OSI Model

• Please
• Do
• Not
• Throw
• Sausage
• Pizza
• Away

This layer interfaces directly with the network-aware application, giving it access to network resources.

Without this layer, no user application would be able to get access to the network.

Encodes the data being sent or recieved into a generic format that will be understood by both devices. _{For example, a web browser might recieve data in HTML format or a picture in JPG format, which are generic and well understood standards}.

Begins, ends, and manages the sessions between devices.

Handles the reliablity of the connection and logical separation of applications. _{For example, if a computer is surfing the internet with a web browser and at the same time listening to internet-radio, this layer ensures the correct data arrives to the correct application.}

In addition, this layer handles flow-control (ensuring one side does not send information faster than the other can receive) and data integrity (ensuring the data is not corrupt).

The most common Transport layer protocol is TCP.

Provides logical addressing services allowing a device to dictate the source and destination address used for end-to-end communication.

This layer is also responsible for routing the packet from its source to its destination.

The most common Network layer protocol is IP.

Provides physical addressing services allowing a device to dictate the source and destination address used for local network communication.

This layer permits communication between devices connected to the same network.

This layer is also responsible for error detection.

Defines the physical standards used for network communication.

• User Interface
• Communication partner identification

• Data format (file format)
• Encrytion, translation, and compression
• Data format and exchange

• Keeps data streams separate (session identification)
• Set up, maintain and tear down communication sessions

• Reliable (connection-oriented) and unreliable (connectionless) communications
• End-to-End flow control
• Port and socket numbers
• Segmantation, sequecing, and combination

• Logical addresses
• Path determination (identification and selection)
• Routing packets

• Convert bitsinto bytes and bytes into frames
• MAC address, aka burned in address (BIA), hardware address
• Logical network topology
• Media access
• Flow control-Acknowledgement, buffering, windowing
• Parity and CRC

• Move bits across media
• Cables, connectors, pin positions
• Electrical signals (voltage, bit synchronization)
• Physical topology (network layout)