The OpenSystemsInterconnect (OSI) model is a top-down analysis set. There are 7 (academically) distinct layers in the Model:

	1. PhysicalLayer
	2. DataLinkLayer
	3. NetworkLayer
	4. TransportLayer
	5. SessionLayer
	6. PresentationLayer
	7. ApplicationLayer

These layers are "stacked" one on top of the other in a cascading fashion. Each layer is dependant and builds on the layer(s) below it.

'''FourLayerArchitecture'''

The most practical implementations of the ISO/OSI model have 4 layers, which merges some of the layers together, splitting them by logical distinctions.
	1. Link 
	2. Network 
	3. Presentation
	4. Application
''Do these layers actually correspond to the listed four layers in the FourLayerArchitecture page? I am finding that they are different: View layer, ApplicationModel layer, DomainModel layer and Infrastructure layer.''
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Reference: http://www.scit.wlv.ac.uk/~jphb/comms/std.7layer.html

Also referred to as: Network Layering Principles, ISO/OSI model
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The long and the short of it is that nobody believes in the OSI protocol stack. People believe in the TCP/IP protocol stack, but not OSI. Hell, the OSI model was only made packet-oriented at the last minute. -- rk

''OSI model has succeeded if only it has served as a reference for start of debate on implementation aspects. Moreover, I have seen a lot of mapping of SecurityManagement material to this model -- dl''

The real reference is the Unix implementation of TCP/IP. The OSI model isn't a reference for anything and the notion that it triggered debate of implementation is absurd. The OSI model wasn't made until long after TCP/IP was a resounding success. You've got your history backward.

*It's like the Library of Congress cataloging system.  Books (and even other taxonomies for knowledge) were around long before such a system was developed; but, after it was developed, it started informing the categorization of all future publications. --MarkJanssen''
 
''If you like to tell us why ISO started an OSI model "LONGAFTER" the TCP/IP stack became popularised, and yet have nothing useful to contribute please do so. I would also advice you to take a look at http://www.sans.org/rr/papers/44/1309.pdf as an example OSI model is quoted as reference, for purposes of information security.''
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By the way, the OSI model is sometimes referred to as "the seven layer salad."
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Contributors: SusanRoy, MartySchrader