What are the five main network models?

This tutorial is about TCP IP layers and how five layer network model works

TCP/IP forms the core mechanism of a conceptual networking model that collectively forms the internet protocol suite. It is responsible for the communication that takes place on the network. In general, TCP/IP has five different layers. Those are:

Application Layer
Transport Layer
Internet Layer
Data Link Layer
Physical Layer

Each of these layers supports a relevant set of protocols that perform unique functions. Notably, contrary to the OSI model that has 7 layers – the TCP/IP model performs all the functions using fewer layers. Its two protocols namely, TCP and IP are main driving force of the modern internet and network paradigm and are responsible for providing a flexible networking functionality, thence streamlining the connectivity of many devices having distinctive architectures.

In TCP/IP, a secure connectivity is ensured by safeguarding the end to end node verification i.e. from source to destination. It helps in a secure data transfer. Dynamic routing is another excellent feature that the TCP/IP model offers. It aids in selecting the shortest and secured path of data packets to their destination. Dynamic routing helps disperse those data packets over a dynamically selected path that remains unknown till the last point, hence providing a much needed data security feature.

We’ve talked about the pros of TCP/IP but it has a few cons too. Not worrying though. Firstly, it’s not very convenient to change the protocol, if required. Secondly, there isn’t too much documentation provided regarding the functionalities of different layers as in the OSI model. So there’s always an element of doubt over what layer does what specifically.

Now, let’s highlight some basic functionality of different layers in a TCP/IP model:

Physical Layer: Situated at the bottom of the TCP/IP model, this layer is responsible for controlling the data bits in a network. It facilitates the host to host communication. It also specifies the data rate, topology of a network, among other things such as mode and medium of transferring data i.e. whether it’s full duplex, half duplex, simplex, over a wired or wireless connection respectively. The protocols used in this layer differ with respect to different networks so it doesn’t specify any particular protocol to be used in it.
Data Link Layer: This layer creates data frames by appending header information of the data packets to be able to deliver it to a correct destination. It is done by adding a physical address to data packets so as to help transfer it over a desired route.
Internet Layer: This layer creates data packets or data-grams by addressing them logically to an IP address. It then routes the data packets with the help of assigned IP addresses using the routers. It is an important layer that specifies different protocols for a logical data transfer over the network. IP, ICMP, ARP, RARP are some of the protocols used in this layer.
Transport Layer: This layer processes data received from the above layers to create data segments. The transport layer then transfers the data by establishing a connection with the layers underneath it. In general, this layer is responsible for the end to end data transmission without any errors, and by controlling the flow rate of data. TCP and UDP are the two protocols used in this layer.
Application Layer: This is a last layer of the TCP/IP model that handles the functionality of network connections, data encryption, decryption, translation, and data synchronization. It provides a mechanism to carry out communication between network services and the computer system application programs for the end users – for services such as internet browsing, ftp transfers, emails, etc. It uses top level protocols such as FTP, Telnet, HTTP, HTTPS, DHCP, SMTP, SNMP, among others.

For data communication to take place and two or more users can transmit data from one to other, a systematic approach is required. This approach enables users to communicate and transmit data through efficient and ordered path. It is implemented using models in computer networks and are known as computer network models.
Computer network models are responsible for establishing a connection among the sender and receiver and transmitting the data in a smooth manner respectively.
There are two computer network models i.e. OSI Model and TCP/IP Model on which the whole data communication process relies.

Computer Network Models

The OSI Model is one of the general purpose networking or communication model among computer network models, which is responsible for establishing connection in an open manner between all the communicable devices present across the globe.
OSI stands for “Open System Interconnection” and the name of this reference model was given by an organization known as “International Organization for Standardization”. The ISO is responsible for generating and promoting industrial and commercial standards applicable for all the users or universally.
OSI model is called as “Open Source” because of its “fit anywhere” ability. Any connection can be established using the OSI model unless and until any protocols are not used as OSI model does not support protocol establishment. It runs without the use of protocols. All the networking devices which are open for communication can be connected together for data communication through the OSI model.
Apart from OSI Model, another computer network models which is widely used is TCP/IP Model.
OSI model having a layered architecture, allows easy data communication as each layer has predefined structured and functionalities.
The functionalities are different for each layer and thus when combined together forms the OSI Model. There are in total seven layers in general purpose OSI model.

The seven layers of OSI model are further categorized into Upper Layers, Network Independent Layer and Lower Layers. Physical Layer, Data link Layer and Network Layer are categorized as Lower Layers. Transport Layer as Network Independent Layer and Session Layer, Presentation Layer, Application Layer as Upper Layers.

Also, these layers are sequenced in fixed manner and this sequence cannot be changed. It means, any alterations in the positions of the layers are not accepted.

A) The Physical Layer

The Physical Layer is the bottom most layer and is associated with electrical, mechanical and functional aspects of the transmission media for information and receiving over internet.

B) The Data Link Layer

The Data Link Layer is second from bottom and comes under the lower layer category. It ensures that the data must be synchronized, error detection and control are enabled.

C) The Network Layer

The Network Layer is third from bottom in OSI model and is responsible for establishing data communication channel between multiple networks or devices or hosts or nodes.

D) The Transport Layer

Transport Layer is the middle most layer in OSI model and it acts as Network Independent Layer. It has no idea about the functioning of lower layer i.e. physical, data link and network layers.

E) The Session Layer

Session Layer is the fifth layer of OSI model and it provides appropriate sessions between users and entities, where user interacts. This layer can be used on the basis of resources available and it can be skipped too if not required.
For example : Login Sessions in online banking.

F) The Presentation Layer

This is the sixth layer of OSI model and it provides appropriate representation of data through various data presentation techniques.

G) The Application Layer

Application Layer is the topmost layer of the OSI model and has the responsibility for providing interface between various users and application.

Computer Network Models : Advantages Of OSI Model

The OSI Model being one of the most widely used computer network models does posses some major advantages which makes it so popular. These are :
1. Each layer has its definite structure and functionality which makes OSI model simple and easy to use.
2. It is a general purpose reference model that can be used for data communication.
3. Connection oriented and connection-less services are supported.
4. Connection between any type of devices or host or hardware or software is possible.

Computer Network Models : Disadvantages Of OSI Model

Because of its inability to fit protocols, this model was replaced by TCP/IP Internet Model.
Session and Presentation layers does not provide high end functionalities and are not of much use as compared to other layers.
Connection oriented and connection-less services are supported.
Connection between any type of devices or host or hardware or software is possible.