TCP/IP is a suite of communications protocols that define how different types of computers talk to one another. It’s named for its foundational protocols, the Transmission Control Protocol and the Internet Protocol. The Internet Protocol provides logical addressing as data moves between hosts: it splits data into packets, which are then forwarded to machines via the network. The Transmission Control Protocol ensures that the packets in a message are reassembled in the correct order at their final destination and that any missing datagrams are re-sent until they are correctly received. Other protocols provided as part of TCP/IP include:
Translates between Internet and local hardware addresses (Ethernet, etc.).
Error-message and control protocol.
Enables TCP/IP (and other protocols) to be carried across both synchronous and asynchronous point-to-point serial links.
Translates between local hardware and Internet addresses (opposite of ARP).
Used by sendmail to send mail via TCP/IP.
Performs distributed network management functions via TCP/IP.
Transfers data without first making a persistent connection between two systems the way TCP does. Sometimes called unreliable transport.
TCP/IP is covered in depth in the three-volume set ...