Chapter 3. Hardware and the OSI Model

Terms you'll need to understand

• Hub

• Bridge

• Layer 2 switch

• Router

• Layer 3 switch

• Repeater

• Star topology

• Bus topology

• Coaxial cable

• Twisted pair

• Collision domain

• Segment

• CSMA/CD

Techniques you'll need to master:

• Ethernet operation

• Store and forward bridging

• Network segmentation

• Strengths and weaknesses of a star topology versus a bus topology

• Identify hardware typical of Layers 1 through 3 of the OSI model

• Understand the functions of and differences of bridges and Layer 2 switches

• Understand the operational differences and functions of Layer 1, 2, and 3 devices

When IBM released its first PC it started a veritable buying frenzy among corporations. What separated the IBM PC from others of the time was not so much technology as it was the IBM logo displayed prominently on the front of each PC. The IBM logos made the PC acceptable for deployment in a corporate environment, and deploy it they did! At the time, businesses were largely dependent upon timesharing vendors to run ad hoc analysis and simulations. The benefit of these real-time applications more than warranted the cost, which in many cases exceeded $40,000 to $50,000 per month. A PC, however, could often run the same application for a one-time cost of $6,000 to $12,000, making deployment a foregone conclusion.

Why Are We Covering History?

You are probably asking yourself, why the history lesson? After all, Exam Crams are supposed to be "the facts, only the facts, and nothing but the facts" right? Well, there are really two reasons for this chapter. The first is that the CCNA exam covers far more material than can be memorized. Many of the questions will require you to determine the best answer based on your knowledge of how and why things work the way they do. Taking some time now to review the reasons behind the technology will not only pay big dividends at test time, but it will also provide a contextual framework for discussing some pretty complex equipment in the chapters to come. The second reason for the history lesson is that it provides a way to remember the low-level properties affecting the design and operation of today's equipment. The alternative is just listing electrical properties, physical design limitations, and the physics behind network operation, which can be drier than Oklahoma dirt. So put your feet up, relax, and let's go back to the time of short sleeve white shirts and pocket protectors.

"Give a man a fish and he will surely want a steak" is a parable that holds true for corporations as well as individuals, and it wasn't long before organizations were demanding even more savings from PC installations. It didn't take a rocket scientist to realize the major cost of PC deployment was in the peripherals, not the PCs. A letter-quality printer could cost as much as a PC and a really big hard drive, say 5MB, could exceed the cost of a PC. With the exception of running back and forth with 5 1/2-inch diskettes (sneaker-net) those peripherals were un-shareable and grossly underutilized . Ahh, if only peripherals could be shared, think of the savings!