Thanks for the question-
A few different confusion acronyms here…
First, there is IOS – the Cisco operating system for routers. I don’t think that has anything to do with what you are asking.
Second, there is the very popular OSI reference model for how different pieces of software, hardware, drivers, and applications all work together to allow computers to communicate over a network. It is called the 7 layer model sometimes because it has the following 7 layers-
Layer 7: Application layer
Layer 6: Presentation layer
Layer 5: Session layer
Layer 4: Transport layer
Layer 3: Network layer
Layer 2: Data Link layer
Layer 1: Physical layer
The International Organization for Standardization (Another ISO), created the OSI reference model. You can read about the ISO here.
Third, there is the TCP/IP Reference model created by the Department of Defense (DoD) that details a similar model to the OSI model. Information on it can be found here.
I hope that helps!
Personal website: HappyRouter.com
Visit my Cisco Blog on ITKE