TCP

Developed in 1974 by engineers in the IEEE, the TCP is defined as a connection-based communication protocol that provides the reliable delivery of ordered packets. It's used to facilitate communication between hosts of all kinds from the internet, to SMTP clients and servers, Secure Shell (SSH) connections, FTP clients and servers, and HTTP. It is ubiquitous as the transport layer protocol of choice for almost all modern applications.

The broad adoption of TCP as the transport layer supporting most application-layer requests is primarily due to the reliability of a TCP connection. By convention, entities that implement TCP are written to detect packet loss and the out-of-order delivery of data streams, to re-request lost data, and to reorder the out-of-order streams. This error correction is resolved prior to returning that data back up the stack to the application layer entities making use of the TCP connection.

Of course, the obvious cost incurred by this error handling is latency and performance. Multiple round-trips to fetch, essentially, the same data two or three times can add substantial downtime to the client application. The reliability of TCP is ensured by leveraging a round-trip chain of request, acknowledgements of the receipt of a request, then another request, and so on. All the chatter incurred by this consistent back-and-forth makes TCP far from ideal for real-time applications, such as for gaming, video streaming, or video conferencing. Instead, where reliability or guaranteed ordering can be sacrificed in favor of performance, UDP or a similar protocol should be used as the transmission layer of choice.