Local Area Networks : Making the Right Choices

Local Area Networks : Making the Right Choices

by Philip Hunter

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Product Details

ISBN-13: 9780201627633
Publisher: Addison Wesley Professional
Publication date: 06/15/1993
Series: Data Communications and Networks Series
Pages: 340
Product dimensions: 6.79(w) x 9.19(h) x 0.74(d)

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PREFACE:

Introduction

The LAN (local area network) is fast becoming indispensablefor small and medium sized businesses for sharing information,applications and resources such as printers. Without a LAN,it is difficult or impossible for companies to exploitinformationtechnology efficiently or competitively, given recent trends incomputing. Yet many smaller businesses still do not have LANs and many that do have made poor choices of technology that makeitdifficult to expand or adopt superior computing technologies as they emerge.

The aim of this book is to help you choose LAN systems that arecompatible with your business objectives and that best exploitthe current technological opportunities. This includes thetechnical components of the LAN itself but perhaps moreimportant,embraces issues such as choice of supplier and how much help toobtain in implementing the LAN. The book also addresses theskills needed to manage a LAN effectively, which is a factor thatneeds to be considered in calculating how much a LAN will cost.But at the same time the potential savings of a LAN need to beconsidered, compared with alternative options. Such issues arediscussed in detail in Chapter 1, which answers the fundamentalquestions: when do I know that I need a local area network?

Subsequent chapters deal with the different components or aspectsof a LAN and issues that arise as the network expands. Runningthrough the whole book is a twin theme: the LAN must solve yourcurrent problems while at the same time keeping future options asopen as possible. The latter is important because bothtechnologyand business needs change at an ever increasing rate and successful companies in the 1990swill be those that are able toreact most quickly to these.

In the rest of the introduction we explain first of all why LANsare becoming so important for almost all companies with more thana handful of employees and then outline the main components of aLAN, thus setting the scene for subsequent chapters.

The fundamental raison d'etre of LANs is that they enablebusinesses to derive maximum benefit from their existing computersystems. In effect they do this by combining the best of the newand old worlds of computing in a cost effective and flexible way.

In the old world, by which I mean in particular the period from1960 up to around 1985, major organizations had large,centralizedcomputers enabling information, software applications andfacilities such as printers to be shared by many users. However, in the old world only specialist programmers and hardware engineers had direct access to computing facilities. Until 1978or so, most users had to submit their applications on punchedcards and often had to wait several hours for the result. Furthermore, worthwhile applications typically took months if notyears to develop, which tended to stifle innovation in the field.

In the new world, ushered in by the personal computer (PC) duringthe early 1980s, computing became far more accessible to ordinaryusers. They now had a desktop machine directly under their control, encouraging greater use of computers to solve problems and save valuable time through applications such as word processing and financial modelling. But the very success of PCsin taking computing to the people introduced a new problem. As PCs proliferated there was a growing need to share common informationand facilities between them. Clearly, if there were ten PCs inan office it made sense to share one or perhaps two printersbetween them rather than, for example, give one to each user. This ledto the introduction of LANs, which within larger organizations,spread rapidly from 1986 onwards. They enabled the advantages ofthe PC, such as ease of use and constant availability to itsuser, to be combined with the information and resource sharing capabilities of the traditional centralized computers. LANs can therefore be regarded as a sharing mechanism, enabling individualusers with PCs to access common information and resources. LANsalso allow computer applications to be shared where appropriate, for example where there are tasks that require a powerful expensive computer to execute. In such cases it makessense toprovide users with common access to just one central machine viaa LAN rather than giving such a machine to each user. This is just another form of resource sharing. Essentially both information and the applications that process that information can reside either in the desktop PC, or in central servers, or in a combination of both. Information or software applications usedby just one person may be best held in a single PC. On the other hand, information that is shared by or needs to be accessed by a number of users may be best held on a central machine. However, this issue of splitting information and applications betweencentral servers and desktop PCs may not be relevant for manysmall businesses. In fact, there does not have to be any centralstore of data or applications at all. LANs make it possible for eachPC to access every other computer on the network. This means that the data and applications held in every single PC attached to the

LAN can be made available to users of all other PCs on that LAN. Networks that provide this ability to share each other's PCs are often called peer-to-peer and are described in Chapter 4. Apartfrom accessing data and applications, the other key feature of LANs is their support for communication between users themselves via electronic mail. This may not count for much when, as sometimes happens, all users of a LAN reside within one room. But it can be effective when users are scattered throughout a building, or, as increasingly happens within largerorganizations, when a variety of LANs are linked together into a bigger enterprise-wide network. Then the ability to deliver memorandaand text messages instantly to any number of recipients can speedup decision making and problem solving.

