OSI model and TCP/IP Model

Computer Network

Computer networks are making easy that sharing resources like software ,hardware as well as the data and information. is it enough to connect one or more computers or other peripherals each other by connecting wires. yes it is obvious….!. There are lots of conflicts, how to transfer data between network devices made by different manufactures by using different technologies how to identify the correct end to send the data, how the identify where the data came from, how to send data without crashing in a huge network. There should be some technological methods which are used to transfer data from one end to another end properly in a computer network system rather than the wire connection in between devices. here the place that our topic culminate in. Under these OSI and TCP/IP model, hardware, software , protocols and security mechanism are maintained properly and easily solving above mentioned problems. Lets we see deep how these models are perform in a network system.

OSI Model vs TCP/IP Model

OSI (Open System Interconnection) Model

When sending data from computer to another computer, Data is flowing thorough main seven layers. This seven layered architecture is called OSI model. If more simple, after sending data from a computer to deliver to the receiving computer that in between process separated to seven layers under this method. This is an internationally certified model.

All different network peripheral manufactures are following this model to manufacturing there devices. therefore it is possible to easily connect different technology based devices each other as a computer network.

here is this seven layers

  1. Application Layer
  2. Presentation Layer
  3. Session Layer
  4. Transport Layer
  5. Network Layer
  6. Data Link Layer
  7. Physical Layer

These layers are performing one after one in both orientations top to bottom and bottom to top. At the end of the sender this layers are performing top to bottom as Application Layer to Physical Layer then after at the end of the receiver this layers are performing bottom to top as Physical Layer to Application Layer.

When transferring data via these layers specially at the receivers end, some additional data are added to the main data. As an example when data flowing from Application Layer to Session Layer receiver’s data added as addition to the main data. Therefore when it comes to the physical layer data size is bigger than the original data to be transformed to the end. But again at the receiver’s end these additional data removing one by one and when the data comes to the user as the Application Layer again it converted to the original data sent by the sender. lets move to discuss one by one these layers .

1. Application Layer

This layer is the one that directly contact with the user in the process of data transferring. Software related to the data transferring is used in here and it is providing different user interfaces to the sender for adding and changing data to send and receiver for refer the data which are received from some sender. File transferring, E mail sending like processes done on this layer. Telnet, FTP, DNS , HTTP, SMTP, POP3 are some of protocols use in this layer.

2. Presentation Layer

Identifying and changing formats of the data file as appropriate to the transfer is done by this layer. As an example when we try to send a video file, in this layer that file is identified as a video file and transfer it to proper format like MPEG or Quick Time. Addition to that data encryption and decryption also done by this layer. ASCII, BCD , EBCDIC are the some of encryption methods.

3. Session Layer

This layer is responsible for few tasks. Identifying devices used to transfer data and Identifying data transferring methods according to that identified devices are done by this layer and when data is transferring, identifying the time to stop the data flow and stop data flow at that time also done by this. In addition to those things , how the data transfer is behave is identifying in here. those methods are Simplex, Half Duplex and Full Duplex. SRT(Session Initiation) Protocol and RPT(Read Time Transport) Protocol are some use in here.

4. Transport Layer

Data exchange in between two ends is done by this layer. partitioning data, data flow control between receivers and senders, Identifying problems during the transferring and fix them and multiplexing are controlling by this layer. TCP(Transmission Control Protocol), UDP(User Datagram Protocol) are some protocols use in this layer.

5. Network Layer

Identifying correct and less traffic paths, and addresses to transfer data and moving data through those paths are responsibilities of Network layer. Here are some protocols use in this layer ,IP(Internet Protocol), (RIP) Routing Information Protocol , ICMP(Internet Control Message Protocol)

6. Data Link Layer

converting data into data packets at the end of sender and at the receiver’s end decoding these data packets into bit is done by this layer. Also some transferring bugs are handled by this layer. As well as if it is a Local Area Network then data transferring through the switches is done by Data Link Layer. This layer is divided into two sub layers as MAC(Media Access Control) and LLC (Logic Link Control Layer). Getting permission to access data to send and send that permitted data is done by MAC while LLC is controlling bugs and data flow. Token Ring and Ethernet are protocols which are use in this layer.

7. physical Layer

This is the most bottom layer in OSI model. Transferring data through a transmission medium is happened by this layer. HUB, Switch, Repeaters, Cables are used in this layer.

Transport Control Protocol — TCP/IP Model

Protocols are some set of agreements and advices which are internationally accepted. According to the need of protocol creators above mentioned 7 layered structure divided into 4 layers is called TCP/IP Model. This one is the mostly using to data communication structure in recent. we cannot see Presentation Layer and Session Layer in this structure as we discussed in OSI model. But the processes done by those layers in OSI model are done by Application layer when it comes to the TCP/IP model. As well as Data Link Layer and Physical layer is merged together as Network Interface.

By using this four layers data transformation is happened as follows:

  1. Application Layer — Software using sender and receiver are belongs to this layer. User is participating to data communication via this layer.
  2. Transport Layer — Sending data in a trustable manner is responsibility of this layer.
  3. Internet Layer — This is where IP addresses and routing live. When data is transmitted from a node on one LAN to a node on a different LAN, the Internet Layer is used
  4. Network interface — Physical devices participating to the data transfer are inter connected together is don through this layer.


In a computer network it is important to connect different devices, software, transmission mediums and protocols. For that it is necessary to follow a standard methods. OSI Model and TCP/IP models are some internationally accepted models to achieve above mentioned objective. In this short article we discussed different layers in both OSI model and TCP/IP model and how each individual layer is participating to data communication within a network. There are seven layers belongs to OSI model and by merging some layers together in this model and newly invented TCP/IP model which has 4 layers is the mostly using model in recent.