The Internet relies heavily on two protocols. In the network layer, IP (Internet Protocol) provides an unreliable datagram service and ensures that any host can exchange packets with any other host. Since its creation in the 1970s, IP has seen the addition of several features, including multicast, IPsec (IP security), and QoS (quality of service). The latest revision, IPv6 (IP version 6), supports 16-byte addresses.
The second major protocol is TCP (Transmission Control Protocol), which operates in the transport layer and provides a reliable bytestream service on top of IP. TCP has evolved continuously since the first experiments in research networks.