Advantages to Layered Networking Models
Networking technology requires contributions from a wide variety of skills. The task of enabling an application on one computer to communicate with an application on another computer requires many different levels of services. The networking industry is fragmented between different specializations, but all are represented by the layered protocol model.
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Specialization
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No one is able to be an expert in all aspects of networking. The discipline requires programmers, designers, graphics artists, electricians, chip makers, hardware producers and mathematicians. Where several people have to contribute to one end goal, the team needs rules and guidelines to ensure that the output of one section of the system complies with the input requirement of another section of the system. Each contributor applies specialized skills to a subset of the total requirements of a networking system. Those rules and guidelines are protocols. Organizing protocols in layers allies technology with skills. Technicians and electricians provide a service creating a physical network over which programmers can send data. Each focuses on his specialization, relying on other levels for support.
Abstraction
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Abstraction is the key to specialization. Each layer provides services to the layer immediately above. A protocol in one layer uses a service provided by the layer immediately below without having to know how that task will be performed. Without reliance on abstraction, every protocol would be lengthy and detailed.
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Networking Models
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The first layered model for networking was TCP/IP. This protocol stack still dominates networking technology. Layers run from physical details at the bottom of the stack up to user-facing applications at the top of the stack. A later stack, called the "Open System Interconnection Model" has a better grading of layers. Most networking professions hold both models in mind. The layers make networking easier to teach and provide a mental shortcut to describe the functions of a protocol. Any networking procedure or device is always described in terms of its position in the protocol stack. Typical statements are "encryption occurs at the Transport Layer," or "a switch is a layer 2 device, a router is layer 3." Anyone schooled in networking theory would instantly know that those two statements mean that encryption is negotiated at session establishment, a switch operates over one link and uses MAC addresses and a router works across links and uses IP addresses.
Industry Segmentation
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The layered model also helps to divide the networking profession into sub-categories. People working in networking can instantly recognize the scope and boundaries of their job, and that of others, by thinking in terms of the layers in the protocol stack.
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References
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