Network Models - Part 2


Network Models - Part 2

The original TCP/IP model was developed in the 1970s for use in ARPANET. ARPANET was a Wide Area Network that predates the Internet. It was thought that this kind of Network would be used by military installations and Universities, and would be used to connect tens to hundreds of machines. Nothing remotely on the scale of what exists today.

TCP/IP Model stands for 'Transmission Control Protocol / Internet Protocol'. It also goes by another name. RFC 1180, RFC stands for 'Request for Comments'.
RFC is document created by the Internet Engineering Task Force (IETF), this is subject to numerous draft copies and peer reviews before it is classed as a standard, as such this can lead to different variations of the model existing at any one time.

Unlike the OSI Model, the TCP/IP Model only consists of four layers. This is because the Model combines the Application Layer with the Presentation and Session Layers.
The layout for this model is as follows:

- Application Layer
- Transport Layer
- Internet Layer
- Link Layer (Network Interface Layer)

Where the OSI Model has the Application, Presentation and Session Layers, the TCP/IP Model combines all of those Layers into the singular Application Layer.

The Application Layer covers the role for all three of those Layers where it is required.
This Layer is responsible for Node-to-Node communication and a number of protocols operate on this layer, include; HTTPS, FTP, Telnet, SMTP and many more. I'm not going to go into detail about the specific protocols here, as I plan on doing that in later postings.

The Transport Layer is responsible for End-to-End Communications. The Transport Layer on the TCP/IP Model matches its counterpart on the OSI Model, and is responsible for establishing the connection between two devices and transferring data.

There are two Protocols that work at this layer. Firstly, there is TCP, which is known as a Connection-Orientated Protocol. This is because, it establishes a connection before it proceeds to send any data. Once the data has been transferred, the connection ceases.
The second protocol that works at this Layer is called; User Datagram Protocol (UDP). UDP is known as the Connection less Protocol, this is because it doesn't wait for communication to be established before sending data

The Internet Layer matches that of the OSI Model. This is the Layer that sends 'Packets' of Data out to the Internet through the Router.
This Layer uses something called 'Routing Protocols' to choose the best method for transmission of data around the globe. Best method in this case means, the quickest route with the highest success rate.
For example; RIP (Routing Information Protocol), works so long as the data doesn't have to go further than fifteen hops, otherwise the transmission fails. By hops, it means, transmitted through Network Nodes.

The bottom layer of the TCP/IP Model can go by many different names, the Link Layer, the network Access Layer, the Network Interface Layer.
For ease, I'm going to be labelling this layer, 'The Network Interface Layer'. This layer consists of the Physical and the Link Layer.
The Network Interface layer is where the physical transmission of data takes place. This is where the data is broken down into the ones and zeroes, and transported through a Network medium.
This Layer also focuses on the Hardware Addressing, such as; Mac Addresses.

To the best of my knowledge, all information displayed here is correct. I'm still trying to get to grips with the TCP/IP Network Model. So, if any information is wrong, please let me know and I shall correct it.