Components Of A LAN

The principal feature of a LAN underpinning the benefits we have already touched on is that it enables PCs and other types of computer to communicate both with each other and with devicessuch as printers that are shared between some or all users of the network. There is also the caveat implicit in the name, which isthat the LAN only allows such communication within a limitedarea. To achieve this we identify two fundamental categories of components: physical ones, such as cabling which can be seen,and logical ones implemented in the software that control access to the network and its resources. Together these comprise acomplete LAN which delivers the required features and benefits. These twocategories in fact overlap. For example, PCs are usuallyattached to the physical cabling by cards, called network interface cards (NICs), in an expansion slot at the back of the PC. This device is physical but it also contains the software code that enables programs in the PC to access the LAN.

An important point to note is that the components of LANs are notfixed in stone but are constantly changing. The majordevelopment during the early 1990s was the emergence of the hub. This originally served as a focal point for cabling but has since evolved to provide additional facilities such as network management and the ability to access other networks. The hub is described in Chapter 3, with more discussion of its role in management in Chapter 10. Another key related development has been the ability to implement LANs on progressively cheaper and thinner cable. The most popular type of LAN, commonly called Ethernet, is now generally implemented over telephone-type cabling, which is cheaper and easier to install. However, such cabling has a more limited range, which has led to changes in thephysical design of Ethernet LANs. Originally Ethernet was laid out in a tree-and-branch structure called a bus, with a maximum span between any two attached nodes of 500 meters, although this could be extended to 2500 meters with the use of repeaters that boost the electrical signal. Over the lower-cost telephone wiring, called twisted pair, the maximum distance allowed betweena pair of devices connected by this cable using Ethernetprotocols was 100 meters. To cover the original distances of up to 2500 meters, hubs are used in which a number of nodes are attached ina star-shaped formation using the lower-cost twisted pair cable. None of these devices can be more than 100 meters from the hub, which is sometimes called a concentrator. To span greater distances the hubs themselves must be connected together with higher-grade cable. This arrangement enables the network to be clustered around workgroups in little constellations andminimizes the amount of expensive cable.

Can Components Be Installed Separately?

LANs can be installed as complete packges but it is also possibleto purchase them piecemeal in their various components. In many cases setting up the most suitable LAN for a given situation requires careful matching of the various components. For this reason the different components are all discussed in detail inthis book.

Relationship Between LAN Components And The StandardInternational Model Specifying How Networks Should Be Built

LANs are designed in layers conforming to an internationally agreed seven layer model which defines how computers should communicate across any network. This model is described in Chapter 9. A complete LAN including PCs and applications spansall seven layers but the basic communications are covered just bythe bottom two. The bottom physical layer specifies the communications medium, which for LANs usually is some type ofcable. We look at cabling in Chapter 3. The second layer then deals with how data is transmitted over that cable-- and it is atthis level that the various types of LAN, suchas Ethernet ortoken ring, are distinguished. We compare Ethernet and token ring in Chapter 2. The other essential componenet of a LAN is some type of operating system for controlling acces to data and to shared resources across the network. In this senseA LAN is rather likea single large computer that supports a number of users. Traditional large computers were accessed via simple terminals that provided just a keyboard and screen with shared access to data, printers and other facilities. A LAN can do just the same,except that now users have a more intelligent device on their desktop, a PC, which enables them to perform tasks without reference to any other system. LAN operating systems are discussed in Chapter 4. A non-essential component but one thatis becoming increasingly important for all but the smallestnetworks, is some management system. For users of smaller networksadequate management facilities will usually be provided within the networkoperating system. This may include security features that can, for example, prevent some users from accessing certain types ofinformation or stop them accessing some zones of the LAN. For larger networks, however there will usually be additionalmanagement systems dedicated to specific parts of the network, providing facilities such as fault detection and management. Management issues in general are discussed in Chapter 10.

