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CCNA RnS Article #2 – Networking Model


Today let’s talk about Networking Models – we’ll talk briefly about TCP/IP Networking Model

Have you ever thought about how networking equipment from different vendors are able to talk to each other? I mean a Laptop from HP is connecting to Wireless Modem installed by your Internet service provider manufactured by some other company.

Networks work perfectly because they speak the common language or follow the same rules. These common rules are defined as standards and protocols. These standards are defined as network models. You can think of these models as a blueprint for designing the network. Different networking companies follow these blueprints during their product development. The final devices in a network will function because follows the standard reference model or blueprint.

I hope you are with me and got a broad idea of why a network model is required in the real world. Now let’s talk about the TCP/IP Networking model. It is a pervasively used networking model in use.

Networking Model

The networking model is also known as the networking blueprint. It can be said to be a detailed document covering all aspects of the network. You can think of Reference Model as multiple blueprint documents that are used when building a house. Everyone who is contributing to building the house with all facility whether it is an architect, electrician, carpenter, or plumber refer to the same document so that they build a house as it was outlined in the blueprint. Similarly, the network model breaks the functions into smaller categories called layers. Each layer contains the related protocols and standards. Different companies build their products and follow the respective layer. It ensures that the newly developed product does not cause any problems with the already running network with other devices. This makes their product compatible with others in the production environment.

Evolution of the Networking Model

Initially, when there was no Networking Model to refer each OEM had its own proprietary networking model. Here I am talking about the 1970s scenario. As you can imagine there used to be different networks talking to devices from the same OEMs. The network team used to manage this different network separately.

Back in the 1980s International Organization for Standardization (ISO) started to work on a project to standardize the networking protocols to allow interoperability across the globe. This work is known as Open System Interconnect (OSI) networking model.

In parallel, open and less-formal vendor-neutral, the project was started by the US Department of Defense (DoD). Further, more volunteered researchers at various universities joined and contributed to the efforts of DoD – and TCP/IP networking model shaped up.

Initially, companies used both OSI & TCP/IP protocols together in their networking development. However, by the end of the 1990s, TCP/IP dominated and become the common choice.

TCP/IP Networking Model

The TCP/IP network model defines the protocols at various layers that allow devices to communicate. TCP/IP uses the documents called Request for Comments. These RFC documents highlight the protocols and their implementation in detail.

Any device that is powered on and connected through the right cable to a network will communicate with other devices on the network. This is because the company that manufactured the device, implemented the TCP/IP functionality when building the device.

TCP/IP breaks the networking functions into multiple layers to understand the networking function.

Figure 1: TCP/IP Networking Model

The top 2 layers (Application and Transport) focus on the applications that need to send and receive data. The bottom layers (Network, Data-link, and Physical Layer) focus on how to transfer bits over individual links. In this layered approach, each layer provides the services to the layer just above that.

  1. Application Layer – defines protocols that provide services to the applications running on a device.
  2. Transport Layer – provides services to the application layer protocols like error recovery, end-to-end same-layer interaction, etc.
  3. Network Layer – includes one major protocol: Internet Protocol (IP). IP provides features like addressing and routing for packets in a network.
  4. Data-Link & Physical Layer – both work closely and defines the protocols and hardware to deliver the data across the physical network. The physical layer defines cabling and energy flow over physical cable. As you know the network layer is more on the routing, data-link information is used by the network layer to perform the packet forwarding to the next-hop device.

I hope you find this informative. See you soon with detailed information on TCP/IP networking model. 

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