Thursday, 22 November 2012

TCP/IP Model Vs OSI Model


Both TCP/IP model and OSI model work in a very similar fashion. But they do have very subtle differences too. Knowing these differences is very crucial to learning computer networking. This article will try to show the comparison between TCP/IP model and OSI model.


Background
Advance research project agency (ARPA) created a OSI reference model so that they could logically group the similarly working components of the network into various layers of the protocol. But after the advent of the Internet, there arose the need for a streamlined protocol suite, which would address the need of the ever-growing Internet. So the Defense Advanced Research Project Agency (DARPA) decided to create the TCP/IP protocol suite. This was going to address many, if not all the issues that had arisen with the OSI reference model.

TCP/IP Model Layers
TCP/IP is a suite of protocol which is named after its most significant pair of protocols. That is Transmission Control Protocol and Internet Protocol. TCP/IP are made up of layers. Each layer is responsible for a set of computer network related tasks. Every layer provides service to the layer above it. In all, there are four layers in the TCP/IP reference model.
  • Application Layer: This is the topmost layer of the TCP/IP suite. This is responsible for coding of the packet data.
  • Transport Layer: This layer monitors end-to-end path selections of the packets. It also provides service to the application layer.
  • Internet Layer: This layer is responsible for sending packets through different networks.
  • Link Layer: It is the closest layer to the network hardware. It provides service to Internet layer.
OSI Model Layers
In OSI reference model there seven layers of protocols. Again, in OSI reference model, each layer provides services to the layer above it. There are in all seven layers of in OSI. They are
  • Physical Layer: It is the lower most layer of the OSI reference model. It is layer which is responsible for direct interaction of the OSI model with hardware. The hardware provides service to the physical layer and it provides service to the datalink layer.
  • Datalink Layer: There may be certain errors which may occur at the physical layer. If possible, these errors are corrected by the datalink layer. The datalink layer provides the way by which various entities can transfer the data to the network.
  • Network Layer: It does not allow the quality of the service to be degraded that was requested by the transport layer. It is also responsible for data transfer sequence from source to destination.
  • Transport Layer: The reliability of the data is ensured by the transport layer. It also retransmits those data that fail to reach the destination.
  • Session Layer: The sessions layer is responsible for creating and terminating the connection. Management of such a connection is taken care of by the sessions layer.
  • Presentation Layer: This layer is responsible for decoding the context (syntax and semantics) of the higher level entities.
  • Application Layer: Whichever software application that implements socket programming will communicate with this layer. This layer is closest to the user.
TCP/IP Model vs OSI Model

Sr. No.TCP/IP Reference ModelOSI Reference Model
1Defined after the advent of InternetDefined before advent of internet
2Service interface and protocols were not clearly distinguished beforeService interface and protocols are clearly distinguished
3TCP/IP supports Internet workingInternet working not supported
4Loosely layeredStrict layering
5Protocol Dependent standardProtocol independent standard
6More CredibleLess Credible
7TCP reliably delivers packets, IP does not reliably deliver packetsAll packets are reliably delivered

The entire communication industry stands on the backbone of TCP/IP and OSI reference model. It is very vital to learn the above differences, if anyone wants to be an expert in the field of communication.