Table of Contents
Transmission Control Protocol (TCP)
Return to Internet topics, Networking topics, List of TCP and UDP port numbers
Transmission Control Protocol (TCP) is one of the foundational protocols of the Internet Protocol (IP) suite, designed to provide reliable, ordered, and error-checked delivery of data over networks. Initially standardized in RFC 793 in September 1981, it has since been updated through various RFCs, with the latest comprehensive specification being RFC 9293. TCP serves as the transport layer protocol that ensures data is reliably delivered from one host to another, making it crucial for applications that require accurate transmission, such as web browsing, email, and file transfers.
TCP is a connection-oriented protocol, meaning that a connection must be established between the communicating parties before any data transfer begins. This process is handled through the well-known three-way handshake mechanism, which ensures that both the sender and the receiver are ready to communicate. This handshake also helps in synchronizing sequence numbers, which are used to ensure that data is transmitted and received in order and without errors.
Reliability in TCP is achieved through a combination of sequence numbers, acknowledgment packets, and retransmissions. Every byte of data sent over a TCP connection is assigned a sequence number, and the receiver acknowledges the receipt of these bytes. If the sender does not receive an acknowledgment within a certain timeout period, it assumes the data was lost and retransmits it. This ensures that no data is lost during transmission, even over unreliable networks.
Flow control is another important feature of TCP, ensuring that a sender does not overwhelm a receiver with too much data at once. This is managed through a sliding window mechanism, where the receiver advertises how much buffer space it has available, and the sender adjusts its transmission rate accordingly. This mechanism helps maintain smooth communication, even when there are disparities in the processing speeds of the sender and receiver.
Congestion control, introduced in later updates such as RFC 5681 and further refined through algorithms like TCP Reno and TCP NewReno, helps manage network congestion by adjusting the rate of data transmission. Congestion control algorithms detect network congestion by monitoring lost packets and reducing the transmission rate to alleviate network overload. This feature has been crucial in preventing network congestion collapse, especially as the internet has grown.
TCP operates using ports to differentiate between multiple connections on the same machine. Each connection is identified by a combination of IP addresses and port numbers, which allows a host to manage multiple simultaneous connections. The use of port numbers also makes it possible to route data to the appropriate application on a host, ensuring that data intended for different applications can be processed concurrently.
One of the security vulnerabilities of TCP is sequence number prediction attacks, where an attacker intercepts or guesses the sequence numbers in an active connection to hijack it. Updates like those in RFC 1948 introduced methods to randomize initial sequence numbers, mitigating the risks of such attacks. Nevertheless, TCP remains vulnerable to certain types of attacks, including TCP spoofing and TCP veto attacks, where attackers manipulate the flow of data without fully interrupting the connection.
Over the years, extensions and improvements to TCP have been introduced to address performance issues and optimize its use in modern networking environments. For instance, TCP Fast Open (specified in RFC 7413) allows data to be sent during the initial handshake, reducing latency for repeated connections. Additionally, Multipath TCP (defined in RFC 6824) allows multiple network interfaces to be used in a single TCP connection, improving redundancy and throughput.
For more detailed specifications, you can refer to these official sources: - RFC 793: https://www.rfc-editor.org/info/rfc793 - RFC 9293: https://www.rfc-editor.org/info/rfc9293 - Wikipedia on TCP: https://en.wikipedia.org/wiki/Transmission_Control_Protocol
Conclusion
TCP remains a critical protocol for reliable data transmission over networks. Its robust features, including flow control, error detection, and congestion control, have evolved through various RFCs like RFC 793 and RFC 9293. Despite its vulnerabilities, TCP continues to be essential for internet communications, with updates ensuring its relevance in modern network infrastructure. Through ongoing advancements, TCP has maintained its position as the protocol of choice for reliable and efficient data transport across diverse applications and environments.
- Snippet from Wikipedia: Transmission Control Protocol
The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered, and error-checked delivery of a stream of octets (bytes) between applications running on hosts communicating via an IP network. Major internet applications such as the World Wide Web, email, remote administration, and file transfer rely on TCP, which is part of the transport layer of the TCP/IP suite. SSL/TLS often runs on top of TCP.
TCP is connection-oriented, meaning that sender and receiver firstly need to establish a connection based on agreed parameters; they do this through three-way handshake procedure. The server must be listening (passive open) for connection requests from clients before a connection is established. Three-way handshake (active open), retransmission, and error detection adds to reliability but lengthens latency. Applications that do not require reliable data stream service may use the User Datagram Protocol (UDP) instead, which provides a connectionless datagram service that prioritizes time over reliability. TCP employs network congestion avoidance. However, there are vulnerabilities in TCP, including denial of service, connection hijacking, TCP veto, and reset attack.