November 10, 2020

What is Transmission Control Protocol (TCP)?

Transmission Control Protocol or TCP is a network standard that refers to how a network conversation can be established and maintained so that the connected applications and programs can share data. TCP and IP (Internet Protocol) work together to define how computers can send packets of data, forming the basic rules of data transfer over the internet.

How Does Transmission Control Protocol (TCP) Work?

TCP works based on a connection-oriented system, meaning that it establishes and maintains the connection until the applications have completed exchanging data at both ends. The TCP layer determines how the data is broken into packets to facilitate its transfer over the network, as well as sends and accepts data packets to and from the network layer. TCP also manages flow control of the application data to ensure error-free transmission. Besides, it also handles retransmission of dropped data packets and makes sure that all the data packets have arrived.

In the Open Systems Interconnection or OSI communication model, TCP covers the transport layer, the session layer, as well as parts of Layer 4 and Layer 5. For instance, when an HTML file is sent by a web server to the client server, it employs the Hypertext Transfer Protocol or HTTP to transmit the data. Then the TCP layer is triggered by the HTTP program layer to establish the connection and transfer the HTML file. The TCP layer breaks the HTML file into data packets, tags them, and forwards them individually to the IP layer for transmission.

Note that even though the packets in the transmission have the same data source as well as destination IPv4 address, the data packets may be sent via multiple routes. In any case, the TCP layer on the client server will wait for the data packets to arrive, then acknowledge the received data, and request retransmission of the missing data packet numbers. When everything is in place, the TCP layer will assemble the data packets into an HTML file and deliver it to the receiving application.

The error detection process by TCP, which includes asking for retransmissions and reorganizing data packets after receiving, can lead to latency in a stream sometimes. That is why highly time-sensitive programs and applications, such as video streaming, VoIP conferences, and gaming, usually rely on the User Datagram Protocol or UDP to transmit data. The UDP layer is known to reduce latency and jitter, as it neither worries about the lost data packets nor reorganizes the received data packets.