The OSI Model

1. Logical connection Interoperability Remote connection Interconnectivity Local connection The OSI Model User Application 7 Presentation 6 Session 5 Transport 4 Network 3 Data Link 2 Physical 1 Cable or other medium

2. Application Presentation Session Transport Network Data Link Physical The Physical Layer • Provides electrical and mechanical interfaces for a network. • Specifies type of medium used to connect network devices. • Specifies how signals are transmitted on network.

3. Application Presentation Data from upper layers Session 010101010011001 Transport Network Data Link Physical 10010011 0000011 1010011 0010111 The Data Link Layer • Controls access to communication channel. • Controls the flow of data. • Organizes data into logical frames. • Identifies specific computer on the network. • Detects errors.

4. Application Presentation Session Transport Network Data Link Physical The Network Layer • Moves information to the correct address. • Assembles and disassembles packets. • Addresses and routes data packets. • Determines best path for moving data through the network.

5. Application Presentation Session Transport Network Data Link Physical The Transport Layer • Takes action to correct faulty transmission. • Controls the flow of data. • Acknowledges successful receipt of data. • Fragments and reassembles data.

6. Application Presentation Session Transport Network Data Link Physical The Session Layer • Establishes and maintains connection. • Manages upper layer errors. • Handles remote procedure calls. • Synchronizes communicating nodes.

7. Application Presentation Session Adl fierwoeiori we’ Adl fierwoeiori we’ Transport Network Data Link Physical The Presentation Layer • Encodes and decodes data. • Determines the format and structure of data. • Compresses and decompresses data. • Encrypts and decrypts. Alice Bob

8. Application Presentation Session Transport Network Data Link Physical The Application Layer • Provides the user interface. • Connects the user to the network. • Provides file transfer service, email service, terminal emulation, and other services.

9. A Network in Action Albert dictates the letter onto a tape. He gives the tape to Penelope, who will translate it to German for him. Penelope listens to the tape and translates it into German. Penelope gives the letter to her assistant, Sam. Sam puts the letter into an envelope and addresses it. Mary gets the letter from Sam’s out box. She stuffs the letter, along with the other letters bound for the office in Germany, into a large courier-service envelope. Mary fills out a slip on the large envelope that will be returned by the courier in Germany to acknowledge successful delivery of the large envelope. Ned, the courier, brings the envelope to the local office of the courier service. He determines the best delivery route to transfer it to its destination. Ann, the shipping clerk, sorts through envelopes on the conveyor, ensuring that they do not get jammed up or damaged. She loads envelopes to the correct vehicle for shipment. The envelope is delivered to its destination.

10. File Transfer and the OSI Model