Network Standards and Models
Before delving into network standards, let's look at an analogy. Esperanto was developed in an attempt to create a language that people all over the world could learn with ease. Its proponents believed that it favored no one people or culture and had straightforward grammar and spelling. Network standards were developed with similar ideals in mind.
A network standard normalizes how different pieces of network equipment connect to each other, whereas a network model provides the guiding principles behind the development of these network standards. The most prevalent network model used today is the Open System Interconnection (OSI) model. This chapter presents an overview of standards and models, and Chapter 2, "Network Models and Standards," delves more deeply into these topics.
A network standard is like a law?it is inviolable. Obviously, if a vendor does not follow network standards, there are no legal penalties. Instead, the use of the equipment produced by that vendor will be limited. Standards are in place to ensure that even the lowest level of communication on the media is possible, so that nodes, networking devices, and applications can all interoperate (or "play well with others"). This is important so that network users can buy equipment from different vendors as their needs dictate, rather than be locked into one specific vendor for the life of the network. The vendors would not mind being the sole equipment provider, but the technology and the user community dictate that these vendors interoperate, and it is network standards that enable this interoperability.
When a vendor implements a feature that does not adhere to network standards, it is called a proprietary feature. Proprietary features often perform specific functions that pertain only to a particular piece of equipment or vendor implementation of a technology, such as a certain way of using the Internet to carry a telephone or a videoconference call.
To continue the subway analogy, network standards are like different subway routes; different standards use network technologies in different ways. These different standards sometimes use similar pieces but in different ways, just as each subway route uses the same-scale tracks, but those tracks are used in a different fashion (such as for different train routes). In New York City, for example, the number 2 train takes you from Houston Street to Times Square and the number 6 train takes you from Grand Central Station to Lexington Avenue, yet both trains use the same-size tracks on their routes. Standards also govern the vehicles (data) that ride on the subway tracks (networks). For instance, railroad cars must be built to standard size/weight to ride over the rails, just as data must be formatted according to certain standards to be carried over the wires.
Digital Equipment Corporation, Intel, and Xerox (DIX) were the inventors of the Ethernet. DIX used one method to transmit data across unshielded twisted-pair (UTP) cabling. In contrast to DIX, IBM, the inventor of Token Ring, uses a different method to transport data across UTP. DIX and IBM represent different network standards, but share the commonality of operating across the same cable type: UTP. The point to remember is that just because organizations transmit data across the same type of cabling (UTP, for instance), that does not mean they can talk with each other, or interoperate. Think of it in terms of a steam locomotive and an electric-powered train: Both use the same type of track, but do not have compatible engines, and therefore cannot be swapped with one another.
As previously mentioned, network standards are like laws: They regulate how different networks talk with each other. Network models, on the other hand, provide the guiding principles for the development of these network standards and for the implementation of these networks.
The most prevalent network model used is the OSI model. Nearly every network standard centers on how the standard fits into the OSI model.
Imagine that your job is to design and build a car, and you want to design a sports car that no one has ever seen before. At the same time, you want this car to fit on the existing roads and in parking lots. Therefore, the car can be only so wide and so long. Standards provide the guidelines that you and other automobile engineers will follow, so that your car can be used on existing roads.