2. The Four Layer Model

Here is an alphabet soup of protocols: TCP/IP, UDP, FTP, POP, IMAP, SMTP, Ethernet, X.25, Telnet, FCNP, TLS, NTP, NNTP - the list goes on (you don't need to learn this list for your exam).

All of these protocols deal with particular aspects of network communications. Some will have to interact with others, while some are direct replacements or alternatives to others and will not be used on the same network.

These network protocols are organised into a conceptual model, with each one residing within a specific layer.

Because there are four layers, this model is called the Four Layer Model, though you may also see it called the TCP/IP Stack in some textbooks.

Four Layer Model
Layer	Layer Name
4	APPLICATION
3	TRANSPORT
2	NETWORK
1	DATA LINK or NETWORK INTERFACE

It is important to remember that the protocols in each layer can only communicate with those in the layers directly above and below it.

Challenge see if you can find out one extra fact on this topic that we haven't already told you

Click on this link: What is the Internet 4 layer model