Robustness of TCP to Non-Congestion Events", RFC 4653, August 2006.
Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick-Start for TCP and IP", RFC 4782, January 2007.
Mathis, M., Heffner, J., and R. Raghunarayan, "TCP Extended Statistics MIB", RFC 4898, May 2007.
Touch, J., "Defending TCP Against Spoofing Attacks", RFC 4953, July 2007.
Eddy, W., "TCP SYN Flooding Attacks and Common Mitigations", RFC 4987, August 2007.
R.T. Braden, D.A. Borman, C. Partridge, Computing the Internet Checksum, RFC 1071.
List of Assigned TCP Port Numbers
West, M. and S. McCann, "TCP/IP Field Behavior", RFC 4413, March 2006
Duke, M., Braden, R., Eddy, W., and E. Blanton, "A Roadmap for Transmission Control Protocol (TCP) Specification Documents", RFC 4614, September 2006.
Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers", RFC 4727, November 2006.
Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, RFC 5382, October 2008.