From Wikipedia, the free encyclopedia
In this context, there are three layers of protocols:
- At the lowest level is IP (Internet Protocol), which defines the datagrams or packets that carry blocks of data from one node to another. The vast majority of today's Internet uses version four of the IP protocol (i.e. IPv4), and although IPv6 is standardised, it exists only as "islands" of connectivity, and there are many ISPs who don't have any IPv6 connectivity at all. 
- Next come TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) - the protocols by which one host sends data to another. The former makes a virtual 'connection', which gives some level of guarantee of reliability. The latter is a best-effort, connectionless transport, in which data packets that are lost in transit will not be re-sent.
- On top comes the application protocol. This defines the specific messages and data formats sent and understood by the applications running at each end of the communication.
Unlike older communications systems, the Internet protocol suite was designed to be independent of the underlying physical medium. Any communications network, wired or wireless, that can carry two-way digital data can carry Internet traffic. Thus, Internet packets flow through wired networks like copper wire, coaxial cable, and fibre optic, and through wireless networks like Wi-Fi. Together, all these networks, sharing the same protocols, form the Internet.
The Internet protocols originate from discussions within the Internet Engineering Task Force (IETF) and its working groups, which are open to public participation and review. These committees produce documents that are known as Request for Comments documents (RFCs). Some RFCs are raised to the status of Internet Standard by the IETF process.
Some of the most-used application protocols in the Internet protocol suite are DNS, POP3, IMAP, SMTP, HTTP, HTTPS and FTP. There are many other important ones; see the lists provided in these articles.
All services on the Internet make use of defined application protocols. Of these, e-mail and the World Wide Web are among the best known, and other services are built upon these, such as mailing lists and blogs. There are many others that are necessary 'behind the scenes' and yet others that serve specialised requirements.
Some application protocols were not created out of the IETF process, but initially as part of proprietary commercial or private experimental systems. They became much more widely used and have now become de facto or actual standards in their own right. Examples of these include IRC chat rooms, and various instant messaging and peer-to-peer file sharing protocols.