TCP, or Transmission Control Protocol, is one of the primary protocols that define the Internet as we know it. It’s one of the main protocols in the TCP/IP networking suite, and it plays a significant role in organizing data transfer across the web. The concept of TCP and the understanding of how it functions are pivotal to networking and the internet’s overall operation.
History of TCP
The roots of TCP date back to the 1970s. Vint Cerf and Robert Kahn initially developed it, two computer scientists who were looking for a reliable way to link different networks together – an early form of the Internet. The protocol was officially standardized in September 1981 in RFC 793. The TCP/IP model itself was adapted in the mid-1980s by the Defense Advanced Research Projects Agency (DARPA), which was responsible for significant developments in computer networking.
How Does TCP Work?
TCP operates at the transport layer of the TCP/IP networking model, which aligns roughly with the fourth layer (transport layer) of the OSI model. The role of TCP is to provide a reliable, ordered, and error-checked delivery of a stream of bytes between applications running on hosts communicating over an IP network.
TCP works by segmenting a stream of data into smaller pieces (TCP segments), which are then sent over the internet to the destination. When they arrive, TCP is also responsible for reassembling the segments and ensuring they are correctly ordered.
In more detail, here are some of the features of TCP:
- Connection-Oriented: TCP is a connection-oriented protocol, which means a connection is established and maintained until the application programs at each end have finished exchanging messages. It dictates that data transfer can only begin after the completion of a three-way handshake, which establishes and configures the connection.
- Reliability: One of the critical features of TCP is its ability to provide a reliable data service. If any data segment is lost during transmission, TCP has mechanisms to detect these issues and ensure that the missing data is retransmitted. It does this by assigning a sequence number to each byte sent, and expects a positive acknowledgment (ACK) from the receiving end.
- Flow Control: TCP uses a mechanism called flow control to prevent a sender from overwhelming a receiver, which might not be able to process the data as quickly.
- Congestion Control: TCP has mechanisms for controlling network congestion that can occur when data transmission volumes are high, thereby maintaining quality of service.
- Ordering of Data Packets: Data packets can take different routes to reach the destination, meaning they can arrive out of order. TCP sequences them so they are presented in their original order to the application.
- Error Checking: TCP includes a checksum in its header for error-checking the header and data.
TCP and Other Protocols
While TCP is a reliable transmission protocol, it is not the only option available for data transmission on the internet. For example, User Datagram Protocol (UDP) is another protocol used for data transmission. However, unlike TCP, UDP is a connectionless protocol and doesn’t provide the same kind of reliability and order, but it requires less overhead and can deliver data faster.
What TCP is used for?
TCP, or Transmission Control Protocol, is used extensively across the internet and private networks to guarantee reliable, ordered, and error-checked delivery of a stream of bytes between systems. It is a protocol used in many applications and services, including:
- Web Browsing: When you browse the internet using web browsers like Chrome, Firefox, or Safari, HTTP (Hypertext Transfer Protocol) or HTTPS (HTTP Secure) are used, which operate over TCP. TCP ensures that all the web page data you request is received accurately and in the correct order.
- Email Services: SMTP (Simple Mail Transfer Protocol), POP3 (Post Office Protocol version 3), and IMAP (Internet Message Access Protocol) are protocols used for sending and receiving emails, and they all use TCP to ensure accurate transmission of messages.
- File Transfers: FTP (File Transfer Protocol) is used to upload and download files between a client and a server, and it operates over TCP.
- Secure Shell (SSH): This protocol provides secure command-line access to remote computers and uses TCP to ensure the reliability of the data stream.
- Database Queries: Many databases use TCP for queries to ensure all data is accurate and correctly ordered.
- VPN Connections: Virtual Private Networks (VPNs) use TCP to ensure reliable and secure data transmission.
- Video Streaming: Although some streaming services are moving toward using protocols like QUIC that incorporate UDP due to its speed, TCP is still commonly used for streaming services to ensure that the video data arrives reliably and in the right order.
The key to TCP’s broad usage is its reliability. Whenever data needs to be transmitted accurately and in sequence over the internet or a network, TCP is likely involved. The trade-off is that it’s slower and requires more processing than less reliable protocols like UDP, but in many cases, the reliability that TCP offers is paramount.
TCP in Everyday Use
In day-to-day Internet use, TCP is everywhere. When you load a webpage, the text, images, and data that make up that page are likely transmitted to your computer over a TCP connection. This is because HTTP and HTTPS, the main protocols used to transfer web data, typically operate over TCP.
Similarly, when you send or receive an email, TCP is typically at work ensuring that all the email data arrives intact and in the correct order. The same goes for many other internet services, from online gaming to video streaming