�OSI MODEL�AND �TCP/IP MODEL

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OSI Model

• OSI stands for Open Systems Interconnection. It has been developed by ISO – ‘International Organization for Standardization‘, in the year 1984.
• It is a 7 layer architecture with each layer having specific functionality to perform.
• All these 7 layers work collaboratively to transmit the data from one person to another across the globe. 

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• The OSI Model can help to break down the problem and isolate the source of the trouble.
• If the problem can be narrowed down to one specific layer of the model, a lot of unnecessary work can be avoided.
• OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task.
• Each layer is self-contained, so that task assigned to each layer can be performed independently.

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TCP/IP Model

• The TCP/IP model was developed prior to the OSI model.
• The TCP/IP model is not exactly similar to the OSI model.
• The TCP/IP model consists of five layers: the application layer, transport layer, network layer, data link layer and physical layer.

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• The first four layers provide physical standards, network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model and these four layers are represented in TCP/IP model by a single layer called the application layer.
• TCP/IP is a hierarchical protocol made up of interactive modules, and each of them provides specific functionality.

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Comparison

TCP/IP Model

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• TCP/IP stands for Transmission Control Protocol/Internet Protocol. It is named after these two protocols, being part of this model.
• It is comparatively simple model.

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OSI Model

• OSI stands for Open System Inter connection. It is called so because it allows any two different systems to communicate regardless of their architecture.
• It is complex model.

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OSI Model

• OSI model has seven layers: Physical, Data Link, Network, Transport, Session, Presentation and Application Layer.
• Separate Session and Presentation layers are present in this model.
• This model provides clear distinction between services, interfaces and protocols.

TCP/IP Model

• TCP/IP model has four layers: Host-to-network, Network, Transport and Application layer.
• There is no session and presentation layer in this model. Session layer characteristics are provided by transport layer and presentation layer characteristics are provided by application layer.
• It does not clearly distinguish between services, interfaces and protocols.

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TCP/IP MODEL

• TCP/IP protocols fit well in this model as model is defined after protocols were implemented.
• TCP/IP model supports only connectionless communication is network layer.
• It does not provide quality of service.

OSI MODEL

• Protocols do not fit well into the model, because model was defined first i.e. before implementation.
• OSI model supports both connectionless and connection oriented communication in network layer.
• OSI model provides quality od service.

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OSI Model

• In OSI model two independent full duplex connections can be established.
• Minimum size of OSI header is 5 bytes.
• The OSI model uses seven different TPDUs.

TCP/IP Model

• In TCP one connection can be established.
• Minimum size of TCP header is 20 bytes.
• TCP/IP model uses only one TPDU.

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Connection oriented �and �connection-less service

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Connection oriented service

• Connection-Oriented Service is basically a technique that is typically used to transport and send data at session layer.
• The data streams or packets are transferred or delivered to receiver in a similar order in which they have seen transferred by sender.

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•  It is actually a data transfer method among two devices or computers in a different network, that is designed and developed after telephone system.
• Whenever a network implements this service, it sends or transfers data or message from sender or source to receiver or destination in correct order and manner.

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Connection-less service

• It is related to the postal system.
• It does not include any connection establishment and connection termination. Connection-less Service does not give a guarantee of reliability.
• In this, Packets do not follow the same path to reach their destination. 

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• The data packets may follow different paths to reach the destination.
• There’s no need to setup connection before sending a message and relinquish it after the message has been sent. The data packets in a connectionless service are usually called datagrams.

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Difference

Connection Oriented

• In connection oriented, the receiver sends an acknowledge the receipt of packets.
• It is reliable service.
• Connection-oriented service is related to the telephone system.

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Connectionless

• In connectionless services, the receiver does not send any acknowledgement back to source.
• It is unreliable service.
• Connection-less service is related to the postal system.

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Connection Oriented

• This type of service is slower than connectionless.
• It provides the provision for retransmission if transmitted data has some problem.
• Connection oriented service is preferred by long and steady communication.

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Connectionless

• It is considered to be faster communication compared to connection oriented.
• There is no provision for retransmission. Here sending device assumes that transmitted data has no problem.
• Connection-less service is preferred by bursty communication.

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Connection Oriented

• In connection oriented service, packets follows the same routes.
• Connection-oriented services require a bandwidth of a high range.
• In connection-oriented Service, Congestion is not possible.

Connectionless

• In connectionless service, packets does not follow the same routes.
• Connection-less Service requires a bandwidth of low range.
• In connection-less Service, Congestion is possible.

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Connection Oriented

• Connection-oriented services require a bandwidth of a high range.
• Ex: TCP (Transmission Control Protocol).
• Connection-oriented requires authentication.

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Connection-less

• Connection-less Service requires a bandwidth of low range.
• Ex: UDP (User Datagram Protocol).
• Connection-less Service does not require authentication.

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