TCP/IP reference model

           The TCP/IP model is the network model used by computer networks today. it was developed in 1970s by DARPA as an open, vendor-neutral, public networking model.The Transmission Control Protocol (TCP) is intended for use as a highly reliable host-to-host protocol between hosts in packet-switched computer communication networks, and in interconnected systems of such networks.

Just like the OSI reference model, the TCP/IP model provides general guidelines for designing and implementing networking protocols. The TCP/IP model has fewer layers than the OSI model. OSI model is made of seven layers, where the TCP/IP model is made of four layers only. These layers describe their different network functions and have their own standards and protocols.


The figure below illustrates difference between OSI model and TCP/IP model layers.

OSI vs TCP/IP model

          TCP/IP model is consist of only four layers from top to bottom Application, Transport, Interface  and Network Interface layer.

          As you can see from the above picture, the Application, Presentation and Session layers of OSI model are merged in only one layer of TCP/IP layer - the Application Layer. The Physical and Data Link layer of OSI model are also merged into the single layer of the TCP/IP  model - the Network Interface layer.

          The Network Interface Layer is sometimes referred as the Link layer. And the Transport layer is sometimes called the Host-to-Host layer.

Now, Why we need TCP/IP  reference model over OSI model?

Because there is some merits/advantages of TCP/IP model as below...

1. It operated Independently.
2. It is scalable
3. Client/server architecture.
4. it supports many routing protocols.
5. Can be used to establish connection between two computers.

Be halve of this advantages, TCI/IP has some disadvantages written below,

1. In this, Transport layer does not guarantee of delivery of packets.
2. The model cannot be used in any other application.
3. Replacing protocols is not easy.
4. It has not clearly separated its services, interfaces and protocols.

OSI model	TCP/IP model
1. OSI is a generic, protocol independent standard, acting as a communication gateway between the network and end user.	1. TCP/IP model is based on standard protocols around which the Internet has developed. It is a communication protocol, which allows connection of hosts over a network.
2. In OSI model the transport layer guarantees the delivery of packets.	2. In TCP/IP model the transport layer does not guarantees delivery of packets. Still the TCP/IP model is more reliable.
3. Follows vertical approach.	3. Follows horizontal approach.
4. OSI is a reference model around which the networks are built. Generally it is used as a guidance tool.	4. TCP/IP model is, in a way implementation of the OSI model.
5. Network layer of OSI model provides both connection oriented and connectionless service.	5. The Network layer in TCP/IP model provides connectionless service.
6.OSI model has a problem of fitting the protocols into the model.	6. TCP/IP model does not fit any protocol.