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Iso osi and tcp-ip reference models


computer networks

computer networks

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  • 1. Reference models
  • 2. Objectives • Understand the architecture of Internet with an analogy. • ISO/OSI Reference model • TCP/IP Reference model • Compare ISO/OSI and TCP/IP
  • 3. Analogy: Airline System
  • 4. Horizontal Layering
  • 5. Protocol Layers • To reduce the design complexity, most networks are organized as a stack of layers or levels, each one built upon the one below it. • The purpose of each layer is to offer certain services to the higher layers, shielding those layers from the details of how the offered services are actually implemented.
  • 6. The OSI Reference Model • The model is called the ISO OSI (Open Systems Interconnection) Reference Model because it deals with connecting open systems—that is, systems that are open for communication with other systems.
  • 7. The OSI Reference Model Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data link layer Physical Layer • The seven layers of ISO/OSI model
  • 8. The OSI Reference Model…
  • 9. • The physical layer is concerned with transmitting raw bits over a communication channel. • The design issues here largely deal with – mechanical, electrical, and timing interfaces, and – the physical transmission medium, which lies below the physical layer The Physical Layer
  • 10. • The main task of the data link layer is to take a raw transmission facility and transform it into a line that appears free of undetected transmission errors to the network layer. • The sender break the input data up into data frames and transmit the frames sequentially. The Data Link Layer Data Frame1 Frame2 Data Link Layer
  • 11. • The network layer is concerned with controlling the operation of the subnet. • A key design issue is determining how packets are routed from source to destination. The Network Layer
  • 12. • The basic function of the transport layer is to accept data from above, split it up into smaller units if need be, • Pass the DU to the network layer, and ensure that the pieces all arrive correctly at the other end. The Transport Layer DU1 DU2 Data Transport Layer
  • 13. • The session layer allows users on different machines to establish sessions between them. • Dialog control – (keepingtrack of whose turn it is to transmit) • Token management – (preventing two parties from attempting the same critical operation at the same time) and • Synchronization – (checkpointing long transmissions to allow they to continue from where they were after a crash). The Session Layer
  • 14. • Concerned with the syntax and semantics of the information transmitted. The Presentation Layer
  • 15. • The application layer contains a variety of protocols that are commonly needed. • One widely-used appplication protocol is HTTP (HyperText Transfer Protocol), which is the basis for the World Wide Web. • When a browser wants a Web page, it sends the name of the page it wants to the server using HTTP. • The server then sends the page back. • Other application protocols are used for file transfer, electronic mail, and network news. The Application Layer
  • 16. The TCP/IP Reference Model • ISO OSI Model TCP/IP Model Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data link layer Physical Layer Application Layer Transport Layer Internet Layer Link Layer Physical Layer
  • 17. • Permit hosts to inject packets into any network and have them travel independently to the destination. • The internet layer defines an official packet format and protocol called IP (Internet Protocol). • The job of the internet layer is to deliver IP packets where they are supposed to go. The Internet Layer
  • 18. • The first protocol defined is TCP(Transmission Control Protocol) • TCP is a reliable connection-oriented protocol that allows a byte stream originating on one machine to be delivered without error on any other machine in the internet. • It fragments the incoming byte stream into discrete messages and passes each one onto the internet layer. The Transport Layer
  • 19. • The second protocol in this layer, UDP (User Datagram Protocol) • UDP is an unreliable, connectionless protocol for applications that do not want TCP’s sequencing or flow control and wish to provide their own. • It is also widely used for one-shot, client-server type request-reply queries and applications in which prompt delivery is more important than accurate delivery, such as transmitting speech or video. The Transport Layer…
  • 20. • It contains all the higher-level protocols. • The early ones included virtual terminal (TELNET), file transfer (FTP), and electronic mail (SMTP) • The TELNET allows a user on one machine to log into a distant machine and work there. • The FTP provides a way to move data efficiently from one machine to another. • SMTP was originally just a kind of file transfer, but later a specialized protocol was developed for it. The Application Layer
  • 21. • Domain Name Service (DNS) for mapping host names onto their network addresses • HTTP, the protocol used for fetching pages on the World Wide Web The Application Layer…
  • 22. • Below the internet layer is a great void. • The host has to connect to the network using some protocol so it can send IP packets over it. • This protocol is not defined and varies from host to host and network to network. The Host-to-Network Layer
  • 23. OSI Vs TCP/IP •Did not originally clearly distinguish between service, interface, and protocol • The protocols came first, and the model was really just a description of the existing protocols. •Four layers •connectionless in the network layer but supports both modes in the transport layer • Three concepts are central: Services, Interfaces, Proto cols • The OSI reference model was devised before the protocols were invented • Seven layers • Connectionless and connection-oriented communication in the network layer, but only connection-oriented communication in the transport layer