Chapter 2. Network Models and Standards

What You Will Learn

On completing this chapter, you will be able to:

  • Describe the OSI model and the major function of each of its layers

  • Explain the process of sending (encapsulating) and receiving (decapsulating) data across a network

  • Summarize the functions of bodies that create standards, such as ANSI, ITU-T, and the IEEE

  • List the Ethernet standards that are relevant to today's networking environment

Switches are one piece of the greater network whole, serving in both wide- and local-area environments. The network model helps explain where switches fit into the network. To set the stage for Chapter 3, "Local-Area Networking Introduction," this chapter discusses network models and standards. To understand local-area network (LAN) switching, you must understand the networking rules and how these rules and switching work together. Networking rules are a combination of network models and standards.

As discussed in Chapter 1, "Networking Basics," network models provide the guiding principles behind the development of network standards, much as automobile design standards for different types of cars around the world determine their components: They have four wheels, an engine, and a steering wheel, and use unleaded gasoline.

Remember that a standard is like a law: It is inviolable and not to be messed with. Network standards are in place to ensure that different equipment vendors produce products that work together, much as different automobile standards are in place so that tire manufacturers make standard-size tires for certain car makes and models. In the network environment, standards are important so that network users can buy equipment from different vendors as needs dictate, instead of being locked into one specific vendor for the life of the network.

When utilizing a one-vendor system, users may gain certain vendor-specific, or proprietary, features, such as special queuing algorithms for managing how information is stored before it's sent across the network. However, a problem arises when users in such a system attempt to send information to someone who is not using the same vendor features. In such a case, the queuing algorithms benefit neither the sender nor the receiver. However, they can still communicate with each other, as long as the differing devices use the same standard to communicate, much as DVD players from two different manufacturers can play same-standard DVDs.

The inventors of Ethernet?Digital Equipment Corporation, Intel, and Xerox (DIX)?used one method to run data across unshielded twisted-pair (UTP) cabling. The inventor of the Token Ring?IBM?used a different method. Ethernet and the Token Ring are different network standards, but share the commonality of operating across UTP cable. The point here to remember is that even though both technologies run data across the same type of cabling, UTP, that does not mean that these different technologies can talk to each other across the same physical cable.