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Section 1
LAN Basics


Positioning any technology for high performance and added value requires mastery of the basics before moving to the next level. The same is true for LANs. To help the LAN manager who needs to make sense of the sometimes bewildering array of ever-changing technology, this section of the handbook provides an orderly survey of basic LAN technologies and standards, with an emphasis on providing a solid, reliable, high-performance network.

The commercial success of LANs during the past decade is a direct result of the development of viable LAN standards. Such standards provide the basis for compatibility across vendor and product lines, while ensuring competitive pricing in the marketplace. By far the most important set of LAN standards in existence is the IEEE 802 family. Covering all LAN-medium types, various LAN access schemes, and such related issues as LAN security, a fundamental understanding of this family of standards is essential to any network or IS manager. Chapter 1-1, “IEEE 802 Standards,” provides the basis of such an understanding, providing detail down to the bit level in many cases. The chapter describes how these standards fit within the Open Systems Interconnection (OSI) reference model, and provides detailed descriptions of the most common 802 standards — 802.3 and 802.5.

One of the most dramatic LAN technology enhancements in recent years is the extension of the IEEE 802.3 family to allow 100M-bps transmission over twisted pair copper, as well as the impending enhancement by another factor of 10 to 1 gigabit per second. These enhancements are the subject of Chapter 1-2, “Fast (and Faster) Ethernet.”

Although it is important to develop an understanding of how LANs work conceptually, it is crucial that systems can actually communicate in practice. A strategically important issue in this regard is that of premises wiring. The importance of this topic is all too well understood by those who overlooked the need for establishing a solid, yet flexible, approach to premises wiring, and who, consequently, have had to endure the expense and agony of rewiring to accommodate change. Chapter 1-3, “Structured Wiring Systems for LANs,” discusses this topic in depth, providing sufficient detail for the reader to turn these concepts into reality.

Chapter 1-4, “Wiring Strategies in the Age of Multimedia,” takes a closer look at some of the challenges facing LAN managers today as a result of multimedia-intensive applications such as the World Wide Web. This chapter describes an evolutionary or incremental approach to the challenge, suggesting ways to adapt existing LANs for the delivery of multimedia applications and reviewing the infrastructure requirements for voice and video communications.

While technologies continue to advance, demanding faster and faster transmission speeds, many readers will undoubtedly wonder how the transmission capacity of medium such as twisted pair can continue to be pushed farther and farther beyond what was once believed to be its theoretical upper limit. Much of the answer lies in the various approaches, known collectively as encoding techniques, that are used to represent binary data as transmitted signaling elements. There are many such schemes available, and the one implemented for a given system impacts both quality and cost. Chapter 1-5, “Encoding Techniques in Local Area Networks,” discusses the major encoding techniques used in standardized LANs today. This chapter provides a basis for understanding the advances made in high-speed LANs, and for understanding the importance of adhering to the electrical and optical specifications at installation time.

Regardless how advanced an organization’s network becomes, a very basic and easy to overlook aspect of any LAN installation is related to the simple need to keep it up and running. Implementing high-quality hardware and software components is a good start, but even the best equipment will fail if the power goes out. Chapter 1-6, “Designing Power Distribution Systems for Fault Tolerant Networks,” provides an in-depth assessment of the concept of fault tolerance, and how system fault tolerance can be enhanced through proper design of the power distribution system.

Taking the concept of fault tolerance a step further, Chapter 1-7, “Fault Tolerance Protection and RAID Technology for Networks: A Primer,” investigates additional factors in the fault tolerance equation. Among these are fault tolerance features built into various LAN devices, and a look at how disk-based data can be protected through the use of redundant arrays of independent disks, more commonly known by their acronym, RAID.

1-1
IEEE 802 Standards

BERTIL C. LINDBERG
ASGHAR I. NOOR
TIM MCSHANE

Most networks are designed and constructed in functional layers, with the quantity, designation, and functions of the layers differing from network to network. Each layer offers certain services to the layers above it, and shields those layers from the implementation of its services. These layers constitute the network protocol architecture, the structure of rules that govern the exchange of information and services through the layers of one system and between two or more distinct systems.

The International Standards Organization (ISO) has defined a seven-layer network architecture that is known as the open systems interconnection (OSI) reference model. In OSI, corresponding layers, or peer processes, on different systems communicate only through the protocol hierarchy (see Exhibit 1-1-1). No data is passed directly from later N of system A to layer N of system B. Instead, each layer passes data and control information to the layer immediately below it, until the lowest layer of the system is reached. The lowest layer of system A then transmits the data to its peer layer on system B by way of the transmission medium.


Exhibit 1-1-1.  Architectural Framework for Protocol

The OSI model is composed of seven layers: the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer. These layers are self-contained and isolated from each other. As a result, a given layer can be replaced and implementation can be changed without affecting the other six layers. Such a layered design is important in accommodating innovations in hardware and firmware technology.


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