Session, Presentation, and Application Layers

The upper layers of the OSI model are closest to the user. Layer 5 is the session layer, Layer 6 is the presentation layer, and Layer 7 is the application layer. These layers manage conversations, format and protect data, and provide the services that programs use. Where the lower layers move bits, these top layers turn raw data into meaningful interactions for people and applications.

The session layer manages the dialogue, or session, between two applications. It opens, maintains, and closes connections in an organized way, and can keep multiple conversations separate. For example, it tracks the back-and-forth of a login session so each side knows where it stands. The session layer keeps related exchanges grouped and orderly over time.