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

2. The Physical Layer Application Presentation Session Transport Network Data Link Physical  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. The Data Link Layer Application Presentation Session Transport Network Data Link Physical  Controls access to communication channel.  Controls the flow of data.  Organizes data into logical frames.  Identifies specific computer on the network.  Detects errors. 10010011 0000011 1010011 0010111 Data from upper layers 01010101001100 1

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

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

7. The Presentation Layer  Encodes and decodes data.  Determines the format and structure of data.  Compresses and decompresses data.  Encrypts and decrypts. Application Presentation Session Transport Network Data Link Physical A       ’ A       ’ Alice Bob

8. The Application Layer Application Presentation Session Transport Network Data Link Physical  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