Crash Course

OSI model: Crash Course


The OSI model is the conceptual backbone of most enterprise networks, but do you remember all the details? Read our rundown of the OSI model

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and what all those layers do.


OSI (Open Systems Interconnection) is a standard description or "reference model" for how messages should be transmitted between any two points in a telecommunication network. Its purpose is to guide product implementors so that their products will consistently work with other products. The reference model defines seven layers of functions that take place at each end of a communication. Although OSI is not always strictly adhered to in terms of keeping related functions together in a well-defined layer, many if not most products involved in telecommunication make an attempt to describe themselves in relation to the OSI model. It is also valuable as a single reference view of communication that furnishes everyone a common ground for education and discussion.

Read the full definition here, courtesy of


FastFacts on the OSI model
Get the history of the OSI model and view our helpful illustration.

Read more OSI model-related tips here.


Why does the OSI model have 7 layers - no more no less?
Expert response: The ISO (International Organization for Standardization) is the mother of the OSI model. Back in 1980 they began work on a set of protocol that would promote open…

What type of security is associated with each level of the OSI model?
Expert response: The OSI security architecture reference model (ISO 7498-2) is also designed around seven layers, reflecting a high level view of the different...

What is the command to ping a TCP port?
Expert response: The OSI model is a 'virtual' model which helps us describe how computers and their protocols communicate between each other and what steps are required to be taken…

Ask our experts your OSI model-related questions and view previously answered Q&As.


Understanding Layer 2, 3, and 4 protocols
Before you can tackle the complexities of content networking, you need to understand how the network works. This chapter of Optimizing Network Performance with Content Switching: Server, Firewall and Cache Load Balancing by Matthew Syme and Philip Goldie offers an in-depth explanation of the layers of the OSI model, switching, TCP, UDP, and VRRP.

Read more OSI model-related white papers here.

This was first published in December 2005

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