3. Bob Baker Open Systems Interconnection OSI Reference model –Layer 7 application –Layer 6 presentation –Layer 5 session –Layer 4 transport –Layer 3 network –Layer 2 data link –Layer 1 physical Channel SenderReceiver

4. Bob Baker Services –Layer 7 application –Layer 6 presentation –Layer 5 session –Layer 4 transport –Layer 3 network –Layer 2 data link –Layer 1 physical –Identification, authentication –Format conversion –Set-up and coordinate conversation –Ensures complete, error-free transfer –Routing of data through network –Error control and synchronisation –Placing signals on the carrier

5. Bob Baker Sample- Internet protocol suite –Layer 7 application –Layer 6 presentation –Layer 5 session –Layer 4 transport –Layer 3 network –Layer 2 data link –Layer 1 physical –POP, SMTP, FTP, HTTP, DNS –TCP –IP –PPP, Ethernet, Token ring –wire, radio, fibre optic Note: In the TCP/IP Suite, the top three layers of the OSI model (Application, Presentation and Session) are often considered as a single Application Layer. More about the Internet Protocol Suite: http://en.wikipedia.org/wiki/TCP/IP

6. Bob Baker Encapsulation Application Presentation Session Transport Network Data Link Physical data Device 1Device 2 data H6T6 data H5T5 data H4T4 (packet) H3 data T3 H2 data T2H1 data T1 carrier frame Application Presentation Session Transport Network Data Link Physical frame A typical frame Destination Address Source Address DataPaddingCRCPreamble