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OSI LAYERS

OSI LAYERS. OSI Model. OSI means Open System Interconnect model. Developed by the International Organization for Standardization in 1974. It consists of seven layers. Each layer has a different but specific processing function. Layer - 7. Upper Layer or Software Layer. Lower Layer

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OSI LAYERS

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  1. OSI LAYERS

  2. OSI Model • OSI means Open System Interconnect model. • Developed by the International Organization for Standardization in 1974. • It consists of seven layers. • Each layer has a different but specific processing function.

  3. Layer - 7 Upper Layer or Software Layer Lower Layer or Hardware Layer Layer - 6 Layer - 5 Heart of OSI Layer - 4 Layer - 3 Layer - 2 Layer - 1 OSI Model Layers Application Presentation Session Transport Network Data Link Physical

  4. Application Presentation Session Transport Network Data Link Physical Application Layer Application Layer is responsible for providing Networking Services to the user. It is also known as Desktop Layer. Identification of Services is done using Port Numbers. Ports are Entry and Exit Points to the Layer Total No. Ports 0 – 65535 Reserved Ports 0 – 1023 Open Client Ports 1024 – 65535 Application

  5. Client FTP Server Example of FTP request ftp://ftp.microsoft.com

  6. Client FTP Server Example of FTP request FTP Request ftp://ftp.microsoft.com FTP Request Listen on Port 21 Sending FTP Reply Received FTP Reply ftp://ftp.microsoft.com

  7. Examples of Networking Services Service Port No. HTTP 80 FTP 21 SMTP 25 TELNET 23 TFTP 69

  8. Presentation 80 21 25 53 67 69 Session Transport Network Data Link Physical Data flow from Application Layer Application Data

  9. Application Presentation Session Transport Network Data Link Physical Presentation Layer Presentation Layer is responsible for converting data into standard format. Examples : ASCII, EBCDIC, JPEG, MPEG, BMP, MIDI, WAV, MP3 Following tasks are perform at Presentation layer : Encoding – Decoding Encryption – Decryption Compression – Decompression Presentation

  10. Application Presentation Session Transport Network Data Link Physical Data flow from Presentation Layer Data Data

  11. Application Presentation Session Transport Network Data Link Physical Session Layer Session Layer is responsible for establishing, maintaining and terminating session. Session ID works at Session Layer. Examples : RPC  Remote Procedure Call SQL  Structured Query Language NFS  Network File System Session

  12. Application Presentation Session Transport Network Data Link Physical Data flow from Session Layer Data Data Data

  13. Application Presentation Session Transport Network Data Link Physical Transport Layer • Transport Layer is responsible for end-to-end connectivity. It is also known as the heart of OSI Layers. Following tasks are performed at the Transport Layer : - • Identifying Service • Multiplexing & De-multiplexing • Segmentation • Sequencing & Reassembling • Error Correction • Flow Control Transport

  14. TCP UDP • Transmission Control Protocol • Connection Oriented • Acknowledgement • Reliable • Slower • Port No. 6 • e.g. HTTP, FTP, SMTP • User Datagram Protocol • Connection Less • No Acknowledgement • Unreliable • Faster • Port No. 17 • e.g. DNS, DHCP, TFTP Identifying Service

  15. Application Presentation Session 80 21 25 53 67 69 Network Data Link TCP - 6 UDP - 17 Physical Multiplexing & De-multiplexing Transport

  16. A B Segmentation Hello! How are you ? Hello! How are you ? Hello! How Are You ?

  17. you Hello! How ? are A B Sequencing & Reassembling Hello! How are you ? Hello! How are you ? You Hello! How ? Are You Hello! How ? Are Hello! Are You ? How

  18. Hello! How are you ? A B Sequencing & Reassembling Hello! How are you ? Hello! How are you ? Hello! How are you ? Hello! 1/5 Hello! 1/5 Are 3/5 Are 3/5 You 4/5 You 4/5 ? 5/5 ? 5/5 How 2/5 How 2/5 You 4/5 Hello! 1/5 How 2/5 ? 5/5 Are 3/5

  19. Hello! 1/5 Are 3/5 You 4/5 ? 5/5 Hello! How are you ? A B Error Correction Segment Missing Hello! How are you ? Hello! How are you ? Hello! How are you ? Hello! 1/5 Hello! 1/5 Are 3/5 Are 3/5 You 4/5 You 4/5 ? 5/5 ? 5/5 How 2/5 How 2/5 You 4/5 Hello! 1/5 ? 5/5 Are 3/5 How 2/5

  20. A B Flow Control - Windowing Sending 3-window Received 3-window PC-A can send 4 Segment at a time to PC-B Ack. Received-4 Ack-Rec-3 Sending 5-window Received 4-window

