The TCP/IP Guide  9  The Open System Interconnection (OSI) Reference Model       9  General Reference Model Issues

General Reference Model Issues 1 Why Understanding The OSI Reference Model Is Important To You

In my introduction to this Guide, I said that networking was complicated—in fact, I probably said it too often. J Well, I wouldn't lie to you—it is. And in fact, it is for that exact reason that special pains must be taken to try to simplify it. One of the ways in which networking technology is made easier to understand is by splitting it into pieces, each of which plays a particular role, or is responsible for a specific job or function.

However, if this is to be done, we must have a way of ensuring that these various pieces can interoperate; that is, each must know what is expected of it, and also what it can expect from the other pieces. This is one of the important roles of networking models. They split the multitude of tasks required to implement modern networks, into smaller chunks that can be more easily managed. Just as importantly, they establish “walls” between those pieces, and rules for passing information over those walls.

A good analogy of a networking model is to that of an assembly line at a manufacturer. No company attempts to have one person build an entire car; even if they did, they wouldn't expect that individual to be able to learn how to do it all at once. The division of labor offers several advantages to a company that builds a complex product, such as an automobile. Generally speaking, these include the following:

• Training and Documentation: It is easier to explain how to build a complex system by breaking the process into smaller parts. Training can be done for a specific job without everyone needing to know how everything else works.
  
  
• Specialization: If everyone is responsible for doing every job, nobody gets enough experience to become an expert at anything. Through specialization, certain individuals develop expertise at particular jobs.
  
  
• Easier Design Modification and Enhancement: Separating the automobile into systems, and particular jobs required to build those systems, makes it easier to make changes in the future. Without such divisions, it would be much more difficult to determine what the impact might be of a change, which would serve as a disincentive for innovation.
  
  
• Modularity: This is related to each of the items above. If the automobile's systems and manufacturing steps are broken down according to a sensible architecture or model, it becomes easier to interchange parts and procedures between vehicles. This saves time and money.

Networking models yield very similar benefits to the networking world. They represent a framework for dividing up the tasks needed to implement a network, by splitting the work into different levels, or layers. Hardware and software running at each layer is responsible for interacting with its corresponding hardware and software running on other devices at the same layer. The responsibilities of each hardware or software element are defined in part by specifically delineating lines that exist between the layers.

The result is that you get all of the benefits listed in the bullet points above: easier training, specialized capabilities at each layer, improved capabilities for modification, and modularity. Modularity is particularly important, as it allows you to interchange technologies that run at different layers. While nobody would try to build a vehicle that is partly a compact sedan, partly an SUV and partly a motorcycle, there are situations in networking where you may want to do something surprisingly similar to this. Networking models help make this possible.

General Reference Model Issues 1 Why Understanding The OSI Reference Model Is Important To You