InternationalInternational StandardsStandards OrganizationOrganization OpenOpen SystemsSystems InterconnectInterconnect (OSI)(OSI) ReferenceReference ModelModel Networks: OSI Reference Model 1 Application A Application B Application Application Layer Layer Presentation Presentation Layer Layer Session Session Layer Layer Transport Transport Layer Communication Network Layer Network Network Network Network Layer Layer Layer Layer Data Link Data Link Data Link Data Link Layer Layer Layer Layer Physical Physical Physical Physical Layer Layer Layer Layer Copyright ©2000 The McGraw Hill Companies Electrical and/or Optical Signals Leon-Garcia & Widjaja: Communication Networks Figure 2.6 Networks: OSI Reference Model 2 Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 2.9 Application A Application B data Application Application Layer data ah Layer Presentation Presentation Layer data ph Layer Session Session Layer data sh Layer Transport th Transport Layer data Layer Network Network Layer data nh Layer Data Link Data Link Layer dt data dh Layer Physical Physical Layer bits Layer Networks: OSI Reference Model 3 HTTP Request Header contains source and TCP destination port numbers Header Header contains source and destination IP addresses; IP transport protocol type Header Header contains source Frame and destination physical Ethernet addresses; network Check protocol type Header Sequence Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Figure 2.15 Networks: OSI Reference Model 4 OSIOSI versusversus TCP/IPTCP/IP Figure 1-21. The TCP/IP reference model. Networks: OSI Reference Model 5 OSIOSI versusversus TCP/IPTCP/IP DCCDCC 66th Ed.,Ed., W.W. StallingsStallings FigureFigure 1.111.11 Networks: OSI Reference Model 6 SevenSeven LayerLayer OSIOSI ModelModel Application Layer Provides users access to the OSI environment and distributed information services.services. Presentation Layer Provides application processes independence from differences in data repreesentationsentation ( e.g. abstract syntax notation). Session Layer Provides the control structure for communicating between applications. Establishes, manages and terminates session connections between cooperating applications. Transport Layer Provides reliable transparent transfer of data between end points. Provides end-to-end flofloww control andand error recovery. Network Layer Provides upper layers with independence from the data transmissioon,n, routing aandnd switchinitchingg technologies used to connect sysystems.stems. Responsible for establishing, managing and terminating connections. Data Link Layer Provides for reliable transfer of information accrossross the physical layer. Sends and receives frames with the necessary synchronization, flow control and error control. Physical Layer Concerned with transmission of an unstructured bit stream over a physical medmedium.ium. Deals with the mechanical, electrical, functional and procedural characteristics to access the phyphysicalsical medium. Networks: OSI Reference Model 7.