OSI

From Bandipedia

Open System Interconnect

The OSI model (also known as the OSI stack), developed by the International Standards Organization, is a conceptual model of a network subsystem architecture, independent of any specific network technology.

It divides the responsibility for data transfer into seven layers.

Layer 7: Application Layer

The highest layer in the model, delivers information to the end user.

Layer 6: Presentation Layer

Normalizes data for delivery to the Application layer, for example converting data representations or potentially handling encryption.

Layer 5: Session Layer

Responsible for negotiating,maintaining and managing connections (sessions). For example SIP is considered to be a layer 5 protocol.

Layer 4: Transport Layer

Ensures reliability of data delivery to Session Layer. The majority of TCP/IP functionality can be considered as part of the transport layer, although there is some overlap with the layers above and below.

Layer 3: Network Layer

This layer handles the addressing, routing and flow control requirements of the data. More advanced network switches work with layer 3 information to more intelligently direct data by looking at not only the layer 2 information, but also having some knowledge of layer 3 protocols.

Layer 2: Data Link Layer

Provides Media Access Control (MAC), and Logical Link control (LLC) for network access. Actions performed at this level include adding CRC information (for error checking) and setting up the network frames. Basic network switches operate at Layer 2


Layer 1: Physical Layer

This layer is responsible for the physical transmission of the data over the medium, for example by encoding it to electrical voltages on a wire. This layer also handles other physical aspects of transmission such as contention and flow control.

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