Data networks are systems of end devices, intermediary devices, and the media connecting the devices. For communication to occur, these devices must know how to communicate.

These devices must comply with communication rules and protocols. TCP/IP is an example of a protocol suite. Most protocols are created by a standards organization such as the IETF or IEEE. The Institute of Electrical and Electronics Engineers is a professional organization for those in the electrical engineering and electronics fields. ISO, the International Organization for Standardization, is the world’s largest developer of international standards for a wide variety of products and services.

The most widely-used networking models are the OSI and TCP/IP models. Associating the protocols that set the rules of data communications with the different layers of these models is useful in determining which devices and services are applied at specific points as data passes across LANs and WANs.

Data that passes down the stack of the OSI model is segmented into pieces and encapsulated with addresses and other labels. The process is reversed as the pieces are de-encapsulated and passed up the destination protocol stack. The OSI model describes the processes of encoding, formatting, segmenting, and encapsulating data for transmission over the network.

The TCP/IP protocol suite is an open standard protocol that has been endorsed by the networking industry and ratified, or approved, by a standards organization. The Internet Protocol Suite is a suite of protocols required for transmitting and receiving information using the Internet.

Protocol Data Units (PDUs) are named according to the protocols of the TCP/IP suite: data, segment, packet, frame, and bits.

Applying models allows individuals, companies, and trade associations to analyze current networks and plan the networks of the future.