Another non-essential but increasingly common element of modernLANs is a central cabling hub, which can also provide networkmanagement and other LAN functions. Having defined LANs andoutlined the areas we are covering, it is worth noting tworelated fields that this book does not cover. It does not tacklewide area networks (WANs) spanning larger distances than LANs cover. WANSutilize telecommunications links to interconnect LANs and other computer systems over large distances, for example between the national branches of a major company. However, we do touch onthe use of telecommunications links to connect two or more remoteLANs in Chapters 6 and 8. The other significant area this book does not address is the use of LANs in manufacturing and process control, which involves real-time control of equipment such as machine tools and robots.

0201627639P04062001

Table of Contents

(Most chapters conclude with "Summary".)
Introduction.
1. How do I Know When I Need a Local Area Network.

Need to Share and Exchange Information.
What is the Main Alternative to a LAN.
Defining the LAN In Brief.
How Lans Evolved From Traditional Centralized Computer Systems.
A Detailed Look at the Criteria for Needing a LAN.
Situations Where a LAN May Not be the Answer.
Summary.

2. Ethernet or Token Ring.
Choice Comes Down to Cost, Flexibility and Compadibility With Any Existing Networks.
Five Factors to Consider When Choosing Between Ethernet and Token Ring.
Comparative Discussion of Ethernet Versus Token Ring Performance.
Reliability Factors.
Fibre Distributed Data Interface (FDDI).
Arcnet.
Summary.

3. Should I go for a Structured Cabling System.
Introduction.
Structured Cabling Systems.
Different Types of Cable.
Cabling Issues Summarized.
Summary.

4. What is a Network Operating System and do I Need One.
Introduction.
What Does a NOS do That a PC Operating System Does Not.
Description of Some Popular Noss.
The Future of Network Operating Systems.
Summary.

5. What Other Devices Can I Put on My Network Apart From Pcs.
Introduction.
What Does a Device Need for Attachment to a Network.
Printers.
File/Database Servers.
NetworkInterface Cards (Nics).
Input Devices.
Image Servers.
Terminal Servers.
Communications Servers: Introduction.
Hubs/Wiring Concentrators.
Summary.

6. Can I Connect My Networks Even if They are Different.
Introduction.
Why Not Have Just One Large Network.
What Types of Network Might You Need to Connect Together.
Introducing the Solutions: What Needs to be Achieved.
Repeaters.
Bridges.
Routers.
Gateways.
Summary.

7. How do I Choose My Own Lan.
Introduction.
Categories of Supplier.
Evaluating Proposals.
Supplier Considerations.
Training.
Other Sources of Information: User Groups and Bulletin Boards.
Summary.

8. How do I Design My Network So That it Will Last and Can be Easily Extended.
Introduction.
NOS is Crucial.
Cabling and Hubs.
LAN Servers.
The Network Operating System (NOS).
LAN Type.
Are Lans Better Able to Support Changing Requirements Than Minicomputers.
Summary.

9. What is An Open System and is it Important to Me and My Network.
Standards are Important.
Introducing the Seven Layers of OSI.
What OSI Standards are Relevant to Lans.
Tcp/Ip.
Other De Facto Standards That You May Encounter.
How Different Standards Groups Fit Together.
Describing the Standards Bodies.
Key Concept: Connection Oriented and Connectionless Protocols.

10. How do I Manage and Maintain My Network.
Defining Scope of Network Management.
Do All Networks Need Management Systems.
What Elements Need to be Managed.
What Functions Should Your Network Management System Provide.
How Universal Protocols - and Hubs - are Bringing Network Management Systems Under One Umbrella.

11. Case Study, Drawing Together the Themes of the Book.
Choosing Consultant to Help Formulate RFP.
The Rfp.
Evaluation of Quotes From Vendors.
Installation Issues.

Appendix 1: ISDN (Integrated Services Digital Network).
Appendix 2: Description of Ethernet and Token Ring Technology.
Appendix 3: Cooperative Processing.
Appendix 4: Costing of a Low-End LAN Solution.
Glossary.
Index.

Preface

Introduction

The LAN (local area network) is fast becoming indispensablefor small and medium sized businesses for sharing information,applications and resources such as printers. Without a LAN,it is difficult or impossible for companies to exploitinformationtechnology efficiently or competitively, given recent trends incomputing. Yet many smaller businesses still do not have LANs and many that do have made poor choices of technology that makeitdifficult to expand or adopt superior computing technologies as they emerge.

