# The OSI Model The Open Systems Interconnection (OSI) model was developed in order to facilitate communication of network devices from different manufacturers. It is the first model that split networking functionality into layers. The [[Internet Protocol Suite]] was developed in parallel, and is actually the model used today, although networking engineers still refer to the TCP/IP's layers as OSI layers. Note that this practice is discouraged by t ## Layered Architecture ![[OSI Model - Wikipedia#^robfxr]] People often struggle to memorize the layer names, leading to these several mnemonics: - All People Seem To Need Data Processing - All People Say They Never Download Porn - Please Do Not Throw Sausage Pizza Away ### Layer 1: The Physical Layer ![[OSI Layer 1 - The Physical Layer#^5l05il]] For more see [[OSI Layer 1 - The Physical Layer]]. ### Layer 2: The Data Link Layer ![[OSI Layer 2 - The Data Link Layer#^tebl0w]] Fore more see [[OSI Layer 2 - The Data Link Layer]]. ### Layer 3: The Network Layer ![[OSI Layer 3 - The Network Layer#^fxxr86]] For more see [[OSI Layer 3 - The Network Layer]]. ### Layer 4: The Transport Layer ![[OSI Model - Wikipedia#^0y8i6x]] ### Layer 5: The Session Layer ![[OSI Model - Wikipedia#^lpimle]] Once the presentation layer has serialized data, the session layer opens a connection (a.k.a. a session) between two or more computers. The session layer is in charge of the connection's setup and tear-down, and authentication. ### Layer 6: The Presentation Layer ![[OSI Model - Wikipedia#^eqiinb]] The job of the presentation layer is to serialize data from the application layer in a format that can be sent over the network. This includes encoding, compression and encryption. ### Layer 7: The Application Layer ![[OSI Model - Wikipedia#^fs70q8]] ![[OSI Model - Wikipedia#^uia1dd]]