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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.
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.
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
| Introduction | ||
| Ch. 1 | How do I know when I need a local area network? | 1 |
| Ch. 2 | Ethernet or token ring? | 29 |
| Ch. 3 | Should I go for a structured cabling system? | 51 |
| Ch. 4 | What is a network operating system and do I need one? | 80 |
| Ch. 5 | What other devices can I put on my network apart from PCs? | 110 |
| Ch. 6 | Can I connect my networks even if they are different? | 139 |
| Ch. 7 | How do I choose my own LAN? | 175 |
| Ch. 8 | How do I design my network so that it will last and can be easily extended? | 203 |
| Ch. 9 | What is an open system and is it important to me and my network? | 226 |
| Ch. 10 | How do I manage and maintain my network? | 253 |
| Ch. 11 | Case study, drawing together the themes of the book | 283 |
| Appendix 1: ISDN (integrated services digital network) | 291 | |
| Appendix 2: Description of Ethernet and token ring technology | 292 | |
| Appendix 3: Cooperative processing | 299 | |
| Appendix 4: Costing of a low-end LAN solution | 302 | |
| Glossary | 304 | |
| Index | 317 |
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.
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.
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.
