Each layer builds on any one of the layers underneath it (exception: A Gateway isn't a layer).
The protocol the application sees and uses.
HyperText Transport Protocol, for web browsers and HTML pages.
Network File System, for accessing disk drives across the network.
Network News Transport Protocol, for USENET newsgroups.
|Mail protocols: Simple Mail Transport Protocol handles the deliveries. Post Office Protocol uses it to drop off messages. Internet Mail Access Protocol uses it, saving messages on the server.|
|File Transfer Protocol (uses TCP), and cousins: Trivial FTP
(uses UDP for small boot files),
File Service Protocol (lets you restart after an interruption)
Breaking up of data into packets (packages of data). Collection and sequencing of packets into a data stream.
Transmission Control Protocol. Ultra-reliable protocol that makes sure all data packets arrived, and are in proper sequence. Reacquires any corrupted or dropped packets from the sender's transport layer.
|UDP||User Datagram Protocol. Doesn't check for dropped or corrupted packets ("unreliable"). Good for audio/video transmissions, and where the application implements error-correcting codes.|
Defines packet APIs. Processes packets. Handles network addressing.
Internet Protocol. What the Web uses. What Java speaks.
A protocol used on NetWare networks.
Apple's networking protocol for MacIntosh.
Microsofts' networking protocol for Windows for Workgroups and Windows NT