The aim of this book is to help you choose LAN systems that arecompatible with your business objectives and that best exploitthe current technological opportunities. This includes thetechnical components of the LAN itself but perhaps moreimportant,embraces issues such as choice of supplier and how much help toobtain in implementing the LAN. The book also addresses theskills needed to manage a LAN effectively, which is a factor thatneeds to be considered in calculating how much a LAN will cost.But at the same time the potential savings of a LAN need to beconsidered, compared with alternative options. Such issues arediscussed in detail in Chapter 1, which answers the fundamentalquestions: when do I know that I need a local area network?

Subsequent chapters deal with the different components or aspectsof a LAN and issues that arise as the network expands. Runningthrough the whole book is a twin theme: the LAN must solve yourcurrent problems while at the same time keeping future options asopen as possible. The latter is important because bothtechnologyand business needs change at an ever increasing rate and successful companies in the 1990s willbe those that are able toreact most quickly to these.

In the rest of the introduction we explain first of all why LANsare becoming so important for almost all companies with more thana handful of employees and then outline the main components of aLAN, thus setting the scene for subsequent chapters.

The fundamental raison d'etre of LANs is that they enablebusinesses to derive maximum benefit from their existing computersystems. In effect they do this by combining the best of the newand old worlds of computing in a cost effective and flexible way.

In the old world, by which I mean in particular the period from1960 up to around 1985, major organizations had large,centralizedcomputers enabling information, software applications andfacilities such as printers to be shared by many users. However, in the old world only specialist programmers and hardware engineers had direct access to computing facilities. Until 1978or so, most users had to submit their applications on punchedcards and often had to wait several hours for the result. Furthermore, worthwhile applications typically took months if notyears to develop, which tended to stifle innovation in the field.

In the new world, ushered in by the personal computer (PC) duringthe early 1980s, computing became far more accessible to ordinaryusers. They now had a desktop machine directly under their control, encouraging greater use of computers to solve problems and save valuable time through applications such as word processing and financial modelling. But the very success of PCsin taking computing to the people introduced a new problem. As PCs proliferated there was a growing need to share common informationand facilities between them. Clearly, if there were ten PCs inan office it made sense to share one or perhaps two printersbetween them rather than, for example, give one to each user. This ledto the introduction of LANs, which within larger organizations,spread rapidly from 1986 onwards. They enabled the advantages ofthe PC, such as ease of use and constant availability to itsuser, to be combined with the information and resource sharing capabilities of the traditional centralized computers. LANs can therefore be regarded as a sharing mechanism, enabling individualusers with PCs to access common information and resources. LANsalso allow computer applications to be shared where appropriate, for example where there are tasks that require a powerful expensive computer to execute. In such cases it makessense toprovide users with common access to just one central machine viaa LAN rather than giving such a machine to each user. This is just another form of resource sharing. Essentially both information and the applications that process that information can reside either in the desktop PC, or in central servers, or in a combination of both. Information or software applications usedby just one person may be best held in a single PC. On the other hand, information that is shared by or needs to be accessed by a number of users may be best held on a central machine. However, this issue of splitting information and applications betweencentral servers and desktop PCs may not be relevant for manysmall businesses. In fact, there does not have to be any centralstore of data or applications at all. LANs make it possible for eachPC to access every other computer on the network. This means that the data and applications held in every single PC attached to the

LAN can be made available to users of all other PCs on that LAN. Networks that provide this ability to share each other's PCs are often called peer-to-peer and are described in Chapter 4. Apartfrom accessing data and applications, the other key feature of LANs is their support for communication between users themselves via electronic mail. This may not count for much when, as sometimes happens, all users of a LAN reside within one room. But it can be effective when users are scattered throughout a building, or, as increasingly happens within largerorganizations, when a variety of LANs are linked together into a bigger enterprise-wide network. Then the ability to deliver memorandaand text messages instantly to any number of recipients can speedup decision making and problem solving.

