Upper OSI Model Layer Facts

Upper OSI Model Layer Facts

The following table summarizes basic characteristics of the upper OSI model layers.

Layer	Description
Application	The Application layer integrates network functionality into the host operating system, and enables network services. The Application layer does not include specific applications that provide services, but rather provides the capability for services to operate on the network. These services include: File services--transferring, storing, and updating shared data Print services--enabling network printers to be shared by multiple users Message services--transferring data in many formats (text, audio, video) from one location to another, or from one user to another Application services--sharing application processing throughout the network and enabling specialized network servers to perform processing tasks Database services--storing, retrieving, and coordinating database information throughout the network The Application layer specifies many important network services that are used on the Internet. These include: HTTP Telnet FTP TFTP SNMP Note: Most Application layer protocols operate at multiple layers down to the Session and even Transport layers. However, they are classified as Application layer protocols because they start at the Application layer (the Application layer is the highest layer where they operate).
Presentation	The Presentation layer formats or "presents" data into a compatible form for receipt by the Application layer or the destination system. Specifically, the Presentation layer ensures: Formatting and translation of data between systems Negotiation of data transfer syntax between systems, through converting character sets to the correct format. Compatibility with the host Encapsulation of data into message envelopes by encryption and compression Restoration of data by decryption and decompression The Presentation layer formats data for the Application layer. Therefore, it also sets standards for multimedia and other file formats. These include standard file formats such as: JPEG, BMP, TIFF, PICT MPEG, WMV, AVI ASCII, EBCDIC MIDI, WAV
Session	The Session layer's primary function is managing the sessions in which data is transferred. Functions at this layer may include: Establishment and maintenance of communication sessions between the network hosts, ensuring that data is transported. Management of multiple sessions (each client connection is called a session). A server can concurrently maintain thousands of sessions. Assignment of the session ID number to each session, which is then used by the Transport layer to properly route the messages. Dialog control--specifying how the network devices coordinate with each other (simplex, half-duplex, and full-duplex). Termination of communication sessions between network hosts upon completion of the data transfer. The Session layer protocols and interfaces coordinate requests and responses between different hosts using the same application. These protocols and interfaces include: Network File System (NFS) Apple Session Protocol (ASP) Structured Query Language (SQL) Remote procedure call (RPC) X Window

 

 

 

 

Credit: Testout 640-802 CCNA Notes