Hi 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! David Davis Personal website: HappyRouter.com Visit my Cisco Blog on ITKE

Hi 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. <a href="http://en.wikipedia.org/wiki/International_Organization_for_Standardization">You can read about the ISO here</a>. Third, there is the TCP/IP Reference model created by the Department of Defense (DoD) that details a similar model to the OSI model. <a href="http://en.wikipedia.org/wiki/TCP/IP_model"">Information on it can be found here</a>. I hope that helps! David Davis Personal website: <a href="http://www.happyrouter.com">HappyRouter.com</a> Visit my <a href="http://itknowledgeexchange.techtarget.com/cisco/">Cisco Blog on ITKE</a>