Components Of A LAN

The principal feature of a LAN underpinning the benefits we have already touched on is that it enables PCs and other types of computer to communicate both with each other and with devicessuch as printers that are shared between some or all users of the network. There is also the caveat implicit in the name, which isthat the LAN only allows such communication within a limitedarea. To achieve this we identify two fundamental categories of components: physical ones, such as cabling which can be seen,and logical ones implemented in the software that control access to the network and its resources. Together these comprise acomplete LAN which delivers the required features and benefits. These twocategories in fact overlap. For example, PCs are usuallyattached to the physical cabling by cards, called network interface cards (NICs), in an expansion slot at the back of the PC. This device is physical but it also contains the software code that enables programs in the PC to access the LAN.

An important point to note is that the components of LANs are notfixed in stone but are constantly changing. The majordevelopment during the early 1990s was the emergence of the hub. This originally served as a focal point for cabling but has since evolved to provide additional facilities such as network management and the ability to access other networks. The hub is described in Chapter 3, with more discussion of its role in management in Chapter 10. Another key related development has been the ability to implement LANs on progressively cheaper and thinner cable. The most popular type of LAN, commonly called Ethernet, is now generally implemented over telephone-type cabling, which is cheaper and easier to install. However, such cabling has a more limited range, which has led to changes in thephysical design of Ethernet LANs. Originally Ethernet was laid out in a tree-and-branch structure called a bus, with a maximum span between any two attached nodes of 500 meters, although this could be extended to 2500 meters with the use of repeaters that boost the electrical signal. Over the lower-cost telephone wiring, called twisted pair, the maximum distance allowed betweena pair of devices connected by this cable using Ethernetprotocols was 100 meters. To cover the original distances of up to 2500 meters, hubs are used in which a number of nodes are attached ina star-shaped formation using the lower-cost twisted pair cable. None of these devices can be more than 100 meters from the hub, which is sometimes called a concentrator. To span greater distances the hubs themselves must be connected together with higher-grade cable. This arrangement enables the network to be clustered around workgroups in little constellations andminimizes the amount of expensive cable.

Can Components Be Installed Separately?

LANs can be installed as complete packges but it is also possibleto purchase them piecemeal in their various components. In many cases setting up the most suitable LAN for a given situation requires careful matching of the various components. For this reason the different components are all discussed in detail inthis book.

Relationship Between LAN Components And The StandardInternational Model Specifying How Networks Should Be Built

LANs are designed in layers conforming to an internationally agreed seven layer model which defines how computers should communicate across any network. This model is described in Chapter 9. A complete LAN including PCs and applications spansall seven layers but the basic communications are covered just bythe bottom two. The bottom physical layer specifies the communications medium, which for LANs usually is some type ofcable. We look at cabling in Chapter 3. The second layer then deals with how data is transmitted over that cable— and it is atthis level that the various types of LAN, suchas Ethernet ortoken ring, are distinguished. We compare Ethernet and token ring in Chapter 2. The other essential componenet of a LAN is some type of operating system for controlling acces to data and to shared resources across the network. In this senseA LAN is rather likea single large computer that supports a number of users. Traditional large computers were accessed via simple terminals that provided just a keyboard and screen with shared access to data, printers and other facilities. A LAN can do just the same,except that now users have a more intelligent device on their desktop, a PC, which enables them to perform tasks without reference to any other system. LAN operating systems are discussed in Chapter 4. A non-essential component but one thatis becoming increasingly important for all but the smallestnetworks, is some management system. For users of smaller networksadequate management facilities will usually be provided within the networkoperating system. This may include security features that can, for example, prevent some users from accessing certain types ofinformation or stop them accessing some zones of the LAN. For larger networks, however there will usually be additionalmanagement systems dedicated to specific parts of the network, providing facilities such as fault detection and management. Management issues in general are discussed in Chapter 10.

Another non-essential but increasingly common element of modernLANs is a central cabling hub, which can also provide networkmanagement and other LAN functions. Having defined LANs andoutlined the areas we are covering, it is worth noting tworelated fields that this book does not cover. It does not tacklewide area networks (WANs) spanning larger distances than LANs cover. WANSutilize telecommunications links to interconnect LANs and other computer systems over large distances, for example between the national branches of a major company. However, we do touch onthe use of telecommunications links to connect two or more remoteLANs in Chapters 6 and 8. The other significant area this book does not address is the use of LANs in manufacturing and process control, which involves real-time control of equipment such as machine tools and robots.

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