The TCP/IP Reference Model
The TCP/IP Reference Model
* Describes how the internet works.
* There are 4 layers: the host to network layer, the internet layer, the transport layer, the application layer.
Host to Network Layer
* The TCP/IP model says very little about the host to network layer.
* It says that the host has to connect to the network using some protocol so it can send IP packets over it.
* The protocol is not defined and varies from host to host, and network to network.
The Internet Layer
* The job of the internet layer is to allow a host to inject packets into any network and have them travel independently to the destination.
* Packet routing is a major issue.
* Also defines an official packet format and protocol called IP (Internet Protocol).
The Transport Layer
* Designed to allow peer entities on the source and destination hosts to carry on a conversation (end-to-end).
* Transmission Control Protocol (TCP) is a reliable connection-oriented protocol that allows a byte stream originating on one machine to be delivered without error to any other machine on the internet.
* The byte stream is fragmented into discrete messages which are passed onto the internet layer.
* At the receiving end, the messages are reassembled into the original byte stream.
The Application Layer
* No need for session or presentation layers was perceived.
* Contains all the higher level protocols including FTP, SMTP (email), NNTP (news), HTTP (web).
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