  21. Application Presentation Session Transport TH Network Data Link Physical Data flow from Transport Layer Data Data Data Segment Data

  22. Application Presentation Session Transport Network Data Link Physical Network Layer • Network Layer is responsible for providing best path for data to reach the destination. Logical Addressing works on this layer. Router is a Network Layer device. • It is divided into two parts • Routed Protocols • e.g. IP, IPX, Apple Talk. • Routing Protocols • e.g. RIP, IGRP, OSPF, EIGRP Network

  23. Segment Hello! How are you ? Segment A B 192.168.1.1 192.168.1.2 Routed Protocols Segment Hello! How are you ? Source IP 192.168.1.1 Destination IP 192.168.1.2 Source IP 192.168.1.1 Destination IP 192.168.1.2

  24. A Routing Protocols www.zoomgroup.com

  25. Application Presentation Session Transport e.g. Router Network NH Data Link Physical Data flow from Network Layer Data Data Data Segment Packet Segment

  26. Application Presentation Session Transport Network Data Link Physical Datalink Layer • Datalink Layer is divided into two Sub Layers : • LLC – Logical Link Control • It talks about Wan protocols e.g. PPP, HDLC, Frame-relay • MAC – Media Access Control • It talks about Physical Address. It is a 48 bit address i.e. 12 digit Hexadecimal Number. • It is also responsible for Error Detection • Devices working on Data Link Layer are Switch, Bridge, NIC. Data Link

  27. Packet A B 192.168.1.1 00-20-18-C0-07-71 192.168.1.2 00-20-18-C0-07-72 Error Detection – CRC Check PC-A CRC No. 33333 PC-B CRC No. 11114 Error Detected For Error Correction Contact Source Transport layer Packet Hello! How are you ? 00000 11114 46323 99434 89696 99323 55434 00000 43434 32434 43434 32434 55434 99323 22222 99434 46323 11114 Error Detected Source MAC 00-20-18-C0-07-71 Destination MAC 00-20-18-C0-07-72 22222 89696 33333

  28. Packet Hello! How are you ? Packet A B 192.168.1.1 00-20-18-C0-07-71 192.168.1.2 00-20-18-C0-07-72 Error Detection – CRC Check Packet 22222 22222 00000 20202 99323 46323 99434 43434 89696 11114 99323 46323 43434 99434 55434 11114 20202 Source MAC 00-20-18-C0-07-71 Destination MAC 00-20-18-C0-07-72 32434 00000 Source MAC 00-20-18-C0-07-71 Destination MAC 00-20-18-C0-07-72 55434 89696 32434

  29. Application Presentation Session Transport Network e.g. Switch Data Link DH DT Physical Data flow from Data Link Layer Data Data Data Segment Packet Frame Packet Packet

  30. Application Presentation Session Transport Network Data Link Physical Physical Layer Physical Layer is responsible for electrical, mechanical and procedural checks. Data will be converted into Binary (i.e) 0’s & 1’s. Data will be in the form of electrical pulses if it is Coaxial or Twisted Pair cable and in the form of Light if it is Fiber Optic Cable. Devices working at Physical Layer are Hubs, Repeaters, Cables, Modems etc. Physical

  31. Frame Hello! How are you ? Frame A B Physical Layer Example Frame 1010101010101010 1010101010101010 1010101101010101010101010 0101011010101010101010101 1010101101010101010101010 0101011010101010101010101 0101011010101010101010101

  32. Application Presentation Session Transport Network Data Link e.g. Hub Physical Data flow from Physical Layer Data Data Data Segment Packet Frame Bits

  33. A B Application Application Presentation Presentation Session Session Transport Transport TH TH TH Data Network Network Segment NH NH NH Data Link Data Link Packet DH Packet DH DH DT DT DT Physical Physical Data Encapsulation & De-capsulation Data Data Data Data Data Data Segment Segment Data Packet Packet Segment Frame Frame Packet Packet Bits Bits

  34. B A Application Presentation Session Transport Network Data Link Physical Simulation Scenario Data Link Physical 1000011110001110000111000 www.google.com Frame Application www.google.com 8787874471797971766944677977 Presentation Port MAC 0/2 2222:2222:2222 0/1 1111:1111:1111 8787874471797971766944677977 87878744717979 71766944677977 Student:1 Session 87878744717979 71766944677977 Student:1 Data TCP:80 TCP:80 Transport Data TCP:80 Network SIP DIP Segment Data Link SIP DIP Segment S MAC D MAC Packet Physical S MAC D MAC Packet 1000011110001110000111000 1000011110001110000111000

  35. Figure 2.21 Port addresses

  36. Figure 2.20 IP addresses

  37. Application Presentation Session Transport Network Data Link Physical Comparing OSI with TCP/IP Layers OSI Layers TCP/IP Layers Application Transport Internet Network Access

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