1. OSI MODEL

3. THE OSI REFERENCE MODEL 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical The OSI Model will be used throughout your entire networking career!

5. The seven layers of the OSI Reference Model

6. This is the layer that actually interacts with the operating system or application whenever the user chooses to transfer files, read messages or perform other network related activities. A P P L I C A T I O N L A Y E R 3 Network 2 Data Link 7 Application 6 Presentation 5 Session 4 Transport 1 Physical This layer deal with networking applications. Examples:  Email  Web browsers PDU - User Data

9. P R E S E N T A T I O N L A Y E R The Presentation layer performs code conversion and data reformatting (syntax translation). It is the translator of the network, making sure the data is in the correct form for the receiving application. This layer is responsible for presenting the data in the required format which may include:  Encryption  Compression PDU - Formatted Data 3 Network 2 Data Link 7 Application 6 Presentation 5 Session 4 Transport 1 Physical

11. RESPONSIBLE FOR THE PRESENTATION LAYER 7. Messages are sent between layers 8. Communicates through GATEWAYS and APPLICATION INTERFACES CORRESPONDING PROTOCOLS JPEG· MIDI· MPEG· All kinds of music pictures & movie formats· CORRESPONDING DEVICES GATEWAY

12. S E S S I O N L A Y E R This Layer establishes, maintains and ends communication with the receiving device. The Session layer decides when to turn communication on and off between two computers It provides the mechanisms that control the data-exchange process and coordinates the interaction between them. It sets up and clears communication channels between two communicating components.

13. S E S S I O N L A Y E R 3 Network 2 Data Link 7 Application 6 Presentation 5 Session 4 Transport 1 Physical This layer establishes, manages, and terminates sessions between two communicating hosts. Example:  Client Software ( Used for logging in) PDU - Formatted Data

15. RESPONSIBLE FOR SESSION LAYER 4. Handles remote procedure calls. 5.Communicates through Gateways & application interfaces. CORRESPONDING PROTOCOLS Network File System (NFS CORRESPONDING DEVICES GATEWAYS S E S S I O N L A Y E R

16. The Transport layer ensures data is successfully sent and received between the two computers. If data is sent incorrectly, this layer has the responsibility to ask for retransmission of the data. This layer acts as an interface between the bottom and top three layers. By providing the session layer with a reliable message-transfer service, it hides the detailed operation of the underlying network from the session layer. This layer maintains flow control of data and provides for error checking and recovery of data between the devices. T R A N S P O R T L A Y E R

17. T R A N S P O R T L A Y E R This layer breaks up the data from the sending host and then reassembles it in the receiver. It also is used to insure reliable data transport across the network. PDU - Segments 3 Network 2 Data Link 7 Application 6 Presentation 5 Session 4 Transport 1 Physical

19. RESPONSIBLE FOR TRANSPORT LAYER 5. Acknowledges successful receipt of data. 6. TCP/SPX - connection oriented communication for applications to ensure error free delivery. 8. Communicates through Gateway Services, routers & Brouters. CORRESPONDING PROTOCOLS TCP, UDP, SPX, NetBEUI CORRESPONDING DEVICES GATEWAYS T R A N S P O R T L A Y E R

21. N E T W O R K L A Y E R 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Sometimes referred to as the “Cisco Layer”. Makes “Best Path Determination” decisions based on logical addresses (usually IP addresses). PDU – Packets

23. RESPONSIBLE FOR NETWORK LAYER 5. Sends messages and reports errors regarding packet delivery (ICMP) 6. Communicates through GATEWAY SERVICES, ROUTERS & BROUTERS CORRESPONDING PROTOCOLS 1. IP 4. ARP 7. ICMP 2. IPX 5. RARP 8. DLC 3. RIP 6. OSPF 9. NetBEUI CORRESPONDING DEVICES ROUTERS & BROUTERS N E T W O R K L A Y E R

25. D A T A L I N K L A Y E R This layer provides reliable transit of data across a physical link. Makes decisions based on physical addresses (usually MAC addresses). PDU – Frames 3 Network 2 Data Link 7 Application 6 Presentation 5 Session 4 Transport 1 Physical

27. RESPONSIBLE FOR DATALINK LAYER 6. CRC is added at this Layer (Error detection). 7. If CRC fails at the receiving computer, this layer will request re-transmission. 8. MAC addresses are resolved at this Layer (switches, brouters and bridges function on this layer using the MAC sub layer) 9. Sends data from network layer to physical layer. D A T A L I N K L A Y E R

32. P H Y S I C A L L A Y E R 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical This is the physical media through which the data, represented as electronic signals, is sent from the source host to the destination host. Examples:  CAT5 (what we have)  Coaxial (like cable TV)  Fiber optic PDU – Bits

34. RESPONSIBLE FOR PHYSICAL LAYER 5. Specifies how signals are transmitted on network 6. Communicates through: REPEATERS, HUBS, SWITCHES, CABLES, CONNECTORS, RECEIVERS, & MULTIPLEXERS CORRESPONDING PROTOCOLS None CORRESPONDING DEVICES 1. Brouters 4. Amplifiers 7. Receivers 10. Cables 2. Hubs 5. Transceivers 8. Transmitters 11. Switches 3. Repeaters 6. Multiplexers 9. Connectors P H Y S I C A L L A Y E R