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Internetworking Models

The Layered Approach
A reference model is a conceptual blueprint of how communications should take place. It addresses all the processes required for effective communication and divides these processes into logical groupings called layers. When a communication system is designed in this manner, it’s known as layered architecture.

Advantages of Reference Models
The OSI model, like the Cisco three-layer model you will learn about later, is hierarchical, and the same benefits and advantages can apply to any layered model. The primary purpose of all models, and especially the OSI
model, is to allow different vendors to interoperate. The benefits of the OSI and Cisco models include, but are not limited to, the following:
The OSI Model
When networks first came into being, computers could typically communicate only with computers from the same manufacturer. For example, companies ran either a complete DECnet solution or an IBM solution—not
both together. In the late 1970s, the OSI (Open Systems Interconnection) model was created by the International Organization for Standardization (ISO) to break this barrier. The OSI model was meant to help vendors create interoperable network devices. Like world peace, it’ll probably never happen completely, but it’s still a great goal.
The OSI model is the primary architectural model for networks. It describes how data and network information are communicated from applications on one computer, through the network media, to an application
on another computer. The OSI reference model breaks this approach into layers.

The Cisco Network Design Model
This Study Guide focuses on another important network model, the Cisco hierarchical network design model. Very different than the OSI model, this model is used as the basis for designing Cisco networks for security and performance. Cisco has also created a three-layer model that is used to help design, implement, and maintain any size network. By understanding the three-layer model, you will gain an understanding of how Cisco views internetworking. Also, by having a fundamental understanding of the devices used at each layer of the model, you can effectively design and purchase the correct Cisco equipment to meet your business needs.

The TCP/IP Suite
The Transmission Control Protocol/Internet Protocol (TCP/IP) suite was created by the Department of Defense (DoD) to ensure and preserve data integrity, as well as maintain communications in the event of
catastrophic war. If designed and implemented correctly, a TCP/IP network can be a dependable and resilient one.