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OSI Model

OSI Model. The OSI Model. Open Systems Interconnection Standard Model for Data Communications Specified by International Standards Organization (ISO) Adopted by CCITT/ITU Official Model Explained in X.200 Series. The OSI Model. Layered Approach to Communications Seven Layers Altogether

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OSI Model

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  1. OSI Model

  2. The OSI Model Open Systems Interconnection • Standard Model for Data Communications • Specified by International Standards Organization (ISO) • Adopted by CCITT/ITU • Official Model Explained in X.200 Series

  3. The OSI Model Layered Approach to Communications • Seven Layers Altogether • Each Layer Performs a Unique Function • Each Layer Has Its Own Protocol • Protocol Messages in Upper Layer is Data to Layer Below

  4. Telnet, FTP, Mail User Level Processing Application Data Representation & Syntax ISO Presentation Presentation ISO Session Sync Points and Dialogs Session TCP Reliable End to End Transport X.25 Pkt, IP Unreliable Thru Multi-Node Network Network Link LAPB, HDLC Reliable Across Physical Line Physical RS232, T1, 802.x Unreliable Wire, Telco Line The OSI Model The Seven Layers Layer Name Description Examples

  5. Application Presentation Session Transport Network Link Physical The OSI Model The Standards Layer Name Standards X.400, Telnet, FTP, Mail ASN.1, X.409 X.225 X.224, TCP X.25 Pkt, Q.931, IP Reliable Across Physical Line X.25 LAPB, Q.921 LAPD, ISO 3309 HDLC Unreliable Wire, Telco Line Unreliable Wire, Telco Line RS232, V.35, EIA530, X.21, T1, E1

  6. Link Layer Begin Data End The OSI Model Physical Layer • Message Has Begin and End • Data in between • Data Passed up to Link Layer

  7. The OSI Model Physical Layer • Begin Can Be Flag or STX • End Can Be Flag or ETX • End May Include Check Sum (CRC) • Data Transparency Link Layer Begin Data End

  8. The OSI Model Link Layer • Link Layer Header Has Frame Type • Sequence and Acknowledgement Numbers • Error Recovery Procedures • Limited to Local Wire or Circuit Network Layer LL Hdr Data

  9. The OSI Model Network Layer • Network Header Has Packet Type • Sequence and Acknowledgement Numbers • No Error Recovery -- Data Can Be Lost • Addressing across Multi-Node Network Transport Layer Net Hdr Data

  10. The OSI Model Transport Layer • Transport Header Has Packet Type • Sequence and Acknowledgement Numbers • Error Recovery Is End to End • Upper Layers Can Count on Reliability Upper Layers Trans Hdr Data

  11. Begin LL Hdr Net Hdr Trans Hdr Data End The OSI Model Complete Picture • A Message with All Headers • Session, Presentation, Application Omitted

  12. The OSI Model End of Presentation

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